Climate risk assessments and management options for redevelopment of the Parliamentary Complex in Samoa, South Pacific

Weather and Climate Extremes 25 (2019) 100214

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Climate risk assessments and management options for redevelopment of the Parliamentary Complex in Samoa, South Pacific

T

John E. Haya,∗, Peter Hartleyb, Jay Roopc,1 a

University of the South Pacific, Rarotonga, Cook Islands AECOM Ltd, Tauranga, New Zealand c Asian Development Bank, Manila, Philippines b

ARTICLE INFO

ABSTRACT

Keywords: Risk assessments Vulnerability Adaptation Cost-benefit Infrastructure Samoa

The site of the Samoan Parliament Complex Redevelopment Project is in a coastal environment hazard zone as a result of high risk of several hazards, including damaging winds and flooding due to stormtides. This paper presents the findings of detailed hazard, vulnerability, exposure and adaptation assessments, and prioritises risk reduction measures based on the findings of cost benefit analyses, as well as other considerations. As a result of higher intensity rainfall events in the future, as well as a general increase in sea level, the frequency and depth of localised flooding of the site during periods of heavy rainfall are expected to increase. No significant change is anticipated in the exposure of the buildings to extreme wind gusts between present day and 2045–2055, but projected increases in the frequency of extreme high temperatures have relatively high certainty and are substantial. Inundation as a result of a cyclone-related stormtides is the highest risk for the site. By 2065, 50- and100-year stormtides could be 3.0 m and 3.2 m above mean sea level, respectively, compared to 2.6 m and 3.0 m for the same events in 1990. Water velocities experienced during such stormtides are projected to increase from 1.5ms−1 (in 1990) to 1.9ms−1 by 2055. Relocating the Parliamentary Complex would alleviate all of the key risks that were identified. However, for cultural and historic reasons this response was not favoured by the Government of Samoa. Two key ways to manage the identified risk of damaging stormtides were assessed, namely to increase the height of building platforms above the business as usual case of meeting the design code in force at the time (i.e. finished floor level at 2.8 m above mean sea level), or to increase protection of the entire site by raising the heights of the surrounding sea wall and embankments. Cost benefit analyses showed that raising finished floor levels was the much more cost-effective option for protecting the new buildings from damage due to stormtides. The new Parliamentary Chamber was officially opened in March 2019. Its climate resilient design reflects the findings of the above assessments, including the prioritised risk reduction measures.

1. Background and introduction Samoa is a small island country located approximately halfway between Hawaii and New Zealand, in the Polynesian region of the Pacific Ocean. To mark the 50th anniversary of Samoan independence, the Government of Australia agreed to fund the Samoan Parliament Complex Redevelopment Project (SPCRP). The Parliamentary Complex is located on the Mulinu'u Peninsula, to the west of Apia, the capital of Samoa (Fig. 1). The Peninsula is a nearly 2 km long barrier spit, and generally 1.0–1.3 m above mean sea level (MSL). It is located in a

Coastal Environment Hazard Zone (MNRE, 2007), as a result of being subject to high wind forces from cyclones, high risk from earthquakes, flooding due to storm surge and to tsunami. The extreme vulnerability of the Mulinu'u Peninsula and the adjacent Apia Harbour was highlighted as early as 1889 when the “Apia Cyclone” determined the future history of the Samoan Archipelago. Until Cyclone Val in December 1991, the Apia Cyclone was considered to be the worst tropical cyclone to affect the Samoan Islands (Ashcroft and Ward, 1998). The Apia Cyclone occurred during a time of domestic Samoan political unrest. This resulted in seven foreign warships of three

Corresponding author. E-mail addresses: [email protected], [email protected] (J.E. Hay). 1 Secondee to Department of Foreign Affairs and Trade, Government of Australia, Canberra, Australia. ∗

https://doi.org/10.1016/j.wace.2019.100214 Received 16 April 2019; Received in revised form 20 June 2019; Accepted 23 June 2019 Available online 26 June 2019 2212-0947/ © 2019 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/BY-NC-ND/4.0/).

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Fig. 1. Location of the Parliament Complex and other features.

protection against present day extreme storm events would have been provided - e.g. flood protection was only required for storms or cyclones of up to a 30-year return period.2 The Code has since been updated (Government of Samoa, 2017). It takes a proactive approach to addressing the impacts of climate change, by ensuring that buildings, facilities and sites are constructed to minimize its impacts. Under the SPCRP, the new building was also designed to satisfy the provisions of other building codes that have particular relevance. This included AS NZS 1170.2 ″Structural Design Actions – Part 2 Wind Actions" (AS/NZS 1170.2:2011) for wind and earthquake. The design standards for the SPCRP were also informed by the findings of the detailed climate risk and adaptation assessments described in the remainder of this paper. The objective of this paper is to provide a case study of a rigorous and comprehensive approach to assessing climate risks, and to identifying, prioritising and applying adaptation measures that reduce the risks in a cost effective manner. By way of cost-benefit and other analyses, the paper makes an important contribution to the practical assessment of “additionality” of adaptation (Olivier et al., 2012).

colonial powers (the United States, Germany and Great Britain) anchoring in Apia's small and very exposed harbour in order to protect their national interests. Because none of the competing maritime powers wanted to leave first, all seven ships were still in the harbour when the cyclone struck. Two German and two American warships were wrecked, with the loss of over 140 lives. Two other ships were beached on the Peninsula. Only the British ship escaped relatively unscathed (HFB, 1891; Bandhauer et al., 2013). The loss of war materials and human lives brought the colonial powers back to the negotiation table (Wehler, 1965). The Germans and Americans decided to settle their claims amicably by dividing their annexations. The islands of Upolu and Savaii were annexed by Germany, to form Western Samoa, while the islands of Tutuila and Manua were annexed by the United States, to form American Samoa. Some protection of the Complex is currently provided by a flood protection embankment on the western side, with an average height of 2.29 m above MSL. This helps protect the site from storm surges and flooding from Vaiusu Bay. A seawall, with a height of between 2.41 and 2.64 m above MSL, provides protection from Apia Harbour to the east. Prior to the SPCRP the Maota Fono (Parliamentary Chamber) was built on a concrete platform at 2.7 m above MSL, to further protect against flooding. However, the existing Legislative Assembly Offices (LAO) and associated facilities, such as parking, sanitation systems and walkways, were not raised. Given the site's location, climate change was identified as a key risk early in the project scoping for the SPCRP (Roop, 2012). The new Maoto Fono (Appendix 1) was officially opened in March 2019. It has a design life of 40–50 years and is therefore designed to accommodate climate conditions out to at least 2065. Had the SPCRP simply complied with the Samoan National Building Code that was in force at the time (Government of Western Samoa, 1992), no allowance would have been made for future changes in climate and only relatively low levels of

2. Methodology The methodology is summarized in Fig. 2. The assessments were undertaken in a four-step process, as described below.

2 Standard practice for flood protection for coastal infrastructure is to design for a one in 100-year event, with an additional allowance for uncertainty provided by requiring floors to be 500 mm above the one in 100-year flood event (i.e. a ‘freeboard’ of 500 mm).

2

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2.4. Propose and evaluate adaptation measures The results of the vulnerability assessment were used to identify the need for, and likely effectiveness of, measures to reduce any unacceptable risks, and to manage the residual risks. Anticipated costs and benefits (including reduced damage and operating costs), and other relevant criteria, were used to prioritise the identified risk reduction measures. Determining the costs and benefits of potential adaptation options involved estimating the incremental costs of managing specific risks to the structures, or to the site as a whole, for specified levels of protection up to a 100-year event. For example, for the Maota Fono and surrounding platform, the ‘business as usual’ (BAU) case of meeting the ‘de facto’ design standard would be to maintain the finished floor level (FFL) at 2.8 m above MSL, maintain the concrete platform at 2.7 m above MSL, increase the platform area to accommodate a larger Maota Fono, and replace the retaining walls to enable these heights and bearing pressures to be achieved. Costs were estimated for increasing the FFL from 2.8 m up to 3.8 m (with the building platform 150 mm below these levels). The incremental costs were estimated for both raising the height of the retaining walls and placement of additional engineered fill. The benefits of implementing the adaptation measures are given by the damages avoided over the lifetime of the Maota Fono and LAO as a result of protecting these structures from the increased height of stormtides over time. The damages avoided were estimated using methods first described in ADB (2005). Annualised damage costs were integrated over all return periods and then integrated over the 50-year lifetime of the structure. A stage-damage curve describes the vulnerability of a structure to damage from a specific hazard (in this case a stormtide), and is determined by the building's design characteristics, the materials of construction, the contents, and the costs of the construction and the contents. Damage to a particular structure will depend on the severity of the event and will cover the range from no damage (minor events) to total destruction. As the severity of events increases, the damage effect takes an “S” shape, i.e. at first the extent of damage rises slowly with event severity, and begins to rise steeply once a given “threshold” severity is exceeded. At the high end of the curve, near-total damage loss occurs across a broad range of extreme events. Stormtide height, and the resulting damage to a structure, corresponds to the return period of the event. The expected value of damage was calculated for all stormtides up to the 1-in-100-year event. The expected value of damage in year one is the product of the array of probabilities of events with return periods from one to 100 years, and the array of damage values associated with each event (i.e. the sumproduct of the probabilities and the associated damage). For subsequent years the damage associated with an event with a given probability will increase due to climate change (e.g. sea-level rise). Thus the sumproduct of the probabilities and associated damage will increase. The benefits of specific adaptation measures were analysed within the same framework. Adaptation results in the stage-damage curve being shifted such that, for a given event, less damage is inflicted than without adaptation. For a particular adaptation measure the calculations described above were repeated in order to determine the net present value of expected damage after an adaptation measure is implemented. The difference between the expected damage in the noadaptation case, and after implementing the adaptation measure, gives the gross benefit of implementing that adaptation option. These calculations were repeated for all feasible adaptation measures. A discount rate was used to calculate the net present value of a stream of future costs, since a given cost incurred in the future is worth less than the same cost incurred today. The actual discount rate chosen reflected a subjective valuation of the present versus the future, with a lower discount rate signalling a higher concern about future costs, and vice versa for a higher discount rate. In the present study a discount rate

Fig. 2. Overview of methodology.

2.1. Review and assess climate hazards In addition to information on current and anticipated climate hazards provided by “Pacific Climate Futures" (www.pacificclimatefutures.net), the assessment updated and expanded on the Climate Risk Profile for Samoa (Young and Hay, 2006). Observed annual maximum values were adjusted based on the projected mean change in the variable, Gumbel parameters recalculated, and relevant return periods determined. Hazard projections for extreme rainfall (5 min to one day duration), maximum temperature, sea level, extreme wind gusts, stormtide3 and drought were prepared for the 2045–2065 time slice, for both low and high greenhouse gas emissions scenarios. The 2045–2065 time slice was chosen since it is within the design life of the SPCRP. High and low emissions scenarios provided an understanding of the range of climate futures within this time slice. 2.2. Assess exposures Exposure is defined as the presence of people, livelihoods, species or ecosystems, environmental functions, services, and resources, infrastructure, or economic, social, or cultural assets in places and settings that could be adversely affected, including by extreme weather and climate events (IPCC, 2014). The likely exposure of key SPCRP elements to the identified hazards was assessed for the 2045–2065 time slice. This step also involved an assessment of the adequacy of Samoa's 1992 building code and other infrastructure design standards, given anticipated exposure levels. 2.3. Assess vulnerabilities Vulnerability is defined here as the degree to which a system is susceptible to, and unable to cope with, adverse effects of climate change, including climate variability and extremes (IPCC, 2001). Vulnerability is a function of the character, magnitude, and rate of climate variability and change to which a system is exposed, its sensitivity, and its ability to adjust. The consequences of the anticipated climate and weather extremes during the 2045–2065 time slice for the key SPCRP elements were determined, including the adequacy of: (i) floor levels only meeting the ‘de facto’ design standard of 2.8 m above MSL; (ii) the existing embankment and seawall design and height; and (iii) the proposed design of service facilities, including cooling, water supply, drainage, parking, and walkways. These findings were used to identify potential risk reduction measures that needed to be costed so they could be prioritised in the next step. 3

See Appendix 2 for definitions of this and related terms. 3

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Table 1 Information sources for the hazard risk analysis. Variable

Historic Trends and Return Periods

Current Baseline

2045–2065 Return Periods

Extreme High Air Temperature

Observed Data 1941–2011 Observed Data 1960–2011 and SOPAC (2006) Observed Data 1993–2011 Apia 1993–2011 Pago Pago 1948–2011 Observed Data 1960–2011

Observed Data 1980–1999 SOPAC (2006)

Pacific Climate Futures Projectionsa

Observed Data 1993–2011 1993–2011

Pacific Climate Futures Outlook

Extreme Rainfall Extreme Wind Gust Extreme High Hourly Sea Level and Stormtide

Drought a

Observed Data 1960–2011

Pacific Climate Futures Projections

Estimated using: a) Pacific Climate Futures Projections; b) Extrapolation of 1993–2011 trends c) Combination of a) and b) d) Hoeke et al. (2013) Pacific Climate Futures Projections

Available at www.pacificclimatefutures.net/.

of 3% was used. This comparatively low discount rate indicates a relatively strong desire to avoid future costs that may affect the economic and social well-being of future generations, as well as awareness of the dynamics of climate change. The latter implies greater confidence in predictions of the rate and degree by which the climate will change in the future. Because of the subjective nature of setting the discount rate, the rate of return that will be generated by a given adaptation investment was also determined. This “internal rate of return” is the interest rate corresponding to a zero net present value for the adaptation investment (ADB, 2005).

4. Hazard, exposure and vulnerability assessments for sea-level rise and stormtides Fig. 3 presents average monthly maximum, mean and minimum sea levels at Apia, for 1993 to 2012. The mean sea level for the duration of the record was 0.777 m. This compares to the “official” 1951–1969 MSL of 0.6937 m above Lowest Astronomical Tide, a datum “equivalent” to chart datum (CD). From February 1993 to December 2018 a relative sea-level rise of +8.9 mm per year was observed (Australian Bureau of Meteorology, 2018). For the Samoa area, the rate of sea-level rise from 1993 to 2017 as measured using satellite altimetry was approximately +3 mm per year (CMEP, 2018) Much if not all of the difference can be attributed to the 2009 Mw 8.1 Samoa-Tonga earthquake and the ongoing land subsidence of 8–16 mm per year (Han et al., 2019). This is likely to continue for decades and result in a sea level rise of 30–40 cm, this being independent of and in addition to the future climate-related sea level rise. It will worsen coastal flooding on the islands leading to regular nuisance flooding (Han et al., 2019). The relative sea level trend for Pago Pago between 1948 and 2009 (i.e. before the earthquake of September 2009 caused an average of 3.6 m vertical displacement) was +2.2 mm per year (http:// tidesandcurrents.noaa.gov/sltrends/sltrends.html). While a longer record than for Apia, the data have less precision and datum control. Table 2 presents return periods for mean hourly sea level for Apia and for nearby Pago Pago. Due to the sheltered location of the Apia tide gauge, the effect of wave setup is likely to be minimal at the site (Hoeke et al., 2013). Hence the return periods of extreme high sea levels for the coastline of the adjacent Mulinu'u Peninsula are likely to be lower. The return periods based on the considerably longer length of record at Pago Pago are substantially higher than those for Apia. Those for the comparable time period are much reduced, indicating that extreme high sea levels have become more common in recent times, at least in part as a result of the increase in mean sea level. Coastal water levels that occur during a storm are influenced by atmospheric and ocean processes which operate on a range of timescales. In the South Pacific, a storm surge and the associated coastal inundation are most commonly associated with tropical cyclones. A tropical storm has passed within 100 km of Apia on average once every eight years (PCRAFI, 2011). Table 3 presents comparable observations and estimates of still water and inundation heights. By way of comparison, the tsunami that devastated Samoa and nearby countries in 2009 caused damage up to 14 m above sea level on the coast of South Upolu, and travelled up to 0.7 km inland (World Bank, 2011). Fig. 4 shows sea levels at a location in front of the sea wall, as calculated by Hoeke et al. (2013). They used a high resolution 1-D model capable of representing the instantaneous movement of waves

3. Information sources and levels of confidence and uncertainty Table 1 describes the main sources of information used to determine recent, current and anticipated climate risks of relevance to the SPCRP. Assessment of the recent and current hazard risks was facilitated by the SPCRP site being very close to locations at which relevant meteorological and sea-level observations are made (see Fig. 1). While the latter commenced only in 1993, the data are of high quality and can be complemented by a longer data record for near by Pago Pago in American Samoa. The climate observations are also of high quality. In some cases these have the added advantage of a much longer period of observation, extending as far back as 1890 in the case of daily rainfall. Assessment of stormtide risks was facilitated by the recent findings of Hoeke at el. (2013), Hoeke et al. (2014) and Hoeke et al. (2015), as summarised by McInnes et al. (2016). They quantified inundation depths and water velocities for the SPCRP site, by undertaking high resolution modelling of the local sea-level response associated with tropical cyclone induced stormtides in the Apia Harbour region. The results were based on the best available science on climate change and coastal processes, using state-of-the-art numerical modelling in complex reef environments, together with high resolution light detection and ranging (LiDAR) data. However, validating the models using available observations was hampered by the absence of observations around the Peninsula. Furthermore, the methods applied to estimate stormtide return periods were also based on assumptions as a result of limited historical records and measurements of tropical cyclones. This necessarily leads to uncertainties in the results (Hoeke et al., 2013). In addition, uncertainties in the assessment of hazard risks increase into the future, as the projected level of risk depends on the assumed rate of greenhouse gas emissions, their build up in the atmosphere, and on the resulting radiative forcing. All projections are therefore based on highly uncertain assumptions of future socio-economic and technological development.

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Fig. 3. Monthly sea level at Apia, 1993–2015. Source: Australian Bureau of Meteorology (2015).

at locations in front of the sea wall. The modelling results indicate that wave setup can more than double the water levels that occur due to the stormtide only. The breaking of individual waves against the sea wall produces run-up and sea levels that are temporarily higher than the average values. These extreme heights, referred to as maximum heights, are defined as the average of those that are attained 2% of the time during each storm event simulation, and represent the actual sea level resulting from stormtide, wave setup and run-up. Under all return periods considered by Hoeke et al. (2013), these transitory extreme sea levels exceed the height of the seawall, which is about 2.4–2.5 m above mean sea level. Hence, during such cyclone events the seawall will experience overtopping, with the amount of overtopping increasing with more extreme storm events (i.e. larger return periods). Indicative sea-level heights and current speeds behind the seawall, determined by Hoeke et al. (2013) for 50- and 100-year stormtides, are shown in Fig. 5 for baseline (current climate) and future conditions. To account for uncertainty in the model results, due to the absence of observational data for model calibration, an upper estimate of sea level is obtained by using model parameter settings that favour more extreme inundation. In terms of exposure in the future, mean sea level is projected to

Table 2 Return Periods (in years) for Mean Hourly Sea Level. For Apia and Pago Pago. Mean Hourly Sea Level (m) of at Least

Apia Observed 1993–2011

Pago Pago Observed 1948–2011

Pago Pago Observed 1993–2011

1.4 1.5 1.6 1.7 1.8 1.9 2.0

1.0 1.5 4.6 18 81 359 1595

2.1 6.7 25 97 383 1516 5996

1.3 2.9 9.2 32 114 413 1497

Sources: National Tidal Centre, Australian Bureau of Meteorology, and University of Hawaii Sea Level Center.

across the reef, as well as wave run-up and overtopping at the seawall. This provides estimates of the instantaneous maximum sea levels and currents that may occur under different time-averaged wave and sealevel conditions (McInnes et al., 2016), as simulated by a lower resolution model for different tropical cyclone conditions. Since these locations have high exposure to incoming waves, wave setup is expected to make the largest contribution to elevated sea levels

Table 3 Observed and estimated still water and inundation heights. For selected locations and events. Location

Source

Height (m)

American Samoa (during Cyclone Val) Samoa (during Cyclone Ofa) Samoa (during Cyclone Ofa) Samoa (during Cyclone Willma) American Samoa (during Cyclone Heta) American Samoa – Maximum Still Water Level American Samoa – Maximum Water Level 100-year storm surge (i.e. excl. tide and run up) for selected locations in Fiji Nadi Lautoka Tailevu Suva Labasa Savusavu

Shernoff et al. (2012) World Bank (2011) Rearic (1990) NDMO, Samoa (2011) Fenner et al. (2008) Militello et al. (2003) Militello et al. (2003) McInnes et al. (2011)

15 1.6 1.4 ≈3.5 13.5 3.2 15.3

5

1.29 1.34 0.61 0.59 1.20 0.76

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the best estimate of inundation height for a 1-in-100-year stormtide being around 2.4 m in 1990, with currents speeds around 1.3 ms−1. The upper estimates of inundation height and current speed for 1990 are 3.0 m and 1.5 ms−1, respectively (Fig. 5). These results suggest that, while under current conditions a 1-in-50year stormtide causes only partial inundation of the western side of Mulinu'u Peninsula where the SPCRP is located, a 1-in-100-year stormtide would completely inundate the Peninsula. By 2055, a 1-in50-year stormtide would also completely inundate the Peninsula. The existing seawall (2.41–2.64 m) would provide some protection from less extreme storm surges in Apia Harbour, as would the embankment (2.29 m) that protects the site from stormtides from Vaiusu Bay. At 2.74 m above current MSL, the present platform for the Maota Fono would also provide some protection against inundation, but again only for stormtides at the lower end of the height range. Even then there is little margin for safety. Allowing the conventional 500 mm for “freeboard”, the minimum floor height under 2055 conditions could be up to 3.7 m above MSL, rather than the ‘de facto’ practice to build to a minimum floor height of 2.8 m above MSL. Since the areas currently occupied by the LOA, as well as associated facilities such as parking, sanitation systems, and walkways, are not raised, these areas are highly exposed to a major stormtide. It is likely that there will be increased frequencies of inundation of some parts of the site (particularly the lower lying areas) as a result of stormtides with return periods of less than 100 years. Consequences include the inability to use low-lying areas of the site (e.g. parking, fields, some access around the grounds). Flooding by saltwater also damages, and can destroy, vegetated areas, especially grassy areas, and also electrical and other services installed at or near ground level. Increases in mean sea level are also expected to have a potentially negative impact on the drainage capacity of the existing grounds. Groundwater tables are expected to rise in accordance with increased sea level, potentially reducing the capacity of on-site soakage. A greater frequency and duration of standing water on the grounds can therefore be expected, although it has not been possible to quantify the extent, and effect, of this. Risk reduction options are to increase on-site surface drainage capacity and/or construct additional drainage channels on site and/or increase the level of footpaths and (new) roads and car parks on the site. An increase in design tailwater levels in accordance with projected mean sea levels would also be warranted.

Fig. 4. Comparison of modelled water levels for 20-, 50- and 100-year return period levels for baseline sea level and climate conditions. Dark blue symbols represent the values calculated by Hoeke et al. (2013). Earlier estimates by Beca (2001) and Carter (1987) are shown in orange and light blue, respectively. ST refers to stormtide, WSU refers to wave setup and RU refers to run-up (see Appendix 2). Water levels are relative to the 1973 MSL datum. Source: Hoeke et al. (2013). (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

increase by between 0.18 m and 0.34 m in 2045–2065, depending on the chosen emission scenario and other assumptions (Hay, 2014). Most of the SPCRP site is around 1.0–1.3 m above MSL. It is also protected by a seawall and embankment that are at least 2.3 m above MSL. Thus, while it is considered that the entire site is unlikely to be inundated as a result of sea-level rise alone (i.e. not including a stormtide), during high tides especially, increased localised flooding is likely to occur in areas adjacent to the relatively porous western embankment, where ground level is slightly less than 1 m above MSL. The SPCRP site is generally made up of alluvial sand, with hard coral at 6 m or deeper. Consequently there is a risk of reduced bearing capacity of the underlying materials as a result of an increase in groundwater tables, potentially by up to 0.34 m. The “best estimate” of Hoeke et al. (2013) for a 1-in-100-year stormtide in 2055 is around 2.6 m, with current speeds around 1.6 ms−1, while the upper estimates for inundation depth and current speed are 3.2 m and 1.9 ms−1, respectively (Fig. 5). This compares to

Fig. 5. Low, best and upper estimates of (a) sea levels and (b) current speeds on the landward side of the sea wall under future scenarios of sea-level rise. The low estimate values are derived from the Apia model since they do not include the effects of transient wave activity (i.e. wave runup and overtopping). The best estimate is derived by adding to the Apia Model results the difference in the 50th and 98th percentile heights estimated from the Peninsula Model, to account for the effects of transient wave activity. The upper estimate is derived in the same way as the best estimate, but using the Peninsula Model values where the parameter settings favour more extreme inundation. Water levels are relative to the 1973 MSL datum. Source: Hoeke et al. (2013).

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likely to be increased surface water and overland flow on site. Moreover, should the SPCRP not include a connection to the wastewater treatment plant this would result in damage and destruction of septic tanks and pipes, leading to increased operational and maintenance costs, an increase in the number of days that the septic system is ineffective, and an increase in septic odour when the septic system is flooded. Internal gutters of buildings are designed for one in 100-year rainfall event. General building drainage, such as eaves and gutters, is designed for a one in 20-year event. These would typically be for a 5 min duration but hourly rainfall intensity is sometimes used. Current and projected (2055) return periods for both these durations are shown in Table 5. For site flooding risk it is necessary to take into account both the increases in extreme rainfall events indicated in Table 5 and the increase in mean sea level, as discussed in Section 4. On site flooding from rainfall, and lack of capacity in the drainage system, will be further exacerbated by increased stormtide levels, resulting in longer surface water retention if additional drainage structures are not built on site. However, while it is assumed there is a strong correlation between storm surge and extreme rainfall events, it is impractical to design any new drainage improvements with an elevated tailwater level that also takes stormtides into account. The consequences of surface flooding resulting from rainfall events with annual recurrence intervals of 10 years would be reduced if floor levels are elevated in order to protect buildings from stormtides. There is considerable inter-annual and inter-decadal variability in the occurrence of drought, with no obvious long term trend (Hay, 2014). Significant droughts were associated with the El Niño events of the early and late 1980s and late 1990s. Little change is projected in the incidence of drought over the course of the 21st century, but there is low confidence in this projection (Australian Bureau of Meteorology and CSIRO, 2011). Drought projections for the 2045–2065 time slice are relatively insensitive to the choice of emissions scenario. As noted earlier, year-to-year climate variability in Samoa and the wider Pacific islands region will continue to be strongly affected by the El Niño–Southern Oscillation. Climate projections show that, by the mid-to late twenty-first century, there will be no discernible change in El-Niño-driven drought occurrences in the Samoan region (Power et al., 2013). Thus for the 2045–2065 time slice droughts are projected to occur approximately seven times every 20 years, with moderate and severe drought occurring approximately once to twice, and once every 20 years, respectively. No significant change is anticipated in the exposure and vulnerability to drought between present day and 2045–2065.

Table 4 One hundred year rainfall intensity-duration-frequency for apia and pago Pago. Return Period 100 years Apia

Pago Pago

Duration

Walker

Punivalu

Rofe et al.

5 min 6 min 10 min 15 min 30 min 45 min 1h 1.5 h 2h 3h 4.5 h 6h 9h 12 h 1 day

30

30

47 59 82

47 59 82

104

104

101

128

128 138

143

Yance

Present Study

Atu'u

Malaeloa

61 76

62 82

113

113

183

192

223

238

234

380

293 385

274 330

26

204 233

47 70 87 103 128 148 177 216 246 288 336

Sources: See text.

5. Hazard, exposure and vulnerability assessments for extreme high rainfall and drought Daily rainfall data are available for Apia for 1960–2011. Six-hourly rainfall data is available from 1969 to 2005, but with a large break between 1975 and 1990. SOPAC (2006) provides depth-duration-intensity information for Apia. Table 4 presents 100-year rainfall intensity duration data for Apia and Pago Pago, as compiled from the following sources: Walker (1975), Punivalu (1983), Rofe and Lapworth (1996), Yance in SOPAC (2006), Hay (2014) and USDA (2005) for Atu'u and Malaeloa in Pago Pago, American Samoa. The data prepared by Yance (in SOPAC, 2006) represent the most comprehensive rainfall intensity-duration-frequency data available for Apia. The values are generally consistent with those prepared in the present study for daily rainfall, based on the longer and more recent period of record, namely from 1960 to 2011. The original data of Yance were adjusted to be consistent with the return periods estimated using the observed data. The current return periods are presented in Table 5. Projections of the annual 99th percentile mean daily rainfall for the 2045–2065 time slice for the Samoan region were generated using the Pacific Climate Futures Exploration Tool, for both low and high emissions scenarios. Projections were prepared using all but two of the 18 available models, namely MIROC(medres) and MIROC(hires). These two models do not provide accurate simulations of the South Pacific Convergence Zone (John Clarke (CSIRO), pers. Comm.). Table 5 also presents the results of applying the ensemble trends in annual 99th percentile mean daily rainfall to the return periods for the baseline. There are small reductions in the return periods for extreme rainfall events, with the change being relatively insensitive to the choice of emission scenario. Year-to-year climate variability in Samoa and the wider Pacific islands region will continue to be strongly affected by the El Niño–Southern Oscillation. Climate projections show that, by the mid-to late twenty-first century, there will be an intensification of El-Niño-driven rainfall increases in the central and eastern equatorial Pacific (Power et al., 2013). These findings suggest that the stormwater collection and disposal systems for the Maota Fono, the LAO and the surrounding areas of the SPCRP site should be designed to take these increases into account. If the designs do not reflect the increase in extreme rainfall events there is

6. Hazard, exposure and vulnerability assessments for extreme wind gusts There is large interannual variability and no significant trend in the annual maximum wind gust recorded at Apia over the period 1993 to 2012 (Hay, 2014). A maximum gust of 61 knots (31.2 ms−1) was recorded in January 2004, during Cyclone Heta, while a maximum gust of 80 knots (41.2 ms−1) was recorded in December 2012, during Cyclone Evan. Projections of the annual 99th percentile mean daily wind speed for the 2045–2065 time slice for the Samoan region were generated using the Pacific Climate Futures Exploration Tool, for both low and high emissions scenarios. For reasons given earlier, projections were prepared using all but two of the 18 available models, namely MIROC(medres) and MIROC(hires). Consistent with the lack of a trend for the observed data for 1993 to 2011, the projections show high uncertainty and little consistency, even in the sign of any trend.

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Table 5 Rainfall amount intensity duration frequency data for apia, for present day and 2055. Rainfall for Given Duration (mm) Return Period Duration

5 min 6 min 10 min 15 min 30 min 45 min 1h 1.5 h 2h 3h 4.5 h 6h 9h 12 h 1 day

5 Year

10 Year

20 Year

50 Year

100 Year

Minutes

Present

2055 (Low)

2055 (High)

Present

2055 (Low)

2055 (High)

Present

2055 (Low)

2055 (High)

Present

2055 (Low)

2055 (High)

Present

2055 (Low)

2055 (High)

5 6 10 15 30 45 60 90 120 180 270 360 540 720 1440

11 16 23 28 41 51 61 75 86 104 127 146 169 191 211

12 17 24 30 44 55 66 80 93 112 136 157 182 206 227

13 18 25 31 46 57 68 83 96 116 141 163 188 213 235

13 18 25 32 47 58 69 85 99 118 143 162 193 224 252

14 19 27 34 51 63 74 92 106 127 154 175 208 241 271

14 20 28 35 52 65 77 95 110 131 159 181 215 249 280

18 21 28 37 56 69 82 101 116 139 173 195 231 260 291

19 23 30 40 60 74 88 108 125 150 186 210 248 280 313

20 23 31 41 62 77 91 112 130 155 193 217 257 290 324

20 24 32 43 64 79 94 116 134 159 198 222 261 300 342

22 26 34 46 69 85 101 124 144 171 213 239 281 323 368

22 27 36 48 71 88 105 129 149 177 220 247 290 334 381

22 26 36 47 70 87 102 127 147 176 215 245 286 334 380

24 28 39 51 75 93 110 136 158 189 231 263 308 360 409

24 29 40 52 78 96 114 141 164 196 239 272 319 372 423

Rainfall Intensity (mm/hour) Return Period Duration

5 min 6 min 10 min 15 min 30 min 45 min 1h 1.5 h 2h 3h 4.5 h 6h 9h 12 h 1 day

5 Year

10 Year

20 Year

50 Year

100 Year

Minutes

Present

2055 (Low)

2055 (High)

Present

2055 (Low)

2055 (High)

Present

2055 (Low)

2055 (High)

Present

2055 (Low)

2055 (High)

Present

2055 (Low)

2055 (High)

5 6 10 15 30 45 60 90 120 180 270 360 540 720 1440

135 159 135 111 83 68 61 50 43 35 28 24 19 16 9

145 172 145 119 89 74 66 53 46 37 30 26 20 17 9

150 177 150 123 92 76 68 55 48 39 31 27 21 18 10

156 177 150 126 94 77 69 57 49 39 32 27 21 19 11

168 191 161 136 101 83 74 61 53 42 34 29 23 20 11

174 197 167 140 105 86 77 63 55 44 35 30 24 21 12

213 209 166 149 111 92 82 67 58 46 38 33 26 22 12

229 225 178 160 120 99 88 72 63 50 41 35 28 23 13

237 233 184 166 124 102 91 75 65 52 43 36 29 24 13

240 240 192 171 128 105 94 77 67 53 44 37 29 25 14

258 258 207 184 138 113 101 83 72 57 47 40 31 27 15

267 267 214 190 142 117 105 86 75 59 49 41 32 28 16

264 263 215 188 139 115 102 85 74 59 48 41 32 28 16

284 283 231 202 150 124 110 91 79 63 51 44 34 30 17

294 292 239 209 155 128 114 94 82 65 53 45 35 31 18

McInnes et al. (2016) did find that factoring in an increase in cyclone intensity, consistent with IPCC projections, increased the projected height of storm tides due to more intense winds. But such changes became significant only for return periods of 200 years or longer, reflecting the influence of the more intense cyclones. Given these findings, the return periods for extreme wind gusts based on current and historic data provide the most appropriate information for conditions in 2045–2065. Therefore no significant change is anticipated in exposure and vulnerability to extreme wind gusts between the present day and 2045–2065.

While considerable interannual variability in the extreme air temperature is evident for Apia between 1941 and 2011, there is an indication of a rising trend in the maximum air temperature. Currently a maximum air temperature of at least 35 C is a relatively rare event at Apia, with a return period of approximately 870 years (Hay, 2014). Projections of the mean maximum air temperature for the 2045–2065 time slice for the Samoan region were generated using the Pacific Climate Futures Exploration Tool, for both low and high emissions scenarios. Again, projections were prepared using all but two of the 18 available models. For the low emissions scenario all 12 models were consistent in estimating a 1 C temperature increase by 2055. For the high emissions scenario an ensemble of seven models estimated a 1.3 C temperature increase, while an ensemble of three models projected an increase of 1.5 C. When the ensemble trends in maximum air temperature are applied to the return periods for baseline conditions, the results show increasing sensitivity to the selection of emissions scenario, and substantial changes in return periods between the baseline and 2045–2065. Given the general agreement between the various models used to

7. Hazard, exposure and vulnerability assessments for extreme high air temperatures Increasing air temperatures are a significant risk to the sustainability of the SPCRP, primarily due to a resulting increase in air conditioning demand and costs. Comfort levels of people attending gatherings held outside the buildings will also decrease as temperatures increase.

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generate the projections, the projected decreases in return periods to 2045–2065 have relatively high certainty and should be taken into consideration. In terms of vulnerability, the SPCRP will be exposed to increasing costs for air conditioning in the absence of attempts to “green” the building design and operations. Likewise, consideration should be given to reducing the exposure of individuals who attend gatherings outside the buildings. The air temperature increase would affect the capacity of the air conditioning plant in two ways. Firstly, the heat gained through the fabric of the building would be greater. Secondly, any air which is provided to the space would need a greater level of pre-conditioning. The design of the building (thermal mass, insulation levels, heat gains within the space) will impact on the first driver, while the ventilation rate will impact on the second driver. The air conditioning system should be designed with a peak capacity which accounts for these projected changes in temperature. It is estimated that the cooling capacity for buildings incorporated into the SPCRP may need to be increased by between 10 and 20% to account for 2055 climate projections. The cost and energy impacts would be highly dependent on the design of both the building and the air conditioning system. Alternatively, and in keeping with a “green” approach, the new buildings could be designed in such a way that appropriate comfort levels are achieved using natural ventilation, even allowing for the projected temperature increase. Occupants feel comfort through a variety of mechanisms. Thus improving air flow, and adding thermal

mass to the building to reduce the peaks in the internal temperature, may well achieve the same results as providing additional air conditioning capacity. 8. Identifying and evaluating adaptation measures Assessment of the need for, and likely effectiveness of, measures to reduce unacceptable risks, and to manage the residual risks, is based on the results of the foregoing exposure and vulnerability assessments. Anticipated costs and benefits (including reduced damage and operating costs), and other relevant criteria, are used to prioritise the identified risk reduction measures. 8.1. Scoping and screening of potential adaptation options Table 6 summarises the adaptation measures that represent possible responses to the vulnerabilities identified in the present assessment. Some measures can be treated as alternatives. For example, generally speaking, protecting the Maota Fono and LAO, or protecting the entire Parliamentary Complex, are alternative ways to reduce the same risk. Table 6 also provides the results of a screening of the potential adaptation options. Each measure was screened in terms of its practicality, acceptability and ability to reduce the identified risk, without consideration of cost and detailed technical requirements. Each measure was then assigned to one of the following categories: (1) unacceptable adaptation measure and no further assessment required; (2) a potentially effective and.

Table 6 Possible adaptation measures. Vulnerability

Screening Assessment

Levela

Site overall is so vulnerable it should not be redeveloped

It is possible to reduce risks to acceptable levels, albeit at a significant cost; the site has high cultural and historic value, which makes relocation highly undesirable Increase capacity of gutters to accommodate a 20-year event in 2055 Increase site drainage to accommodate a 100-year rainfall event in 2055 and an increase in MSL of 0.33 m; all runoff from the roof and platform of new buildings piped to mangrove area behind embankment; outlet at seaward end to be fitted with non-return flap; Adaptation measures reflected in stormtide protection and in site drainage Increase height of building platform to accommodate a stormtide (depth and velocity) for an acceptable level of risk Increase height of building services to accommodate a stormtide (depth and velocity) for an acceptable level of risk Increase height of seawall to accommodate a stormtide (depth and velocity) for an acceptable level of risk Increase height of existing flood embankment to accommodate a stormtide (depth and velocity) for an acceptable level of risk Extend the current “ornamental” wall in front of the Members' Offices to the north, making the entire wall higher and stronger; procure and have available removable flood gates that would be installed across the entrances when a cyclone warning is issued for Apia; extending the “ornamental” wall has already been considered, and rejected due to safety issues because of large crowds occupying the area in front of the Maota Fono during national celebrations Construct a new flood embankment to the north of the site, to accommodate a stormtide for an acceptable level of risk Rehabilitate and plant mangroves to west of the site and protect the mangrove ecosystem to ensure its health Procure and have available removable flood gates that would be installed in the access gaps in the seawall when a cyclone warning is issued for Apia Install adequate water storage tanks in both building platforms, not only for fire fighting but also for building water supply purposes to reduce costs and ensure adequacy of supply when the mains supply was inadequate No adaptation measures required Building fittings and other services should reflect the high salt loadings in this environment Design buildings to keep heat loads to a minimum New buildings to be designed in such a way that appropriate comfort levels are achieved using natural ventilation, even allowing for the projected temperature increase Plant appropriate shrubs and trees on retaining wall batter in order to provide shade and reduce heat load on buildings Adjust the Design Day temperature for the building cooling system to reflect the projected increase in temperature

1

Extreme Rainfall

Sea Level Stormtideb

Buildings Site

Buildings Services Parliament Complex Site

Drought Extreme Wind Gust Salt Spray Extreme High Temperature

3 3 3 3 2 3 3 1

3 2 3 2 N/A 2 2 2 2 2

a 1 = unacceptable adaptation measure; no further assessment required; 2 = a potentially effective and efficient adaptation measure; 3 = a proven adaptation measure that should be assessed in terms of cost and benefits. b Not all measures would be implemented – protecting the buildings or protecting the entire Complex are alternative ways to mitigate the same risk.

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Table 7 Estimated costs (AUD) for raising the platform level for the maota fono. Finished Floor Level (RL)

Engineered Fill

Retaining Walls

Concrete Slab

Total

Cost

Climate Change Component

Cost

Climate Change Component

Cost

Climate Change Component

Cost

Climate Change Component

2.8 2.9 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8

$83,000 $100,000 $130,000 $160,000 $190,000 $220,000 $250,000 $281,000 $311,000 $341,000 $371,000

$0 $17,000 $47,000 $77,000 $107,000 $137,000 $167,000 $198,000 $228,000 $258,000 $288,000

$168,000 $171,000 $175,000 $179,000 $182,000 $186,000 $189,000 $193,000 $197,000 $200,000 $204,000

$0 $3,000 $7,000 $11,000 $14,000 $18,000 $21,000 $25,000 $29,000 $32,000 $36,000

$331,000 $331,000 $331,000 $331,000 $331,000 $331,000 $331,000 $331,000 $331,000 $331,000 $331,000

$0 $0 $0 $0 $0 $0 $0 $0 $0 $0 $0

$582,000 $602,000 $636,000 $670,000 $703,000 $737,000 $770,000 $805,000 $839,000 $872,000 $906,000

$0 $20,000 $54,000 $88,000 $121,000 $155,000 $188,000 $223,000 $257,000 $290,000 $324,000

Efficient adaptation measure that could be considered further during the detailed design of the SPCRP; and (3) a viable adaptation measure that should be assessed in the present study, in terms of both costs and benefits. Table 6 also provides a summary of the reasons for allocating a potential measure to a specific category.

usual case of meeting current design codes (i.e. finished floor level at 2.8 m above MSL). The results in Table 8 are based on the “upper estimates” of Hoeke et al. (2013). Table 8 also presents the resulting decreases in damage costs. These are expressed as both total damage costs summed over 50 years, and as the net present value of these costs assuming a discount rate of 3%. The internal rate of return on investing in protecting the Maota Fono over the 50 years is also given. The nature of the assumed stage-damage curves is such that most of the reduction in damage costs, and hence the highest internal rates of return, occur for the initial steps of increasing the platform height. The results suggest that all reasonably foreseeable damages to the Maota Fono over its proposed 50 year lifetime as a result of stormtides up to a 100-year event can be avoided by raising the platform by 0.4 m above its current level (i.e. to a FFL of 3.7 m above MSL).

8.2. Damage costs and adaptation benefits for protecting the Maota Fono This section provides an illustrative example of estimating the costs and benefits of a category 3 adaptation option. Table 7 presents the estimated costs for raising the platform level. Allowance has been made for replacing the existing retaining walls as well as replacing the existing concrete slab across the top of the platform. The costs for risk reduction include new fill material and increasing the height of the retaining walls. Fig. 6 presents the adaptation costs as a function of the return period for the stormtide. Three scenarios are presented - low, best and upper projections of stormtide heights in 2065, reflecting the range of uncertainty in estimating stormtide height and demonstrating the additional cost of the 500 mm of “freeboard”. Table 8 presents an analysis of the changes in incremental costs of raising the platform level for the Maota Fono above the business as

8.3. Damage costs and adaptation benefits for protecting the site Table 9 presents the total costs of raising the existing seawall and embankment, was well as extending the latter. It also lists the resulting decreases in damage costs to both the Maota Fono and the LAO. The results in Table 9 are also based on the “upper estimates” of Hoeke et al. (2013). The decreases in damage costs are expressed as both the total of

Fig. 6. Adaptation costs for projected stormtide heights (Hoeke et al., 2013) for the Maota Fono (FFL allows 500 mm freeboard above estimated stormtide level).

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Table 8 Costs and benefits of protecting the maota fono. By increasing the platform height. Height of Platform Above Mean Sea Level (m)

Incremental Cost to Raise Platform

Damage Costs

Reduction in Damage Costs

Net Present Value of Damage Costs

Internal Rate of Return (%)

2.8 2.9 3.0 3.1 3.2

0 0.020 0.054 0.088 0.121

3.907 1.788 0.521 0.058 0.000

0.000 2.119 3.386 3.849 3.907

NC 0.023 0.003 0.000 0.000

NC 88.7 8.5 NC NC

(Costs are in AUD million; NC = not calculated).

the reduced costs summed over 50 years, and the net present value of these costs, assuming a discount rate of 3%. The internal rate of return on investing in protecting the site in this manner over the 50 years is also given. The nature of the assumed stage-damage curves is such that most of the reduction in damage costs, and hence the highest internal rates of return, occur over the first few height increments. The results suggest that all reasonably foreseeable damages to the Parliamentary complex over its proposed 50-year lifetime as a result of stormtides up to a 100year event can be avoided by the heights of the seawalls and embankments being at least 3.2 m above MSL. The costs of providing drainage from the upgraded Maota Fono structure (and platform) and the new LAO building, in accordance with current design standards, were also assessed. Based on the rainfall projections provided in Table 5, consideration was given to determining whether additional costs would be incurred to provide drainage from the Maota Fono platform and LAO building to accommodate projected increases in rainfall intensity related to climate change. The analysis indicated that a standard size pipe with the capacity to drain current rainfall intensities will also have the capacity to cope with future extreme rainfall events. A similar approach was taken when considering roof drainage requirements for both the Maota Fono and LAO buildings. As for the general site drainage, the capacity of a standard sized gutter that can accommodate current rainfall intensities should also be able to cope with anticipated future rainfall scenarios. No additional costs are therefore expected to be incurred when constructing the buildings.

9. Summary of the assessment findings and adaptation recommendations This study confirmed that, due to the location of the site on the low lying Mulinu'u Peninsula, inundation as a result of a cyclone-related stormtides is the highest risk for the SPCRP. By 2065, 50- and 100-year stormtides could be 3.0 m and 3.2 m above MSL, respectively, compared to 2.6 m and 3.0 m for the same events in 1990. Velocities experienced during such stormtides are projected to increase from 1.5 ms−1 (in 1990) to 1.9 ms−1 in 2055. Table 11 identifies and describes the recommended adaptation measures. Relocating the Parliamentary Complex further inland and to higher ground would alleviate all of the key risks that have been identified. However, the Government of Samoa does not consider this an acceptable risk reduction option. Raising the finished floor level of the Maota Fono to accommodate a future stormtide as large as a 100year event (i.e. floor level 3.7 m above MSL) has been shown to be a highly cost effective option. The internal rate of return is as high as 89% - for a finished floor level of 3.4 m above MSL. A comparable rate for the LAO is 159% (Hay, 2014). These rates can be compared to an internal rate of return of 20% for protecting the entire SPCRP site by raising the existing sea wall and embankment to 3.2 m above MSL, as well as extending the latter. Rainfall intensities are projected to increase with climate change under both low and high emission scenarios. However, for the SPCRP it is expected that drainage infrastructure (pipes and gutters) designed for current rainfall intensities will also be able to cope with any increases in rainfall intensities over the proposed life time of the new buildings. This means there will be no significant increase in risk mitigation costs due to increased rainfall intensities. It was recommended that future high emission rainfall intensities be adopted during the detailed design phase of the project, and that an estimated increase in MSL of 0.33 m be used for setting tail water levels in the design. A significant portion of the overall site is low lying and prone to inundation during periods of heavy rainfall. It is not considered that the site is at risk of inundation resulting from general sea-level rise (i.e. excluding stormtide situations). However, with higher intensity rainfall events and a general increase in sea level, the frequency and depth of

9. Prioritization of adaptation options The internal rate of return can be used as one criterion for prioritizing the potential adaptation measures that have been identified in this study. However, as was noted earlier, consideration should also be given to non-financial factors such as aesthetics and public perception. Table 10 presents a prioritization of the level three adaptation measures identified in Table 6, using both economic performance and non-financial considerations. Table 9 Costs and benefits of protecting the site with a seawall and embankments. Height of Seawall and Embankment above Mean Sea Level (m)

Cost to Increase Height

Damage Costs

2.8 2.9 3.0 3.1 3.2

0.884 1.159 1.218 1.277 1.338

13.654 6.306 1.844 0.205 0

(Costs are in AUD million; NC = not calculated).

11

Reduction in Damage Costs

Net Present Value of Damage Costs

Internal Rate of Return (%)

7.348 11.810 13.449 13.654

0.2210 0.0823 0.0104 0 0

20.09 7.27 NC NC NC

Weather and Climate Extremes 25 (2019) 100214

High

Low

See entry for stormtide High See entry for stormtide

Internal rate of return evaluated as part of above measure, which had an internal rate of return of 20%

The assessment findings and recommendation described above contributed to the decision that the SPCRP would involve retaining the existing podium of the Maota Fono and construction of a new building with a finished floor level of 3.5 m above MSL. This height is equivalent to the upper estimate of the height of a stormtide with a 50-year return period, thus taking into account the major risks and their uncertainties (Fig. 6). It is informative to consider the costs of the studies that informed the adaptation planning and decision making, and of the chosen adaptation measures. These are summarised in Table 12, and show that the total costs of adaptation to protect the Maota Fono from sea-level rise and 100-year event stormtides over the design life of the building are minor relative to the overall costs of the redevelopment.4 Once this and related decisions were made, the Project moved into a detailed design phase, taking into account other findings of the current

Procure and have available removable flood gates that would be installed in the access gaps in the seawall when a cyclone warning is issued for Apia

Increase height of existing seawall and embankment and construct new embankment to north of site

More cost effective to protect buildings, rather than the site; high internal rates of return, with highest values for raising the FFL of the LAO Relatively low internal rates of return

10. Design, construction and opening of the Maota Fono

4 The acquisition cost for the LiDaR data (approx. AUD500,000) used by Hoeke et al. (2013) has not been included in Table 12 as the information forms part of Australia's wider contribution to data bases that are relevant to Samoa and the wider Pacific islands region. Thus the purpose of the data investment for Samoa specifically, including the bathymetric component of the LiDaR acquisition, was to understand risks to all low-lying infrastructure of Apia, including roads, ATMs and commercial buildings. A key intent of investment was to also understand exposure of the international airport. This is why the entire northern portion of the island was flown. However, the timing of the LiDaR project in Samoa was advanced, to ensure the data would be available for the study undertaken by Hoeke et al.

Stormtide

Adaptation measures reflected in stormtide protection and in site drainage Increase height of building platform to accommodate a stormtide (depth and velocity) for an acceptable level of risk Sea Level

localised flooding during periods of heavy rainfall, as well as lower intensity stormtide events, is expected to increase. It was therefore recommended that provision be made during any future upgrade of the LAO to elevate the new staff parking area behind the building to above existing ground levels. It was also recommended that drainage through the south western end of the existing embankment be provided as part of the SPCRP. This should reduce, but not eliminate, the frequency and duration of standing water in this area during periods of heavy rainfall. During the geotechnical design component of the project consideration should be given to the risk of reduced bearing capacity of the underlying materials resulting from an increase in groundwater tables. In terms of water supply it is noted that the SPCRP site will be connected to the Apia Town Water supply, with on-site storage of rain water for fire fighting purposes. While no significant change is anticipated in drought vulnerability between present day and 2045–2055, it was recommended that rain water harvesting initiatives be investigated in conjunction with on-site fire fighting water storage, in order to mitigate against existing drought vulnerability. No significant change is anticipated in the exposure of the buildings to extreme wind gusts between present day and 2045–2055. The recommendation that AS/NZS 1170 Part 2 continue to be used for structural design is reflected in the new National Building Code of Samoa (Government of Samoa, 2017). It was also recommended that projected increases in mean maximum air temperatures be incorporated into the design of the Maota Fono and the LAO. Increased capacity may need to provide for air conditioning plants, with design of the buildings seeking to maximise natural cooling mechanisms. The current study also highlighted the value of revising Samoa's 1991 National Building Code, in terms of providing a more consistent set of guidelines regarding design principles to be adopted to protect future coastal developments from stormtides, and to provide adequate primary and secondary drainage capacity. Ideally, improved climate risk considerations should be incorporated into any upgrade of the Building Code. As noted earlier, the building code for Samoa has since been revised.

Platform of the Maota Fono could be as much as 0.5 m above current height, in order to provide adequate protection Entire site will be protected, but increased height of sea wall and embankments will have adverse impact on views Flood gates would increase the effectiveness of the existing seawall as a protection measure, which would therefore be no regrets

High Since a “business as usual” response is involved, these are no regrets adaptation initiatives Increase site drainage to accommodate a 100-year rainfall event in 2055 and an increase in MSL of 0.33 m; all runoff from the roof and platform of new buildings piped to mangrove area behind embankment; outlet at seaward end to be fitted with non-return flap

High Since a “business as usual” response is involved, this is a no regrets adaptation initiative

No additional costs are expected to be incurred, as “business as usual” gutters will have the capacity for the projected future high emission rainfall intensities No additional cost for providing drainage, as “business as usual” drainage will have the ability to cope with future rainfall intensities over the proposed 50-year lifetime of the buildings; increasing tail water levels to allow for the increase of MSL by 0.33 m should be cost neutral See entry for stormtide Increase capacity of gutters to accommodate a 20-year event in 2055 Extreme Rainfall

Table 10 Prioritization of adaptation measures identified as level 3 in Table 6.

Priority Non-financial Factors Cost - Benefit Adaptation Measure Risk

J.E. Hay, et al.

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Table 11 Recommended adaptation measures. Climate Risk Extreme Rainfall

Recommended Risk Mitigation Buildings

Parliament Complex Site

Sea-level rise and stormtide Drought

Buildings Services Parliament Complex Site

Extreme Wind Gust Salt Spray Extreme High Temperature

Increase capacity of box gutters to accommodate a 100-year rainfall event annual recurrence interval of 5 min duration in 2055 (294 mm/h) Increase capacity of eaves gutters to accommodate a 20-year annual recurrence interval of 5 min duration in 2055 (237 mm/h) Increase site drainage to accommodate a 10-year annual recurrence interval 10 min storm (167 mm/h) and an increase in MSL of 0.33 m; all runoff from the roof and platform of new buildings piped to mangrove area behind embankment; outlet at seaward end to be fitted with non-return flap; elevate the new staff parking area behind the Legislative Assembly Office to above existing ground levels; provide drainage through the south western end of the existing embankment Increase height of building platforms to accommodate a stormtide (depth and velocity) for an acceptable level of risk Increase height of building services to accommodate a stormtide (depth and velocity) for an acceptable level of risk Rehabilitate and plant mangroves to west of the site and protect the mangrove ecosystem to ensure its health Install adequate water storage tanks in both building platforms, not only for fire fighting but also for building water supply purposes, to reduce costs and ensure adequacy of supply when the mains supply is inadequate No adaptation measures required Building fittings and other services should reflect the high salt loadings in this environment Design buildings to keep heat loads to a minimum New buildings to be designed in such a way that appropriate comfort levels are achieved using natural ventilation, even allowing for the projected temperature increase Plant appropriate shrubs and trees on retaining wall batter in order to provide shade and reduce heat load on buildings Adjust the Design Day Temperature for the building cooling system to reflect the projected increase in temperature – it is expected that the Design Day Temperature may increase by up to 1.5C (i.e. increase to 32.6C).

Samoa.

Table 12 Adaptation and overall costs of the redevelopment. Activity

Cost (AUD)

Expenses related to preparing the Adaptation Brief (Roop, 2012)a Climate Risk and Adaptation Assessments (Hay, 2014) High Resolution Met-Ocean Modelling for Storm Surge Risk Analysis in Apia Redevelopment of Maota Fono (excl. CMS and Taxes) Estimated additional cost to raise the FFL to 3.5 m AMSL

5,000 71,225 320,000

Adaptation Costs as Portion of Redevelopment Costs Return on Investment

Per Cent 3.5 > 200

a

Acknowledgements The following are thanked for their contributions to the original assessments that are presented as a case study in this paper: Frances Sutherland; Bob Ale; Shin Furuno; Peter Kelly; Rhona McPhee; John Clarke; Rhys Gwilliam; Peter Lawther; Tom Tinai; Christopher Cheatham; Kevin Hennessy; Kathleen McInnes; Ron Hoeke; Isikuki Punivalu; Paul Davill; Cecilia Amosa; Mulipola Ausetalia Titimaea; and Sunny Seuseu. We also thank two reviewers for their constructive comments. Our assessments benefitted from information made available through several Australian-funded projects, namely: the South Pacific Sea Level and Climate Monitoring Project; climate data curation by the Bureau of Meteorology and the Commonwealth Scientific and Industrial Research Organisation (CSIRO); the Pacific-Australia Climate Change Science and Adaptation Planning Program, and its antecedents, the Pacific Climate Change Science Program and the Pacific Adaptation Strategy Assistance Program, under which the Pacific Climate Futures web tool was developed and LiDaR data acquisition was funded to support site specific stormtide modelling; and. the Pacific Catastrophe Risk Assessment and Financing Initiative, funded in part by Australia.

14 million 0.1 million

Plus three weeks technical and two weeks administrative time.

study. The new building meets the Samoan Building Code 2017 as well as relevant Australian and New Zealand Construction Standards. Thus the design takes into account the need for climate resilience, such as increasing the elevation of building services to accommodate a storm surge, including water storage tanks for firefighting, reducing the amount of glass in the east and west elevations, and using a higher Design Day temperature for the building cooling system, to reflect the projected increase in temperature. Tenders for construction of the new building were called in April 2015, construction began in May 2016, and the Maota Fono was officially opened in March 2019. In August 2018 Australia announced that it will also help fund a new office for the Legislative Assembly in Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.wace.2019.100214.

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J.E. Hay, et al.

Appendix 1 Photo of the new Maoto Fono.

Appendix 2 Definition of Storm Tide and Related Terms.(after Hoeke et al., 2013). Astronomical tides - tidal levels and character resulting from gravitational effects, e.g. of the Earth, Sun and Moon, without any atmospheric influences. Inverse barometer effect – adjustment of sea level to changes in barometric pressure, with low pressure allowing the sea level to rise and a high pressure tending to depress it. Run-up - the maximum vertical extent of uprush on a beach or structure above the still water level. Stormtide - the combination of astronomical tides, inverse barometer effect and wind setup. Storm surge - the combination of the inverse barometer effect and wind setup. Wave setup – the increase in mean water level due to the presence of breaking waves. Wind setup - the vertical rise in the stillwater level on the leeward side of a body of water caused by wind stresses on the surface of the water.

Geophys. Res.: Solid Earth 124. https://doi.org/10.1029/2018JB017110. Hay, J.E., 2014. Strengthened Climate Risk and Adaptation Assessments for the Samoa Parliament Complex Redevelopment Project. Submitted to AusAID through Cardno Emerging Markets (Australia) Pty Ltd 75pp. HFB, 1891. The Samoan cyclone of March 16, 1889. Nature 45 (1155), 161–162. Hoeke, R., McInnes, K., O'Grady, J., Lipkin, F., Colberg, F., 2013. High Resolution MetOcean Modelling for Storm Surge Risk Analysis in Apia, Samoa. Final Report. Commonwealth Science and Industrial Research Organization (CSIRO) December 20, 2013, 60pp. Hoeke, R., McInnes, K., O'Grady, J., Lipkin, F., Colberg, F., 2014. High Resolution MetOcean Modelling for Storm Surge Risk Analysis in Apia, Samoa – Final Report. Centre for Australian Weather and Climate Research (CAWCR), Bureau of Meteorology, Melbourne, Australia CAWCR Technical Report No. 071, 80pp. Hoeke, R., McInnes, K., O'Grady, J., 2015. Wind and wave setup contributions to extreme sea levels at a tropical high island: a stochastic cyclone simulation study for Apia, Samoa. J. Mar. Sci. Eng. 3 (3), 1117–1135. IPCC, 2001. Climate change 2001: impacts, adaptation and vulnerability. In: McCarthy, J.J., O, F., Canziani, N.A. Leary, Dokken, D.J., White, K.S. (Eds.), Contribution of Working Group II to the Third Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, UK. IPCC, 2014. Climate change 2014: impacts, adaptation, and vulnerability. In: Barros, V.R., Field, C.B., Dokken, D.J., Mastrandrea, M.D., Mach, K.J., Bilir, T.E., Chatterjee, M., Ebi, K.L., Estrada, Y.O., Genova, R.C., Girma, B., Kissel, E.S., Levy, A.N., MacCracken, S., Mastrandrea, P.R., White, L.L. (Eds.), Part B: Regional Aspects. Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 688. McInnes, K.L., O'Grady, J.G., Walsh, K.J.E., Colberg, F., 2011. The role of climate variability on storm surge risk in Fiji. J. Coast. Res. 1121–1124 SI 64 (Proceedings of the 11th International Coastal Symposium). McInnes, K.L., Hoeke, R.K., Walsh, K.J.E., O'Grady, J.G., Hubbert, G.D., 2016. Tropical cyclone storm tide assessment for Samoa. Nat. Hazards 80, 425–444. https://doi.org/ 10.1007/s11069-015-1975-4. Militello, A., Scheffner, N.W., Thompson, E.F., 2003. Hurricane-induced Stage-Frequency Relationships for the Territory of American Samoa. Technical Report CHL-98-33 Revised. U.S. Army Engineer District, Honolulu, Ft, Shatter, HI, USA 226pp. MNRE, 2007. Coastal Infrastructure Management Plan, Vaimauga Sisifo District, Implementation Guidelines. Samoa Ministry of Natural Resources and Environment

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