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Hydrologic sciences and water resources management issues in a changing world
Hydrologic Sciences and Water Resources Management Issues in a Changing World SOROOSH SOROOSHIAN, BISHER IMAM, SHAYESTEH MAHANI, THOMAS PAGANO and MARTHA WHITAKER University of Arizona, Department of Hydrology and Water Resources, Tucson, Arizona. E-mail: [email protected]
ABSTRACT: The need for more effective management of water resources is greater than ever, particularly in arid and semi-arid regions of the world. Water resources managers must utilize more sophisticated hydrologic prediction tools. Depending on the problems, the hydrologic information needed may range from hourly forecasts (i.e., in the case of flash floods) to seasonal to interannual (i.e., in the case of reservoir operation), and to decadal to century (i.e., in the case of water supply structural design). A further complication arises from the additional uncertainty resulting from global climate change and, hence, the intensification of the hydrologic cycle. Therefore, there is no doubt that climate variability and change will have a great impact on regional water resources and the way they should be managed. Further research and datacollection activities are needed in order to quantify the impact of the intensification of the hydrologic cycle on the magnitude, direction, and frequency of floods, droughts, and other weather hazards which impact water resources management. A number of international projects have been initiated for this purpose, including the Global Energy and Water cycle EXperiment (GEWEX) of the World Climate Research Program (WCRP) and the Earth Observing System (EOS) of NASA in the United States. These projects have a strong emphasis on state-of-the-art remotesensing satellites which are capable of providing useful information for a variety of purposes related to hydrology and water resources. A review of these projects and their potential benefits to water resources management issues, particularly in the context of arid/semi-arid regions, will be presented.
INTRODUCTION There is no doubt in the minds of many experts and scientists that issues related to worldwide water resources, both in terms of quantity and quality, will be in the forefront of challenges to be addressed in the 21 st Century. The population of the Earth is expected to grow to about 8.3 billion by the year 2025 from the most recent estimate of 6.4 billion in 2000, with the largest potential increases in semi-arid regions, as shown in Figure 1. The availability of water resources will definitely be the most challenging in arid/semiarid regions of the world. These regions constitute nearly one-third of the world's land mass and, as shown in Figure 2, they span all continents, with a dominant presence in Africa, the Middle East, central Asia, and western China. Several recent reports and discussions at international forums have brought much-needed attention to the various types of water resources stresses being experienced in major river basins worldwide. This challenge, of course, is not exclusive to the developing countries, but applies also to several countries in the developed world. The water problems of arid/semi-arid regions are caused primarily by rapidly growing populations in most countries located in these areas. For instance, the most rapidly growing U.S. states are located in the semi-arid Southwest, where the population is expected
to increase from 45 million in 1995 to over 70 million by the year 2025. An example of the water resources stresses on the Colorado River basin in the southwest United States is given in Figure 3. This river basin is the primary source of water for a number of states in this area, including California, Arizona, New Mexico, Nevada, Utah, Colorado, and Wyoming. In addition, the discharge graph given in Figure 3 shows that, with the construction of the last major reservoir (Glen Canyon Dam) in 1960, all of the water resources of this fiver basin are fully utilized by the time the water reaches the Mexico border near the city of Yuma, Arizona. We may be facing a highly unsustainable situation with respect to the future availability of water, and all its intended purposes, to meet the needs of the added population. Further complicating the situation is the issue of water quality. The head waters of the Colorado River are of excellent quality, where the Total Dissolved Solids (TDS) are about 55 ppm. By the time the flow reaches the border of Arizona and Mexico, the TDS concentration has increased to 800 ppm, primarily a result of the return flow from irrigated fields, as well as from some natural causes. The status of ground-water resources worldwide is a major concern for the new millennium, particularly for the arid and semi-regions of the world. Many regions of the world are relying increasingly on
Water ResourcesPerspectives:Evaluation, Management and Policy. Edited by A.S. Alsharhan and W.W. Wood. Published in 2003 by Elsevier Science, Amsterdam, The Netherlands, p. 83-92.
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Figure 2. Global distribution of Arid/Semi-arid regions derived from USGS land cover data.
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ground-water resources, not only for domestic consumption but also for irrigation and industrial purposes. The invention of electrical and mechanical pumps has resulted, over the past 100 years, in a rapid utilization of ground-water resources in many regions of the world. Because this ground-water utilization has far exceeded the natural processes that recharge the ground-water aquifers, many areas are experiencing land subsidence and, hence, a major loss of aquifer storage capacity, which can never be replenished. Examples of localized and regional land subsidence due to depletion of water supplies are numerous worldwide (i.e., Beijing and southeastern Iran). The impact on land subsidence has varied from a uniform settling of ground levels to the occurrence of sinkholes, depending on the underlying geological stratiform. Examples from southeastern Iran, where ground-water depletion is now showing its impact through the occurrence of sinkholes, are given in Figure 4. The impacts of excessive ground-water pumping on water quality of the aquifers are of even more concern and are discussed extensively in the literature, not requiring further coverage in this paper. It is clear that, from the perspective both of surface water and ground water, the potential for sustainable development will vary significantly from one place to another. Hence, uniform solution approaches, which use the philosophy of a "one size fits all" will not work. The emphasis must be placed on the regional strategies to address these problems, with special attention paid to sociocultural and geopolitical considerations.
An additional complicating dimension is the potential effect of future climate and global change on the hydrologic cycle, which may impact the development of long-term strategies for water resources management. This is a particularly critical issue in arid/semi-arid regions, because even minor changes in climate regimes are likely to have a significant incremental impact on the hydrologic cycle, both in terms of seasonal, interannual, and decadal variability and long-term trends in precipitation and drought patterns. Evidence in support of climatically induced changes in hydrologic regimes can be seen in analyses of historical records, as well as climate model scenarios. Analyses of observational records over the past 100 years by the United States National Climatic Data Center (Quayle and Karl, 1996) show an increase in annual mean in both global temperature and precipitation. In their latest assessment, the Intergovernmental Panel on Climate Change (IPCC, 2000) provided the scenario analyses by a number of climate models, in which the global mean temperature will increase over the next 100 years, ranging from 1.4-5.8~ In the same report, climate models projected a trend in increased global mean precipitation, estimated from 7 to 15%, depending on the model. This trend suggests that the global hydrologic cycle is intensifying. The above information supports the intensification hypothesis of the hydrologic cycle at the global scale. However, from a water resources point of view, knowledge of these changes will provide little guidance for developing long-term strategies in water resources management. Most water resources issues
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s. SOROOSHIAN, B. IMAM, S. MAHANI, T. PAGANO and M. WHITAKER
are regional in nature, and decisions are often made at river basin to catchment scales. Therefore, it is of paramount importance that future climate impacts are appropriately observed and studied at regional scales to make relevant and accurate information available for decision-making purposes. The remaining sections of this paper will focus on two aspects, namely our current understanding of the climate of the Middle Eastern region and some state-of-the-art global observational systems with potential benefit to the Middle Eastern region.
Hydroclimatology of the Middle Eastern Region November 2001 marked the third consecutive year of drought in the Middle East. This drought has been the worst since 1964, inflicting at least $3.5 billion (U.S. dollar equivalent) in damages, killing 800,000 head of livestock, and drying up major reservoirs (UN OCHA, 2000). By understanding the interannual variability of precipitation in the Middle East, it is possible to predict and prepare for such droughts, thereby mitigating the damages they incur. Indeed, the International Research Institute (IRI) produces seasonal climate forecasts for the entire globe and, over the past several winters, has predicted the development and intensification of the current drought over the eastern Arabian Peninsula, Pakistan and Afghanistan.
The Middle East, which is bisected by the Tropic of Cancer, is the nexus of several different synoptic weather features. Around the Persian Gulf, a semipermanent trough of low pressure is capped at higher altitudes by anticyclone-inhibiting cloud growth and rainfall. The local seas somewhat influence the passage of cyclones, but the surrounding land masses diminish the effects which the seas may have. Strong orographic spatial heterogeneity in Iran and Turkey creates a complex mixture of orographic lifting, rain shadows, and small-scale local weather phenomena (such as intense localized seasonal winds). For further descriptions of the climatology of Iran and Turkey, see respectively, Ganji (1954) and Cullen and deMenocal (2000). Generally during winter, the Icelandic Low, the Azores (Bermuda) High, and the Asiatic High modulate the passage of frontal cyclones over Europe and the Middle East (see Figure 5). Rainfall increases to the north, to the west, and with an increase in altitude, with Turkey, the eastern Mediterranean coast, and the Zagros Mountains receiving the greatest share of precipitation for the Middle East. Winter temperature variability is greatly affected by the Atlantic Ocean features (positively correlated with Icelandic Low intensity and negatively correlated with the Azores High [r = +0.4, -0.4, respectively, not shown]). The influence of the Atlantic Ocean features, especially on precipitation, diminishes to the east as more localized phenomena gain influence. Beyond Greece, individual depressions can take a mazy path before their eventual eastern exit from the region (Ganji, 1954). It is possible that the Pacific Ocean features (the Aleutian Low and the Hawaiian High) begin to gain influence as these features move eastward (i.e., Iran, Afghanistan).
Figure 4. Example of sinkholes occurring due to over pumping of the groundwater in southeast Iran.
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Hydrologic Sciences and Water Resources Management Issues in a Changing World
During spring, the Asiatic High begins to weaken and, before the summer circulation is set into place, convective rainfall occurs over the snow-covered slopes of the northern Zagros Mountains. During the summer, strong subsiding outflow from the Indian monsoon makes the region oppressively hot, humid, and without cloud cover. Many locations, particularly central Saudi Arabia, Iraq, and Syria, have zero average rainfall during the summer months. The forested southern coast of the Caspian Sea experiences year-round rainfall associated with sea breezes and orographic lifting of local winds. Another exception during the wet summer is the portion of the southern Arabian Peninsula (i.e., Yemen) that comes under the influence of the Intertropical Convergence Zone and the rains of eastern Africa. For years, scientists have attempted to detect linkages between seasonal precipitation and remote ocean temperatures (called "teleconnections"). For example, the most widely studied climate phenomenon is the E1 Nifio/Southern Oscillation (ENSO). E1 Nifio refers to an aperiodic warming of tropical Pacific Ocean surface temperatures, and the Southern Oscillation refers to the associated shifts in pressure and wind patterns in the tropics. La Nifia is the opposite of E1Nifio, in the sense that it describes a cooling of the tropical Pacific Ocean. These events occur every 2-8 years and generally last from 1 to 3 years. For example, an extremely strong E1Nifio event occurred during 1997-1998, and a moderate-to-weak La Nifia event followed during 1998-2001. A variety of local studies have linked ENSO and Middle Eastern precipitation, although none specifically investigated the United Arab Emirates.
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Alpert and Reisin (1986) recognized an enhancement of snowfall in Jerusalem during E1Nifio events. Yakir et al. (1996) verified this precipitation enhancement during E1 Nifio by using tree ring reconstructions. From October through April, Israeli rainfall is positively correlated with various E1Nifio indices (i.e., E1Nifio bringing wet conditions; Price et al., 1998). Kadioglu et al. (1999) found a positive but small and spatially heterogeneous relationship between Turkish December rainfall and E1Nifio. Compositing revealed December precipitation enhancement in the northwest and a precipitation decrease in the southcentral and eastern parts of Turkey during E1 Nifio. Cullen and deMenocal (2000) linked Turkish climate with various large-scale climate indices. They found insignificant correlations between an E1 Nifio ocean temperature index and a composite index of 23 Turkish winter (DJFM) temperature stations and 27 winter (DJFM) precipitation stations. The correlations from 1930-1995 were 0.2 and 0.04 for temperature and precipitation, respectively (El Nifio warms and wettens Turkey). Given that the correlation coefficients were so small, the authors dismissed this result as insignificant. Felis et al. (2000) detected climate teleconnections in a 245-year coral oxygen isotope record from the northern tip of the Red Sea (south of E1 Tor, Egypt). The correlation varied from one decade to the next, but their results confirmed general impressions that E1 Nifio brings wet conditions to northeastern Africa and the Arabian Peninsula. Nazemosadat and Cordery (2000a) and Nazemosadat (1999) detected an enhancement in Iranian autumn precipitation during E1 Nifio. The correlation reaches its maximum strength in the northwestern and central parts of Iran (northwest of Tehran) and then diminishes near the Caspian Sea. The signal of E1Nifio diminishes in Iran as one enters the heart of the winter. Seasonally, less (more) than usual winter precipitation on the west coast of the Caspian Sea tends to be weakly associated with E1 Nifio (La Nifia). In contrast, during the autumn, more (less) precipitation can be weakly associated with E1 Nifio (La Nifia) over the same area. Nazemosadat (1999) also studied the influence of ENSO on summer precipitation in Oman and found that precipitation is enhanced during La Nifia and suppressed during E1 Nifio. While many of the cited authors studied specific parts of the Middle East, Barlow et al. (2002) were recently able to see the "big picture" with respect to E1 Nifio and the Middle East. During the current drought in the Middle Eastern region, the area surrounding Indonesia has been exceptionally wet. This ocean region is often called the western Pacific "warm pool"
87
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because of its very warm surface temperatures. The warm pool creates intense rainfall over most of southeastern Asia. Barlow et al. (2002) correlated warm pool ocean temperatures with global winter precipitation and found a relatively strong horseshoeshaped negative correlation from the Middle East to eastern Africa to the southern Indian Ocean (see Figure 6 for a similar analysis). By using a simplified linear dynamic model, they showed that heating in the warm pool produces Rossby waves, which disturb the jet stream over the Middle East. The authors attributed the recent extended drought in the Middle East to exceptionally warm pool temperatures. This new work is particularly exciting because it documents a physical mechanism for the linkage between the tropical Pacific Ocean and the Middle East. It also explains why past authors found weak correlations when directly comparing precipitation and ENSO: the Middle East is influenced by warm pool ocean temperatures, which are influenced (but not entirely determined) by E1 Nifio. The effect is generally strongest during the fringe of the Middle Eastern rainy season, namely September to November and March to May. During the heart of winter, it is believed that the North Atlantic Oscillation (NAO) dominates. The NAO describes interactions between the ocean and atmosphere in the North Atlantic region, modulating the strength and position of the subtropical high and polar low air masses. NAO is often measured by the pressure difference between Iceland and Gibraltar, and this difference is strongest in winter. "Low" NAO years favor the passage of winter frontal cyclones over
the Middle East, leading to wetter and warmer conditions9 In "high" NAO years, these storm tracks are pushed farther to the north, causing the Middle East to dry out. Preliminary research has shown that this band of drying and cooling during high NAO years extends from Spain through northern Africa and Italy to Turkey and the Middle East (Figure 7). This signal for temperature in Iraq is exceptionally strong, with NAO explaining nearly 50% of the variance in wintertime temperatures (Figure 8). Such a strong signal is rare among climate studies, and it indicates a potential for accurate seasonal forecasts. NAO is also strongly linked to the flow of the Tigris-Euphrates River, and the recent upward trend in NAO has been responsible for unusually low streamflow in the Middle East. While the impacts of NAO on the Middle East appear to be relatively strong, the specific impacts have not been studied in detail. Finally, there has been increasing interest in predicting climate on relatively short time scales. In the early 1970s, researchers discovered a distinct 4050 day oscillation in tropical Pacific Ocean winds and rainfall, propagating from west to east. It wasn't until the mid- to late-1980s that this oscillation, the "Madden Julian Oscillation" (MJO), received much attention. The MJO explains a significant amount of short-term variability in precipitation in the tropics. However, fairly weak correlations with mid-latitude precipitation have been documented. If a forecaster recognized the development of a wave of convection over tropical Africa, s/he could predict subsidence and drier-than-normal conditions 10-15 days later over the Middle East as the wave propagates into the Arabian
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Over the past several decades, utilization of spacebased remote sensing of the various components of the Earth, oceans, and atmosphere has increased. NASA has been planning and launching sophisticated satellites with specific sensors designed to measure different fluxes and parameters of our environment, i.e., chemistry of the atmosphere, clouds, precipitation, vegetation, and ocean temperature. It is true that the application of remote sensing in fields such as meteorology and oceanography has progressed much further than we have experienced in hydrologic sciences. With the launch of NASA' s comprehensive program, the Earth Observing System (EOS), in 1990, the scientific community began to develop and design special sensors that are becoming useful to hydrologists. The EOS satellites now allow for the study of clouds, water and energy cycles, land-surface features (such as areas of deforestation with potential for major erosion), and various aspects of the ecosystem processes. Several pictures of EOS-related satellites, which have either been recently launched or are in the final preparation launch phase, are given in Figure 9. The first primary EOS satellite, named TERRA, was launched in December 1999 and has numerous high-resolution instruments onboard its platform. Among these instruments are the Moderate Resolution Imaging SpectroRadiometer (MODIS), Clouds and the Earth's Radiant Energy System (CERES), and the Multi-angle Imaging SpectroRadiometer (MISR). The scientific community has been heavily engaged in the development of various algorithms for extraction of useful information from TERRA data. We can expect that, in a few years, TERRA data will become very helpful in areas such as parameterization of distributed hydrologic rainfallrunoff models and land-surface atmosphere models.
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Figure 8. Correlation of a North Atlantic Oscillation index with monthly mean station temperatures at Bahrain International Airport for January-April. The overall strength of this correlation is -0.64, which is exceptionally strong among climate studies.
Traditional rainfall measurements from gauges are relatively sparse and are located primarily over the land. The use of ground-based radar now enables the measurement of rainfall over a larger area, but the coverage is essentially limited to land surface and coastal regions of developed countries. Recent
89
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Coverage of PERSIANN system rainfall products is shown in Figure 10. This area covers 50~ to 50~ globally. The system uses grid infrared images of global geosynchronous satellites (GOES-8, GOES9/10, GMS-5, METEOSAT-6, and METEOSAT-7) provided by NCDC, NOAA, and TRMM TMI instantaneous rainfall products (2A12) of NASA. The "elemental" 0.25 ~ x 0.25 ~ rain rates at 30-minute intervals are aggregated to various rainfall products of resolution 1~ x 1~ 6-hour, daily, and monthly. The next phase in our development of the PERSIANN system is to move towards the finer spatial resolution of 4 km x 4 km. Other Promising Areas Applications in Hydrology
of Remote-Sensing
The Soil Moisture and Ocean Salinity (SMOS) mission is under development by the European Space Agency (Kerr et al., 2001). The baseline SMOS payload is an L band (1.4 GHz) 2D interferometric radiometer. SMOS aims at providing global maps of soil moisture over the land surfaces, with an accuracy better than 0.035 m3/m3 every 3 days, a space resolution better than 60 km, as well as vegetation water content with an accuracy of 0.2 kgm 2. Soilmoisture estimates provided by SMOS over the continents provide system continents provide system memory that can be exploited for seasonal forecasting and improving our ability to monitor water reservoirs, which are critical to the climate and economy. The Gravity Recovery and Climate Experiment (GRACE) satellite mission, sponsored by NASA, provides promising opportunities for monitoring ground-water storages. GRACE will use a pair of satellites to map tiny variations in the Earth's gravitational field. Because variations in water storage on land affect the time-dependent component of the Earth's gravitational field, GRACE will accurately map the gravity field at 2- to 4-week intervals and may soon provide global data on temporal changes in continental water storage, particularly ground-water storage (Rodell and Famiglietti, 1999). SUMMARY
In this paper, a brief review of some of the emerging water resources management issues that require a better understanding and characterization of the elements of the hydrologic cycle was presented. The potential impact of climate change and variability was discussed, with special emphasis on the Middle East region. In addition, the promising opportunities provided by state-of-the-art satellite remote sensing
for observing and estimating a number of important hydrologic fluxes and variables were also discussed were also discussed. As arid and semi-arid countries of the Middle East continue to plan for the future with various water resources issues, they may find that participation in international projects sponsored by a number of organizations, such as the World Climate Research Programme (WCRP), may be useful to their objectives. One such project is the Global Energy and Water cycle EXperiment (GEWEX), which was initiated by WCRP in 1988. The objectives of GEWEX are to observe (primarily through remote sensing) and model the hydrologic cycle and energy fluxes in the atmosphere and at the land and ocean surfaces. GEWEX is an integrated program of research, observations, and scientific activities ultimately leading to the prediction of variations in regional water resources. Given various scenarios of global climate change, arid and semi-arid countries may wish to investigate how the global hydrologic objectives of GEWEX can be of value, as we gain a greater understanding of the potential effects of hydrologic and climate variability on various parts of the globe. At a smaller, more localized scale is the National Science Foundation (NSF)-funded Science and Technology Center at the University of Arizona, entitled "Sustainability of semi-Arid Hydrology and Riparian Areas" (SAHRA). The aim of SAHRA is to integrate stakeholder-driven research, education, and knowledge transfer efforts in semi-arid regions. The research being addressed by S AHRA proceeds in five major trends, or thrust areas (TAs). The primary focus of Thrust Area 1 is measuring precipitation and snowpack above the treeline and improving predictions of runoff. This research is critical because snowpacks are often the main source for streamflow and ground-water recharge in many basins. Forecasts of spring snowmelt runoff are often critical for operating reservoirs and for planning water allocations that ultimately affect the economic and environmental health of a community. Modeling recharge and salt transport across basin floors and in ephemeral and intermittent water courses is the emphasis of Thrust Area 2. This work is of particular importance in arid and semi-arid areas, because recharge is a critical part of quantifying a basin's water budget, and knowledge of a basin's water budget is a basic facet of water resources planning. The emphasis of Thrust Area 3 is to improve our understanding of water, energy, and nutrient fluxes in riparian areas. In many arid and semi-arid regions, riparian areas support unique ecosystems and often serve as migratory flyways for a continent's bird populations.
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S. SOROOSHIAN, B. IMAM, S. MAHANI, T. PAGANO and M. WHITAKER
Human communities often reside near riparian areas because of the accessibility to ground water and river water. Thrust Area 4 works in cooperation with researchers in all of the TAs to integrate physical models with policy tools, so that the models and/or the subsequent results will be of practical use for water policies and decision-makers. Finally, Thrust Area 5 uses decision support models and policy analyses to facilitate sustainable water resource management practices among policy and decision makers. While the research that takes place within SAHRA spans both the physical and behavioral sciences at local and basin scales, researchers are also committed to producing information, analyses, curricula, expertise, and information that can ultimately increase hydrologic literacy and positively impact water policy and water resources management. It is an excellent, smaller-scale example of how one might consider more broad-reaching management of water resource issues in semi-arid regions. The integrated research of SAHRA, combined with the insight and experience of global hydrologic research and research-coordinating programs (e.g., NASA's EOS program, GEWEX, etc.), provide excellent examples of how one might consider the imperative, broad-reaching management water resource issues facing water resource managers and policy makers, particularly in arid and semi-arid regions of the world.
ACKNOWLEDGEMENTS This work was supported by NASA grants (NAG8502 and NAG8503), NOAA OGP grant (NA16GP1577), and NASA Raytheon award (300623). The authors also wish to thank Ms. Corrie Thies and Ms. Carly Davis for their help in proofreading and editing this manuscript.
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REFERENCES Alpert P. and T. Reisin, 1986. An early winter polar air mass penetration to the eastern Mediterranean. Monthly Weather Review 114:1411-1418. Barlow, M., H. Cullen, and B. Lyon, 2002. Drought in central and southwest Asia: La Nina, the warm pool, and Indian Ocean precipitation. Journal of Climate, 15(7):697-700. Cullen, H.M. and P. deMenocal, 2000. North Atlantic influence on Tigris-Euphrates streamflow. International Journal of Climatology 20(8):853-863. Felis, T. et al., 2000. A coral oxygen isotope record from the northern Red Sea documenting NAO, ENSO, and North Pacific teleconnections on Middle East climate variability since the year 1750. Paleoceanography 15(6):679-694. Ganji, M.H., 1954. A contribution to the climatology of Iran. Ph.D. Thesis, Clark University. Worcester, Massachusetts. 333 p. Kadioglu, M., Y. Tulunay, and Y. Borhan, 1999. Variability of Turkish precipitation compared to E1 Nifio events. Geophysical Research Letters 26(11): 1597-1600. Kerr, Y.H., P. Waldteufel, J.P. Wigneron, J.M. Martinuzzi, J. Font, and M. Berger, 2001. Soil moisture retrieval from space: the Soil Moisture and Ocean Salinity (SMOS) mission. IEEE Transactions in Geosciences and Remote Sensing 39(8):1729-1735. Nazemosadat, M.J., 1999. ENSO's impact on the occurrence of autumnal drought in Iran. Drought Network News 11(2):15-16. Nazemosadat, M.J. and I. Cordery, 2000a. On the relationships between ENSO and autumn rainfall in Iran. International Journal of Climatology 20:47-61. Price, C. et al., 1998. A possible link between E1Nifio and precipitation in Israel. Geophysical Research Letters 25(21):3963-3966. United Arab Emirates Ministry of Communications, Department of Meteorology, 1996. UAE Climate. Cultural Foundation Publications, Abu Dhabi, UAE. 217 p. United Nations Office for the Coordination of Humanitarian Affairs (OCHA), 2000. Iran-Drought. OCHA Situation Report No. 5. OCHA/GVA-2000/0227. Geneva, Switzerland. Yakir, D., S. Lev-Yadun, and A. Zangvil, 1996. E1 Nifio and tree growth near Jerusalem over the last 20 years. Global Change Biology 2:101-105.
ABSTRACT: The need for more effective management of water resources is greater than ever, particularly in arid and semi-arid regions of the world. Water resources managers must utilize more sophisticated hydrologic prediction tools. Depending on the problems, the hydrologic information needed may range from hourly forecasts (i.e., in the case of flash floods) to seasonal to interannual (i.e., in the case of reservoir operation), and to decadal to century (i.e., in the case of water supply structural design). A further complication arises from the additional uncertainty resulting from global climate change and, hence, the intensification of the hydrologic cycle. Therefore, there is no doubt that climate variability and change will have a great impact on regional water resources and the way they should be managed. Further research and datacollection activities are needed in order to quantify the impact of the intensification of the hydrologic cycle on the magnitude, direction, and frequency of floods, droughts, and other weather hazards which impact water resources management. A number of international projects have been initiated for this purpose, including the Global Energy and Water cycle EXperiment (GEWEX) of the World Climate Research Program (WCRP) and the Earth Observing System (EOS) of NASA in the United States. These projects have a strong emphasis on state-of-the-art remotesensing satellites which are capable of providing useful information for a variety of purposes related to hydrology and water resources. A review of these projects and their potential benefits to water resources management issues, particularly in the context of arid/semi-arid regions, will be presented.
INTRODUCTION There is no doubt in the minds of many experts and scientists that issues related to worldwide water resources, both in terms of quantity and quality, will be in the forefront of challenges to be addressed in the 21 st Century. The population of the Earth is expected to grow to about 8.3 billion by the year 2025 from the most recent estimate of 6.4 billion in 2000, with the largest potential increases in semi-arid regions, as shown in Figure 1. The availability of water resources will definitely be the most challenging in arid/semiarid regions of the world. These regions constitute nearly one-third of the world's land mass and, as shown in Figure 2, they span all continents, with a dominant presence in Africa, the Middle East, central Asia, and western China. Several recent reports and discussions at international forums have brought much-needed attention to the various types of water resources stresses being experienced in major river basins worldwide. This challenge, of course, is not exclusive to the developing countries, but applies also to several countries in the developed world. The water problems of arid/semi-arid regions are caused primarily by rapidly growing populations in most countries located in these areas. For instance, the most rapidly growing U.S. states are located in the semi-arid Southwest, where the population is expected
to increase from 45 million in 1995 to over 70 million by the year 2025. An example of the water resources stresses on the Colorado River basin in the southwest United States is given in Figure 3. This river basin is the primary source of water for a number of states in this area, including California, Arizona, New Mexico, Nevada, Utah, Colorado, and Wyoming. In addition, the discharge graph given in Figure 3 shows that, with the construction of the last major reservoir (Glen Canyon Dam) in 1960, all of the water resources of this fiver basin are fully utilized by the time the water reaches the Mexico border near the city of Yuma, Arizona. We may be facing a highly unsustainable situation with respect to the future availability of water, and all its intended purposes, to meet the needs of the added population. Further complicating the situation is the issue of water quality. The head waters of the Colorado River are of excellent quality, where the Total Dissolved Solids (TDS) are about 55 ppm. By the time the flow reaches the border of Arizona and Mexico, the TDS concentration has increased to 800 ppm, primarily a result of the return flow from irrigated fields, as well as from some natural causes. The status of ground-water resources worldwide is a major concern for the new millennium, particularly for the arid and semi-regions of the world. Many regions of the world are relying increasingly on
Water ResourcesPerspectives:Evaluation, Management and Policy. Edited by A.S. Alsharhan and W.W. Wood. Published in 2003 by Elsevier Science, Amsterdam, The Netherlands, p. 83-92.
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ground-water resources, not only for domestic consumption but also for irrigation and industrial purposes. The invention of electrical and mechanical pumps has resulted, over the past 100 years, in a rapid utilization of ground-water resources in many regions of the world. Because this ground-water utilization has far exceeded the natural processes that recharge the ground-water aquifers, many areas are experiencing land subsidence and, hence, a major loss of aquifer storage capacity, which can never be replenished. Examples of localized and regional land subsidence due to depletion of water supplies are numerous worldwide (i.e., Beijing and southeastern Iran). The impact on land subsidence has varied from a uniform settling of ground levels to the occurrence of sinkholes, depending on the underlying geological stratiform. Examples from southeastern Iran, where ground-water depletion is now showing its impact through the occurrence of sinkholes, are given in Figure 4. The impacts of excessive ground-water pumping on water quality of the aquifers are of even more concern and are discussed extensively in the literature, not requiring further coverage in this paper. It is clear that, from the perspective both of surface water and ground water, the potential for sustainable development will vary significantly from one place to another. Hence, uniform solution approaches, which use the philosophy of a "one size fits all" will not work. The emphasis must be placed on the regional strategies to address these problems, with special attention paid to sociocultural and geopolitical considerations.
An additional complicating dimension is the potential effect of future climate and global change on the hydrologic cycle, which may impact the development of long-term strategies for water resources management. This is a particularly critical issue in arid/semi-arid regions, because even minor changes in climate regimes are likely to have a significant incremental impact on the hydrologic cycle, both in terms of seasonal, interannual, and decadal variability and long-term trends in precipitation and drought patterns. Evidence in support of climatically induced changes in hydrologic regimes can be seen in analyses of historical records, as well as climate model scenarios. Analyses of observational records over the past 100 years by the United States National Climatic Data Center (Quayle and Karl, 1996) show an increase in annual mean in both global temperature and precipitation. In their latest assessment, the Intergovernmental Panel on Climate Change (IPCC, 2000) provided the scenario analyses by a number of climate models, in which the global mean temperature will increase over the next 100 years, ranging from 1.4-5.8~ In the same report, climate models projected a trend in increased global mean precipitation, estimated from 7 to 15%, depending on the model. This trend suggests that the global hydrologic cycle is intensifying. The above information supports the intensification hypothesis of the hydrologic cycle at the global scale. However, from a water resources point of view, knowledge of these changes will provide little guidance for developing long-term strategies in water resources management. Most water resources issues
85
s. SOROOSHIAN, B. IMAM, S. MAHANI, T. PAGANO and M. WHITAKER
are regional in nature, and decisions are often made at river basin to catchment scales. Therefore, it is of paramount importance that future climate impacts are appropriately observed and studied at regional scales to make relevant and accurate information available for decision-making purposes. The remaining sections of this paper will focus on two aspects, namely our current understanding of the climate of the Middle Eastern region and some state-of-the-art global observational systems with potential benefit to the Middle Eastern region.
Hydroclimatology of the Middle Eastern Region November 2001 marked the third consecutive year of drought in the Middle East. This drought has been the worst since 1964, inflicting at least $3.5 billion (U.S. dollar equivalent) in damages, killing 800,000 head of livestock, and drying up major reservoirs (UN OCHA, 2000). By understanding the interannual variability of precipitation in the Middle East, it is possible to predict and prepare for such droughts, thereby mitigating the damages they incur. Indeed, the International Research Institute (IRI) produces seasonal climate forecasts for the entire globe and, over the past several winters, has predicted the development and intensification of the current drought over the eastern Arabian Peninsula, Pakistan and Afghanistan.
The Middle East, which is bisected by the Tropic of Cancer, is the nexus of several different synoptic weather features. Around the Persian Gulf, a semipermanent trough of low pressure is capped at higher altitudes by anticyclone-inhibiting cloud growth and rainfall. The local seas somewhat influence the passage of cyclones, but the surrounding land masses diminish the effects which the seas may have. Strong orographic spatial heterogeneity in Iran and Turkey creates a complex mixture of orographic lifting, rain shadows, and small-scale local weather phenomena (such as intense localized seasonal winds). For further descriptions of the climatology of Iran and Turkey, see respectively, Ganji (1954) and Cullen and deMenocal (2000). Generally during winter, the Icelandic Low, the Azores (Bermuda) High, and the Asiatic High modulate the passage of frontal cyclones over Europe and the Middle East (see Figure 5). Rainfall increases to the north, to the west, and with an increase in altitude, with Turkey, the eastern Mediterranean coast, and the Zagros Mountains receiving the greatest share of precipitation for the Middle East. Winter temperature variability is greatly affected by the Atlantic Ocean features (positively correlated with Icelandic Low intensity and negatively correlated with the Azores High [r = +0.4, -0.4, respectively, not shown]). The influence of the Atlantic Ocean features, especially on precipitation, diminishes to the east as more localized phenomena gain influence. Beyond Greece, individual depressions can take a mazy path before their eventual eastern exit from the region (Ganji, 1954). It is possible that the Pacific Ocean features (the Aleutian Low and the Hawaiian High) begin to gain influence as these features move eastward (i.e., Iran, Afghanistan).
Figure 4. Example of sinkholes occurring due to over pumping of the groundwater in southeast Iran.
86
Hydrologic Sciences and Water Resources Management Issues in a Changing World
During spring, the Asiatic High begins to weaken and, before the summer circulation is set into place, convective rainfall occurs over the snow-covered slopes of the northern Zagros Mountains. During the summer, strong subsiding outflow from the Indian monsoon makes the region oppressively hot, humid, and without cloud cover. Many locations, particularly central Saudi Arabia, Iraq, and Syria, have zero average rainfall during the summer months. The forested southern coast of the Caspian Sea experiences year-round rainfall associated with sea breezes and orographic lifting of local winds. Another exception during the wet summer is the portion of the southern Arabian Peninsula (i.e., Yemen) that comes under the influence of the Intertropical Convergence Zone and the rains of eastern Africa. For years, scientists have attempted to detect linkages between seasonal precipitation and remote ocean temperatures (called "teleconnections"). For example, the most widely studied climate phenomenon is the E1 Nifio/Southern Oscillation (ENSO). E1 Nifio refers to an aperiodic warming of tropical Pacific Ocean surface temperatures, and the Southern Oscillation refers to the associated shifts in pressure and wind patterns in the tropics. La Nifia is the opposite of E1Nifio, in the sense that it describes a cooling of the tropical Pacific Ocean. These events occur every 2-8 years and generally last from 1 to 3 years. For example, an extremely strong E1Nifio event occurred during 1997-1998, and a moderate-to-weak La Nifia event followed during 1998-2001. A variety of local studies have linked ENSO and Middle Eastern precipitation, although none specifically investigated the United Arab Emirates.
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Alpert and Reisin (1986) recognized an enhancement of snowfall in Jerusalem during E1Nifio events. Yakir et al. (1996) verified this precipitation enhancement during E1 Nifio by using tree ring reconstructions. From October through April, Israeli rainfall is positively correlated with various E1Nifio indices (i.e., E1Nifio bringing wet conditions; Price et al., 1998). Kadioglu et al. (1999) found a positive but small and spatially heterogeneous relationship between Turkish December rainfall and E1Nifio. Compositing revealed December precipitation enhancement in the northwest and a precipitation decrease in the southcentral and eastern parts of Turkey during E1 Nifio. Cullen and deMenocal (2000) linked Turkish climate with various large-scale climate indices. They found insignificant correlations between an E1 Nifio ocean temperature index and a composite index of 23 Turkish winter (DJFM) temperature stations and 27 winter (DJFM) precipitation stations. The correlations from 1930-1995 were 0.2 and 0.04 for temperature and precipitation, respectively (El Nifio warms and wettens Turkey). Given that the correlation coefficients were so small, the authors dismissed this result as insignificant. Felis et al. (2000) detected climate teleconnections in a 245-year coral oxygen isotope record from the northern tip of the Red Sea (south of E1 Tor, Egypt). The correlation varied from one decade to the next, but their results confirmed general impressions that E1 Nifio brings wet conditions to northeastern Africa and the Arabian Peninsula. Nazemosadat and Cordery (2000a) and Nazemosadat (1999) detected an enhancement in Iranian autumn precipitation during E1 Nifio. The correlation reaches its maximum strength in the northwestern and central parts of Iran (northwest of Tehran) and then diminishes near the Caspian Sea. The signal of E1Nifio diminishes in Iran as one enters the heart of the winter. Seasonally, less (more) than usual winter precipitation on the west coast of the Caspian Sea tends to be weakly associated with E1 Nifio (La Nifia). In contrast, during the autumn, more (less) precipitation can be weakly associated with E1 Nifio (La Nifia) over the same area. Nazemosadat (1999) also studied the influence of ENSO on summer precipitation in Oman and found that precipitation is enhanced during La Nifia and suppressed during E1 Nifio. While many of the cited authors studied specific parts of the Middle East, Barlow et al. (2002) were recently able to see the "big picture" with respect to E1 Nifio and the Middle East. During the current drought in the Middle Eastern region, the area surrounding Indonesia has been exceptionally wet. This ocean region is often called the western Pacific "warm pool"
87
S. SOROOSHIAN, B. IMAM, S. MAHANI, T. PAGANO and M. WHITAKER
because of its very warm surface temperatures. The warm pool creates intense rainfall over most of southeastern Asia. Barlow et al. (2002) correlated warm pool ocean temperatures with global winter precipitation and found a relatively strong horseshoeshaped negative correlation from the Middle East to eastern Africa to the southern Indian Ocean (see Figure 6 for a similar analysis). By using a simplified linear dynamic model, they showed that heating in the warm pool produces Rossby waves, which disturb the jet stream over the Middle East. The authors attributed the recent extended drought in the Middle East to exceptionally warm pool temperatures. This new work is particularly exciting because it documents a physical mechanism for the linkage between the tropical Pacific Ocean and the Middle East. It also explains why past authors found weak correlations when directly comparing precipitation and ENSO: the Middle East is influenced by warm pool ocean temperatures, which are influenced (but not entirely determined) by E1 Nifio. The effect is generally strongest during the fringe of the Middle Eastern rainy season, namely September to November and March to May. During the heart of winter, it is believed that the North Atlantic Oscillation (NAO) dominates. The NAO describes interactions between the ocean and atmosphere in the North Atlantic region, modulating the strength and position of the subtropical high and polar low air masses. NAO is often measured by the pressure difference between Iceland and Gibraltar, and this difference is strongest in winter. "Low" NAO years favor the passage of winter frontal cyclones over
the Middle East, leading to wetter and warmer conditions9 In "high" NAO years, these storm tracks are pushed farther to the north, causing the Middle East to dry out. Preliminary research has shown that this band of drying and cooling during high NAO years extends from Spain through northern Africa and Italy to Turkey and the Middle East (Figure 7). This signal for temperature in Iraq is exceptionally strong, with NAO explaining nearly 50% of the variance in wintertime temperatures (Figure 8). Such a strong signal is rare among climate studies, and it indicates a potential for accurate seasonal forecasts. NAO is also strongly linked to the flow of the Tigris-Euphrates River, and the recent upward trend in NAO has been responsible for unusually low streamflow in the Middle East. While the impacts of NAO on the Middle East appear to be relatively strong, the specific impacts have not been studied in detail. Finally, there has been increasing interest in predicting climate on relatively short time scales. In the early 1970s, researchers discovered a distinct 4050 day oscillation in tropical Pacific Ocean winds and rainfall, propagating from west to east. It wasn't until the mid- to late-1980s that this oscillation, the "Madden Julian Oscillation" (MJO), received much attention. The MJO explains a significant amount of short-term variability in precipitation in the tropics. However, fairly weak correlations with mid-latitude precipitation have been documented. If a forecaster recognized the development of a wave of convection over tropical Africa, s/he could predict subsidence and drier-than-normal conditions 10-15 days later over the Middle East as the wave propagates into the Arabian
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Over the past several decades, utilization of spacebased remote sensing of the various components of the Earth, oceans, and atmosphere has increased. NASA has been planning and launching sophisticated satellites with specific sensors designed to measure different fluxes and parameters of our environment, i.e., chemistry of the atmosphere, clouds, precipitation, vegetation, and ocean temperature. It is true that the application of remote sensing in fields such as meteorology and oceanography has progressed much further than we have experienced in hydrologic sciences. With the launch of NASA' s comprehensive program, the Earth Observing System (EOS), in 1990, the scientific community began to develop and design special sensors that are becoming useful to hydrologists. The EOS satellites now allow for the study of clouds, water and energy cycles, land-surface features (such as areas of deforestation with potential for major erosion), and various aspects of the ecosystem processes. Several pictures of EOS-related satellites, which have either been recently launched or are in the final preparation launch phase, are given in Figure 9. The first primary EOS satellite, named TERRA, was launched in December 1999 and has numerous high-resolution instruments onboard its platform. Among these instruments are the Moderate Resolution Imaging SpectroRadiometer (MODIS), Clouds and the Earth's Radiant Energy System (CERES), and the Multi-angle Imaging SpectroRadiometer (MISR). The scientific community has been heavily engaged in the development of various algorithms for extraction of useful information from TERRA data. We can expect that, in a few years, TERRA data will become very helpful in areas such as parameterization of distributed hydrologic rainfallrunoff models and land-surface atmosphere models.
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Figure 8. Correlation of a North Atlantic Oscillation index with monthly mean station temperatures at Bahrain International Airport for January-April. The overall strength of this correlation is -0.64, which is exceptionally strong among climate studies.
Traditional rainfall measurements from gauges are relatively sparse and are located primarily over the land. The use of ground-based radar now enables the measurement of rainfall over a larger area, but the coverage is essentially limited to land surface and coastal regions of developed countries. Recent
89
Hydrologic Sciences and Water Resources Management Issues in a Changing World
Coverage of PERSIANN system rainfall products is shown in Figure 10. This area covers 50~ to 50~ globally. The system uses grid infrared images of global geosynchronous satellites (GOES-8, GOES9/10, GMS-5, METEOSAT-6, and METEOSAT-7) provided by NCDC, NOAA, and TRMM TMI instantaneous rainfall products (2A12) of NASA. The "elemental" 0.25 ~ x 0.25 ~ rain rates at 30-minute intervals are aggregated to various rainfall products of resolution 1~ x 1~ 6-hour, daily, and monthly. The next phase in our development of the PERSIANN system is to move towards the finer spatial resolution of 4 km x 4 km. Other Promising Areas Applications in Hydrology
of Remote-Sensing
The Soil Moisture and Ocean Salinity (SMOS) mission is under development by the European Space Agency (Kerr et al., 2001). The baseline SMOS payload is an L band (1.4 GHz) 2D interferometric radiometer. SMOS aims at providing global maps of soil moisture over the land surfaces, with an accuracy better than 0.035 m3/m3 every 3 days, a space resolution better than 60 km, as well as vegetation water content with an accuracy of 0.2 kgm 2. Soilmoisture estimates provided by SMOS over the continents provide system continents provide system memory that can be exploited for seasonal forecasting and improving our ability to monitor water reservoirs, which are critical to the climate and economy. The Gravity Recovery and Climate Experiment (GRACE) satellite mission, sponsored by NASA, provides promising opportunities for monitoring ground-water storages. GRACE will use a pair of satellites to map tiny variations in the Earth's gravitational field. Because variations in water storage on land affect the time-dependent component of the Earth's gravitational field, GRACE will accurately map the gravity field at 2- to 4-week intervals and may soon provide global data on temporal changes in continental water storage, particularly ground-water storage (Rodell and Famiglietti, 1999). SUMMARY
In this paper, a brief review of some of the emerging water resources management issues that require a better understanding and characterization of the elements of the hydrologic cycle was presented. The potential impact of climate change and variability was discussed, with special emphasis on the Middle East region. In addition, the promising opportunities provided by state-of-the-art satellite remote sensing
for observing and estimating a number of important hydrologic fluxes and variables were also discussed were also discussed. As arid and semi-arid countries of the Middle East continue to plan for the future with various water resources issues, they may find that participation in international projects sponsored by a number of organizations, such as the World Climate Research Programme (WCRP), may be useful to their objectives. One such project is the Global Energy and Water cycle EXperiment (GEWEX), which was initiated by WCRP in 1988. The objectives of GEWEX are to observe (primarily through remote sensing) and model the hydrologic cycle and energy fluxes in the atmosphere and at the land and ocean surfaces. GEWEX is an integrated program of research, observations, and scientific activities ultimately leading to the prediction of variations in regional water resources. Given various scenarios of global climate change, arid and semi-arid countries may wish to investigate how the global hydrologic objectives of GEWEX can be of value, as we gain a greater understanding of the potential effects of hydrologic and climate variability on various parts of the globe. At a smaller, more localized scale is the National Science Foundation (NSF)-funded Science and Technology Center at the University of Arizona, entitled "Sustainability of semi-Arid Hydrology and Riparian Areas" (SAHRA). The aim of SAHRA is to integrate stakeholder-driven research, education, and knowledge transfer efforts in semi-arid regions. The research being addressed by S AHRA proceeds in five major trends, or thrust areas (TAs). The primary focus of Thrust Area 1 is measuring precipitation and snowpack above the treeline and improving predictions of runoff. This research is critical because snowpacks are often the main source for streamflow and ground-water recharge in many basins. Forecasts of spring snowmelt runoff are often critical for operating reservoirs and for planning water allocations that ultimately affect the economic and environmental health of a community. Modeling recharge and salt transport across basin floors and in ephemeral and intermittent water courses is the emphasis of Thrust Area 2. This work is of particular importance in arid and semi-arid areas, because recharge is a critical part of quantifying a basin's water budget, and knowledge of a basin's water budget is a basic facet of water resources planning. The emphasis of Thrust Area 3 is to improve our understanding of water, energy, and nutrient fluxes in riparian areas. In many arid and semi-arid regions, riparian areas support unique ecosystems and often serve as migratory flyways for a continent's bird populations.
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S. SOROOSHIAN, B. IMAM, S. MAHANI, T. PAGANO and M. WHITAKER
Human communities often reside near riparian areas because of the accessibility to ground water and river water. Thrust Area 4 works in cooperation with researchers in all of the TAs to integrate physical models with policy tools, so that the models and/or the subsequent results will be of practical use for water policies and decision-makers. Finally, Thrust Area 5 uses decision support models and policy analyses to facilitate sustainable water resource management practices among policy and decision makers. While the research that takes place within SAHRA spans both the physical and behavioral sciences at local and basin scales, researchers are also committed to producing information, analyses, curricula, expertise, and information that can ultimately increase hydrologic literacy and positively impact water policy and water resources management. It is an excellent, smaller-scale example of how one might consider more broad-reaching management of water resource issues in semi-arid regions. The integrated research of SAHRA, combined with the insight and experience of global hydrologic research and research-coordinating programs (e.g., NASA's EOS program, GEWEX, etc.), provide excellent examples of how one might consider the imperative, broad-reaching management water resource issues facing water resource managers and policy makers, particularly in arid and semi-arid regions of the world.
ACKNOWLEDGEMENTS This work was supported by NASA grants (NAG8502 and NAG8503), NOAA OGP grant (NA16GP1577), and NASA Raytheon award (300623). The authors also wish to thank Ms. Corrie Thies and Ms. Carly Davis for their help in proofreading and editing this manuscript.
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