The Tigris–Euphrates river basin is known for supporting ancient human civilizations because of rich agricultural land around the rivers. The basin lies primarily in the three present-day countries of Turkey, Syria, and Iraq, and still provides crucial resources for the surrounding communities and ecosystems. Since 2002, less rainfall and more evaporation has led to water shortages in the rivers and groundwater supply, a trend that is likely to continue under a warming climate. Inconsistent monitoring and a lack of transparency surrounding hydrological data have led to an incomplete understanding of water availability and use in this region, though satellite data has provided some information on water storage in recent decades. A recent paper, supported in part by the Climate Program Office’s Climate Observations and Monitoring (COM) Program, uses the satellite observations in conjunction with a process-based land surface model to better understand climate impacts on water storage in the Tigris–Euphrates river basin.
Li-Ling Chang of Harvard University and COM-supported scientist Guo-Yue Niu of the University of Arizona, engineered three model experiments to look at climate impacts seasonally, from year to year, and on a decadal time scale. The results, published in the Journal of Hydrometeorology, show that climate variability from year to year has the greatest impact on water storage in this region, primarily due to long droughts and quick drying processes accelerated by plant transpiration. Decadal variability plays the next largest role, because of a long-term trend in less rainfall with more evaporation. Satellite measurements show that water storage in the rivers and groundwater decreased by 0.93 millimeters per month from 2002 through 2017, and this study determined that about 61% of this trend was due to changes in climate, while 39% was due to direct human activities like groundwater pumping and surface withdrawal. These results provide a critical framework to be used in future research to simulate the link between climate and water storage, as well as highlighting the importance of plant processes and drought on water resources and ecosystem health. This work contributes to a COM goal to use both observations and modeling to develop and analyze datasets that can be readily utilized by the earth system/climate modeling community.