Beyond peak reservoir storage? A global estimate of declining water storage capacity in large reservoirs
Water storage is one of the primary mechanisms for coping with increasing variability of water supply and demand that can be expected with growing population and a changing climate. Man-made reservoirs can currently store about 15% of the global annual runoff. A similar amount of water is stored in one of the most important natural storage components - seasonal snow packs. The amount of water stored in each of those man-made and natural systems is roughly equivalent to the total annual anthropogenic water withdrawals. Storage in seasonal snow packs is declining as a result of climate-driven changes in snowfall and snowmelt. At the same time, reservoir storage is declining as a result of sedimentation and limited construction of new reservoirs. We use a global hydrological model, combined with a global data set of ~6000 large reservoirs to simulate changes in reservoir and snow pack water storage and analyze impacts of those changes on seasonal water availability using a set of scenarios for changing climate conditions. Reservoir sedimentation is simulated using global erosion and sedimentation data sets and validated with observed reservoir storage loss. Results indicate annual loss rates between 0.5 and 1.0% of the installed capacity for most reservoirs, outpacing the storage increases through the construction of new reservoirs for the last decades so that reservoir storage is declining globally. With most reservoirs being about 50 years old, these losses threaten the sustainability of reservoir operation and can pose significant challenges to water resources management. Similarly, seasonal snow storage is declining at about 0.5% per year for the last 20 years. Even without changes in the magnitude of total precipitation, there can be significant changes in basin hydrology if there are climate-driven changes in snowfall and snowmelt, potentially away from the period (summer) when demand for irrigation, water supply, or hydropower production is high. These shifts in the timing can therefore result in significant socio-economic impacts through effects on food production or hydropower. Regions must vulnerable to dwindling total storage capacity include the southern slopes of the Himalaya, the east slopes of the Tibetan Plateau, and the basins in the Western US.
Fall Meeting, American Geophysical Union (AGU)
American Geophysical Union Publications
Wisser, D., Frolking, S., Wada, Y. and Bierkens, M. (2012), Beyond peak water storage? A global estimate of declining water storage in reservoirs and snow packs, Abstract GC31D-08 presented at 2012 Fall Meeting, AGU, San Francisco, Calif., 3-7 Dec.