Beyond peak reservoir storage? A global estimate of declining water storage capacity in large reservoirs

Water storage is an important way to cope with temporal variation in water supply anddemand. The storage capacity and the lifetime of water storage reservoirs can besignificantly reduced by the inflow of sediments. A global, spatially explicit assessment ofreservoir storage loss in conjunction with vulnerability to storage loss has not been done.We estimated the loss in reservoir capacity for a global data set of large reservoirs from1901 to 2010, using modeled sediment flux data. We use spatially explicit population datasets as a proxy for storage demand and calculate storage capacity for all river basinsglobally. Simulations suggest that the net reservoir capacity is declining as a result ofsedimentation ( $5% compared to the installed capacity). Combined with increasing needfor storage, these losses challenge the sustainable management of reservoir operation andwater resources management in many regions. River basins that are most vulnerable includethose with a strong seasonal flow pattern and high population growth rates such as the majorriver basins in India and China. Decreasing storage capacity globally suggests that the roleof reservoir water storage in offsetting sea-level rise is likely weakening and may bechanging sign.