Abstract
Many thousands of large dam reservoirs have been constructed worldwide during the last seventy years to increase reliable water supplies and support economic growth. Because reservoir storage measurements are generally not publicly available, so far there has been no global assessment of long-term dynamic changes in reservoir water volume. We overcame this by using optical (Landsat) and altimetry remote sensing to reconstruct monthly water storage for 6,743 reservoirs worldwide between 1984 and 2015. We relate reservoir storage to resilience and vulnerability and analyse their response to precipitation, streamflow and evaporation. We find reservoir storage has diminished substantially for 23 % of reservoirs over the three decades but increased for 21 %. The greatest declines were for dry basins in southeastern Australia (−29 %), the USA (−10 %), and eastern Brazil (−9 %). The greatest gains occurred in the Nile Basin (+67 %), Mediterranean basins (+31 %) and southern Africa (+22 %). Many of the observed reservoir changes were explained well by changes in precipitation and river inflows, emphasising the importance of multi-decadal precipitation changes for reservoir water storage, rather than changes in net evaporation or (demand-driven) dam water releases.
Highlights
20 Globally the number of large reservoirs - dams impounding more than 3 million m3 (ICOLD 2020) - reached 58,713 in 2020 with a combined capacity of more than 10,000 km[3] (Chao et al 2008)
This study reconstructed monthly reservoir water storage dynamics from 1984-2015 at global scale based on satellite-derived water extent (Zhao and Gao 2018) and altimetry measurements (Birkett et al 2010)
There does not appear to be any systematic global decline in global reservoir water availability, but we found significantly decreasing trends in reservoir water volumes in southeastern Australia, southwestern USA and eastern Brazil, creating the risk that storages fall to low capacity more often (i.e., 300 weakened resilience) and endure larger deficits
Summary
20 Globally the number of large reservoirs - dams impounding more than 3 million m3 (ICOLD 2020) - reached 58,713 in 2020 with a combined capacity of more than 10,000 km[3] (Chao et al 2008). By 2015, reservoirs provide 30–40% of global irrigation water requirements, 17% of electricity generated, and various other services, including domestic and industrial water supply, recreation, fisheries, and flood and pollution control (Maavara et al 2020; REN21 2016; Yoshikawa et al 2014). Demand for water and electricity are expected to increase substantially (Crist 25 et al 2017; Zarfl et al 2015). More dams will likely be built to support increased irrigation for food production and to meet energy demand. By 2014, there were 3,700 hydropower dams either under construction or planned worldwide. The majority of these are in developing countries, in South America, Southeast Asia and Africa (Bonnema et al 2016; Zarfl et al 2015).
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