Research Spotlight: Reservoirs affect irrigation and river discharge to oceans



[1] Humans have long altered the water cycle by damming rivers to create reservoirs to store water. To examine the effects of large reservoirs on the global water cycle and the availability of water for irrigation, Biemans et al. analyzed reservoir operations with a global-scale hydrology and vegetation model. They found that at continental and global scales, irrigation and reservoir operation affect the timing and amount of water reaching the oceans. For instance, in Europe, reservoir operation increased February river discharge to oceans by 8% but decreased May discharge by 10%. Over a year, irrigation decreases global discharge to oceans by about 2.1%. Furthermore, the researchers found that global surface water extractions for irrigation have increased substantially along with the construction of large reservoirs during the past century. They estimate that around 460 cubic kilometers of water for irrigation is withdrawn from reservoirs annually. The authors note that by storing water and redistributing it, reservoirs significantly increase the amount available for irrigation, but in some regions the current reservoir system might not be enough to meet growing demand for water. (Water Resources Research, doi:10.1029/2009WR008929, 2011)