After accounting for evapotranspiration and runoff due to local water management strategies, humans may be consuming more fresh water and altering the water cycle to a greater degree than previously thought, a new study suggests. If correct, the results raise the total global freshwater footprint of humanity by 18%. In the past much research has focused on how water management affects factors such as river fragmentation and diversion, but only recently has the importance of more inconspicuous factors, such as evapotranspiration, become evident. Fernando Jaramillo and Georgia Destouni sought to determine whether water management strategies (e.g., dams and irrigation) are affecting the ratio of evapotranspiration to precipitation. They analyzed physical changes of 100 basins between two periods, 1901-1954 and 1955-2008. Results from their models reveal a significant increase in evapotranspiration in the latter period, as well as a decrease in the rates of water runoff. This change in evapotranspiration was more likely to be affected by local water management of humans compared to other variables tested, such as geographic location of the basin or atmospheric climate change. These human-induced local changes in evapotranspiration were found to have a significant impact on a global level, increasing the average human consumption of fresh water by 3563 km3/year, or 18% higher than a recent estimate of humanity's current global water footprint. The authors suggest this new estimate is a considerably more unsustainable level.
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Science