Global Warming Affecting Global Water Budget
New research published in the Proceedings of the National Academy of Sciences indicates that global warming is accelerating the rate of evaporation from the ocean in lower latitudes, increasing the intensity of storms in the tropics and Arctic area, and overall causing more fresh water to flow from rivers into the ocean. Researchers from the University of California at Irvine, the Indian School of Mines, and elsewhere used satellite data—a novel approach in contrast to standard computer models—to look at precipitation, evaporation, and sea level for a 13-year period from 1994 to 2006 to evaluate changes in the global water budget. The satellite data were used in the absence of worldwide records of river discharge, and showed that global freshwater discharge varies considerably from year to year and is strongly influenced by El Niño cycles, such that less than normal discharge occurs during El Niño years.
During the study period, discharge into oceans increased on average 540 km3 per year, due largely to a corresponding increase in ocean evaporation of 768 km3 per year—an increase of 18 percent. The scientists acknowledged that 13 years is not sufficient to determine long-term global discharge trends, but noted that if the existing trend does continue, that would indicate an increasing intensity of the global hydrologic cycle.
In an interview with ScienceDaily, lead researcher Jay Famiglietti noted that the increase of discharge results from increased precipitation on land, which might at first seem a good thing, except it is falling in places that don’t need more water, and in heavier storms that cause considerable damage.