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Saturday, April 30, 2011

F. Giorgi et al., J. Climate (2011), Higher hydroclimatic intensity with global warming

Higher hydroclimatic intensity with global warming

F. Giorgi*, E-S. Im*, E. Coppola*, N. S. Diffenbaugh**, X. J. Gao***, L. Mariotti*, and Y. Shi***
* Earth System Physics Section, International Centre for Theoretical Physics, Trieste, Italy
** Department of Environmental Earth System Science and Woods Institute for the Environment, Stanford University, Stanford, CA, USA
*** National Climate Center, Chinese Meteorological Administration, Beijing, China


Because of their dependence on water, natural and human systems are highly sensitive to changes in the hydrologic cycle. We introduce a new measure of hydroclimatic intensity (HY-INT), which integrates metrics of precipitation intensity and dry spell length, viewing the response of these two metrics to global warming as deeply interconnected. Using a suite of global and regional climate model experiments, we find that increasing HY-INT is a consistent and ubiquitous signature of 21st century greenhouse gas-induced global warming. Depending on the region, the increase in HY-INT is due to an increase in precipitation intensity, dry spell length, or both. Late 20th century observations also exhibit dominant positive HY-INT trends, providing a hydroclimatic signature of late 20th century warming. We find that increasing HY-INT is physically consistent with the response of both precipitation intensity and dry spell length to global warming. Precipitation intensity increases due to increased atmospheric water holding capacity. Rather, increases in mean precipitation are tied to increases in surface evaporation rates, which are lower than for atmospheric moisture. This leads to a reduction in the number of wet days and an increase in dry spell length. Our analysis identifies increasing hydroclimatic intensity as a robust integrated response to global warming, implying increasing risks for systems that are sensitive to wet and dry extremes and providing a potential target for detection and attribution of hydroclimatic changes.

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