RAPID: Initial Assessment of IPCC AR5 Multi-model Ensembles for Hydroclimatic Features at Global and Regional Scales

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This is one of 16 Rapid Response (RAPID) projects funded as the result of a Dear Colleague Letter (NSF 11-006) encouraging diagnostic analyses of climate model simulations prepared for the Intergovernmental Panel on Climate Change Fifth Assessment Report (IPCC AR5). Research conducted in these projects is expected to lead to more detailed model intercomparisons, better understanding of robust model behaviors, and better understanding and quantification of uncertainty in future climate simulations.This project examines changes in hydroclimate in model simulations prepared for the AR5, using observational datasets to evaluate model performance in variables including precipitation, evapotranspiration, soil moisture, and runoff. A key issue to be addressed is the effect of land use and land cover change (LULC), which is expected to be significant for the hydrological cycle on regional spatial scales. Between 1700 and 2000, the global extent of natural vegetation decreased by 45%, and agricultural land area increased by 500%. In addition, a number of LULCC impacts have been found in model sensitivity studies, including radiative cooling of global and regional climate as a result of increase in surface albedo, regional warming due to decrease in evapotranspiration, and global warming due to CO2 emission from land cover change. The simulation ensemble prepared for the AR5 is the first of its kind to include simulations of the response to LULC alone, so that the climatic impact of this potentially important forcing can be assessed through comparisons of model simulations forced by LULC, greenhouse gas increases, and other forcing factors. Thus, work under this grant will explore both the ability of climate models to simulate important hydroclimate variables and the extent to which these variables are affected by LULC.The broader impact of the project lies in its support of the IPCC AR5, which is intended to provide information on climate change and its consequences to decision makers worldwide. Decision makers will benefit from an assessment of the quality of the climate models used to project climate changes due to global warming, as well as an evaluation of the impact of LULC on climate (particularly the hydrological cycle) at regional and global scales.