Quantifying and Comparing the Intensification of Extreme Rainfall Frequency from NCEP and ERA40 Reanalysis Data

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Monday, 18 January 2010: 4:15 PM
B304 (GWCC)
Shih-Chieh Kao, ORNL, Oak Ridge, TN; and A. R. Ganguly

More intense and frequent rainfall extremes may be expected in a warming climate. A plausible physical mechanism is the increased moisture-holding capacity of the warmer atmosphere according to the Clausius-Clapeyron relation, along with a positive feedback caused by increased evaporation and updraft leading to an amplification of rainfall extremes. In order to confirm and quantify the intensified frequency of extreme rainfall events, the return period of annual maximum precipitation from both National Centers for Environmental Prediction 50-year Reanalysis (NCEP) and European Centre for Medium-range Weather Forecasts 40-year Reanalysis (ERA40) data are evaluated on a grid-by-grid basis using the generalized extreme value distribution associated with a 30-year moving window on 6-hourly rainfall. Both NCEP and ERA40 rainfall return periods are found to consistently decrease with time, indicating that extreme storms have progressively become more frequent. More drastic changes are projected over certain regions of the globe owing to large geographical variability of the return periods. The non-stationary and non-homogeneous nature of rainfall extremes has implications for the management of water resources, flood hazards, and hydraulic infrastructures.