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PCMDI > WCRP CMIP3 Model Output > Diagnostic Subprojects Printer Friendly Version
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  • Pryor, S.C. and J.T. Schoof, Changes in precipitation seasonality over the contiguous USA.. J. Geophys. Res. In press.

Consequences of possible changes in annual total precipitation are dictated, in part, by the timing of precipitation events, and changes therein. Herein we investigate historical changes in precipitation seasonality over the US using observed station precipitation records to compute a standard seasonality index (SI) and the day-of-year on which certain percentiles of the annual total precipitation were achieved (percentile day-of-year). Mean SI from the majority of stations exhibits no difference in 1971-2000 relative to 30-year periods earlier in the century (1911-1940 and 19741-1970). However, analysis of the day-of-year on which certain percentiles of annual total precipitation were achieved indicate spatially coherent patterns of change. In some regions the mean day of the year on which the 50th percentile of annual precipitation was achieved differed by 20-30 days between 1971-2000 and 1911-1940 and 1971-2000 and 1941-1970. Output from 10-AOGCM simulations of 1971-2000, 2046-2065 and 2081-2100 are used to determine whether AOGCMs are capable of representing the seasonal distribution of precipitation, and to examine possible future changes. Many of the AOGCMs qualitatively capture spatial patterns of seasonality during 1971-2000, but there is considerable divergence between AOGCMs in terms of future changes. Seven of the ten 10 AOGCM indicate some evidence for earlier attainment of the 50th percentile accumulation in 2047-2065 over Missouri and Kansas, implying a continuation of the C20th tendency towards relative increases in precipitation receipt during winter and early spring. However, this is also a region in which the AOGCM exhibit substantial biases in percentile day-of-year during the historical period.

Last Updated: 2008-08-21

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