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A comparative study of precipitation and evaporation between CMIP3 and CMIP5 climate model ensembles in semi-arid regions

March 4, 2014

The 20th-century climatology and 21st-century trend in precipitation (P), evaporation (E), and P-E for selected semi-arid Southwest U.S. and Mediterranean regions are compared between CMIP3 and CMIP5 ensembles. The 20th-century simulations are validated with precipitation from observation and evaporation from reanalysis. It is found that the SRES A1B runs in CMIP3 and RCP4.5 and RCP8.5 runs in CMIP5 produce qualitatively similar seasonal cycles of the 21st-century trend in P-E for both semi-arid regions. For Southwest U.S., it is characterized by a strong drying trend in Spring, a weak moistening trend in Summer, a weak drying trend in Winter, and an overall drying trend for the annual mean. For the Mediterranean region, a drying trend is simulated for all seasons with an October maximum and July minimum. The consistency between CMIP3 and CMIP5 scenarios indicates that the simulated trend is robust; however, while the trend in P-E is negative in spring for Southwest U.S. for all CMIP ensembles, CMIP3 predicts a strongly negative trend in P and minor negative trend in E while both CMIP5 scenarios predict a nearly zero trend in P and positive trend in E. For the 20th-century simulations, the P, E, and P-E of the two model ensembles are statistically indistinguishable for most seasons. This “stagnation” of the simulated climatology from CMIP3 to CMIP5 implies that the hydroclimatic variable biases have not decreased in the newer generation of models. Notably, over the southwestern U.S. the CMIP3 models produce too much precipitation in the cold season. This bias remains almost unchanged in CMIP5.

Baker NC, Huang H-P, 2014, A comparative study of precipitation and evaporation between CMIP3 and CMIP5 climate model ensembles in semi-arid regions, Journal of Climate, doi: 10.1175/JCLI-D-13-00398.1. Article (subscription required).

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