An assessment of simulated warm-season rainfall variability over the Great Plains and associated land surface conditions

The warm-season rainfall variability over the US Great Plains is examined in CAM3-CLM3 climate simulations and compared with observations. The results show that compared to observations, the model simulations underestimate summertime rainfall but overestimate its standard deviation, especially for the interannual variability. Linear regression shows that the rainfall variability is connected with evapotranspiration (ET) anomalies, but mostly to evaporation rather than transpiration. Since the evaporation represents an immediate response of the land surface to atmospheric conditions but the transpiration reflects soil moisture memory with considerably longer time scales, the realism of the correlated variability between separate ET components and precipitation is an important aspect of how climate models realistically address land-atmosphere interaction. As this region is a “hot spot” of soil moisture-precipitation coupling in GLACE climate models [Koster et al. 2004], the corresponding soil moisture conditions are also examined.