This study uses a regional climate model including a land-surface scheme of intermediate complexity to investigate the issue for the American Midwest. A surrogate climate-change scenario is used for the simulation of a warmer climate. The control runs are driven by observations, while the sensitivity experiments are forced by a modified set of initial and lateral boundary conditions. The modifications consist of a uniform 3K temperature increase and an attendant increase of specific humidity (unchanged relative humidity). The atmospheric CO2 concentration of the sensitivity experiments is set to four times its pre-industrial value. The simulations are conducted for the springs and summers of 4 years, corresponding to drought (1988), normal (1986, 1990) and flood (1993) conditions.
The numerical experiments do not present on average any large enhancement of summer drying under warmer environmental conditions. First, the overall changes in the hydrological cycle are of small magnitude despite the strong forcing applied. Second, precipitation increases in spring lead to a higher water storage during this season, compensating for the enhanced soil moisture depletion occurring later in the year. Though further processes would need to be accounted for in order to fully understand the potential mechanisms at play, our results suggest that the risk of enhanced summer dryness in the studied region might be less acute than previously assumed.