Abstract Author: Randal Koster
Abstract Title: Drought-Induced Increases in Air Temperature: Variations with SST Regime
Abstract: The ability of drier-than-average conditions to induce locally warmer temperatures is strongly dependent on hydroclimatological regime. If a region is normally very wet, evaporation may be insensitive to soil moisture changes, so that a drier-than-average soil would produce the same evaporation rates and thus no change in evaporative cooling. If, on the other hand, the region is not so wet, then drier conditions can reduce evaporation (and evaporative cooling), leading to a general warming.
The experiments performed by the U.S. CLIVAR Drought Working Group provide a unique opportunity to examine how different SST regimes can lead to different hydroclimatological regimes over land and thus to changes in the nature of evaporation/temperature feedback. The analyses show, for a number of AGCMs, a tendency for anomalously warm Pacific temperatures to lead to wetter soil conditions in the U.S. Great Plains and thus to a reduction in the ability of the land to increase air temperature during (relatively) dry periods. When the Pacific is anomalously cold, on the other hand, the opposite occurs, at least for some models: the land is shifted into a drier regime, leading to a greater impact of (relative) dryness on temperature.