Wednesday, 17 January 2007: 4:30 PM
Impact of vegetation feedback on the response of precipitation to antecedent soil moisture anomalies over North America
213A (Henry B. Gonzalez Convention Center)
To investigate how vegetation feedback modifies the impact of initial soil moisture anomalies on the subsequent precipitation over North America, a series of ensemble simulations are carried out with the coupled CAM-CLM model. The CLM model includes a predictive vegetation phenology scheme so that the coupled model can represent interactions between soil moisture, vegetation and precipitation at the seasonal timescale. The focus of this study is on how vegetation feedback varies with the timing and direction of initial soil moisture anomalies. During summer, wet soil moisture anomalies lead to increased vegetation growth, and the resulting vegetation anomalies enhance the response of precipitation to the initial soil wetness via increased evapotranspiration and surface heating. Therefore, the soil moisture-vegetation-precipitation feedback is positive under wet summer soil moisture anomalies. The response of vegetation to dry soil moisture anomalies in the summer months, however, is not significant due to a dry bias in the model, so the resulting vegetation feedback on precipitation is minimal. To soil moisture anomalies in spring, vegetation shows delayed response since vegetation growth is limited by both cold temperature and water availability in that time of the year. During the summer following spring soil moisture anomalies, vegetation feedback is negative, i.e., it tends to suppress the response of precipitation.