SENSITIVITY OF EVAPOTRANSPIRATION OF COTTON AND SORGHUM IN WEST TEXASTO CHANGES IN CLIMATE AND CO2

In regions such as west Texas where water is scarce, changes in the wa ter balance may have a significant impact on agricultural production a nd management of water resources. We used the mechanistic soil-plant-a tmosphere simulation model ENWATBAL to evaluate changes in soil water evaporation (E) and transpiration (T) in cotton and grain sorghum that may occur due to climate change and elevated CO2 in west Texas. Clima tic and plant factors were varied individually, and in combination, to determine their impact on E and T. Of the climatic factors, E was mos t sensitive to changes in vapor pressure, and T to changes in irradian ce. Simulations suggest that if warming is accompanied by higher humid ity, the impact of climate change may be minimal. However, if the clim ate becomes warmer and less humid, ET may increase substantially. Simu lations also suggest that enhanced growth due to elevated CO2 may have a greater impact on ET than climatic change.