Thursday, 13 February 2003
A Test of Irrigation's influence on Precipitation using RAMS
The Texas High Plains hosts one of the largest hydrologic disturbances in North America, with an area of over 6 x 109 m3 of irrigation water annually. Irrigation enhances precipitation downwind, yielding storms of greater duration, length, and accumulation. Previous research has estimated that a 6% to 18% enhancement of summer precipitation attributable to irrigation falls ~90 km downwind of the irrigated region. Qualitatively, this phenomenon can be explained by the increase in instability and latent heat flux caused by the irrigation water. Here we test this influence quantitatively through the use of a mesoscale circulation model (RAMS). Simulations of precipitation based on observed irrigation rates produce realistic (but not identical) spatial precipitation patterns in comparison to those observed in nature; relative humidity, surface temperature and other quantities showed a tendency towards drier and warmer conditions. We examine what threshold in irrigation is necessary to significantly influence precipitation patterns from a series of simulations at various levels of irrigation, ranging from 10% to 100% of current application rates.