Thursday, 13 January 2005: 11:30 AM
Increasing Midwestern dew points: Is this a result of changing agricultural practices?
Daily average dew points (DADPs) were examined at 64 central U.S. NWS first-order stations from 1949-2000 to identify temporal trends in the occurrence of summer (June-August) extreme surface dew point days (DADP equal to or greater than 22°C). Temporal patterns based on four 13-year periods indicated that much of the Midwest experienced a consistent increase in extreme DADPs through time while those along the Gulf Coast remained generally unchanged until the last 13-year period (1988-2000). A comparison of the mean frequency of extreme DADPs from an earlier (1949-1976) to later (1977-2000) period indicated that the greatest percent increases also occurred in the Midwest. Smaller increases to the south of this area suggest that these increases are not primarily linked to advection from the Gulf of Mexico, rather they are related to changes in a regional moisture source. This moisture source appears to be related to enhanced levels of evapotranspiration from corn and soybean crops, which have experienced a near doubling in total acreage from 1950 to 2000. Thus, even minor regional land-use changes, such as changing from one type of agricultural focus (general farming) to another (primarily row crop farming of corn and soybean), can have enormous implications on the regional climate.