| The objectives of this study are to evaluate the impacts of land use and climate changes on streamflows and corn grain yields and to determine appropriate corn production response strategies at a small watershed scale. A hypothetical watershed was designed for this study, consisting of upstream and downstream watersheds separated by a reservoir used for irrigation. The downstream watershed is planted to grain corn.; A simulation procedure was developed containing four component models: crop physiology and soil moisture model, reservoir model, the modified GWLF streamflow model, and a weather generation model producing daily weather data from weather types which were classified by an angle-based procedure. These models were tested for sites in Indiana, New York, and Texas.; Two climate scenarios (current and future climates) and three upstream land use alternatives (forest, urban, and agricultural land uses) were designed. Future climates corresponding to a doubling of atmospheric CO{dollar}sb2{dollar} were modified from current climates based on climate changes predicted by the GFDL model. Three corn production response strategies were considered, including hybrid selections, planting date thresholds, and irrigation policies. The simulation study was applied by using weather data from Indianapolis, IN, Grand Island, NE, Albany, NY, Oklahoma City, OK, and Houston, TX.; Forest watersheds have the lowest annual streamflows and highest variations for both climatic conditions. Urban watersheds have smaller within-year variations in monthly streamflows currently, but agricultural watersheds may have smaller within-year variations in future climatic conditions.; Upstream land uses affect the availability of streamflow for irrigation. Corn grain yields are influenced by the land use effects on streamflows at the locations in Nebraska and Oklahoma with current climate. Because of precipitation increases, no land use effects were apparent under future climatic conditions.; In future climatic conditions, higher temperatures cause more serious moisture stress, higher crop maintenance respiration, and shorter grain filling periods, all of which reduce corn grain yields. However, higher temperatures also result in longer growing seasons which may allow double cropping or new longer season hybrids which may increase annual grain yields. |
