Agricultural Policy Environmental eXtender model simulation of climate change impacts on runoff from a small no-till watershed

Long-term hydrologic data sets are required to quantify the impacts of management and climate on runoff at the field scale where management practices are applied. This study was conducted to evaluate the impacts of long-term management and climate on runoff from a small watershed managed with no-till (NT) system. The Agricultural Policy Environmental eXtender (APEX), a field scale hydrologic model which is capable of simulating the management and climate impacts on runoff, was used in this study. The specific objectives of the study were to (1) simulate the impacts of cropping management and tillage system on runoff and (2) simulate climate change impacts on runoff using different temperature, precipitation, and carbon dioxide (CO2) scenarios generated from the APEX model. The study was conducted on a small watershed located on the North Appalachian Experimental Watershed (NAEW) near Coshocton, Ohio. This watershed (WS 118, similar to 0.79 ha [1.95 ac]) includes NT management with two periods of crop rotations: corn (Zea mays L.)-soybean (Glycine max L.)-rye (Secale cereale L.) (CSR; 2000 to 2005) and continuous corn (CC; 2006 to 2011). The results from this study indicate that the CSR rotation showed 37% lower simulated mean annual runoff compared with that of CC under NT system. The climate change scenarios indicated runoff was most sensitive to the precipitation, and interactions of precipitation, temperature, and CO2 concentrations. The highest increase of runoff (61%) was observed with 15% increase of precipitation, and the highest reduction in runoff (47%) with 15% decrease in precipitation, demonstrating the nonlinearity of hydrological systems. The results demonstrate the benefits of cover crops in the CSR over the CC rotation under NT system and show the significant impacts of climate change on runoff response from a small, upland, agricultural watershed. For future research, climate change impacts on runoff can be assessed using downscaled climate models that take into consideration interaction among weather parameters.