IMPROVING THE VALIDATION OF MODEL-SIMULATED CROP YIELD RESPONSE TO CLIMATE-CHANGE - AN APPLICATION TO THE EPIC MODEL

Crop models have been used extensively to simulate yield response to v arious scenarios of climate change. Such simulations have been inadequ ately validated, limiting their utility in policy analysis. In this re search, it is argued that the performance of crop models during recent years of extreme weather conditions relative to current normals may g ive a better indication of the validity of model simulations of crop y ields in response to climate change than performance during the full r ange of climate conditions (as is done now). Twenty years of the clima te record (1971-1990) are separated into different growing season temp erature and precipitation classes (normal years, hot/cold extremes, we t/dry extremes) for 7 weather stations in eastern Nebraska, USA. The E rosion Productivity Impact Calculator (EPIC), a crop growth model, is used to simulate crop yields with each of the above weather classes. S tatistical comparisons are made between simulated yields, observed yie lds and observed yields detrended of technology influences. Based on t hese comparisons, we conclude that EPIC reliably simulates drop yields under temperature extremes, some which approach the types of climate conditions that may become more frequent with climate change. Simulati ons with precipitation extremes are less reliable than with the temper ature extremes but are argued still to be credible. Confidence in crop simulations during years mimicking climate warming scenarios appears warranted.