THE EFFECT OF CHANGES IN DAILY AND INTERANNUAL CLIMATIC VARIABILITY ON CERES-WHEAT - A SENSITIVITY STUDY

We investigate the effect of changes in daily and interannual variabil ity of temperature and precipitation on yields simulated by the CERES- Wheat model at two locations in the central Great Plains. Changes in v ariability were effected by adjusting parameters of the Richardson dai ly weather generator. Two types of changes in precipitation were creat ed: one with both intensity and frequency changed; and another with ch ange only in persistence. In both types mean total monthly precipitati on is held constant. Changes in daily (and interannual) variability of temperature result in substantial changes in the mean and variability of simulated wheat yields, With a doubling of temperature variability , large reductions in mean yield and increases in variability of yield result primarily from crop failures due to winter kill at both locati ons. Reduced temperature variability has little effect. Changes in dai ly precipitation variability also resulted in substantial changes in m ean and variability of yield. Interesting interactions of the precipit ation variability changes with the contrasting base climates are found at the two locations. At one site where soil moisture is not limiting , mean yield decreased and variability of yield increased with increas ing precipitation variability, whereas mean yields increased at the ot her location, where soil moisture is limiting. Yield changes were simi lar for the two different types of precipitation variability change in vestigated. Compared to an earlier study for the same locations wherei n variability changes were effected by altering observed time series, and the focus was on interannual variability, the present results for yield changes are much more substantial. This study demonstrates the i mportance of taking into account change in daily (and interannual) var iability of climate when analyzing the effect of climate change on cro p yields.