Technical Abstract: Soil erosion under future climate change is very likely to increase due to projected increases in frequency and magnitude of heavy storms. The objective of this study is to quantify the effects of common cropping and tillage systems on soil erosion and surface runoff during 2010-2039 in central Oklahoma. A combination of 18 cropping and tillage systems is evaluated using the Water Erosion Prediction Project (WEPP) model for 12 climate change scenarios projected by four GCMs (CCSR/NIES, CGCM2, CSIRO-Mk2, and HadCM3) under three emissions scenarios (A2, B2, and GGa). Tillage systems include conventional, reduced, delayed, and no-till. Cropping systems include continuous monoculture (winter wheat, soybean, sorghum, and cotton) and double crops of winter wheat and summer soybeans. Compared with the present climate, overall t-tests (n=12) show that during the next 30 years mean precipitation will decrease by some 6% (>98.5% probability), daily precipitation variance increase by 12% (>99%), and mean temperature increase by 1.36 °C (>99%). Despite the projected decreases in precipitation amounts, the overall averaged runoff and soil loss will increase by 19.5% and 43.5%, respectively, due to increased occurrences of large storms. Soil loss rates are positively related to the degree of tillage disturbances in all cropping systems. Compared with the conventional tillage, reduced till, delayed till, and no-till substantially reduce soil loss rates, showing that adoption of conservation tillage systems will be effective in controlling soil erosion in the next 30 years. Cropping systems also affect runoff and soil loss under climate change. Both simulated runoff and soil loss decrease from continuous cotton to soybean to sorghum to wheat in all four tillage systems, indicating that winter wheat is a preferred choice for controlling runoff and soil loss in the region.