This paper addresses the optimal operation of a group of dam reservoirs in a snowy region for adaptation to the water shortages that are expected to result from climate change. In snowy regions, climate change is likely to cause snow accumulation to decrease. This is expected to shift the snow-melting season earlier, to decrease river discharge and, consequently, to reduce water availability. Thus, the operation of existing dams should be improved. Research was made on the operation of two multipurpose dams in the Toyohira river basin, which supplies water to Sapporo (population 2 million). Using reproductions (1981-2000) and projections (2081-2100) provided by the Regional Climate Model (RCM20) of the Japan Meteorological Agency, we estimated the optimal operation of a group of reservoirs by dynamic programming. The simulation suggests that shortages of dam storage will occur if each dam is operated separately, but that coordinating the discharge operations of two dams can make up for those shortages.