As a result of modelling of climate change, continental runoff is estimated to be more sensitive to changes in precipitation than temperature. For a 1øC warming it is estimated that there would be some decrease in runoff in North America and Europe but increases throughout much of the southern hemisphere. A 3-4øC warming would result in a global increase in runoff of 17-18 percent with only North America showing a slight decrease. Runoff from snowmelt may occur earlier in the year in higher latitudes reducing the runoff during the later spring and summer. In the Colorado river basin, a significant increase in potential evapotranspiration could cause a 20 percent reduction in runoff relative to precipitation and a 58 percent decrease in soil moisture storage. The change in the water balance could affect the composition of forests in the region.