This chapter examines CO2-induced change in hydrology, using of general circulation models of climate with various complexities. Two long-term integrations of a climate model are performed with normal and above-normal concentration of carbon dioxide. To facilitate the identification of the CO2-induced change superposed on natural hydrologic fluctuation, it is assumed that the above-normal concentration has four times the normal value. The temperature of the continental surface is determined such that the condition of the local thermal equilibrium is satisfied among various surface heat balance components. A change in snow depth is computed as a net contribution from snowfall, sublimation, and snowmelt that is determined from the requirement of surface heat balance. In order to balance the quasi-steady state of the model atmosphere, the increase in the area mean rate of evaporation should be matched by a similar increase of precipitation. It is suggested to extend the period of numerical time integration of a model in a climate sensitivity experiment in order to obtain a result with higher statistical significance.
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