The results of the modeling of the surface run-off in the basins of Kulunda and Suetka rivers (with the one month step) are presented. Numerical experiments show that the error of the run-off estimation for the single month of the real year can reach 50%. When mean annual values are used the error of calculation the surface run-off for the balance year makes up 15%. The calculations show that under the change of the summer thermal regime (precipitation is constant) slight change of the surface run-off is observed (when temperature varies from #2 to +2 ^oC the maximum change of the surface run-off constitutes 5%). When annual rainfall changes (from +200 to #200 mm) more significant change of the run-off takes place (from +150 to #75%, correspondingly). The latter indicates that the closed lakes (for example, Lake Kulundinskoye and Lake Chany) are important indicators of the territory paleomoistening.