Estimation of changes in river runoff of Belarus for the period from 1961 to 2015 is made. There was a slight increase of 0.5 to 4.0% of the annual runoff due to the Western Dvina River basin and Northern and North-Eastern parts of the Dnieper River basin. The non-uniformity of changes in runoff has increased in connection with climate change, both on the territory of Belarus and its intra-annual distribution of the seasons. The forecast of runoff for the period up to 2035 showed the possibility of sharp differences between the Northern and Southern parts of the Republic, between small and large rivers. With little change in average annual runoff there is a high probability of its uneven and multi-directional in the seasons and months. Especially much the runoff can change in summer months with its decreasing in all seasons in the South part of Belarus. However, for the North part of Belarus is forecasted not as significant runoff changes like for the South.