River runoff formation

Runoff occurs as a result of rainfall or melting snow and ice  in the mountains. In both cases, part of the water flowing to the surface of the earth is spent primarily on filling negative forms of microrelief (depressions) and absorbing into the soil. Only after filling individual depressions and, moreover, after the moment when the intensity of rain or melting of snow and ice begins to exceed the intensity of infiltration, a runoff occurs

Water flows down the surface of the earth, usually not in a continuous layer, but in the form of separate thin streams or rivulets, which merge together, reach the channels of first temporary streams, and then form constant streams carrying their waters in the formed channel. Runoff occurring at the surface of the earth is called surface or slope runoff. Runoff occurring along the channel network of the catchment area is called channel or river runoff. Surface runoff is not identified with the concept of surface water. Surface waters include the waters of rivers, lakes, and reservoirs. In many places, such as, for example, in the forest zone, surface runoff is usually small, and sometimes even absent. Most of the rain and snow water flows down in other ways.  As it percolates through the soil, these waters replenish the stocks of soil and groundwater and enter the river network by underground routes in the form of soil and groundwater runoff from the aeration zone and the groundwater itself from deeper aquifers.

In this regard, soil (subsurface) runoff and underground (ground) runoff are distinguished. River runoff is the total surface and groundwater runoff. The total river runoff is divided into two components by means of hydrograph dismemberment: surface (flood) and underground runoff. The latter is the most stable.

 different landscape zones and within zones, the ratio between surface and underground runoff are not the same, which creates specific features of the river runoff regime and its distribution over the territory. The climate affects the runoff not only directly, but also through other natural factors: soil, vegetation, relief. 

Runoff is a complex natural process due to the influence of a complex of physical and geographical factors and economic activity. The main factors of runoff, which determine its development, are climatic. Against the general background of climate influence on the formation of runoff and its value, the influence of other, non-climatic factors is manifested.