Climatic factors are the most important of all the factors that influence the hydrograph shape of a river; this is because they are dynamic in space and time. The presence of hydrographs with a similar shape in long-term observation series of water runoff indicates that from time to time in the catchment of a river the same conditions of water runoff formation repeat. This is due to the cyclicity of climatic and – as a consequence – hydrological processes. The classification of hydrographs based on the similarity of their shapes on the Desna River (observation period 1885- 2010) was carried out using the geometrical similarity criterion (ρ) and the average Euclidean distance between values of hydrograph pairs (η). 41 classes of hydrographs, which included from 1 to 6 hydrographs, were obtained. Among them were determined 12 classes with low probability, 9 classes with medium probability and 20 classes with high probability. An analysis of the conditions of hydrograph formation for each of the identified classes was performed for the following factors: the sums of daily air temperatures and precipitation during the period of positive air temperature (from July) and the period of negative air temperatures, and also during the period of temperature transition through 0ºC up to the peak discharges, index of depth of soil freezing, index of snow water equivalent, index of soil moisture content, and index of snowmelt. In general, hydrographs which are included in one class have similar climatic conditions to those of water runoff formation. However, in some cases, a combination of different values and dynamic factors can lead to the formation of similar hydrograph shapes.
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