CONDITIONS FOR THE FORMATION OF SURFACE RUNOFF, WHICH IS FORMED AS A RESULT OF HEAVY AND DANGEROUS PRECIPITATION WITHIN URBANIZED AREAS

Abstract

The research investigates atmospheric precipitation, which according to Ukrainian national regulation has reached the criteria of heavy (≥ 50 mm at ≤ 12 hours) and dangerous (15 – 49 mm at ≤ 12 hours). A total of 98 cases of heavy precipitation (2005 – 2018), and 14 cases of dangerous precipitation (2017 – 2018) were analyzed. The research focuses on the formation conditions and volumes of surface runoff that forms on various types of underlying surface. To obtain a statistically valid classification, a cluster analysis of heavy and dangerous precipitation was carried out. The analysis allowed to distinguish three blocks or clusters, one of which corresponds to the type “mix” of heavy and slight precipitations during the development of frontal stratus clouds with so-called “submerged or flooded” convection, the second cluster corresponds to the type “heavy precipitations”, the third cluster is similar to the first cluster, but is marked by a decrease in the intensity of processes. The degree of connection between the intensity of heavy precipitation and the height of the clouds top was investigated. As a result, it was found that there is an inverse relation between the values. The physical features of the processes of cloud and precipitation formation was considered. The exceptional role of convective clouds in individual frontal massifs and also in the form of “submerged or flooded convection” in the massifs of stratus clouds in the formation of significant volumes of rainwater on the underlying surface was noted. The structure of the temporal changes in precipitation intensity was established: the maximum intensity values, the time of their occurrence, the availability and number of amplification waves and their temporal parameters. On the basis of the obtained indicators, the quantity of the surface runoff for determined processes and for amplification periods were calculated. As a result, it was found that the surface runoff, which formed in the built-up areas, exceeds the surface runoff from the moderately built-up area with almost no artificial pavement by 100 – 300 %.