Home – Home – Jornals – Geography and Natural Resources 2019 number 3

The characteristics of heavy rains are of key importance in to calculating the maximum water flow in small rivers. We pres ent the results from studying the main regularities in the intra-annual distribution of the characteristics (precipitation amount, total precipitation and duration) of flood-forming Ural rainstorms, with the total precipitation amount over 10 mm per rainstorm, based on analyzing more than 25 thousand single rainstorms from pluviographic observations covering the 80-year-long period obtained at all available meteorological stations located in the Russian part of Tobol river basin. The average number of flood-forming rainstorms in a year is 10.1, ad in mountainous areas the number of rainstorms is 20-30 % higher than on the plain. The greatest heterogeneity in the number of rainstorms across the territory is recorded in April and October. The average month ly total precipitation amounts for rainstorms are constant throughout the year, whereas absolute maxima are observed everywhere in June. The largest duration of rainstorms is observed in the spring and autumn months. Data on the classification procedures of the behavior of precipitation within a 24-hour period are provided. It is established that for 75 % of the observed rainstorms, more than 50 % of the total precipitation amount correspond to the first one-third of their duration. Uniform precipitation amounts are characteristic only for 5 % of the observed rainstorms. A simulation of the rainstorm characteristics over an 80-year-long period has been carried out for a number of meteorological stations, based on the log-normal law; good results were obtained in the range of rare probabilities of excess (less than 10 %). The findings are of significant importance in stochastic models for the formation of heavy rains and in deterministic models based on using radar information on clouds and precipitation.