ДОСЛІДЖЕННЯ ДЕФІЦИТІВ ВОДНОСТІ ТА ІНДЕКСІВ ПОСУХИ ДЛЯ ЗОНИ НЕДОСТАТНЬОЇ ВОДНОСТІ УКРАЇНИ

Abstract

The study of the formation of water deficits on rivers in the zone of the insufficient water content of Ukraine is presented in the article. To determine the deficits, the “threshold” method was used, which involves comparing the daily water discharges in the low water period with the values of the minimum runoff of a given probability of exceeding. Long-term data of average daily and average monthly minimum water discharges during the winter and summer-autumn period on rivers located in different areas of river basins and significantly differing in the catchment area, namely the Southern Bug River – Oleksandrivka (A = 46200 km2), Kinska River – Pologi (A = 353 km2), Obitichna River – Primorsk (A = 1300 km2) for the observation period from 1953 to 2018 inclusive was used. In cases where runoff values ​​were less than Q90% or Q97%, they were considered deficient (90%) or extremely deficient (97%). The dynamics of deficits in time are analyzed, and the number of such events by decades, frequency, average volume, duration, and intensity are determined. The chronological course of runoff volumes and deficits (90%) is graphically presented. Analyzing the obtained diagrams, it can be noted that naturally, the largest water deficit was observed in low-water years (below normal), and accordingly, the lack of deficit is characteristic of multi-water periods (above normal). Additionally, extreme deficits were also estimated (97%) for the Southern Bug River – Oleksandrivka township. The study also presents the results of the calculation of various drought indices. For the rivers of the study area, using the DrinC drought calculator were calculated – the river runoff drought index (SDI), standardized precipitation index (SPI), agricultural standardized precipitation index (aSPI), drought research index (RDI), effective drought research index (eRDI) , and its relationship with water discharges during the summer-autumn period was analyzed. Long-term data of average monthly water discharges at 6 hydrological gauge (Kodyma river – Katerynka river, Ingul river – Novogorozhene river, Ingul river – Sednivka village, Kinska river – Polohy town, Kilchen river- Oleksandrivka Persha village, Kalchyk river – Kremenivka village) were used as initial information and as also average monthly air temperature and monthly precipitation at 6 meteorological stations (Odessa, Kherson, Kropyvnytskyi, Zaporizhia, Dnipro, and Mariupol). Analyzing the obtained results, it can be noted that drought indices provide an opportunity to study climatic and hydrological trends, characterize drought, assess the severity of drought, and promote early assessment of the effects of drought. In particular, the SDI index correlates well with water discharges, which opens up opportunities for forecasting runoff in the dry period.