Application of the method of territorial long-term forecasts to determine the maximum water discharge rates under the conditions of spring flood 2022-2023 formation across the Desna basin

Abstract

Despite the conditions of both climate change and long-term trend to decrease of hydrological characteristics of the Ukrainian rivers' spring flood that was established by many authors, the formation of high-water river floods accompanied by rising water levels and release of water to floodplains still remains probable.
 Thus, according to the data of the Ukrainian Hydrometeorological Center (UkrHMC) of the State Emergency Service of Ukraine (web: www.meteo.gov.ua), the hydrometeorological conditions of snowmelt and rain runoff formation during the autumn-winter and spring periods of 2022-2023 across the basins of the Dnipro and Desna rivers and their tributaries were characterized as those having a complex nature. This led to a rise of these rivers' water levels with flooding of floodplains, disruption of transport connections, as well as flooding of populated areas in Kyiv, Chernihiv and other Ukrainian regions.
 The purpose of this study is the issues related to determination of natural factors that lead to extreme large-scale spring floods, and long-term forecasting of maximum runoff of spring floods in 2022-2023 across the Desna River basin.
 To ensure operational forecasting support and assessment of the spring floods size across the basin of the Desna River and other left tributaries of the Middle Dnieper, the research used a method of territorial long-term forecasts of spring floods maximum runoff. The method takes into account a complex of hydrometeorological factors which, when combined annually, lead to the formation of spring floods of different sizes.
 The results of the long-term forecast for maximum water discharge rates during the spring flood in 2022-2023 retrieved from the forecasting computer complex "SEYM" show satisfactory statistical estimates of the forecast for maximum water discharge rates during a spring flood provided that a high pre-flood water content of the rivers during recession of a winter flood is considered. The forecast lead time for maximum water discharge rates of the spring flood in 2022-2023 varied from 20-30 days for small tributaries of the Desna River to two months for the Desna and Seim rivers themselves.
 Application of the method of territorial long-term forecasts of characteristics of river spring floods allows spatial monitoring of the rivers' water content provided that forecasting is conducted using the methodology of maximum water discharge rates for any rivers of a certain territory, including those with relation to which there are no observations of their water runoff.
 An early warning about a dangerous river water level during winter-spring periods can significantly reduce the scale of negative consequences and ensure achievement of socio-economic and environmental effects.