SUBORDINATION OF FLUCTUATIONS OF GROUNDWATER LEVELS IN THE SOUTHERN BUG RIVER BASIN TO CLIMATE CHANGE

Abstract

Problems Statementand Purpose. Prolonged flooding of territories, as well as modern drought, are only polar consequences of one, so far irreversible process – rising air temperature. And these events do not fit into normal cycles with high and low water levels. The aim of this work is to find evidence that the driving force or the main factorin changing the groundwater regime is the increase in air temperature and related meteorological events that affected the intra-annual redistribution of precipitation, groundwater recharge and surface runoff. Data & Methods. The degree of connection of GWL fluctuations with regime-forming factors was determined by statistical methods: wavelet analysis and multiplecorrelation analysis. Results. It is established that the depth of groundwater level (GWL), which was affected by the temperature in the upper part of the basin of the Southern Bug river, reaches 3.5–4.5 m after 1989. Signs of changes in the groundwater regime are manifested in the results of assessing the degree of violation of the statistical stability of a number of observations of GWL: the transition from random to hyperrandom data occurs in 1982–1983. According to the results of different statistical analysis over the past 40 years, the temperature has become dominant in terms of the impact on the regime of GWL 2.5–4.0 m. This refutes the traditional (based on observations of 1950–1970’s) statement that that the regime of groundwater with GWL 3.0–4.5 m is determined primarily by the regime of precipitation, and the active influence of surface air temperature (evaporation from GWL) in the forest-steppe zone extends only to a depth of 2.0–2.5 m. Extremes on the chronological graphs of the GWL regime and on integral curves are associated with abnormal changes in seasonal and monthly temperatures, which reflect the manifestations of global warming. It is likely that these anomalous events (primarily the transition to positive valuesof winter temperatures) cause changes in rhythm in the GWL mode (from 5–6 years cycles to 7–8 years ones and vice versa), which can be used for forecasting. From 1975 for GWL 0.5–2.0 m and from 1986 for GWL 2.5–4.0 m, due to the increase in the temperature of the cold period and increased GWL supply through infiltration, the GWL was raised. This process was accompanied by a 7–8 year cycle of changing. Deepening of the drought in the Southern Bug River Basin upper waters from 2003–2004, is manifested by the appearance and consolidation of 5–6 year cycle for smaller, and from 2011–2014 – for larger GWL, and by a significant weakening and disappearance of 7–8 year rhythms.