IMPACT OF CLIMATE VARIABILITY ON GROUNDWATER RECHARGE IN BULGARIA (AN EXAMPLE OF KOTLENSKI SPRINGS REGION)

Abstract: Groundwater resources in Bulgaria are important sources for rural and industrial water supply. Some of the existing scenarios for future climatic development of the country predict more frequent droughts. The last drought period 1982-1994 observed in Bulgaria had negative impact on groundwater resources in the country. This paper presents the first attempt to quantify the recharge fluctuation to a karstic aquifer in Bulgaria in response to climate variability. The estimates are based on previous studies and observations on spring flows made in the frames of National Hydrogeological Network located in NIMH-BAS. More than 40-year time series are available for the most important aquifers in Bulgaria. During the 1982-1994 drought period increased air temperatures were registered, reduction in precipitation amounts and in river runoff, as well as reduced spring discharges and declining of groundwater levels. Estimate of regional recharge and its variations is made on the base of the spring flow data. The application of the method requires good knowledge of hydrogeological background and hydrological data on springs draining the massive. An example for quantifying groundwater recharge is given for the Kotelski springs region that is well studied although very complicated. Groundwater in Bulgaria is vulnerable to drought. Nowadays the groundwater management should take into consideration possible impact of climate variability and climate change on groundwater resources