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The main goal of the analysis presented in the paper is to contribute to a clearer understanding of climate changes in Bulgaria, assessing the long-term changes in annual characteristics of surface temperature and precipitation in the period 1961-2020 and providing climate projections to the end of the 21st century. During the last decades of the 20th century, a tendency towards warming occurred in Bulgaria. Since the 1990s, only four years have had negative temperature anomalies compared to the reference period 1961-1990. Changes in the precipitation regime are also apparent, with increasing frequency of days with both torrential rainfall and dry, hot weather. The analysis of future climate is focused on the projected changes under the four RCP climate change scenarios for selected ETCCDI climate indices, computed on a yearly basis: absolute maximum temperature (TXx), absolute minimum temperature (TNn), the maximum number of consecutive frost days (CFD), the maximum number of consecutive summer days (CSU), precipitation sum (RR), number of heavy precipitation days (RR10mm) and maximum number of consecutive dry days (CDD). The projected significant warming is manifested in the spatial patterns and temporal evolution of all considered temperature indicators. Despite the predicted decreasing precipitation trend, especially in Southeast Bulgaria, the changes are statistically significant only for scenario RCP8.5. [ABSTRACT FROM AUTHOR]

Many studies confirm a shift to warmer climate in South East Europe. In Bulgaria, warming trends have been registered since the end of the last century, and different scenarios show increased air temperatures in the future. In the face of climate change, it is a challenge to assess its effect on water resources. The aim of the paper is to evaluate the possible impact of climate change on the discharge of two springs from the Lovech Tarnovo karst basin. This study uses the monthly water balance method to compare the future regime with the baseline regime for two karst springs. For calculations, the software WaterbalANce is applied, which is based on the Thornthwaite–Mather method. The monthly time series of temperature and precipitation for simulations are used from the meteostations neighbor to the springs (stations Pleven for Krushuna and Veliko Tarnovo for Musina). For the purposes of this study, monthly water balance calculations are performed for the baseline scenario S00 (1976–2000) and a set of future climate development scenarios Snn. The first index refers to absolute change of temperature, and the second – to relative change of precipitation. The scenarios S10 and S20 mean change only of temperature, +1.5°C and +3.5°C respectively. The S11 and S21 scenarios assume a 10% decrease in precipitation in addition to the corresponding temperature changes. The input data for any scenario other than the baseline scenario are obtained by corresponding changes in the time series of temperature and precipitation. The results of the water balance calculations show the negative impact of the increased temperature (flow reduction for the Musina spring by 13% and 25%, respectively, only for temperature change, +1.5°C and +3.5°C, respectively). An additional 10% reduction in precipitation will lead to a 33% and 44% drop in average discharge, respectively. Similar results are obtained for the flow rate of the Krushuna spring. Overall, these results show the serious negative impact of future climate change on the discharge of the studied springs. [ABSTRACT FROM AUTHOR]