Rainfall and runoff regime trends in mountain catchments (Case study area: The upper Hron River basin, Slovakia)

Abstract

Thisaperresents an analysis of trends and causes of changes of selected hydroclimatic variables influencing the runoff regime in the upper Hron River basin (Slovakia). Different methods for identifying trends in data series are evaluated and include: simple mass curve analysis, linear regression, frequency analysis of flood events, use of the Indicators of Hydrological Alteration software, and the Mann-Kendall test. Analyses areerformed for data from twoeriods (1931-2010 and 1961-2010). The changes in runoff are significant, especially in terms of lower QMax and 75ercentile values. This fact is also confirmed by the lower frequency and extremity of flood events. The 1980s are considered a turningoint in the development of all hydroclimatic variables. The Mann-Kendall test shows a significant decrease in runoff in the wintereriod. The main causes of runoff decline are: the considerable increase in air temperature, the decrease in snow cover depth and changes in seasonal distribution ofrecipitation amounts.