Evaluation of the hydroclimatic extremes in the upper Hron River basin, Slovakia

Abstract

This paper deals with the occurrence of hydroclimatic extremes in the upper Hron River basin in Slovakia in 1951/61–2010. Select trends in hydroclimatic parameters in 1931/61–2010 are also studied. Emphasis is placed on the occurrence, frequency, and seasonality of dry episodes and flood events. The de Martonne index, the relative precipitation index, base flow index, low flow index, linear regression, the Mann-Kendall test and IHA software were used in the analyses. Mann-Kendall test pointed to significant changes in runoff of the upper Hron River basin. The annual runoff has decreased. Changes in minimums and maximums have had a fundamental influence on this decrease, particularly in the cold half year. Major changes occurred in Q1, QMax, Q75pct and 1-day, 3-day and 7-day maximum values. Approximately since the 1980s there has been a decrease in discharge events equal to or greater than one-year flood Q1. Events where discharges were equal or greater than Q5 occurred only in the first period 1951–1980 (in 1954 and 1974). The de Martonne index, the relative precipitation index and the low flow index show similar results, the longest aboveaverage period of annual values reached from 2007 to 2010 and the longest below-average period from 1990 to 1993.