Long-term trends of rainfall and runoff regime in upper Otava River basin

The floods experienced recently in the Czech Republic gave rise to numerous discussions over the changed environment and related potential impacts on the rainfall and runoff processes. The main aim of our research project was to determine long term trends of rainfall and runoff regime in Otava River basin. The rainfall-runoff analyses using both the single and double mass curves over the period of the hydrologic observations were taken as a basic method. Beside mean discharge, precipitation, snow and air temperature trends, analysis of land cover change and human impact on the river network and drainage areas development were applied too. The greatest deviations were widely observed in the period between the 2nd half of the seventies and in the 1st half of the eighties. It has been related to the one of repeatedly coming rather humid episodes and correspond to major human influences on the river network. The whole system came slowly back to its initial condition in the early nineties. Standard statistical testing methods were applied to confirm the trends. The Wilcoxon single and paired samples test, and furthermore the Mann-Kendall non-parametric test were used. Trend detection using both tests also confirmed a different development of the discharges and precipitation regime in the Ostružná and upper Blanice River basins in the period 1975-1982. The runoff trend deviation has been related to the nature and human factors, mainly to current climatic changes and changes of landscape retention potential.