Ilgalaikių hidrologinių eilių (debitų) statistinis tyrimas

Abstract

Results of statistical tests on trend detection in hydrological time series of annual peak discharge of Ne¬munas River and some of its tributaries are presented. The longest data series of River Nemunas at Smali-ninkai (194 year) and Nemajunai (85 year), data of some other rivers - mainly tributaries of River Nemunas with a data series of 50 year was selected for analysis of change detection in peak flow. All data are without missing values and gaps in records, 15 rivers representing all hydrological regions of Lithuania with the least impact of human activity (no reservoirs, water transfer etc.) were selected. One parametric (Linear regression) and two nonparametric statistical tests applied to for trend detections in peak discharges. The significant decreasing trend in longest data series 1812-2005 of River Nemunas was de¬tected; however significant jump at 1956-1960 was detected. Then splitting this data into two series were de¬tected different trends 1812-1955 - positive trend, and 1956-2005 negative trend. To estimate possible impact on test results of Kaunas hydropower another records (gauging station in the upstream from Kaunas HP) were tested and results were almost identical. I show a void effect of hydropower on trends of peak flow. Analysis of other 15 rives with records of 50 years (12 of them belongs to Nemunas basin) gave different results - 7 of them has statistically significant decreasing trends and the rest not significant decreasing trends. The impact of global climate change on peak flow during spring floods is evident, and changes in seasonal redistribution of river flow is a most resulting factor.