River streamflow changes in the catchment of the Vilyuy reservoir, Eastern Siberia

The aim of the study is to assess river streamflow changes in the catchment area of the Vilyuy reservoir in the upstream area of the Vilyuy River, tributary of the Lena River. We analysed 2,556 time series with duration of 30, 35, 40 and 45 years sampled from the dataset of monthly discharges for eight hydrological gauges with data availability periods from 40 to 50 years. The result of a statistical trend test depends on the time series length and the coverage. The May and June river streamflow practically does not change. Most of the statistically significant positive trends were found in April, September and November. Among the eight gauges, the largest fractions of positive trends were found for the Akhtaranda River and the Vilyuy River, the northern tributaries of the Vilyuy Reservoir. Negative trends prevail on the Chona River that flows from the south and has discontinuous permafrost in the basin.