Trends in river runoff in Latvia for the period 1951-2020

Abstract

A time series of monthly, seasonal and annual mean specific runoff of rivers in Latvia are analysed in order to detect trends for the period 1951–2020. Trend analysis is performed by applying the Mann-Kendall test and the trend slope is calculated using Sen’s method. There were significant seasonal changes in the time series of specific runoff measured at 32 stations during the study period. In all hydrological regions, the trend values obtained for the winter season are statistically significant, but they are relatively weaker in the Eastern region. At the same time, river runoff in April and May has notably decreased, indicating a shift of the runoff maximum to an earlier time. Long-term changes in specific runoff are statistically significant in April in all hydrological regions, and only in May for the Eastern region. Generally, statistically insignificant trends in specific runoff are observed for the summer and autumn months. Annual mean specific runoff has not revealed any strong trends in spite of the increased precipitation and temperature. Clear seasonal changes have been found in several earlier studies in the Baltic countries, and they are confirmed by the current one.