ИСТИНА

Our study is aimed at detection of directional trends in streamflow data observed in four large rivers (Lena, Selenga, Vyatka, and Pechora) located in different climatic zones and attribution of the detected changes to climate drivers. We consider detection and attribution as interrelated study stages within a suggested hypothesis testing framework with the use of a hydrological model developed on the basis of the ECOMAG modelling platform. First, we test the significance of the trends in the observed streamflow data series of 74 to 82 years long and evaluate the model’s ability to reproduce the trends, so that the trends in the simulated data are statistically indistinguishable from the corresponding observed trends.Herewith, the model is forced by the reanalysis climate data. Then, for the basins where the model reproduces the trends, we move to the attribution stage of the study. At this stage, the hydrological model is forced by the counterfactual (detrended) climate data prepared within the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP3a) (Mengel et al., 2021). If the trend is not detected in the counterfactual-climate-forced simulations, we conclude that the detected observed changes are likely to be attributed to the climate trend. We found that the trends fitted to the observed annual flow series are statistically significant for all the four basins, and the trends fitted to the corresponding simulated series are significant too. Herewith, the differences between the detected trends in the observation and simulation data are insignificant for three basins out of four (except the Pechora). For high flow indicators, the trend detection conditions were met for two basins – the Lena and the Selenga, while for the Vyatka and Pechora the model overestimated the changes. Use of the counterfactual data as the input into the hydrological model resulted in removing trends from simulated annual and high flow series, which allowed us to conclude that the directed changes statistically detected in the observed flow series, are most likely to be attributed to climate change for the periods of observations. In terms of annual flow, we consider this proven for the Lena, Selenga and Vyatka rivers; in terms of high flow - for the Lena and Selenga rivers. Regional differences in basin mechanisms governing the detected changes are analyzed. Powered by