Impacts of climate change on river discharge in the northern Tien Shan: Results from long-term observations and modelling

Abstract

This paper presents preliminary results of investigation of the observed and projected changes in discharge of the snow- and glacier-nourished rivers of the Balkhash-Alakol basin, Kazakhstan using the long-term homogeneous records and climate projections from an ensemble of climate simulations. Positive trends in discharge were registered at most sites between the 1950s and 2010s. An increase in discharge was observed at all sites between May and October in 2000 – 2013 in comparison with the previous decades which was particularly strong in July-August at the rivers with a high proportion of glacierized area. This positive trend in discharge appears to be driven primarily by an increase in temperature. Results for four climate scenarios with spatial resolution of 25 km are presented. These scenarios were generated using regional climate model PRECIS driven by HadGEM GCM for RCP 2.6 and RCP 8.5 scenarios, HadCM3Q0 and ECHAM5 GCM for A1B scenario. While all climate experiments project increase in temperature, precipitation projections vary between models, seasons and spatially. HBV-ETH model was used to simulate the observed and future discharge for the Ulken and Kishi Almatinka rivers using climate projections from PRECIS-HadCM3Q0 simulation for A1B scenario. The results show that peak flow has already been reached at both rivers and is likely to continue for the next 10-15 years. A small decrease of 7-10% in annual discharge is projected for the Ulken and Kishi Almatinka for the 2025-2044 period increasing thereafter and the projected decline in discharge is more significant in summer.