Okan Aygün, John W. Pomeroy, Martyn P. Clark, Alain Pietroniro (2022). Predicting water futures in Central Asia using a Hydrological-Glaciological Land Surface Model. Proceedings of the GWF Annual Open Science Meeting, May 16-18, 2022.

Spatial mismatches between water availability and land resources are the main triggers for current water conflicts in Central Asia. Projected glacier losses and snow shrinkage, resulting from climate change, will likely further exacerbate this mismatch, limiting water availability in the region. The impacts to the hydrological cycle resulting from the changes in climate in the region, have not previously been diagnosed using physically based glacio-hydrological models that can resolve mountain snow and glacier hydrology with confidence. This study assesses the impacts of projected climate change on the hydrology of Syr Darya River Basin, one of the two major basins in Central Asia. Syr Darya originates from the glaciated Tien Shan Mountains, crosses a semi-arid region to the Aral Sea and river water is heavily used for water supply and irrigation by four Central Asian countries. Current and future hydrological processes and natural flows were diagnosed using MESH, a Canadian physically based hydrological land surface scheme with comprehensive representation of cold regions processes. Due to the lack of observational data across the Syr Darya River Basin, we first set up, calibrated and validated a MESH model for the Ala-Archa River basin, a heavily studied headwater basin in the region, and then the modelling concepts and parameters were transferred to Syr Darya model setup. Both MESH Ala-Archa and MESH Syr Darya models were forced by the EM-Earth (0.1°) and ERA-5 (0.25°) datasets. Temperature and precipitation forcing data over 1991-2010 were seasonally perturbed using outputs of CMIP5-AR5 subset based on RCP 8.5 for the region during the 2081-2100 period. The MESH Ala-Archa model performed well on predicting streamflow, with Kling-Gupta Efficiency (KGE) scores above 0.9 and percent bias below ±1% over both calibration and validation periods. Under the climate change scenarios examined, the snowcovered period in Sry Darya River Basin decreased by more than three months, and peak SWE declined by 45%. The timing of peak streamflow advanced by a month from mid-June to mid-May, and peak discharge decreased by about 35% for the 2081-2100 period compared to recent conditions, primarily due to reduction of seasonal snow cover and secondarily due to deglaciation. The projected glacier loss was reflected by the reduced runoff in irrigation season. This study allows understanding the role of snow and glacier melt in controlling the water availability in Central Asia and can be used to inform climate adaptation strategies in the region.

AOSM2022 GWF Planetary Water Prediction (PWP) Initiative First Author: Okan Aygün (Centre for Hydrology, University of Saskatchewan, Canmore, Alberta) Additional Authors: John W. Pomeroy (Centre for Hydrology, University of Saskatchewan, Canmore, Alberta), Martyn P. Clark (Centre for Hydrology, University of Saskatchewan, Canmore, Alberta), Alain Pietroniro (Dept of Civil and Environmental Engineering, University of Calgary, Calgary, Alberta)