Abstract/Summary

This thesis examines stable isotope composition of precipitation, groundwater, components of the cryosphere, and streamflow in six glacierized catchments in Central Asia. Runoff from the mountain catchments sustains river flow in this water-deficient region but contributions of water sources vary temporally and spatially. These variations are examined and contributions are quantified using the newly established data set of isotopic ratios of oxygen and deuterium and deuterium excess derived from 6295 water samples collected in 2019-2021. Local meteoric water lines, groundwater lines, and surface water lines are presented. Isotopic composition of precipitation shows strong seasonal cycles with more enriched values in summer and more depleted in winter and exhibits positive correlation with latitude. The back trajectory analysis identified the main source regions of moisture as distant (the Black and Caspian Seas region, Iran, and northern Kazakhstan - Siberia), regional (irrigated land in the Aral Sea basin) and local (catchments) sources. The inland re-evaporated moisture from the irrigated land in the Aral basin and local sources exceeded the contribution of the longer-distance transport associated with the westerly depressions. There are statistically significant differences between isotopic signatures of precipitation, groundwater, snowmelt, runoff from glacier surfaces, rock glaciers and permafrost, and between the snowmelt and glacier ice melt components of the runoff from glacier surfaces. The end member mixing models (EMMA) and Bayesian mixing models are applied to assess contributions of water sources to streamflow. Glacier ice melt contributions in July-August are 68%, 33-46%, 39%, and 16% in the Chon Kyzyl-Suu, Ulken Almaty, Ala-Archa and the Chirchik catchments, respectively. Over the observation period, snowmelt dominated in the Chirchik (66%), groundwater (37±5.5%) contribution exceeded that of glacier ice melt (31±6.7%) in the Ulken Almaty while in the Ala-Archa, groundwater, snowmelt and ice melt contributed 21±9.7%, 35±1.5%, and 26±3.0%, respectively.