Abstract
Water resources in Central Asia strongly depend on glaciers, which in turn adjust their size in response to climate variations. We investigate glacier runoff in the period 1981–2019 in the upper Naryn basin, Kyrgyzstan. The basins contain more than 1,000 glaciers, which cover a total area of 776 km2. We model the mass balance and runoff contribution of all glaciers with a simplified energy balance melt model and distributed accumulation model driven by ERA5 LAND re-analysis data for the time period of 1981–2019. The results are evaluated against discharge records, satellite-derived snow cover, stake readings from individual glaciers, and geodetic mass balances. Modelled glacier volume decreased by approximately 6.7 km3 or 14%, and the majority of the mass loss took place from 1996 until 2019. The decreasing trend is the result of increasingly negative summer mass balances whereas winter mass balances show no substantial trend. Analysis of the discharge data suggests an increasing runoff for the past two decades, which is, however only partly reflected in an increase of glacier melt. Moreover, the strongest increase in discharge is observed in winter, suggesting either a prolonged melting period and/or increased groundwater discharge. The average runoff from the glacierized areas in summer months (June to August) constitutes approximately 23% of the total contributions to the basin’s runoff. The results highlight the strong regional variability in glacier-climate interactions in Central Asia.
Highlights
Ice and snow-melt are principal water resources for the highly populated lowlands of Central Asia (Konovalov and Shchetinnicov, 1994; Schaner et al, 2012; Chen et al, 2016), and have a crucial role for mountain communities (Parveen et al, 2015; Nusser, 2017, 2019)
The model runs at daily time steps, and the cumulative mass balance bc on day t+1 is calculated for every time step and over each grid cell of the digital elevation model (DEM) according to Oerlemans (2001): bc(t + 1)
In the Small Naryn catchment, glacier meltwater contributing to the discharge shows an increasing trend, while no trends are observed for the Big Naryn catchment, but the melt intensity of the shrinking glaciers is increasing
Summary
Ice and snow-melt are principal water resources for the highly populated lowlands of Central Asia (Konovalov and Shchetinnicov, 1994; Schaner et al, 2012; Chen et al, 2016), and have a crucial role for mountain communities (Parveen et al, 2015; Nusser, 2017, 2019). It has been observed that summer precipitation increases towards the East in the Tien Shan mountains (Dyurgerov et al, 1994; Shahgedanova et al, 2018) resulting in frequent summer snowfalls in the study area. Glaciers and permafrost release most of their meltwater during July to September. In these precipitation-poor periods, glacier melt is a vital fresh water source (Kaser et al, 2010; Pohl et al, 2017). In these precipitation-poor periods, glacier melt is a vital fresh water source (Kaser et al, 2010; Pohl et al, 2017). Pritchard (2019) showed that the amount of net glacier melt in Aral and Chu-
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