Glacier melt buffers river runoff in the Pamir Mountains

Abstract

Newly developed approaches based on satellite altimetry and gravity measurements provide promising results on glacier dynamics in the Pamir‐Himalaya but cannot resolve short‐term natural variability at regional and finer scale. We contribute to the ongoing debate by upscaling a hydrological model that we calibrated for the central Pamir. The model resolves the spatiotemporal variability in runoff over the entire catchment domain with high efficiency. We provide relevant information about individual components of the hydrological cycle and quantify short‐term hydrological variability. For validation, we compare the modeled total water storages (TWS) with GRACE (Gravity Recovery and Climate Experiment) data with a very good agreement where GRACE uncertainties are low. The approach exemplifies the potential of GRACE for validating even regional scale hydrological applications in remote and hard to access mountain regions. We use modeled time series of individual hydrological components to characterize the effect of climate variability on the hydrological cycle. We demonstrate that glaciers play a twofold role by providing roughly 35% of the annual runoff of the Panj River basin and by effectively buffering runoff both during very wet and very dry years. The modeled glacier mass balance (GMB) of −0.52 m w.e. yr−1 (2002–2013) for the entire catchment suggests significant reduction of most Pamiri glaciers by the end of this century. The loss of glaciers and their buffer functionality in wet and dry years could not only result in reduced water availability and increase the regional instability, but also increase flood and drought hazards.

Bridging Glaciological and Hydrological Trends in the Pamir Mountains, Central Asia

“…These results are in line with the results of Kääb et al [20], who estimated thinning rates between 0.3 and 0.8 m·y −1 for the Southern Pamirs (mean 0.55 m·y −1 ; Table 3), using ICESat laser altimetry data. Glacier wastage estimated with GRACE and a mass balance model ( [26]; expressed as m of water column) is 15% larger (Table 3), but still within the range of the parameter uncertainty of the GlabTop results (Appendix A.1).…”

“…The results of the three above-mentioned methods are compared with a focus on basin-wide glacial mass changes and their approximate contribution to river runoff (Table 3). Pohl et al [26] Table 1); (DD) perennial snow cover: glacier area (in the model context) is defined as "permanent snow and ice", according to Pohl et al [26,32], using MCD12Q1 gridded land cover classification (in total 7.5% or 1020 km 2 ); 707 km 2 are glaciers according to Lindner [23]; the difference of 313 km 2 is considered here as perennial snow cover; (E) [33] glacier melt is defined as meltwater from snow-free glacier ice; (F) [26,32] glacier melt is defined as the sum of snowmelt and glacier meltwater from "permanent snow and ice"-covered areas (see (DD) ).…”

“…Pohl et al [26] applied a scaling procedure to ship around the above-mentioned issue: a glacio-hydrological model was calibrated in the Gunt River Basin (14,000 km 2 ) and validated at the entire Panj River Basin (ca. 100,000 km 2 ), which drains major parts of the Pamirs.…”

“…Furthermore, their resolution can be too coarse to be applied on the catchment scale. [26] w.e. = water equivalent; ∆A = glacier area change; ∆T = glacier terminus change; MB = mass balance: designations in mm are mean values for glaciated areas, not for corresponding river basins; Numbers 1-13 refer to case studies in Figure 1; Numerals I-IV refer to large-scale remote sensing-based glacier studies (not shown graphically); ICESat stands for the "Ice, Cloud and land Elevation Satellite" (NASA); GRACE stands for "Gravity Recovery And Climate Experiment" (NASA/DLR).…”

“…Contrarily, Kure et al [31] "found that the annual mean river discharge is increasing in the future" by applying a similar model approach. Recently, Pohl et al [26,32] estimated total glacier melt to contribute ca. 30% to the annual runoff of the Gunt River (Southern Pamirs), while Tarasova et al [33] quantified glacier retreat contribution to be 10% ± 4% of annual runoff at the same river.…”