5 | CONCLUSIONS

In this paper, we verified the critical parameters of GlabTop2 through GPR-measured ice thickness on six typical glaciers of the UIB region, and accomplished GlabTop2 estimates with SRTM-C DEM and PGI as inputs, then deduced the spatial distribution characteristics of ice thickness and ice reserves in the UIB sub-basins, certain conclusions are as follows.
We compared the plots and profiles of GPR-surveyed ice bed elevation versus GlabTop2-simulated results under nine parametric schemes, selected the parametric scheme that owns appropriate RMSE, MD, and NSE-values, it was found that they were fit better on several profiles when τ = 120 kPa. Moreover, the IDW interpolated results maintained the most similar ice thickness and ice volume quantity with GlabTop2 simulates when τ = 120 kPa and f = 0.8 than GlabTop and Volta model, it is more realistic to choose this comprehensive scheme applied to vast amounts of various sized glaciers.
GlabTop2-modeled results indicated that ice thickness of the UIB sub-basins was varied from 0 to 488 m, with an average value of 74.4 m, the average ice thickness in the Karakoram range (81.5 m) was slightly thicker than Western Himalaya (60.3 m) and Hindukush (45.0 m), significant heterogeneity was existing. The most abundant ice reserves was focused on the Karakoram range, Shyok (46.1%), Shigar (18.2%), and Hunza (17.7%) high-altitude sub-basins that dominated an absolute advantage. Less ice resources were stored in the Western Himalaya range that Astore (1.2%), Shiquanhe (0.6%) and Kharmong (9.5%) sub-basins included, the least quantity was found in the Hindukush range consists of Gilgit (3.9%) and UIB_D (2.9%) sub-watershed just accounted for a small proportion. Moreover, Shigar (29.3 m) possessed the most abundant water resources per square kilometers because of the limited basin area, Shyok (15.9 m) and Hunza (14.7 m) ranked behind inseparable, the WLE-values of Gilgit, Astore, Kharmong, and Astore sub-basins are all below 10 m.
The available consumption time of the converted water resources of the UIB sub-basins various in magnitude, the ice resources of Shyok will be depleted within 46.0 y without considering the glacier process and other variables, then Shigar (31.6 y) and Hunza (21.4 y) ranked behind. In contrast, Kharmong (7.6 y) and Gilgit (5.0 y) will be depleted within less than 8.0 y, outstandingly, the exhausting time of Astore (2.9 y) and Shiquanhe (2.9 y) were less than 3.0 y, Astore is confronting with the lack of precipitation replenishment and accelerated glacier melting, the water resources of headwater region, The water resource of Shiquanhe subbasin is in short supply mostly. Not only the water supply of the upper reaches is basically in deficit condition, but also the downstream area is not optimistic, the UIB will be up against water shortage evenly in the future, especially for the Shiquanhe and Astore sub-basins. Nevertheless, the UIB depends on the ice melting of the middle reaches (Shigar, Shyok, and Hunza) because they are staying in a self-sufficient even surplus state, A total of 1269.7 km3 ice reserves was equivalent to 1142.7 km3 water resources, it can supply at least 16.1 y for the Besham hydrological station as runoff.
With global warming and rapid glacier shrinkage in recent decades, accurate ice volume estimates in this hot region will receive unprecedented attention. The integration of GPR, GPS, GIS, and GlabTop2 will make the glacial field working more dynamic and predictive, our estimates make the audience have a clear cognition of the magnitude and distribution characteristic of ice reserves in the UIB sub-basins. Synthesizing knowledge of the ice thickness and ice reserves provides critical information for water resources management and regional glacial scientific research, it is also essential for several other fields of glaciology, including hydrological effect, regional climate modeling, and assessment of glacier hazards.