Simulating the hydrological regime of the snow fed and glaciarised Gilgit Basin in the Upper Indus using global precipitation products and a data parsimonious precipitation-runoff model

Aftab Nazeer,Shreedhar Maskey,Thomas Skaugen,Michael E Mcclain

doi:10.1016/j.scitotenv.2021.149872

Abstract

In many high altitude river basins, the hydro-climatic regimes and the spatial and temporal distribution of precipitation are little known, complicating efforts to quantify current and future water availability. Scarce, or non-existent, gauged observations at high altitudes coupled with complex weather systems and orographic effects further prevent a realistic and comprehensive assessment of precipitation. Quantifying the contribution from seasonal snow and glacier melt to the river runoff for a high altitude, melt dependent region is especially difficult. Global scale precipitation products, in combination with precipitation-runoff modelling may provide insights to the hydro-climatic regimes for such data scarce regions. In this study two global precipitation products; the high resolution (0.1° × 0.1°), newly developed ERA5-Land, and a coarser resolution (0.55° × 0.55°) JRA-55, are used to simulate snow/glacier melts and runoff for the Gilgit Basin, a sub-basin of the Indus. A hydrological precipitation-runoff model, the Distance Distribution Dynamics (DDD), requires minimum input data and was developed for snow dominated catchments. The mean of total annual precipitation from 1995 to 2010 data was estimated at 888 mm and 951 mm by ERA5-Land and JRA-55, respectively. The daily runoff simulation obtained a Kling Gupta efficiency (KGE) of 0.78 and 0.72 with ERA5-Land and JRA-55 based simulations, respectively. The simulated snow cover area (SCA) was validated using MODIS SCA and the results are quite promising on daily, monthly and annual scales. Our result showed an overall contribution to the river flow as about 26% from rainfall, 37–38% from snow melt, 31% from glacier melt and 5% from soil moisture. These melt simulations are in good agreement with the overall hydro-climatic regimes and seasonality of the area. The proxy energy balance approach in the DDD model, used to estimate snow melt and evapotranspiration, showed robust behaviour and potential for being employed in data poor basins.

Highlights

Precipitation (P) is the major component in the hydrological cycle but its estimation is the most difficult (Herold et al, 2017)
The fixed lapse rate (FLR) for the whole time series is estimated as −5.74 °C km−1
For monthly lapse rate (MLR), twelve mean values were derived for all months showing maximum lapse rate of −7.04 °C km−1 for the month of March and minimum values as -−.81 °C km−1 for the month of September

Summary

Introduction

Precipitation (P) is the major component in the hydrological cycle but its estimation is the most difficult (Herold et al, 2017). The Eastern and South Eastern parts of the HKH region receive summer precipitation due to the Indian monsoon, while the Western part receives most of its precipitation in winter and spring seasons (mostly as snow) under the westerlies effect from the Caspian and Mediterranean seas (Minora et al, 2016). This east to west synoptic scale inconsistency in the precipitation system in the HKH region leads to variations in glacier accumulation (Kaab et al, 2012). There is a persistent need to develop and improve the quantification of precipitation at high-altitudes (Immerzeel et al, 2015; Lutz et al, 2014)

Results

Discussion

Conclusion