Climatic and anthropogenic drivers of a drying Himalayan river

Gopal Penny,Zubair A Dar,Marc F Müller

doi:10.5194/hess-26-375-2022

Abstract

Abstract. Streamflow regimes are rapidly changing in many regions of the world. Attribution of these changes to specific hydrological processes and their underlying climatic and anthropogenic drivers is essential to formulate an effective water policy. Traditional approaches to hydrologic attribution rely on the ability to infer hydrological processes through the development of catchment-scale hydrological models. However, such approaches are challenging to implement in practice due to limitations in using models to accurately associate changes in observed outcomes with corresponding drivers. Here we present an alternative approach that leverages the method of multiple hypotheses to attribute changes in streamflow in the Upper Jhelum watershed, an important tributary headwater region of the Indus basin, where a dramatic decline in streamflow since 2000 has yet to be adequately attributed to its corresponding drivers. We generate and empirically evaluate a series of alternative and complementary hypotheses concerning distinct components of the water balance. This process allows a holistic understanding of watershed-scale processes to be developed, even though the catchment-scale water balance remains open. Using remote sensing and secondary data, we explore changes in climate, surface water, and groundwater. The evidence reveals that climate, rather than land use, had a considerably stronger influence on reductions in streamflow, both through reduced precipitation and increased evapotranspiration. Baseflow analyses suggest different mechanisms affecting streamflow decline in upstream and downstream regions, respectively. These findings offer promising avenues for future research in the Upper Jhelum watershed, and an alternative approach to hydrological attribution in data-scarce regions.

Highlights

Water resources are changing throughout the world under anthropogenic pressures, including climate change, land use change, and changes in water management (Vörösmarty et al, 2004; Milly et al, 2008; Ceola et al, 2019)
We develop an empirical approach to hydrological attribution, using the method of multiple hypotheses, to understand the drivers of dramatic changes in the annual streamflow of the Upper Jhelum river
We find that much of the observed decrease in streamflow is associated with decreases in westerly precipitation in spring, in addition to greater evapotranspiration

Summary

Introduction

Water resources are changing throughout the world under anthropogenic pressures, including climate change, land use change, and changes in water management (Vörösmarty et al, 2004; Milly et al, 2008; Ceola et al, 2019). In arid and semi-arid regions, these concerns are alarming, given the concurrent challenges of increasing hydrological uncertainty and competition for scarce water resources (Flörke et al, 2018; Aeschbach-Hertig and Gleeson, 2012) In many such regions, mitigation and adaptation strategies are urgently needed but require accurate understanding of the underlying drivers of change (Thompson et al, 2013; Penny et al, 2020a). The Upper Jhelum watershed provides essential ecosystem services in the Kashmir Valley, yet in recent decades many of these services have been threatened with lakes and wetland shrinking, fish populations declining, and less water available for agriculture (Wetlands International South Asia, 2007) Each of these ecosystem services depends on streamflow, which has de-

Methods

Results

Discussion

Conclusion