Precipitation Characteristics and Moisture Source Regions on Mt. Everest in the Khumbu, Nepal

L Baker Perry,Tom Matthews,Heather Guy,Inka Koch,Arbindra Khadka,Aurora C Elmore,Dibas Shrestha,Subash Tuladhar,Saraju K Baidya,Sunny Maharjan,Patrick Wagnon,Deepak Aryal,Anton Seimon,Ananta Gajurel,Paul A Mayewski

doi:10.1016/j.oneear.2020.10.011

Abstract

Summary Precipitation is critical to the water towers of the Hindu Kush-Himalaya-Karakoram region, exerting an important control on glacier mass balance and the water resources for 1.65 billion people. Given that hydroclimatic extremes and water stress have emerged as key hazards in the context of climate change, Nepal's Khumbu region overlaps key vulnerabilities. Here, we investigate the region's precipitation characteristics and moisture sources through analysis of data from a new high-altitude network of automatic weather stations, which allows for a more complete understanding of the climatological precipitation data that are critical information for local communities in the Khumbu region, visitors, and downstream populations. Our findings demonstrate that the northern Bay of Bengal is potentially an important moisture source during the monsoon period (June to August) and that westerly trajectories over land predominate for precipitation events during the post-monsoon, winter, and pre-monsoon seasons.

Highlights

The Hindu Kush-Karakoram-Himalaya (HKH) are critical water towers for 1.65 billion people across Asia.[1,2] Downstream communities suffer disproportionately from floods[3] and are dependent on meltwater from seasonal snow and glacier ice, during the pre-monsoon and drought periods.[2,4,5,6] It causes concern that glacier loss has accelerated across the Himalayas in recent decades[7,8] and that projections suggest large-scale reductions in stream discharge by 2050,6,9 yet more frequent episodes of intense precipitation.[10]
An altitudinal and south-north gradient in precipitation is evident from the longerterm Department of Hydrology and Meteorology (DHM) datasets, which are generally consistent with previous studies,[21] with an $50% reduction in precipitation moving from Chaurikhark to Namche Bazaar, further decreasing upslope to Syangboche and Khumjung (Table 1)
The relationship becomes more complex in the upper Khumbu region due to terrain shadowing and is not consistent with the findings of Salerno et al.[21] that indicate negative altitudinal gradients in precipitation throughout the upper Khumbu; our analyses show that Pyramid (5,035 m asl) reported consistently higher precipitation totals than Pheriche (4,260 m asl) during 2016–2019

Summary

Introduction

The Hindu Kush-Karakoram-Himalaya (HKH) are critical water towers for 1.65 billion people across Asia.[1,2] Downstream communities suffer disproportionately from floods[3] and are dependent on meltwater from seasonal snow and glacier ice, during the pre-monsoon and drought periods.[2,4,5,6] It causes concern that glacier loss has accelerated across the Himalayas in recent decades[7,8] and that projections suggest large-scale reductions in stream discharge by 2050,6,9 yet more frequent episodes of intense precipitation.[10] There is, much uncertainty about such projections, not least because of the limited understanding of the region’s contemporary hydroclimate.

Results

Discussion

Conclusion