Warming and drying over the central Himalaya caused by an amplification of local mountain circulation

Jesse Norris,Leila M. V. Carvalho,Charles Jones,Forest Cannon

doi:10.1038/s41612-019-0105-5

Abstract

Climatic changes over the central Himalaya are critical for water resources in downstream regions where hundreds of millions of people live. Warming and drying in this region have both occurred in recent decades, but the associated meteorological factors are difficult to diagnose based on observations from unevenly distributed weather stations, reanalyses, and global climate models that poorly reproduce the orographic diurnal cycle. Here, recent trends in the summer diurnal cycle over the central Himalaya are investigated using a 36-year high-resolution dynamical downscaling. We illustrate contrasting trends over the diurnal cycle of circulation and convection over the Himalaya. In the daytime, warming of the slopes has enhanced anabatic upslope winds. At night, clearer skies have radiatively cooled the slopes, enhancing katabatic downslope winds. The enhanced upslope winds have prevented any drying over the mountains in the daytime, while the enhanced downslope winds are associated with significant nocturnal drying at high elevations. This amplification in the diurnal cycle is critical for projecting the future hydroclimate over the region’s complex terrain.

Highlights

Among the most impacted regions around the world by recent climate change is the central Himalaya
This diurnal cycle over the Himalayan peaks and slopes is consistent with that described in the literature based on observations[19] and has been described in more detail for a single year of this Weather Research and Forecasting (WRF) downscaling.[23]
Because the WRF simulations are forced by CFSR, we subsequently interpret these reanalysis trends and discuss their reliability

Summary

Introduction

Among the most impacted regions around the world by recent climate change is the central Himalaya. In recent decades, this region has experienced rapidly increasing temperature[1,2,3] and decreasing monsoon precipitation.[4] These meteorological trends are likely major factors in the rapid retreat of glaciers in the region.[5,6,7] These glaciers are depended upon as reservoirs of moisture, which provide water for agriculture, hydropower, and household use as they melt annually. Melting of snow and ice provides a third of annual discharge in the central Himalaya.[8] More broadly, the central Himalaya is the source of some of the world’s great rivers, including the Ganges and Brahmaputra, so that precipitation in the region is critical to water resources in the Indian subcontinent

Methods

Results

Conclusion