A Circulation Index for the Himalayan Mountain Arc: Reconciling Conflicting Signals of Climate Change Along the Third Pole”

Abstract:

Rivers of high mountain Asia are of tremendous importance for livelihoods and well-being of hundreds of millions of people [1]. Independent of climate change the population of the Indus basin will experience water scarcity due to demographic pressures [2]. Recent geophysical research focusing on the Karakoram has revealed patterns of change in both climate [3,4] and cryosphere [5,6] which diverge from the trajectories expected in a globally warming climate. Additional studies have underlined the influence of large-scale atmospheric circulation on glacier mass balance status [7,8].

This study identifies and quantifies a regional feature of atmospheric circulation, the latitudinal position of the westerly jet “immediately upstream” of the Karakoram, which has substantial influence of surface air temperature variability across the Himalayan Mountain Arc and adjacent Indo-Gangetic plains. Characteristics of this feature, and its correlation to local air temperatures, are compared amongst an ensemble of meteorological reanalyses: ERA-40, ERA-Interim, NCEP CFSR, NASA MERRA and JRA-55.

Correlations between the westerly jet position and local observations indicate a strong causal mechanism of short term near surface air temperature variability. Furthermore, the Karakoram and NW UIB respond differently during the Summer season to this circulation mode than both the plains of the lower Indus as well as the Central and Eastern Himalaya. This differentiated response provides a plausible explanation for differences in summer temperature trends along the Himalayan arc and by substantiating differences in melt season energy inputs provides a clear climatic mechanism to explain the “Karakoram anomaly.”

[1] DOI:10.1126/science.330.6004.585-a

[2] DOI:10.5194/hess-14-1669-2010

[3] DOI:10.1175/JCLI3860.1

[4] DOI:10.3354/cr00957

[5] DOI:10.1038/ngeo1450

[6] DOI:10.1038/nature11324

[7] DOI:10.1038/nclimate1580

[8] DOI:10.1038/nclimate2055