『Abstract
The interplay between topography and Indian summer monsoon circulation
profoundly controls precipitation distribution, sediment transport,
and river discharge along the Southern Himalayan Mountain Front
(SHF). The Higher Himalayas from a major orographic barrier that
separates humid sectors to the south and arid regions to the north.
During the Indian summer monsoon, vortices transport moisture
from the Bay of Bengal, swirl along the SHF to the northwest,
and cause heavy rainfall when colliding with the mountain front.
In the eastern and central pats of the Himalaya, precipitation
measurements derived from passive microwave analysis (SSM/I) show
a strong gradient, with high values at medium elevations and extensive
penetration of moisture along major river valleys into the orogen.
The end of the monsoonal conveyer belt is near the Sutlej Valley
in the NW Himalaya, where precipitation is lower and rainfall
maxima move to lower elevations. This region thus comprises a
climatic transition zone that is very sensitive to changes in
Indian summer monsoon strength. To constrain magnitude, temporal,
and spatial distribution of precipitation, we analyzed high-resolution
passive microwave data from the last decade and identified a abnormal
monsoon year (AMY) in 2002. During the 2002 AMY, violent rainstorms
conquered orographic barriers and penetrated far into otherwise
arid regions in the northwest Himalaya at elevations in excess
of 3 km asl. While precipitation in these regions was significantly
increased and triggered extensive erosional processes (i.e., debris
flows) on sparsely vegetated, steep hillslopes, mean rainfall
along the low to medium elevations was not significantly greater
in magnitude. This shift may thus play a important role in the
overall sediment flux toward the Himalayan foreland. Using extended
precipitation and sediment flux records for the last century,
we show that these events have a decadal recurrence interval during
the present-day monsoon circulation. Hence, episodically occurring
AMYs control geomorphic processes primarily in the high-elevation
arid sectors of the orogen, while annual recurring monsoonal rainfall
distribution dominates erosion in the low- to medium-elevation
parts along the SHF.
Keywords: Asian monsoon; precipitation; Himalayas; debris flows;
landscape evolution.』
1. Introduction
2. The Indian summer monsoon (ISM)]
2.1. Determining precipitation from passive microwave data
2.2. Moisture transport and precipitation gradients during the
ISM
2.3. Precipitation patterns, erosional hillslope processes, and
sediment flux in the northwest Himalaya
3. Conclusion
Acknowledgements
Appendix A. Supplementary data
References