Climate change has led to increase in the extreme precipitation and temperature fluctuations in Himalayas. In this study the Indus River system of the Himalayas has been selected to understand the changes in few meteorological parameters such as precipitation, temperature and their impact on the changes in sediment budget. The two moisture sources affecting the study area are SW monsoon and Westerlies with erratic dominance. The increasing trend of the extreme precipitation and temperature in the study area due to changing climate leads to rise in the extreme events like landslide, cloudburst, snow avalanche etc., which ultimately account for the differential erosional activities. The flipping geological and meteorological events have led to significant transformation in the sediment budget of the Himalayan River systems. Post Industrial scenario, there has been drastic decrease in sediment yield of the Indus River system. The orography of the Himalayas controls the extreme precipitation to its lower elevation zones. The areas of corresponding elevations are found to be more effected by the extreme events like landslides, debris flow, rock fall, etc. which result into significant sediment washing in different river catchments. The tectonic activity and lithology of the study area also plays a very important role in the erosional activities and the changing river morphology. However, the high elevated Himalayan zones are mainly affected by the glacial erosion and release of trapped sediments which account for drastic rise in sediment budget of the river systems. In addition to aforementioned factors, anthropogenic intervention has led to momentous and enduring footprints over these natural Himalayan River systems.

The Sikkim region of the Himalayas (NE India) may form an important microplate between Nepal and Bhutan. Here we report high-resolution pressure-temperature (P-T) paths taken from garnet-bearing rocks across the northern and eastern portion of the region’s Main Central Thrust (MCT) shear zone. The MCT separates units affiliated with the Greater Himalayan Crystallines (GHC) in its hanging wall from the Lesser Himalayan Formation (LHF). Late Miocene monazite ages are reported from the LHF (10–14 Ma), whereas those from the GHC are Miocene (18–20 Ma). Some paths from the LHF and GHC show a P decrease before burial, consistent with erosion before compression. MCT shear zone and GHC rocks show a P increase and then decrease over a short T interval. This hairpin P-T path is consistent with an imbrication model for the Himalayas. LHF P-T path conditions and those obtained using conventional thermobarometry are best in agreement. These paths also are consistent with observed mineral assemblages and garnet zoning. Although we have the most confidence in LHF results, MCT shear zone and GHC P-T path shapes suggest processes to establish imbrication tectonics may have occurred here as early as the Miocene.

Keywords: River discharge Suspended sediment load Sediment rating curve Himalayas Indian summer monsoon Sutlej river basin A B S T R A C T The Sutlej River basin of the western Himalaya (study area), owing to its unique geographical disposition, receives precipitation from both the Indian summer monsoon (ISM) and the Westerlies. The characteristic timing and intensity of the ISM and Westerlies, leaves a distinct footprint on the sediment load of the River. Analysis with the last forty years data, shows an increasing trend for temperature. While for precipitation during the same period, the Spiti watershed on the west has highest monthly accumulated precipitation with long term declining trend, in contrast to the other areas where an increasing trend has been observed. Thus, to probe the hydrological variability and the seasonal attributes, governed by the Westerlies and ISM in the study area, we analyzed precipitation, temperature, snow cover area (in %), discharge, suspended sediment concentration (SSC) and suspended sediment load (SSL) for the period 2004-2008. To accomplish the task, we used the available data of five hydrological stations located in the study area. Inter-annual shift in peak discharge during the monsoon period is controlled by the variation in precipitation, snow melt, glacier melt and temperature. Besides seasonal variability has been observed in generation of the sediments and its delivery to the river. Our analysis indicates, dominance of the Westerlies footprints in the hydrological parameters of the Spiti region, towards western part of the study area. While, it is observed that the hydrology of the Khab towards eastern part of the study area shows dominance of ISM. Further downstream, the hydrology of Nathpa station also shows dominance of ISM. It also emerged out that the snowmelt contribution to the River flow is mostly during the initial part, at the onset of the monsoon, while for rest and major part of the summer monsoon season, the River flow is augmented by the precipitation, glacial melt and some snow melt. We observed, that the SSC increases exponentially in response to increase in temperature and correlates positively with River discharge. The average daily SSL in the summer monsoon is many times more than that in the winter monsoon. The downstream decrease in steepness of the sediment rating curve is attributed to either a change in the River-sediment dynamics or on account of the anthropogenic forcing. The top 1% of the extreme summer monsoon events (only 4 events) in our study area contribute up to 45% of SSL to the total sediment load budget. It has also been observed that the River-sediment dynamics in the upstream catchments are more vulnerable and sensitive to the extreme events in comparison to the downstream catchments. The present study for the first time gives a holistic insight in to the complex dynamics of the hydrological processes operational in the study area. The research findings would be crucial for managing the water resources of the region and the linked water and food security.

The paper gives an insight into the tectonic evolutionary history of the Northeast India Himalaya since India-Asia collision. The assessment of the paper takes the aggregated data of the Himalayan lateral correlation for crustal-shortening variation and unroofing history. The calculation of shortening magnitude and unroofing height, extrapolated from the balanced cross-sections are introduced in this paper to apprehend evolutionary history. The result uncovers a maximum shortening of83.28 % with concentrated unroofing in the eastern Arunachal Himalaya of Northeast India. Further, the complete erosion of Siwalik strata is also noticeable with missing Tethyan rocks (Lhasa-Block) on the eastern flank of Eastern Syntaxis. These occurrences could be the result of excessive crustal compression, structural complexity and geological set-up in the region. Additionally, the study area occurs within the triple-plate junction of the Indian, the Asian and the Myanmar Plates. Meanwhile, there is an assumption that a focused erosion in some specific regions provides the best evidence for the lateral variation of crustal shortening and unroofing in the Himalayan orogen. Our findings suggested that the world’s highest peak would have been somewhere in the Arunachal mountain range (which is now unroofed to a maximum level) rather than the Mt. Everest.