Using remotely sensed Tropical Rainfall Measuring Mission (TRMM) 3B42 rainfall and topographic data from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Digital Elevation Model (DEM), the impact of oroghraphical aspects such as topography, spatial variability of elevation and altitude of apexes are examined to investigate capacious summer monsoon rainfall over the Western Ghats (WG) of India. TRMM 3B42 v7 rainfall data is validated with Indian Meteorological Department (IMD) gridded rainfall data at 0.5 ∘ resolution over the WG. The analysis of spatial pattern of monsoon rainfall with orography of the WG ascertains that the grade of orographic precipitation depends mainly on topography of the mountain barrier followed by steepness of windward side slope and altitude of the mountain. Longer and broader, i.e. cascaded topography, elevated summits and gradually increasing slopes impel the enhancement in precipitation. Comparing topography of various states of the WG, it has been observed that windward side of Karnataka receives intense rainfall in the WG during summer monsoon. It has been observed that the rainfall is enhanced before the peak of the mountain and confined up to the height about 800 m over the WG. In addition to this, the spatial distribution of heavy and very heavy rainfall events in the last 14 years has also been explored. Heavy and very heavy rain events on this hilly terrain are categorized with a threshold of precipitation (R) in the range 150 > R > 120 mm day −1 and exceeding 150 mm day −1 using probability distribution of TRMM 3B42 v7 rainfall. The areas which are prone to heavy precipitation are identified. The study would help policy makers to manage the hazard scenario and, to improve weather predictions on mountainous terrain of the WG.

Mass balance is an important metric to assess the growth or decline of water stored in a glacier. The Accumulation Area Ratio (AAR) method where mass balance is proportional to AAR has been used to estimate glacier mass balance by several studies in the past. Since field estimates of AAR are not feasible on every glacier, it is usually estimated by identifying the snowline at the end of ablation season as a proxy of Equilibrium Line Altitude (ELA) on satellite images. However, locating ELA on satellite images is challenging due to temporal gaps, cloud cover and fresh snowfall on glaciers. Hence, the highest observed snowline has been traditionally used to estimate AAR, which usually leads to an underestimate of mass loss. To rectify this problem we propose a method to estimate the position of ELA by combining satellite images with in situ meteorological observations and a snowmelt model. The main advantage of this method is that it can be used to estimate the mass balance of individual glaciers and basins. Application of the method to eight glaciers in the Chandra basin, Western Himalaya is found to reduce the bias in mass balance estimates compared to the traditional AAR technique and the modelled estimates are in good agreement with the geodetic method. When applied to 12 selected glaciers in the Chandra basin, the modelled cumulative mass balance is -1.67  0.72 Gt (-0.79  0.34 m w.e. a -1 ) during 1999/2000-2008/09. This method can also be used to estimate the future deviations in mass balance using climate change projections of temperature and precipitation.

ABSTRACT. An improved understanding of fresh water stored in the Himalaya is crucial for water resource management in South Asia and can be inferred from glacier mass-balance estimates. However, field investigations in the rugged Himalaya are limited to a few individual glaciers and short duration. Therefore, we have recently developed an approach that combines satellite-derived snowlines, a temperature-index melt model and the accumulation-area ratio method to estimate annual mass balance of glaciers at basin scale and for a long period. In this investigation, the mass balance of 146 glaciers in the Chandra basin, western Himalaya, is estimated from 1984 to 2012. We estimate the trend in equilibrium line altitude of the basin as +113 m decade −1 and the mean mass balance as −0.61 ± 0.46 m w.e. a −1 . Our basin-wide mass-balance estimates are in agreement with the geodetic method during 1999-2012. Sensitivity analysis suggests that a 20% increase in precipitation can offset changes in mass balance for a 1°C temperature rise. A water loss of 18% of the total basin volume is estimated, and 67% for small and low-altitude glaciers during 1984-2012, indicating a looming water scarcity crisis for villages in this valley.

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The Himalayan glaciers are a major source of Perennial River systems in South Asia and the retreat of these glaciers under climate change could directly affect millions of people who depend on them. In this study, we assess the glacier mass balance, area and volume changes at basin scale for the Chandra Basin in the western Himalaya due to projected climate change in the 21st century. The Chandra basin occupies ∼2440 km 2 of area and hosts ∼200 glaciers and 23 small villages. The multi-model projections used in this study indicate a temperature increase of 2.2°C-2.9°C and 4.3°C-6°C for the RCP 4.5 and RCP 8.5 scenarios by the end of the century with a steady or decreasing trend in snowfall in the basin. In response to the projected climate, the basin is likely to retain only 50%-52% (RCP 4.5) and 40%-45% (RCP 8.5) of the areal extent of glaciers by the end of the century. Corresponding volumes of glacier water retained are much lower at 40%-43% and 29%-34%, but the volume loss could be as high as 97% for low altitude glaciers. Overall, our study highlights the likely severe impacts to water resources in the Himalaya if CO 2 emissions follow the high-emission scenario of RCP8.5.