Impact of warmer climate on melt and evaporation for the rainfed, snowfed and glacierfed basins in the Himalayan region

The impact of warmer climate on melt and evaporation was studied for tainted, snowfed and glacierfed basins located in the western Himalayan region. Hydrological processes were simulated under current climatic conditions using a conceptual hydrological model, which accounts for the rainfall-runoff, evaporation losses, snow and glacier melt. After simulations of daily observed strearnflow (R-2 = 0.90) for 6 years, the model was used to study the impact of warmer climate on melt and evaporation. Based on the future projected climatic scenarios in the study region, three temperature scenarios (T + 1, T + 2 and T + 3 degreesC) were adopted for quantifying the effect of warmer climate. The comparison of the effect of warmer climate on different types of basins indicated that the increase in evaporation was the maximum for snowfed basins. For a T + 2 degreesC scenario, the annual evaporation for the rainfed basins increased by about 12%, whereas for the snowfed basins it increased by about 24%. The high increase of the evaporation losses would reduce the runoff. It was found that under a warmer climate, melt was reduced from snowfed basins, but increased from glacierfed basins. For a T + 2 degreesC scenario, annual melt was reduced by about 18% for the studied snowfed basin, while it increased by about 33% for the glacierfed basin. Thus, impact of warmer climate on the melt from the snowfed and glacierfed basins was opposite to each other. The study suggests that out of three types of basins, snowfed basins are more sensitive in terms of reduction in water availability due to a compound effect of increase in evaporation and decrease in melt. For a complex type of basin, the decrease in melt from seasonal snow may be counterbalanced by increase in melt from glaciers. However, on long-term basis, when the areal extent of glaciers will decrease due to higher melt rate, the water availability from the complex basins will be reduced. (C) 2004 Elsevier B.V. All rights reserved.