TR(BR)-3/97-98 : Sensitivity analysis of melt runoff due to temperature and precipitation

Abstract

The effect of climate change on snow water equivalent, snowmelt runoff, glacier melt runoff and total stream flow and their distribution is examined for the Spiti river. It is a high altitude Himalayan river located in the western Himalayan region and total stream flow of this river has a significant contribution from snow and glacier melt runoff. Plausible hypothetical scenarios of the temperature and precipitation changes based on the simulation of climate change over Indian sub-continent by Hamburg climate model are adopted in the present study. The UBC Watershed Model was used to simulate the hydrological response of the basin under changed climatic scenarios. The adopted changes in temperature and precipitation covered a range from 1 to 3°C and -10 to +10 %, respectively.

Snow water equivalent reduces with an increase in air temperature. However, no significant change is found in the snow water equivalent of the Spiti basin by the projected increase in air temperature (T + 1 to T+3 °C). An increase of 2°C in air temperature reduced annual snow water equivalent in the range of 1 to 7%. Changes in precipitation caused proportional changes in snow water equivalent. It is found that annual snowmelt runoff, glacier melt runoff and total stream flow increase linearly with changes in temperature (1-3°C), but most prominent effect of increase in temperature has been noticed on glacier melt runoff for this high altitude basin. For example, an increase of 2°C in air temperature has enhanced annual snowmelt runoff, glacier melt runoff, and total stream flow in the range of 4-18%, 33-38% and 6-12%, respectively. The effect of change in precipitation (P-10 to P+10%) suggests a linear increase in snowmelt runoff and total stream flow, while in general, glacier melt runoff in inversely related to changes in precipitation. Snowmelt runoff is found more sensitive than glacier melt runoff to changes in precipitation (P-10 to P+ 10 %). Under a warmer climate scenario, snowmelt runoff and glacier melt runoff cause an earlier response of total stream flow and change in flow distribution. The seasonal analysis of total stream flow indicates that an increase in air temperature produces an increase in the pre- monsoon season (April-June) followed by an increase in the monsoon season (July- September). Implications of such seasonal changes are also discussed in brief.