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The discharge of the rivers in the Himalaya, also known as third pole, is largely governed by seasonal snow cover extent (SCE). Being highly dependent on snow storage, these are susceptible to suffer from the effects of global warming. Therefore, knowledge about snow cover and snow melt dynamics is required for better understanding of the Himalayan system. Accurate estimation of SCE is a tedious task in mountainous terrain due to inaccessibility to remote areas. Here, remote sensing emerges as a promising tool for monitoring spatial and temporal changes at various scales than that of conventional tools. The resulting information is useful for snowmelt runoff modeling and stream flow prediction. Such modelling can be used for predicting impact of climate change on hydrological processes. Hence, in order to develop water resource management strategies, it is essential to examine SCE changes and its impacts on the river systems using runoff modelling techniques.
In the present study snow cover variation was monitored in Northwest Himalaya (NWH) at different spatial levels using topographically corrected 10-daily maximum snow cover product from MODIS sensor data (2000-12). The analysis was conducted in entire NWH (three climatic zones, eight river basins and four sub-basins). SCE inventory was prepared based on intensive inter/intra-annual analysis in relevance to local geophysical parameters and climate. Results were validated with in-situ metrological data (precipitation and temperature). The study indicates significant differences in accumulation-ablation pattern of the SCE in all spatial levels. In the NWH, within three climate zones strong SCE variability exists and it was observed that regional climatology is a dominating factor. At river basin level it is strongly influenced by corresponding climatic zone and basin topography. Similar patterns were observed at sub-basin level with pronounced effect of elevation and orientation. Inter-annual time series analysis of SCE shows an insignificant decreasing trend in entire NWH. The non-parametric (Mann-Kendall’s test) and parametric test (t-test) showed a significant (α=0.05) trend.
The study also evaluated implication of climate change on the streamflow of Jhelum (snowfed) and Chenab (glaciated) river basin by simulating river discharge in present and future scenarios using temperature index snowmelt runoff models. High correlation was observed between in-situ and simulated streamflow. The futuristic streamflow was simulated using SRM model assuming two real time climate change scenarios; Scenario–1 represents warming trends based on reported temperature data analysis in past century in entire NWH and Scenario–2 assumed air temperature trends during last two decades in the respective river basins. The simulated results show, implications of regional warming can be more threatening to Jhelum basin as compared to Chenab basin. In the scenario-1, spring-summer (March-May) discharge of both the rivers would increase in 2030 and 2050. Whereas, in March-April higher discharge (10-16%) was observed in Jhelum basin and an increment (2-15%) was observed in Chenab basin. In subsequent months significant reduction in streamflow of Jhelum basin was indicated (f+8% to -12%). In the scenario-2 similar trends of discharge variation were observed. In both the years, higher discharge was observed in Jhelum as well as Chenab river basin during March-April. The streamflow of Jhelum River will reduce considerably from +20% to -30% and +32% to -50% in comparison to baseline year in subsequent months. However, the streamflow of Chenab river basin showed significant change in March and April with gradual increment till September months. The study concludes with a quantitative account that in NWH significant difference exists in inter/intra annual pattern of SCE at various spatial levels and regional warming has strong implications for the streamflow of a snowfed river basin in comparison to glaciated river basins.
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