There are gaps in climate and hydrological modeling capability over mountainous regions especially the Hindu Kush and Himalayas. Glacier melt in the Himalayas is projected to increase flooding within the next two to three decades. This will be followed by decreased river flows as the glaciers recede (IPCC AR4 2007). Pakistan has been at a high risk of flooding for the last four years. In recent months the country has been under flood and 93 deaths have been reported. The Indus River Basin plays a significant role in the availability of water in Pakistan and most floods occur in this Basin. About 60% of the inflow to Upper Indus Basin is contributed by glaciers melting. There is thus a need to study climatic and hydrological changes across the Himalayan region and Upper Indus Basin. The objective of this study is to explore the performance and sensitivity of climate and hydrological models across the Himalayan region for the projection of climatic and hydrological changes over the next ten years.
The REGional Climate Model 4.3 (RegCM4.3) of ICTP and hydrological model of University of British Columbia (UBC) was used in this study. The RCM model was run at a horizontal resolution of 20 km with ERA-Interim15. Six different simulations were carried out for the periods 1997-2002 using all the available options of the model's convective parameterization scheme. The UBC model was first calibrated with observed data from 1995-2004 and the higher correlation of 0.9. RCM data achieved was used as an input to the hydrological model after bias correction from 2001-2010, 2041-2050, and 2071-2080 as, respectively, base period, future one (F1), and future two (F2), under scenarios RCP8.5 and RCP4.5.
The models results were compared with TRMM, station, CRU, and runoff data. The first results showed the RCM performing very oddly over the Himalayan region; however, after bias correction the results were with close agreement with observed data for the spatio-temporal change of precipitation and temperature. Three climatic variables, that is, maximum temperature, minimum temperature, and precipitation show that there is climate change in the region. The results of the UBC model are quite satisfactory and showing a higher increasing trend during 2041-2050, while the increase trend in 2071-2080 is relatively low. The possible reason for this may be faster glacier melt and reduction in size of glaciers during the first half of the century. In last decades of the century, as the size of the glacier decreases, so it contributes less to inflow.
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Last edited: 19 August 2015
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