Linking basin-scale hydrology with climatic parameters in western Himalaya:Application of satellite data,temperature index modelling and in-situ observations

Due to limited spatial and temporal in-situ runoff data availability,Himalaya-Karakoram(HK)glaciohydrology has a significant knowledge gap between large-scale and small-scale runoff modelling studies.This study reconstructs longest basin-wide runoff series in Chandra-Bhaga Basin by applying a high-resolution glaciohydrological model SPHY(Spatial Processes in Hydrology)over 1950–2022.Two-tier model calibration is done using in-situ basin-wide runoff(1973–2006)and MODIS snow cover(2003–2018).Model validation is done against in-situ Chhota Shigri Glacier catchment-wide runoff(2010–2015).The modelled mean annual basin-wide runoff is 60.21±6.17 m^(3)/s over 1950–2022,with maximum runoff in summer-monsoon months,peaking in July(182.69 m^(3)/s).Glacier runoff(ice melt+snowmelt over glacier)contributes maximum(39%)followed by equal contributions from snowmelt runoff from non-glacierized basin area and baseflow(25%),while rainfall-runoff contributes minimum(11%)to total runoff.There is a significant volumetric increase by∼7%from pre-(59.17 m^(3)/s)to post-2000(63.47 m^(3)/s)mainly because of early onset of snowmelt post-2000 that resulted in a hydrograph shift by∼25 days earlier in spring.The glacier runoff is overestimated by 3%from RGI 7.0 inventory compared to different manually delineated inventories over 1950–2022,because of higher glacierized area from RGI 7.0.The precipitation shows a negative trend,but total runoff shows a positive trend due to positive trend of temperature that resulted in more glacier runoff and rainfall-runoff for basin over last 72 years.Basin-wide runoff is mainly governed by summer temperature which directly controls the amount of glacier and snowmelt runoffs and is supported by summer rainfall.This study highlights importance of basin-scale model calibration with in-situ data in large scale studies and stresses the need for in-situ observations in high-altitude Himalayan region.Basin-scale calibrated model parameters are transferable to glacier catchment scale within Chandra-Bhaga Basin,showing the model robustness at a small catchment scale.