Climate sensitivity of the summer runoff of two glacierised Himalayan catchments with contrasting climate

Abstract

The future changes in runoff of Himalayan glacierised catchments will be determined by the local climate forcing and the climate sensitivity of the runoff. Here, we investigate the sensitivity of summer runoff to precipitation and temperature changes in the winter-snow-dominated Chandra (the western Himalaya) and summer-rain-dominated upper Dudhkoshi (the eastern Himalaya) catchments. We analyse the interannual variability of summer runoff in these catchments during 1980–2018 using a semi-distributed glacio–hydrological model, which is calibrated with the available runoff and glacier mass-balance observations. Our results indicate that despite the contrasting precipitation regimes, the catchments have a similar runoff response: the summer runoff from the glacierised parts of both catchments is sensitive to temperature changes and insensitive to precipitation changes; the summer runoff from the non-glacierised parts of the catchments has the exact opposite pattern of sensitivity. The precipitation-independent glacier contribution stabilises the catchment runoff against precipitation variability to some degree. The estimated sensitivities capture the characteristic “peak water” in the long-term mean summer runoff, which is caused by the excess meltwater released by the shrinking ice reserve. As the glacier cover depletes, the summer runoff is expected to become more sensitive to precipitation forcing in these catchments. However, the net impact of the glacier loss on the catchment runoff may not be detectable, given the relatively large interannual runoff variability in these catchments.