Role of glaciers in watershed hydrology: ''Himalayan catchment'' perspective

Abstract

Abstract. A large number of Himalayan glacier catchments are under the influence of humid climate with snowfall in winter (November–April) and South-West monsoon in summer (June–September) dominating the regional hydrology. Such catchments are defined as ''Himalayan catchment'', where the glacier melt water contributes to the river flow during the period of annual high flows produced by the monsoon. Other two major glacio-hydrological regimes of the Himalaya are winter snow dominated Alpine catchments of the Kashmir and Karakoram region and cold-arid regions of the Ladakh mountain range. Factors influencing the river flow variations in a ''Himalayan catchment'' were studied in a micro scale glacier catchment in the Garhwal Himalaya, covering an area of 77.8 km2. Discharge data generated from three hydrometric stations established at different altitudes of the Din Gad stream during the summer ablation period of 1998, 1999, 2000, 2001, 2003 and 2004. These data has been analysed along with winter/summer precipitation, temperature and mass balance data of the Dokriani glacier to study the role of the glacier and precipitation in determining the runoff variations along the stream continuum from the glacier snout to 2360 m a.s.l. Study shows that the inter-annual runoff variations in a ''Himalayan glacier catchment'' is directly linked with the precipitation rather than mass balance changes of the glacier. Study suggest that warming induced initial increase of glacier degraded runoff and subsequent decline is a glaciers mass balance response and cannot be translated as river flow response in a ''Himalayan catchment'' as suggested by the IPCC, 2007. Study also suggest that the glacier runoff critically influence the headwater river flows during the years of low summer discharge and proposes that the Himalayan catchment could experience higher river flows and positive glacier mass balance regime together in association with strong monsoon. This paper intended to highlight the importance of creating credible knowledge on the Himalayan cryospheric processes to develop a global outlook on river flow response to cryospheric change and locally sustainable water resources management strategies.

Water storage change in the Himalayas from the Gravity Recovery and Climate Experiment (GRACE) and an empirical climate model

“…The mountain valleys, depressions, and canyons provide abundant storage for summer rainwater and meltwater [ Ageta et al , 2000]. The tectonic glacial lakes occur at altitudes below 5000 m and generally diminish in size at higher elevations [ Thayyen and Gergan , 2009]. Pangong Tso, the largest endorheic lake in the region is ≈134 km long.…”

“…Above‐16°С summer temperatures are not uncommon on the valley slopes [ Dulal et al , 2006]. At elevations over 5000 m, above‐zero temperatures only occur during the daytime [ Thayyen and Gergan , 2009]. Because of rising temperatures, snow precipitation is increasingly shifting toward rain.…”

“…While the western phase of the Himalayas has a generally warm and humid monsoon climate, a typical mountain desert cold climate dominates on the northern slopes and Tibetan Plateau [ Goswami et al , 2003]. As Asia's main source of water, the Himalayas and Tibetan Plateau snow and glaciers greatly influence the hydrology, ecology, and livelihoods of millions of people in the subcontinent [ Burbank et al , 2003; Qiu , 2008; Thayyen and Gergan , 2009; Immerzeel et al , 2010].…”

“…Accelerated glacier melt may trigger rock‐ice avalanches, high‐debris flows, and floods [ Ageta et al , 2000; Li et al , 2007]. On the other hand, enhanced glacier melt could threaten long‐term water availability [ Thayyen and Gergan , 2009]. Acute water shortages would jeopardize agroindustrial systems, the backbone of modern societies [ Immerzeel et al , 2010].…”

The Indus Basin of Pakistan

“…Thayyen and Gergan (2009) Hunza Gilgit ranges, and they grow or shrink in response to the interaction between a regional climate and the topography of the mountains. The regional climate is modified by the topography of the mountains into a three-dimensional environmental mosaic, referred to as "topoclimates" (Thornthwaite 1953).…”