Role of glaciers in watershed hydrology: a preliminary study of a "Himalayan catchment"

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 meltwater contributes to the river flow during the period of annual high flows produced by the monsoon. The winter snow dominated Alpine catchments of the Kashmir and Karakoram region and cold-arid regions of the Ladakh mountain range are the other major glacio-hydrological regimes identified in the region. 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. Three hydrometric stations were established at different altitudes along the Din Gad stream and discharge was monitored during the summer ablation period from 1998 to 2004, with an exception in 2002. These data have been analysed along with winter/summer precipitation, temperature and mass balance data of the Dokriani glacier to study the role of glacier and precipitation in determining runoff variations along the stream continuum from the glacier snout to 2360 m a.s.l. The study shows that the inter-annual runoff variation in a "Himalayan catchment" is linked with precipitation rather than mass balance changes of the glacier. This study also indicates that the warming induced an initial increase of glacier runoff and subsequent decline as suggested by the IPCC (2007) is restricted to the glacier degradation-derived component in a precipitation dominant Himalayan catchment and cannot be translated as river flow response. The preliminary assessment suggests that the "Himalayan catchment" could experience higher river flows and positive glacier mass balance regime together in association with strong monsoon. The important role of glaciers in this precipitation dominant system is to augment stream runoff during the years of low summer discharge. This paper intends to highlight the importance of creating credible knowledge on the Himalayan cryospheric processes to develop a more representative global view on river flow response to cryospheric changes and locally sustainable water resources management strategies.

Recent changes in the snout position and surface velocity of Gangotri glacier observed from space

“…Gangotri and other glaciers in this region are mostly fed by the summer monsoon and partly by winter snow. Western disturbances cause heavy snowfall from December to March over this region (Thayyen and Gergan 2010). Generally, seasonal melting starts in the month of May and continues till October (Dobhal, Gergan, and Thayyen 2008).…”

Review of the status and mass changes of Himalayan-Karakoram glaciers

“…Total discharge at any basin outlet is the sum of rain runoff, snow melt, glacier melt and base flow (Lutz and others, 2014). A variety of methods with different complexity such as empirical relationships between precipitation and discharge (Thayyen and Gergan, 2010), ice ablation models (Racoviteanu and others, 2013), the hydrograph separation method Khan, 2014a, 2015), chemical tracer methods (Racoviteanu and others, 2013) and distributed glacio-hydrological models (Lutz and others, 2014;Ragettli and others, 2015) are used to understand the discharge composition in the HK. Generally, the meteorological stations are installed at valley bottoms; knowledge of the precipitation distribution at glacier altitudes is nearly lacking, which makes it difficult to develop hydrological models.…”

Modeling Slope Environmental Lapse Rate (SELR) of temperature in the monsoon glacio-hydrological regime of the Himalaya

“…Solid precipitation collected in the standard rain gauges were measured as water equivalent after melting as per the India Meteorological Department (IMD) standard procedure. Further, standing snow depth and density were monitored 10 four times during the December-April period at different altitudes along the valley bottom from Gujjar Hut to the Basecamp and accumulated snow water equivalent was calculated (Thayyen and Gergan, 2010). Many of these surveys conducted immediately after the snowfall events have shown that the precipitation measured by the rain gauge underestimate it by 26-32%.…”

“…Himalayan system with dominant ISM, (2) Alpine system with dominant IWM and (3) Cold-arid system characterised by the absence of ISM in summer and subdued influence of IWM in winter (Thayyen and Gergan, 2010). In this paper we analyse the role of orography-moisture interplay in controlling the temperature distribution along the Himalayan slopes and high elevation cryospheric regions under monsoon regime and propose a modeling solution for estimating the SELR.…”

“…Moreover, understanding the physical processes that control the temperature of the Himalayan slopes in 10 different glacio-hydrological regimes (Thayyen and Gergan, 2010) is paramount to the understanding of the climate forcing on the Himalayan cryosphere and regional variability of emerging water scenarios. This understanding is also inevitable for climate downscaling over the higher Himalayan region for a better estimate of future climate trends.…”