Regional differences in response of flow in glacier‐fed Himalayan rivers to climatic warming

Abstract

Abstract:River flow from glacierized areas in the Himalaya is influenced both by intra-annual variations in precipitation and energy availability, and by longer term changes in storage of water as glacier ice. High specific discharge from ice melt often dominates flow for considerable distances downstream, particularly where other sources of runoff are limited, providing a major water resource. Should Himalayan glaciers continue to retreat rapidly, water shortages might be widespread within a few decades. However, given the difference in climate between the drier western and monsoonal eastern ends of the region, future warming is unlikely to affect river flow uniformly throughout.A simple temperature-index-based hydro-glaciological model, in which glacier dimensions are allowed to decline through time, has been developed with a view to assessing, in data-sparse areas, by how much and when climate warming will reduce Himalayan glacier dimensions and affect downstream river flows. Two glaciers having the same initial geometries were located (one each) in the headwaters of two identical nests of hypothetical catchments, representing contrasting climates in the west and east of the region. The hypothetical catchments were nested such that percentage ice cover declined with increasing basin area. Model parameters were validated against available but limited mass-balance and river flow measurements. The model was applied for 150 years from an arbitrary start date (1990), first with standard-period climate data and then with application of a 0Ð06°C year 1 transient climatic warming scenario.Under this warming scenario, Himalayan rivers fed by large glaciers descending through considerable elevation range will respond in a broadly similar manner, except that summer snowfall in the east will suppress the rate of initial flow increase, delay peak discharge and postpone eventual disappearance of the ice. Impacts of declining glacier area on river flow will be greater in smaller and more highly glacierized basins in both the west and east, and in the west, where precipitation is scarce, for considerable distances downstream.  Crown

Historical trends and future predictions of climate variability in the Brahmaputra basin

“…The hydrograph shows that discharge responds directly to rainfall with a typical lag of one month and there is no additional peak in spring related to snow and glacial melt. This does comply with earlier studies that report synchronous accumulation and melt in eastern Himalayan basins (Rees and Collins, 2006). In addition to this summer precipitation in all zones is much larger than winter precipitation in the TP and HB (Figure 2).…”

“…Within the Himalayan region there are however large differences in the contribution of melt water in total annual run-off. Rees and Collins (2006) show that the melt water component in the total run-off rapidly decreases rapidly from west to east. Summer precipitation declines from east to west.…”

“…Therefore stream flow in basins in the west is for a major part determined by melt water while in the east run-off generated by monsoonal precipitation is the most important constituent of downstream discharge. Rees and Collins (2006) also argue that glaciers experience winter accumulation and summer ablation in the west, but there is predominantly synchronous summer accumulation and summer melt in the east. Singh and Bengtsson (2004) confirm the strong dependence of stream flow on melt water in basins originating in the western part of the basin and stress the difference in melt water contribution to stream flow between rain fed, snow fed and glacial fed river basins.…”

Response of hydrological processes to land‐cover and climate changes in Kejie watershed, south‐west China

“…There is a conviction that recent regional changes in temperature have had discernible impacts on physical and biological systems (IPCC, 2007). Recent studies show that climate change has altered water flows and resources in river basins (Chen et al, 2006;Rees and Collins, 2006). Current research into the effects of land-cover/climate changes on hydrological processes and water-related environmental services, and who are the winners and losers on different scales, is insufficient for formulation of useful policies (Calder, 2007;Noordwijk et al, 2004).…”

The Hydrology and Water Resources of the Proglacial Zone of a Monsoonal Temperate Glacier

“…But as glaciers diminish, the variability of river flows will increase and the river runoff decline in the long run [5]. The understanding of the mountain hydrology in the proglacial zones remains largely limited due to scanty observed data and complex modeling conditions [6,7].…”