The Role of Glaciers in the Hydrologic Regime of the Nepal Himalaya. Donald Alford Richard Armstrong NSIDC Adina Racoviteanu NSIDC

Transcription

1 The Role of Glaciers in the Hydrologic Regime of the Nepal Himalaya Donald Alford Richard Armstrong NSIDC Adina Racoviteanu NSIDC

2 Outline of the talk Study area and data bases Area altitude distributed process models overview Orographic streamflow model Glacier mass balance model The Role of Glaciers in the Hydrologic Regime of the Nepal Himalaya Summary and findings Recommendations

3 The Role of Glaciers in the Hydrologic Regime of the Nepal Himalaya Problem: The lack of a basic understanding of runoff sources in the rivers of South and Central Asia creates problems in resolving questions related to specific aspects of the water budget cycle, such the current concern over the impact of the retreat of Himalayan glaciers on water supplies Purpose of this study: To begin an assessment of the hydrologic regime of the Nepal Himalaya to assess the role of glaciers in the hydrologic regime of the Nepal Himalaya, to develop methodologies that will quantify this role To develop estimates of the potential water related impacts of a retreat of Himalayan glaciers Procedure: Extensive literature review Acquisition of representative data development of area altitude distributed process models of streamflow volume and glacier mass balance

4 Glaciers are Found at High Latitudes and High Altitudes Source: National Snow and Ice Data Center

5 The Nepal Himalaya These mountains rise 7000 meters above the adjacent lowlands. The summits exist in an arctic desert, rising above a subtropical forest.

6 The Gangotri glacier, Indian Himalaya Believed by many to be the source of the Ganges River

7 Glaciologists at work on the Langtang Glacier, Nepal Himalaya. This glacier has been studied intermittently by Japanese, Nepalese, European and American scientists.

8 IPCC Scenario The current trends of glacial melt suggest that the Ganga, Indus, Brahmaputra and other rivers that criss cross the northern Indian plain could likely become seasonal rivers in the near future as a consequence of climate change and could likely affect the economies in the region.

9 Rivers, Catchment Basins and Glaciers The Data Bases

10 Where the glaciers exist at the headwaters of gauged sub basins, it is possible to compare estimates of glacier melt and streamflow

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14 Data sources Digital elevation model (DEM) from the 2000 Shuttle Radar Topography Mission (SRTM) data v.4 (90m spatial resolution) Glacier outlines from topographic maps (ICIMOD) Catchment basins from ICIMOD this is the basic topographic unit in water budget analysis.

15 Area Altitude Distributed Process Models Define boundary of topographic unit Define and measure surface area of altitudinal belts, Develop orographic curves of specific process from data or theory, From orographic curves, select values for altitudinal belts, Specific process X area of altitudinal belt = volume of belt, Sum of volumes for altitudinal belts = total volume

16 Catchment basin hypsometry A histogram of the area altitude distribution in the Dudh Kosi Basin, derived from SRTM data. This information is a component of the area altitude distributed process models developed for this study.

17 The Orographic streamflow model

18 Glacierized Catchments in study River ID Name Specific Streamflow Avg altitude runoff (mm) (m 3 / sec) (m) Karnali Narayani Sapta Kosi 270 Bheri Kali Gandaki Budhi Gandaki Trisuli Marsyangdi Tama Kosi Likku Khola Dudh Kosi Tamur

19 The Orographic runoff gradient The general trend of mean specific runoff, mm, with mean basin altitude, m, for the Nepal Himalaya. While there is considerable scatter at t lower altitudes, the trend is one of decreasing runoff with increasing altitude. Based on data from Department of Hydrology and Meteorology, Nepal

20 Calculated streamflow volumes for altitudinal belts and basin total Dudh Kosi Basin Altitude, m Area, km2 Specific Runoff, m Streamflow Volume, mcm Total

21 The orographic streamflow volume gradient Dudh Kosi basin, Sapta Kosi river

22 The Glacier Mass Balance Model

23 Elements of The Area Altitude Mass Balance Model Glacier Zones Glaciers are divided into two zones, a lower ablation zone, and an upper accumulation zone. Most melt water produced in the ablation zone Equilibrium Line Altitude Accumulation and ablation zones are separated by the Equilibrium Line Altitude, ELA The ELA is defined here by the mean monthly altitude of the 0 deg. C. isotherm during the summerseason, 5400 m in the Nepal Himalaya during June, July and August Ablation Gradient There may be minimal melt above the ELA. Below the ELA, the ablation gradient is 1.4 m/100 m. Glaciers and Climate Change As he climate warms, the ELA will move vertically on the glacier. This will cause a change in the relative area altitude distribution above, and below, the ELA. The end result will be a change in the areas of the ablation and accumulation zones, as well as the volume of the glacier.

24 The Ablation Gradient and the Equilibrium Line Altitude ( Firn Limit ) Source: Haefeli, 1962

25 Specific Net Budget, (The Ablation Gradient ) Yala Glacier, Central Nepal Himalaya (Fujita, et.al, 1998). The line has a slope of 1400 mm/100 m.

26 Area Altitude Distribution of Glaciers in the Dudh Kosi Basin based on glacier areas from ICIMOD and elevations from SRTM data Estimated ELA altitude

27 The Accumulation and Ablation Zones Dudh Kosi basin The mass balance volume is the product of the specific net budget and surface area of altitudinal belts on the glacier mcm = million cubic meters

28 The Role of Glaciers in the Hydrologic Regime of the Nepal Himalaya

29 Total Mean Annual Basin Discharge Volume, Million Cubic Meters Basin: Glacierized Basins, 4 5 K: meter belt within the basins, Glacier Melt: Glacier melt at the headwaters of each basin..

30 Climate Change and Glacier Retreat A Steady State Analysis of The WWF/IPCC Scenario There are many scenarios for the retreat of glacier ice as a result of climate change. the World Wildlife Fund (2005) and the Intergovernmental Panel on Climate Change (2007) suggest that mean air temperature will increase 3 0 C by 2100 with no significant change in existing precipitation patterns. This temperature increase will produce a gradual rise in the equilibrium line altitude, ELA, of an estimated 450 meters, producing a steady decrease in the surface areas of both the accumulation and ablation zones during the century. Based on a steady state area altitude model assessment of this scenario, the glacier volume of the Nepal Himalaya will decrease by 60% during the period , from approximately 480 km3 in 2000 to approximately 200 km 3 by the year In 2100, the general area altitude distribution of glacier ice will be similar to that existing today, but with a greatly reduced surface area from approximately 5000 km2 at the present time to approximately 1600 km2 in 2100.

31 Area Altitude Distribution of Glaciers, Nepal Himalaya 2000 Glacier area based on data from ICIMOD and elevations from SRTM DEM Estimated ELA altitude

32 Estimated Area Altitude Distribution of Glaciers, Nepal Himalaya for 2100, based on WWF/IPCC scenario Estimated ELA altitude

33 Summary and findings Area Altitude Streamflow Model 1. The gradient of water exchange with altitude in the Nepal Himalaya is moderately to strongly curvilinear, with maximum exchange occurring at mid altitudes, and minima at the altitudinal extremes. 2. At the upper minimum of this gradient, Himalayan glaciers exist in what has been characterized as an arctic desert. Area Altitude Glacier Mass Budget Model 1. The altitude of zero mass balance for glaciers of the Nepal Himalaya, the ELA, is approximately 5400 m. Above this altitude no snow or ice melt occurs under presentday climate 2. Between the ELA and the glacier terminus, the specific net budget the ablation gradient is 1.4 m/100m Findings 1. The contribution of glacier annual melt water to annual streamflow volume varies among catchment basins from 2 13% of total annual flow from the basin, 2. This represents 2 3% of the total annual streamflow volume of the rivers of Nepal.

34 Recommendations Continuing Studies 1. Many years will be required to fully understand the glacier climate river relationships in the mountain catchments of the Hindu Kush Himalaya region. Model Verification 1. The orographic streamflow gradient could be checked, and refined, with streamflow measurements at intermediate altitudes in the basins. 2. Periodic measurement of glacier surface area, using best available methods based on satellite imagery could be undertaken.. 3. The ablation gradient could be measured at a few accessible glaciers.. 4. The locations of hydrometric gauging stations could be resurveyed using Global Position System GPS. Training 1. Training program could be prepared to teach the fundamentals of area altitude distributed process analysis,.. Atlases of Mountain Hydrology 1. Data driven, supply use analyses of the hydrologic regime of the mountain catchment basins are needed.