Impacts of Climate Change on Water Resources and Challenges for Mainstreaming Adaptation Concerns in the Nepal Himalaya
Danda Pani Adhikari
Lecturer, Department of Geology, Tri-Chandra Campus
Tribhuvan University, P.O. Box 13644
Kathmandu, Nepal
Nepal occupies the central one-third of the Himalayan arc. 83% of its territory is mountainous terrain and the remaining 17% lies in the alluvial plain of the Gangetic Basin in the south. The altitude within the 130-255 km wide-country varies between 69 and 8848 m, and gives rise to steep and rugged topography. Nepal lies in the south Asian summer monsoon regime where 70-93% of the annual precipitation, which is estimated at an average of 1400 mm, occurs from June to September. Snow occurs in the areas above 3000 m in winter and above 6000 m even in the summer monsoon season.
About 43% of the total area of Nepal is above 3000 m in altitude. The permanent snow line lies near to 5000 m and about 23% of the total land area is located above it. In winter, nearly a quarter of Nepal is covered by snow, but snow and glaciers permanently cover about 10% of the territory and the melt water contributes about 12% of the river flow. Glaciers develop in the areas above 4000 m, and currently, about 3.6% of the total area of Nepal is occupied by glaciers. It has about 3252 glaciers and 2315 glacial lakes at present. Large areas of snow and ice, high precipitation and large numbers of perennial rivers originating from the glacier sources make Nepal rich in hydropower potential. It is estimated that about 42,000 MW of hydropower energy could be generated commercially from the theoretical hydropower potential of about 83,000 MW.
Consistent with, but higher than, the global increasing trend, all-Nepal temperature shows 0.9 oC rise since 1977, where the trend is higher in the high altitude in the north (0.06 - 0.12 oC yr-1) than in low lying areas in the south (less than 0.03 oC yr-1). In response to the accelerating warming, glaciers are retreating at rates of few meters to nearly 100 m yr-1, eliminating many small glaciers, and creating new and enlarging existing glacial lakes at the termini of glaciers. Breaching of such lakes resulted into seven major Glacier Lake Outburst Flood (GLOF) events in the past 30 years, and 26 glacial lakes are reported to be potentially dangerous for GLOF. Based on some research findings on Mass Balance and Equilibrium Line Altitude (ELA) in the eastern Nepal Himalayas, the average rate of upward shift of ELA between 1959 and 1992 was 0.76 m per year.
High mountains in the north receive more snow in the summer monsoon than in the winter season, which is a typical characteristic of Nepalese glaciers compared to glaciers in the European Alps and other regions where accumulation occurs mainly in winter. Due to this typical characteristic, Nepalese glaciers are more vulnerable to climatic change than glaciers of other regions because the [expected increases in] temperature will accelerate the melting of glaciers on one hand and on other hand more precipitation in summer will occur in the form of rain rather than snow. The pattern of monsoon precipitation since the mid-1970s reveals that the numbers of rainy days are decreasing and the high-intensity rainfall events appear to be increasing. Crops in the southern flat lands receive irrigation mostly through the use of groundwater, but the changing precipitation pattern is adversely affecting groundwater recharge and hence agriculture.
Snow and glaciers in the Himalayas are considered as the natural storehouse of fresh water. The Initial National Communication to the Conference of the Parties of the United Nations Framework Convention on Climate Change reported that almost 20% of the glaciated areas above 5000 m are likely to be snow and glacier free area at an increase of air temperature by 1oC. Two degree centigrade rise in temperature can cause the loss of almost 40 % of the areas. Similarly, 3oC and 4oC rise in temperature can result in the loss of 58% and 70% of snow and glacier areas, respectively. The implication has direct impact on hydropower generation, irrigation and even for drinking water supply as population growth rate is exceeding 2% and water demand in Nepal is estimated to increase by seven-fold within the next 25 years with development and urbanization. Building of more storage structures could help, but it is always not the best alternative because of the fragility and high seismicity of the Himalaya.
A detailed mass balance analysis of several glaciers in central Nepal show that about 73% of the present glacier area, about 87% of the present ice reserve and about 98.5% of present glaciers in Nepal Himalayas will disappear by 2100, if their current melting rate continues. This will cause a reduction in annual glacier-melt water in Nepal from 10.5 km_ in 2000 to 2.9 km_ in 2100. Disappearances of glaciers not only reduce the total water availability required for socio-economic activities of millions of people living downstream, but also result in more pronounced seasonal imbalances of flows and consequently more floods during summer and more droughts during other seasons. This will cause water stresses in dry seasons despite too much of water in the summer-monsoon. The anticipated changes in hydrological cycle and the depletion of water resources therefore are one of the biggest challenges Nepal is going to face due to climate change.
Nepal emits less than 0.025% of the global Greenhouse Gas emission, but it is likely to be one of the countries hardest hit by the impacts of climate change. The most critical impacts of climate change in Nepal can be expected to be on its water resources, particularly hydropower generation and irrigation. Water supply infrastructure and facilities are at risk from increased flooding, landslides, sedimentation and more intense precipitation events which have already been observed. Hydroelectric plants are highly dependent on river flow pattern and therefore, increased climate variability, which can affect frequency and intensity of flooding and drought, could affect Nepal severely. GLOF and increased flow variability threatens the potentials for hydropower generation. GLOFs have already been associated with the loss of hydropower facilities, as well as significant loss of other infrastructure such as roads, bridges, and loss of livelihoods and human life. Given Nepal’s reliance on hydropower ? nearly 91% of the nation’s power comes from this source- reduced hydropower potential might require Nepal to seek for alternative sources of power generation if adequate adaptation measures are not adopted effectively. However, uncertainties in climate projections and lack of reliable hydrological records remain an important constraint for effective anticipatory planning.
Despite the series of observable impacts mentioned above, very little adaptation efforts have been undertaken in national and community level, except some rainwater harvesting and flood control measures. Nepal is making vulnerability assessment in the process of preparing National Adaptation Programmes of Action (NAPA) for mainstreaming adaptation concerns in the agriculture and water resource sectors. They include improved hydrological forecasting, introduction of less water intensive crops, strengthening watershed management, more efficient management of existing poor water supply infrastructure, drip irrigation scheme, promotion of groundwater recharge technologies, and making water storage structure for electricity and irrigation etc.