Climate change projections for Nepal
This work is part of a Policy Brief on Climate Change in Nepal produced by Practical Action in 2008 and provides a summary of climate change as currently experienced in Nepal, and projections of future changes.
Climate change in Nepal
Some level of uncertainty is inevitable in measuring and anticipating climate change. Attributing individual current events to climate change is impossible due to inherent climate variability, whilst a lack of observations over a sufficiently long time frame or narrow geographical area can hamper the analysis of climate trends. However, the degree of certainty over all aspects of climate change has increased in recent years, and in particular between the publication of the IPCC's reports in 2001 and 2007.
As a result, there is now higher confidence in climate projections, including regional-scale warming, wind patterns, precipitation and some aspects of extreme events. Country-scale trends and projections, however, remain difficult to discern and as a result there have been many more studies focussed on South Asia than on Nepal. However, many regional observations and predictions have particular relevance for Nepal and are therefore included in the following summary of current and future climate change and the associated impacts.
The following is drawn predominantly from the IPCC's 2007 report but also relies in places on Nepal government sources, and Practical Action's own experiences in Nepal.
Climate change today
The South-Asia region is broadly defined by the IPCC as consisting of Pakistan, India, Nepal, Sri Lanka, Bhutan, Bangladesh, Myanmar and the Tibetan Plateau. However, the whole region has large climate variability, making climate change harder to identify and meaning that the current level of understanding of how the climate is influenced by human activity is low. Despite this, climate anomalies and changes in extreme events have been observed throughout the region, with intense rains, floods and droughts reported. Of particular note is severe and recurrent flooding in Nepal. More gradual year-on-year changes in temperature have also been observed, with a 0.09°C per year increase in recorded in the Himalayas and 0.04°C per year increase in the Terai (with higher increases in winter).
These regional climate extremes and climate changes have produced multiple impacts across the South Asia region and in Nepal in particular.
• Many parts of the region have suffered a reduction in food production due to reduced water availability, increases in temperature and a reduction in rain fall days.
• Water shortages and poor water quality have been attributed to the effects of rapid urbanisation and industrialisation, aggravated by climate change, in India, Pakistan, Nepal and Bangladesh.
• The incidence of diarrhoeal diseases and other infectious diseases such as cholera, hepatitis, malaria and dengue fever is expected to increase due to severe floods, rainfall and droughts in combination with poverty, poor access to safe water and poor sanitation. High temperatures and poor hygiene contribute to bacterial proliferation.
A study by Practical Action in the Jugedi watershed region in Chitwan District has revealed the range of problems that the changing climate has brought in Nepal. The weather has been observed to have become be hotter in the summer months, yet colder in the winter, whilst the number and quality of water resources have fallen. Monsoon rainfall has increased whilst winter rainfall has become scarcer and periods of drought have become longer. Higher levels of sediment have altered the course of rivers, liver disease has been observed in cattle and cereal crop production has fallen. The effect on livelihoods has been seen through an increase in alcohol production to offset the failure of agriculture, whilst paddies have been converted to maize, millet and gram fields as the agricultural conditions change.
The vast majority of climate change predictions relevant to Nepal have been made using regional climate models. These indicate that warming across Asia will accelerate. The rate of warming in the South Asia is projected to be significantly faster than that seen in the 20th century, and more rapid than the global mean rate of warming.
• Extreme weather events are projected to increase in frequency in South Asia, including heatwaves and high rainfall.
• During December, January and February warming is expected to be at its greatest and associated with a decrease in precipitation, whilst the consensus of regional models is that summer rainfall will increase.
• Nepal's National Communication to the UNFCCC - one of few reports that attempts climate modelling at the national scale - agrees with regional precipitation change predictions. The report suggests that an overall increase in precipitation is to be anticipated, but with the increase greater in the east of the country than in the west.
The predicted seasonal changes for the South Asia region are summarised in graph form here. The changes have been calculated relative to the average temperature and precipitation in the period 1961-1990. Note that the results of climate projections for high and low future global greenhouse gas emissions are presented - demonstrating the enormous difference in the impacts that result from alternative future levels of greenhouse gas emissions, particularly by the end of the century. The figures also demonstrate the impact that the highest emitting countries - the most developed countries in the West - have on South Asia. The 'high emissions' figures assume rapid, fossil fuel-intensive economic growth over the coming century: very much a business as usual in the global economy. The 'low emissions' figures, on the other hand, assume reductions in the use of natural resources and the introduction of clean and resource-efficient technologies during the course of this century. The implication is clear - large cuts in carbon emissions and radical changes in global patterns of consumption, particularly in the West, will be required to prevent climate change from bringing catastrophic changes across South Asia.
Future impacts and vulnerabilities
The IPCC offer the following summary of the vulnerability of key sectors in the South Asia region. In keeping with the IPCC approach, the summary reports both the degree of vulnerability and the level of confidence. The South Asia region has the highest proportion of 'highly vulnerable' sectors of all the Asia sub-regions.
In keeping with the regional assessment, the most profound impacts of climate change in Nepal will be in agriculture and food security, water, biodiversity changes, and human health.
• Agriculture and food security: Overall crop yield (wheat, maize and rice) could decrease in South Asia by up to 30% by the end of this century (compared with an increase of up to 20% in East and South East Asia). In Nepal, the predicted decrease in precipitation during the winter months will reduce winter and spring crop production. Temperature increases are also expected to reduce wheat and maize yields, whilst increased variability in both temperature and precipitation will present significant challenges to farming practices. Irrigation fed agriculture will be increasingly threatened as water resources deplete. Landslides and flash floods have already reduced the area of land available for cropping and are likely to continue to reduce productivity in the future. However, some estimates suggest that rice production will increase if there are moderate temperature and precipitation increases, whilst wheat production may increase the westernmost areas of Nepal.
• Water resources: Reductions in winter snow means less precipitation stored on the glaciers, in turn decreasing spring and summer runoff. However, earlier snowmelt and precipitation falling as rain rather than snow due to increased temperatures will increase winter runoff. Glacier melting has a significant impact. As glaciers start to melt, river runoff will initially increase during winter or spring, but beyond 2050 the ice resource is predicted to deplete and the supply of water will reduce. Those areas that rely on irrigation for agriculture will be particularly affected. Another impact of these changes is the increased likelihood of glacial lake outburst flooding (GLOF), whilst increased annual precipitation of more than 20% will contribute to significantly increased sediment deposits - silting up river beds and increasing flood risk. Irrigation problems will be compounded by changing rainfall patterns, which are predicted to provide greater rainfall during monsoon when river flow is already high, and lower rainfall during the already dry winter months. As ice stocks decrease and winter precipitation reduces, the areas in water stress will increase. Ground water depletion is likely due to long dry seasons, irregular rains, and high intensity rainfall leading to high run-off rather than water absorption. Water stress is predicted to become one of the most pressing environmental problems in South Asia: all future emissions scenarios predict increasing water stress, with the effects being felt as early as 2020.
• Energy infrastructure: The glacial runoff and rainfall changes described above pose particular problems for hydropower infrastructure, which will have to adapt to changing patterns of flow and ranges of volume of runoff. Whilst additional problems will result from reservoir evaporation and increased sedimentation, perhaps the most dramatic impact would result from glacial lake outburst flood (GLOF), which has the potential to destroy hydropower installations.
• Ecosystems and biodiversity: In South Asia, grasslands are particularly under threat. Large decreases in grasslands are likely as temperatures rise and evaporation increases, threatening the livelihoods of livestock keepers. Significant changes in vegetation are anticipated in Nepal under the models considered in the National Communication: tropical wet forest and warm temperate rain forest will disappear, and cool temperate vegetation will turn into warm temperate vegetation. Currently, there is no rain forest in tropical and subtropical regions in the Nepal, but a doubling in carbon dioxide would see an emergence of rain forest in these regions. The sub-alpine and alpine regions of Nepal will be significantly changed by warming, and the altitude at which vegetation is found could rise by up to 500m, extending the area with potential for cultivation for those living on the hills. However constraints in soil fertility and irrigation water restrict the chance of harnessing this opportunity.
• Human health and migration: The burden of climate attributable diarrhoea and malnutrition is already high in Nepal relative to elsewhere in Asia. Future climate projections suggest that this large relative risk is expected to continue, with flooding causing pollution in surface water and an increase in cholera and diarrhoeal diseases. Analysis suggests that the risk of malaria and kalaazar (a deadly disease transmitted by sandfly bite) is likely to increase, particularly in the subtropical and warm regions of Nepal, with Japanese encephalitis risk also rising the subtropical region. Generally, increasing temperatures are likely to yield a spread in insect borne diseases and exposure of communities to diseased that they have no experience of or immunity to. Human migration following extreme weather events is also to be anticipated.