The Himalayas has the most extensive ice and snow cover outside the Polar Regions. It is also one of the most important mountain systems in the world and is also known as the “third pole” and “water tower of Asia.” The mountain range is extended along the northern edge of the Indian Subcontinent. It stretches from the Brahmaputra River in the east to the bend of the Indus River in the northwest. The mountain system directly or indirectly affects more than 300 million people in the region. Due to its massive ice reserves, the Himalayas contributes to the flow of thousands of rivulets and rivers that later converge to form the main river systems; the Ganges, Indus, and Brahmaputra, which is also known as Yarlung Zangbo in China.
There is growing concern about the current and future impact of climate change on the Himalayas since it has a fragile landscape that is highly susceptible to natural hazards. The concerns are multifaceted encompassing landslides, floods, drought, biodiversity, human health, endangered species, and food security. Temperature data shows a warming trend in the mountain range, albeit in different periods depending on seasons and regions and at different rates. A recent regional study that used the Climate Research Unit’s reconstructed temperature dataset showed that the Himalaya and the Tibetan plateau were warming up at a higher rate in the last few decades than in the last century. The report reveals that the western Indian Himalayas had a 33.620F temperature rise over 102 years (1901-2003). According to the report, much of the observed trend is related to increases after 1972.
Data on monthly winter temperatures between 1975 and 2006 indicated that there was a warming trend in the western Indian Himalayas with the highest increase in annual average maximum temperature being 33.980F to 36.50F. The northwest Indian Himalayas has been warming at a rate of 32.30F in every decade in the last century. An increase in the annual average maximum temperature and the seasonal average of daily maximum temperature has also been observed in all seasons except monsoon over the lower Indus basin in the northwest Indian Himalayas. Between 1961 and 2000, winter temperatures have been increasing in the upper Indus basin (Pakistan) at varying warming rates of 32.1-32.270F every decade in annual mean temperature and 32.18-32.990F every decade in annual average maximum temperature.
Most reports on Himalayan precipitation lack spatially consistent long-term trends. The lack of homogeneity in trends reflects the influence of local orographic and thermodynamic processes over large scale ocean-atmospheric processes. A difference in precipitation is also observed across seasons. According to a recent study, on Climate Change and Precipitation Variations in the North-western Himalayas conducted by Bhutiyani, V.S. Kale, and N.J. Pawar, a statistically significant downward trend in monsoon and average annual rainfall was observed between 1866 and 2006. A similar trend was noted from 1960 to 2006 over the western Indian Himalayas region. Other studies have shown intra-regional differences in winter rainfall trends in the Western Indian Himalayas.
Several studies involving satellite imagery, repeat photography, and field-based observation have shown that glaciers in the Himalayas are retreating. The Karakoram region is, however, a notable exception as some glaciers have shown some advancements over the years. The Karakoram region has different climatic conditions compared to other regions due to several factors, including orographic conditions in the area that enhance precipitation in the source area. Other factors include ablation buffering due to thick debris cover, concentration and the role of avalanches, and an all-year accumulation regime. Analysis of satellite images of 26 glaciers in the western Indian Himalayas over the years has shown that all of them are retreating. Fluctuation in retreat rates has been observed, with the maximum retreat occurring during the 1989/1992-2001 period. In the Dudh Koshi basin in Nepal, several glaciers have retreated while a few of them have shown stability.
The Gangotri glacier, in India, has shown temporal variability, with no retreat having been observed between 2006 and 2010 despite recording a high retreat rate in previous decades. A recent study of 286 mountain glaciers across the Himalayas found that more than 65% of mountain glaciers in areas influenced by the monsoon were retreating with several glaciers covered in heavy debris being stable. About 58% of glaciers in the westerlies-influenced Karakoram region were either slowly advancing or stable. In Nepal, the glacier snow and ice reserves in 2001 and 2010 declined by 21% and 28% respectively.
Glacier Lake Expansion
The rising temperatures in many mountainous regions across the world have resulted in the retreat of glaciers and the formation of moraine-dammed glacial lakes. In the Nepalese Himalayas, the area occupied by moraine-dammed lakes is increasing. The eastern Himalayas (in Bhutan, Nepal, the sub-basin of the Ganges in China, and Sikkim) have more glacier lakes compared to the western Indian Himalayas. A study of 50 moraine-dammed lakes at the China-Bhutan border region found that 14 lakes had grown between the late 1960s and 2001. Studies have suggested a 25-45 ha per year growth rate for glacial lakes in the Bhutanese and Nepalese Himalayas between 1990 and 2009. In the Indian Himalayas, the average growth rate has been 4ha per year.
Climate Change And Glacier Dynamics
Glacier length (glacier retreat) and flow rate have longer response times to climate change compared mass balance (thickness), which has a near-immediate response. The response rate of most glaciers in the Himalayas is in the range of 10 to 200 years. The largest glaciers in the Himalayas are responding to changes that occurred nearly 100 years ago. Climatic factors such as precipitation type and amount, temperature, and non-climatic factors such as slope, debris cover, elevation, and aspect all influence glacier retreat. Glacial mass balance (change in volume and thickness) changes in direct response to annual atmospheric conditions. Research has shown a negative mass balance across the Himalayas. A study of three small, relatively debris-free glaciers in Nepal, found considerable thinning in two of them in a humid climate in recent decades.
Black carbon has recently come under increased attention as a factor triggering accelerated glacial mass loss. Black carbon is produced as a result of incomplete combustion of coal, diesel, and biomass fuels. Scientists have found that black carbon has accelerated warming trends across Asia. The black carbon concentration has increased threefold from 1975-2000 relative to 1860-1975 at higher elevations of the Himalayas. Black carbon deposited in ice and snow increases melting through reduced surface albedo while atmospheric black carbon cause glacial melting through warming related to light absorption. Black carbon deposited on glaciers in China has been identified as an important factor contributing to rapid glacial retreat.
Mixed Stream-flow Trends
Both climate change and land-use change influence Stream-flow trends. Stream trends have significant implications for flood risk and water availability. A significant increase in the number of high-magnitude flood events has been observed in rivers in the north-western Indian Himalayas. In the last three decades. On the Tibetan Plateau, a 5.5% increase in river runoff has been noted, which is attributed to glacier melting. The Trim River basin has also had a 13% increase in river runoff.
Importance Of The Himalayas
The Himalayas is key to the economies of nations such as Bhutan and Nepal that depend on the mountain system for water supply, hydropower, tourism, and agriculture. For example, Hydropower exports from Bhutan contributed 39% of the nation’s total exports in 2009/2010 and 16.3% of the nominal gross domestic product (GDP). In Nepal, agriculture, a key sector in the economy contributed about 34% of the GDP in 2009 and employed 93% of the workforce in 2004. Nepal’s long-term economic development plan is also centred on the resources provided by the mountain range, in areas such as hydropower where its current capacity is barely 1.5% of its 43,000 MW potential. Xizang Province in China and the Himalayan states of India also rely on agriculture, tourism, and hydropower to sustain their economies.
All the countries mentioned have a tremendous hydropower potential that has not been adequately harnessed so far. In recent years, the Indian government released a report showing that the Himalayan states had over 70% on the nation’s hydropower potential in terms of installed capacity greater than 25 MW. The Himalayas region also holds rich biological and social-cultural diversity. The region is listed as one of 34 biological hotspots by Conservation International, meaning that the natural environment has high biodiversity that includes a large number of endangered endemic species. Indigenous people living in the region consider the mountain as sacred and therefore, invaluable to the communities.
Effects Of Climate Change On Agriculture In The Himalayas Region
Agriculture in the Himalayan region is mainly rain-fed, which, therefore, means that it is vulnerable to climate change. Apart from water availability, crop yield also depends on variables such as humidity, thermal stress, solar radiation, fertilization effect of CO2, and nitrogen stress. A study of apple yield in the Himachal Pradesh region revealed a decline in yields. In Nepal, the winter crop yield from 1997-1998 decreased by between 11-38% of the previous 10-year average due to severe overcast associated with a drop in solar radiation. In 2006, poor monsoon rainfall in Nepal led to a 30% decline in rice production in eastern Terai, while in western Nepal, heavy rain and flooding led to reduced production by the same percentage. Global climate model projections point to a warmer Himalayan region in the future. The region is also expected to experience warming at rates above the global average. Experts believe that agriculture is likely to be severely affected by climate change going into the future.