Melting glaciers below 6000 metres create problems for Himalayan farmers.
It is well documented that temperatures in the Himalayas have risen in recent decades and that glaciers in the region are losing mass. According to a study by Ren et al., many of the glaciers on the south slope of the central Himalayas have retreated during the past century, especially after 1960. The researchers point out that the annual mean temperature in the region has gradually increased and that the strongest warming has occurred in the past 30 years. Shrestha et al. have shown that temperatures in the mountain areas of Nepal rose between 0.06 and 0.12 degrees per year from 1971 to 1994 and that the mountains experienced greater warming than the lowlands. While the development of the precipitation pattern is highly complex and general trends are difficult to predict, there is widespread agreement among researchers that increased melting of snow and ice is occurring in many areas of the Himalayan region.
Melting mainly in lower-lying glaciers
A recently published study by Jacob et al. in the journal Nature shows that the glaciers in the Antarctic, Greenland and the Himalayas are melting and that this is contributing to sea level rise. For the Himalayas, the study shows that a slight increase in the mass of the glaciers at high elevations has compensated somewhat for increased melting of the glaciers at lower elevations. Overall, though, melting in the Himalayas is contributing to a rise in sea levels, even though the study shows that the contribution is smaller than previously estimated. In an interview with The Guardian, one of the authors makes it clear that the lower-lying glaciers in the Himalayas are definitely melting. In other words, Jacob et al. do not contradict previous research on this point.
The melting in the Himalayas is different for glaciers at higher and lower elevations. Up to now, only a few of the glaciers above 6000 metres have lost any mass, and some of these high-lying glaciers have increased. The most extensive melting is occurring in the many glaciers located below 6000 metres. Kehrwald et al. noted this difference in the ice melt between the high-lying and low-lying glaciers in their study from 2008. For people in the Himalayas, however, the low-lying glaciers are particularly important for the local water supply in the spring, before the arrival of the monsoon rains. Precipitation that falls in the form of snow over the glaciers is stored there over the winter. When spring and summer come, the melted water runs down from the mountains to the valleys where people cultivate the land.
Melted water crucial for the farmers
For the farmers, the most important function of the glaciers is to store precipitation in the mountains until spring arrives and the crops need irrigation. According to Xu et al., on an annual basis the melted water from the glaciers accounts for only 9 percent of the river flow in the Ganges, but in the spring and autumn seasons the melted water from snow and ice comprises 70 percent of the Ganges’ river flow. The melted water is crucial for the water supply for agriculture during periods when the monsoons do not provide enough water for the crops. As temperatures rise, less precipitation will be stored in the form of snow and ice in the lower-lying glaciers. As a result, much of the water will bypass the fields at a time of year when the farmers cannot make use of it for cultivation. The net mass loss of the lower-lying glaciers will lead to increased annual runoff and thus greater water supply as long as the melting continues. When the glaciers have either disappeared completely or reached a new, lower equilibrium point, the river flows will then suddenly be drastically reduced, particularly during the dry season. In a study from 2009, Xu et al. illustrate the connection between a temperature increase, the response of the glaciers and the effect on the river flows.
In Nepal, two-thirds of the population depend on agriculture for their livelihood, either fully or partly. The farmers in the mountain regions of Nepal cultivate the land up to 4000 metres above sea level. Like people in other parts of the Himalayas, many of the farmers rely on the melted water streaming from small, local and low-lying glaciers. The Himalayan region spans great variations in local climate, even across small distances. Due to the high mountains, steep slopes and deep valleys, obtaining sufficient water supply for agriculture is often a matter of making highly local adjustments to the surroundings. Looking at the entire region as a whole, increased snowfall over the high-elevation glaciers can compensate for increased melting at lower elevations. However, this is little help to the farmers who depend on the melted water from their local mountains at the right time of year.
People in the lower-lying areas of Nepal also need melted water in the spring. In the most densely populated areas of the country, rain is the main source of water and many areas receive more than enough precipitation. According to Merz et al., however, 85 percent of the annual precipitation falls during the monsoon season from June to September. During the remaining eight months, melted water from many small glaciers and snow-covered areas makes an important contribution to the river flows. Even though the precipitation patterns vary greatly from place to place, melted water remains essential for those farmers who need this water for agricultural purposes. Enough water at the right time of year is vital for the farmers, both in the high mountains and in the hills and plains at the foot of the Himalayas.
In short, higher temperatures in the Himalayas have caused increased melting of snow and glaciers located below 6000 metres. A reduction in these glaciers’ ice mass means that less water is stored in the form of snow and ice in the mountains, which leads to greater seasonal water shortages for agriculture. The Himalayan farmers still need their glaciers.
Carrington, D. 2012. The Himalayas and nearby peaks have lost no ice in the past 10 years, study shows. The Guardian.
Jacob, T., Wahr, J., Pfeffer, W.T. & Swenson, S. 2012. Recent contributions of glaciers and ice caps to sea level rise. Nature Research Letter. Published on the Internet on 8 February 2012.
Kehrwald, N. M., Thompson, L. G., Tandong, Y., Mosley-Thompson, E., Schotterer, U., Alfimov, V., Beer, J., Eikenberg, J. & Davis, M. E. 2008. Mass loss on Himalayan glacier endangers water resources. Geophysical Research Letters, 35 (L22503), 1–6.
Merz, J., Nakarmi, G., Shresta, S. K., Dahal, B. M., Dangol, P.M., Dhakal, M. P., Dongol, B. S., Sharma, S., Shah, P.B. & Weingartner, R. 2003. Water: A Scarce Resource in Rural Watersheds of Nepal’s Middle Mountains. Mountain Research and Development, 23 (1), 41–49.
Ren, J., Jing, Z., Pu, J. & Qin, X. 2006. Glacier variations and climate change in the central Himalaya over the past few decades. Annals of Glaciology, 43, 218–222.
Shrestha, A. B., Wake, C. P., Mayewski, P.A. & Dibb, J. E. 1999. Maximum Temperature Trends in the Himalaya and Its Vicinity: An Analysis Based on Temperature Records from Nepal for the Period 1971–94. Journal of Climate,12, 2775–2786.
Xu, J., Grumbine, R. E., Shresta, A., Eriksson, M., Yang, X., Wang, Y. & Wilkes, A. 2009. The Melting Himalayas: Cascading Effects of Climate Change on Water, Biodiversity and Livelihoods. Conservation Biology, 23 (3), 520–530.
Denne artikkelen ble opprinnelig publisert i Magasinet Klima nummer 2, 2012