Sikkim braces for climate extremes

Boys play cricket by the riverside in Dikchu, Sikkim. Photo by Ullasa Kodandaramaiah.

  • A study on the Teesta river basin in Sikkim by IIT Guwahati researchers projects drastic changes in climate extremes in the 21st century. The basin lies in the states of Sikkim and West Bengal, primarily covering Sikkim.
  • The analysis shows an increase in both rainfall and temperature in the Teesta basin, but there is a large variation across the basin.
  • The study reaffirms the findings from a recent IPCC report that points out the rapidly changing climatic conditions in the Hindu-Kush Himalayan region.
  • The focus on preparedness is on a rise with Sikkim even introducing disaster studies as part of its school curriculum.

Even as Sikkim introduces climate change disaster studies as part of its school curriculum to aid community preparedness, latest research emphasises the need for the state to be equipped with resources to respond and to recover from climate disasters.

The study on the Teesta river basin in Sikkim in the Eastern Himalayas shows a clear sign of an increase in rainfall and temperature in the 21st century. This could lead to flash floods and further impact human health and water availability, notes the study, highlighting that the findings can be used by policymakers for climate adaptation strategies. 

The Teesta basin in India, drained by the river Teesta and its tributaries, extends over an area of 9,855 square km, which is nearly 0.28 percent of the total geographical area of the country. The basin lies in the states of Sikkim (72.43 percent) and West Bengal (27.57 percent). 

Teesta river is one of the largest tributaries of river Brahmaputra, which is often called the lifeline of northeast India. It is a 414 km long river flowing through India and Bangladesh and has been a source of a long-drawn diplomatic stand-off between the two neighbours. The basin completely covers Sikkim.

The IIT Guwahati scientists investigated the changes in rainfall and temperature along with the climate extremes in the Teesta basin, up to Teesta Bazar gauge station (hydro-meteorological observation point) in north West Bengal.

The study projects “drastic changes in climate extremes”.

Running multiple models for two different greenhouse gas concentration scenarios for the 21st century, the scientists project an increase in extreme rainfall events in the basin, which can cause sudden expansion of glacial lakes leading to Glacial Lake Outburst Floods (GLOF).

According to ICIMOD, GLOF, is the sudden release of water from a lake fed by glacier melt that has formed at the side, in front, within, beneath, or on the surface of a glacier.

The Sikkim Himalayan region has over 300 glacial lakes of which 10 have been identified as vulnerable to outburst floods, as per data supplied to Mongabay-India by the Sikkim State Disaster Management Authority.

“Our analysis clearly shows an increase in both rainfall and temperature in the basin, but there is a large variation across within the Teesta basin,” IIT Guwahati’s M.K. Goyal and study co-author told Mongabay-India.

Map of study area. Photo by Goyal et al

However, Goyal said it is hard to tell how much of an increase is expected because of the spatial variation and also because of the uncertainties linked to different greenhouse gas concentration scenarios (Representative Concentration Pathways or RCPs) and climate models.

The study parsed through two RCPs (RCP 4.5 and 8.5. RCPs), that are among a suite of potential pathways developed by IPCC considering greenhouse gas emissions, land-use changes, demographic changes and the mitigation strategies. The RCPs characterise climate change projections.

“We can say that RCP 8.5 is the scenario of maximum emissions and least mitigation efforts. RCP 4.5 is an intermediate scenario, which assumes that the emissions will be reduced by 2050, and different mitigation measures will be considered,” explained Goyal. Goyal stressed that despite uncertainties in projections, there is a “clear sign of increasing temperature and precipitation” which is significant. “It can’t be ignored,” he underlined.

Climate models suggest that there could be a 1 to 1.2 degree Celsius rise in daily mean temperature by 2100 under RCP 4.5, and it could go up to as high as two degrees Celsius if RCP 8.5 unfolds (increased emissions and no mitigation). 

“These numbers represent the change in annual mean temperature (average of temperature on all days in a year). A change of one degree Celsius in the annual mean is very significant,” Goyal said.

Sikkim State Disaster Management Authority’s G.C.Khanal confirmed to Mongabay-India that there has been an unprecedented melting of glaciers and the development of glacial lakes with an increasing volume of water.

“The frequent and unprecedented rainfall has led to the occurrence of major and minor landslides. The winter dry season has often seen instances of forest fires. The most prominent effect has been on the higher Himalayan region of the state where continuous melting of glaciers has led to the formation of several moraine-dammed glacial lakes,” Khanal told Mongabay-India in an email, discussing a slew of interventions.

Of the lakes, South Lhonak glacial lake, in North Sikkim, is one of the fastest-growing lakes in Sikkim Himalaya and has become a major concern for the state.

Khanal said SSDMA has initiated interventions at South Lhonak glacial lake in North Sikkim through mitigation by way of siphoning the excess water from the lakes to lessen the threat for events like GLOF and capacity building of downstream communities including installation of suitable early warning systems. “We have also initiated the study of other ten vulnerable glacial lakes for the threat of GLOF,” said Khanal.

From the forthcoming school session, content on climate change and disasters has been introduced.

“Teachers’ Training Handbook contains a chapter on climate change for Classes I to VIII which was already available on our website. From the next school session, this will be complemented with content in textbooks,” Khanal said.

“We understand the need to focus on climate-induced disasters and the authority has been working on activities to build the resilience of the state towards all disaster including the climate-induced ones,” he added.

Rapidly changing climate in the Hindu Kush Himalayas

From a hydrological point of view, Teesta River is one of the most suitable catchments to study the impact of climate change. It has a large, snow-covered region and many glaciers. The impact of climate change (increase in temperature) can be clearly seen in these regions, the scientist said.

Rising up from 200 metres to an elevation of 8376 metres, the basin has forest and grassland as the most dominant land covers followed by snow or ice (12.2 percent).

A substantial increase in the warm days and warm nights, whereas a substantial decrease in the cool night and cool days was found. The study notes an increasing trend both monsoon and non-monsoon precipitation in the projected climate.

Further, Goyal adds that any disruption in the flow of Teesta will impact millions of lives in downstream regions of Brahmaputra. 

“When there is flood or drought, downstream regions are also affected. Though rainfall extremes are localised compared to temperature extremes, we have seen in many cases that floods affect the downstream regions as well. Increasing temperature will result in a decrease in snowfall, which will also impact the streamflow during the lean period,” Goyal explained.

Anjal Prakash, climate adaptation expert and coordinating lead author for the IPCC Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC), said the IIT Guwahati study reaffirms the findings from the recent IPCC- SROCC report that has pointed out the rapidly changing climatic conditions in Hindu-Kush Himalayan (HKH) region.

The HIMAP Assessment and HI-AWARE reports are all pointing towards this direction, Prakash added.

All these reports have shown that HKH regions are extremely susceptible to temperature increase. Under a 1.5 degree Celsius global warming scenario, the areas are projected to warm up by more than two degrees Celsius on average by the end of this century, underscored Prakash, research director and adjunct associate professor, Bharti Institute of Public Policy, Indian School of Business.

The Gurudongmar glacial lake in Sikkim. Photo by SangitaChatterjee/Wikimedia Commons.

At higher altitudes, this warming will be even more marked, due to elevation-dependent warming. A two-degree Celsius global warming scenario could lead to a warming of around 2.7 degrees Celsius in glaciated river basins.

Expanding on the HKH river basins, Prakash said the likely climate change scenarios, specific to these river basins, suggest regional temperature increases between 3.5 and 6 degrees Celsius by 2100. 

“Most of the projections also indicate overall wetter conditions in the future and increases in extreme precipitation events. This will lead to significant losses in glacier volume, from 36 to 64 percent depending on the warming scenario, and impact timing of water flows and water availability. So, the rate of risk is extremely high in the present emission scenario,” Prakash added.

“Looking at the Teesta river basin, the study clearly shows how and when these changes are going to happen. While IPCC provides a bird’s eye view, we need such studies which give a worm eye view of the situation,” he said.

A recent study where Prakash was involved, shows how people perceive climate change in the Teesta region and this corroborates the scientific work, the IIT Guwahati authors have undertaken, said Prakash.

In the up-streams, the wage earners, women, tourism workers, small traders, pastoral groups and lower caste people have been found highly vulnerable to both climate change and social stresses in the Teesta basin as also in Upper Ganges and Gandaki.

“In the mid-streams, horticulturists, tea workers, wage earners, subsistence farmers, women and socially excluded groups have been identified as the most vulnerable sections. In the down-streams, small farmers, seasonal migrants, traditional fishers, women, char-dwellers and temporary settlers on embankments are the most vulnerable groups,” said the people’s perception-based study.

“We hope these studies translate into appropriate policy actions leading to preparedness and adaptation from a swiftly changing climate system,” he added.


Sharma, A., & Goyal, M. K. (2020). Assessment of the changes in precipitation and temperature in Teesta River basin in Indian Himalayan Region under climate change. Atmospheric Research231, 104670.


Banner image: The Teesta riverside in Dikchu, Sikkim. Photo by Ullasa Kodandaramaiah.

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