Keywords

Introduction

The Hindu Kush Himalaya (HKH) region, also mentioned as the “third pole,” is the most significant mountain ecosystem on the earth and a critical geo-ecological asset of South Asia (Bolch et al. 2019). The glacier of HKH covers ~59 × 103 km2, out of the world's total of ~540 × 103 km2 mountain glacier area (Dyurgerov and Meier 1997, 2005). Further, the Himalaya and the trans-Himalaya regions consist of nearly 50% of all glaciers outside the polar region (Mayewski and Jeschke 1979). Sangewar and Shukla (2009) provided the glacier inventory and reported the 9575 mountain glaciers in the Indian Himalayan Region (IHR). Further, in the IHR, many authors have reported a total of ~10,000 glaciers, excluding the ~2000 glaciers in Nepalese and Bhutanese Himalaya (Raina and Srivastava 2008; Bajracharya and Shrestha 2011; Bajracharya et al. 2015). However, the glacier distributions in the Himalayas are controlled by altitude, orientation, slope, and climate zone in which they are located. The precipitation's contributions to the glacier mass budget in the Central, Western, and Eastern Himalaya are distinctly variable. As per the study conducted by Ageta and Pokhral (1999), monsoonal rain contributes approximately 80% of the mass balance inputs in the Eastern Himalaya. In contrast, monsoonal rain adds about 15% of the mass balance flux in the Central Himalaya. However, in the Western Himalaya, winter precipitation controls 85% of the mass balance influx. Therefore, there is a diverse range of climatic variability in Eastern, Central, and Western Himalayan regions. About ~80% supply of the freshwater on earth originates from the mountain regions (Barry and Chorley 1998), where glaciers, snow-clad regions, and glacial lakes are significant freshwater sources. Due to climate change, the melting glaciers will adversely affect the water supply in the most critical hugely populated region like Indus and Brahmaputra basins (Barnett et al. 2005).

Generally, the Himalayan region is witnessing a warmer climate. The Intergovernmental Panel on Climate Change (IPCC) (2014) reported that the warming trend in the Himalaya is more than the global averages supported by the evidence-based scientific reports (Shrestha et al. 1999; Ali et al. 2018). The retreat of glaciers in Himalaya and other parts of the world due to climate warming is evident since the beginning of the last century (Dyurgerov and Meier 1997; Paul et al. 2007; Bolch et al. 2012; Kääb et al. 2012; Gardelle et al. 2013; Shea et al. 2015a); however, the glaciers in the Karakoram have reported as surging (Copland et al. 2011; Bhambri et al. 2013; Quincey et al. 2015).

On the other hand, climate-induced glacier's retreat is usually associated with the formation and expansion of glacial lakes in the Himalayan belts (Costa and Schuster 1988; Richardson and Reynolds 2000; TanDong et al. 2010; Raj 2010; Petrakov et al. 2011; Raj et al. 2012; Sharma et al. 2018). It is reported that the expansion of glacial lakes can pose a possible risk of glacial lake outburst floods (GLOFs). GLOF is a destructive geomorphological hazard associated with the disastrous release of impounded water from the glacial lake (Richardson and Reynolds 2000; Clague and Evans 2000; Benn et al. 2012; Westoby et al. 2014; Worni et al. 2014). The high-speed water release due to the glacial lake outbursts can erode and carry enormous sediments downstream (Breien et al. 2008). It is one of the most destructive hazards that can cause risk to human life and property (Raj et al. 2013).

Despite such importance, the studies on glacier retreat and glacial lakes in Eastern Himalaya, particularly in Sikkim Himalaya, are very few. On the other hand, there are reports that the overall annual temperature rise is 0.01–0.04 °C (Sharma et al. 2009), and the rate of warming is the highest during the winter season in the Eastern Himalayan region (Chettri et al. 2010). As a result, Sikkim Himalaya is reported to have a substantial increase in temperature from the past and warmer winter due to the impact of climate change (Sharma and Shrestha 2016). A systematic mapping of glaciers in Sikkim Himalaya started way back in 2000 through remote sensing satellite images that record ~84 Himalayan glaciers located primarily in west and north districts (Bahuguna et al. 2001). However, there are no reports of in situ-based monitoring of glaciers in Sikkim Himalaya till 2013. Few glaciological interventions have been carried out in the northern part of Sikkim way back in the 1980s and 1990s. However, the policy and plans related to glacier management and mitigation of GLOFs in the region are scarce. Further, there are no systematic approaches to the management of freshwater in the area. Therefore, the present chapter critically examines and deals with the following scientific facts and policy gaps in the Sikkim Himalayan region:

  • Qualitative analysis of the glaciological studies in the higher catchment of Sikkim Himalaya.

  • Critical reviews on the probability of GLOFs.

  • Climate-induced vulnerability and associated adaptation and mitigation programs.

  • Observed climate and people perceptions on climate change.

  • Scientific gaps and challenges in the glaciology and glacier-related hazards.

  • Policy recommendations on climate change and glaciers.

Study Area

Sikkim (a state), situated in the northeastern part of India, is selected for the present study. It is considered as a biodiversity hotspot in the Eastern Himalaya. It shares 52.03% of the aerial extent of Eastern Himalaya in India with other northeastern states of India and Darjeeling Hills of the state of West Bengal (Tse-ring et al. 2010). It covers a total area of 7096 km2 and is one of the highest national parks in the world; i.e., Khangchendzonga National Park is located in Sikkim Himalaya that covers about 35% of the total geographical area. Sikkim has four districts (Sikkim Primary Census Abstract 2011); however, it shares the borders with China in the north and east districts, Bhutan in the east, Nepal in the west, and West Bengal in the south district, making it a geographically important area. The Tista River, flowing in the north–south direction, is the main river of the state and is joined by the Rangit River in the downstream areas (Krishna 2005). As per the latest population census, Sikkim's total population is 610,577, which consists of 456,999 (~75%) people residing in rural areas (Sikkim Primary Census Abstract 2011). Sikkim, being a high earthquake-prone environment (Nath et al. 2005), lies in Zone IV of the seismic zonation map of India. However, many developmental actions have been carried out in Sikkim, but there is no scientific account that directly shows the quantum of climate change impacts and vulnerability in the region (Sharma and Shrestha 2016). Though small in areal extent, Sikkim Himalaya covers the various eco-zones from subtropical, temperate, and subalpine to alpine due to sharp elevation gradients of 300–8586 m above mean sea level (AMSL) (Krishna 2005; Basnet et al. 2013). According to the Forest Survey of India (FSI) Report (2017), 3344 km2 of the area is covered by forests that comprise 47.13% of the total geographical area of Sikkim. As per the latest glacier inventory of the Geological Survey of India (GSI), there are 449 glaciers in Sikkim Himalaya covering an area of 705.54 km2 distributed in different sub-basins, viz., East Rathong (36 glaciers; 58.44 km2), Talung (61 glaciers; 142.90 km2), Changme Khangpu (102 glaciers; 144.35 km2), and Zemu (250 glaciers; 359.85 km2) (Raina and Srivastava 2014). The location map of Sikkim, together with the elevation gradients and drainage system, is shown in Fig. 8.1.

Fig. 8.1
figure 1

Location and extent of Sikkim state of India showing the elevation gradients (as per ASTER DEM) and drainage system

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Status of Glaciological Studies in Sikkim Himalaya

The first in situ-based study in the Sikkim Himalayan glacier was carried out at Changme Khangpu Glacier on different study components like radiometric chronology, glacio-hydrology, suspended sediment, and accumulation rate of the glacier during the 1980 and 1990s in the North Sikkim Himalaya (Shukla et al. 1983; Nijampurkar et al. 1985; Puri 1999). However, after almost three decades, Debnath et al. (2019) studied the time series satellite data from 1975 to 2016 and reported that ~20% of glacier area (18.56 ± 2.61 km2) had lost since 1975 at an average rate of −0.453 ± 0.001 km2 a−1 with a higher rate of area shrinkage (−0.665 ± 0.243 km2 a−1) during the recent decades (2001–2016). The largest glacier of Sikkim is Zemu Glacier, which is situated below Mount Kanchenjunga (8586 m AMSL). As reported, the glacier was first mapped during an expedition of German researchers (Finsterwalder 1935). After many decades, Basnet et al. (2013) reported that the Zemu Glacier shows no substantial changes in the terminus from 1990 to 2010. Their assumption was based on its large size, steep slope, and thick debris cover at the glacier's tongue (Venkatesh et al. 2011). However, they did not study the vertical mass loss/mass balance of the glacier. A recent geodetic study carried out by Rashid and Majeed (2020) found that the Zemu Glacier has lost 6.78 ± 2.05 Gt of mass at a rate of 84.8 Mt a−1 between 1931 and 2012 with an accelerated mass loss rate of 276.5 Mt a−1 during 2000 and 2012. They also recorded the terminus retreat of ~797 m (±19.7 m) during 1931 and 2018 at a rate of 9.1 m a−1 and projected the formation of a potential future proglacial lake in the area. Therefore, systematic mapping and in-depth understanding of the glacier–climate relationship are the need of the present time.

A joint program of the Space Applications Centre-Indian Space Research Organisation (SAC-ISRO) and State Remote Sensing Applications Centre (SRSAC) of Sikkim State Council of Science and Technology (SSCST) carried out extensive glacier inventory for the Sikkim Himalaya using satellite-based images in the year 2001. The inventory shows that Sikkim Himalaya records ~84 glaciers located mostly in west and north districts (Bahuguna et al. 2001). Aggrawal et al. (2017) mapped the glaciers in Sikkim Himalaya and reported a total glacier area of 883 km2 in the year 2013 that accounts for 12% of the total geographical area. In the IHR, the glacier area changes have been comparatively well documented and recorded in the Western and Central Indian Himalayas. However, limited and fragmented information is available for the Eastern Himalayas, including the Sikkim Himalayan glaciers. Most of the significant scientific study on the glaciers and glacial lakes in Sikkim Himalaya begins from the last one to two decades; however, they are fragmented and are not consistent. This inconsistency in the glaciological study may be attributed to the harsh climate, steep and rugged terrain and remote location of glaciers, and inadequate capacity for field-based glacio-hydrological studies (Kumar et al. 2020b). Therefore, most of the published information about glacier's retreat and mass loss in Sikkim Himalaya is based on remotely sensed satellite information.

Further, Basnet et al. (2013) carried out the area change analysis of 39 glaciers in Sikkim Himalaya and estimated that the overall area loss of 6.9 ± 1.5 km2 (3%) with an annual loss rate of 0.16 ± 0.10% a−1 during 1989–2010 due to climate warming in the area. Another published report by Racoviteanu et al. (2015) using multi-temporal satellite images shows deglaciation of 20.1 ± 8% during 1962–2000 in the Sikkim and adjacent areas. Garg et al. (2019) carried out a remote sensing-based multi-parametric assessment of 23 representative glaciers in Sikkim Himalaya and estimated a significant retreat of 17.78 ± 2.06 m a−1 during 1991–2015. They further stated that Sikkim glaciers are strongly imbalanced due to higher mass loss than other Himalayan regions because of rising summer temperature. In Sikkim Himalaya, the Tista and Rangit are only the two major river systems. These rivers are contributed mainly by the snow and glacial melts from the upper reaches. Therefore, the temperature rise is likely to accelerate the glacier retreat that further increases the streamflow in the Sikkim Himalayan glaciers.

Luitel et al. (2012) estimated that the East Rathong Glacier's snout had retreated 460 m from 1980–2012 at an average retreat rate of 13.9 m a−1. Aggarwal and Tayal (2015) attempted the mass balance of East Rathong Glacier using remote sensing methods. They reported a significant negative mass balance for the glacier, with a loss of ~11 m w.e. or 0.047 km3 during 48 years (1963–2011). In the extreme northwestern side of Sikkim Himalaya, the South Lhonak Glacier is reported to retreat by 1.9 km during 1962–2008 (Raj et al. 2013). Very recently, Zhou et al. (2018) estimated the mass loss for the glaciers of Qinghai-Tibet Plateau and its surroundings and found the highest negative mass balance of −0.32 ± 0.12 m w.e. a−1 in the Sikkim Himalaya between 1970 and 2000. In an almost similar year of observations, Bhattacharya et al. (2018) reported that the glaciers in the northwestern part of Sikkim Himalaya and surrounding areas (including Nepal) were losing mass moderately during 1975–1999 (0.10 ± 0.11 m w.e. a−1). However, they observed accelerated mass loss of −0.48 ± 0.51 m w.e. a−1 during recent years (1999–2006) with an overall mass budget −0.19 ± 0.16 m w.e. a−1 during the entire study period (1975–2006). This difference in the mass loss may be subject to various possible reasons, viz., differences in spatial resolution of digital elevation model (DEM), human errors (including mapping, processing, and pixel errors), and errors involved in the area's delineation. Therefore, these variations in the results using satellite images and DEM further require field-based validation. However, it is evident from the above-published reports that glaciers in Sikkim Himalaya have been facing the consequences of climate change as in other parts of the world. Therefore, it is expected that future projections on the climate and its impact on freshwater resources would be very crucial for building adaptation and mitigation plans to combat climate change.

In the Himalaya, in situ-based mapping and monitoring of every glacier are not possible due to the harsh environment and steep terrain. However, there are many benchmark glaciers in the Himalayas where in situ-based records of mass loss, snout retreat, and glacier runoff are vital to know the flow forecasting and establish climate–glacier relationships. In Sikkim Himalaya, the in situ-based study on glacier dynamics is very minimal. Kumar et al. (2020b) carried out the first in situ-based study on glacier's melt runoff process and hydro-meteorological characteristics of East Rathong Glacier. They concluded that there is a significant hydro-meteorological relationship of meltwater discharge with the temperature, rainfall, and relative humidity in the East Rathong Glacier catchment. Recently, Sharma et al. (2021) also studied the in situ-based suspended sediment dynamics for three consecutive melt seasons (2013–2015) and reported substantial meteorological controls on the sediment transport process in the East Rathong meltwater stream. However, the data on the contribution of glacier's melts and sediment transport to the streamflow during the melting (ablation) season in the Eastern Himalaya are very few that necessitate an in-depth investigation of different glacier's catchments to understand insights of glacio-hydrological processes in the Sikkim Himalaya. The major glaciers in Sikkim Himalaya are shown in Fig. 8.2.

Fig. 8.2
figure 2

Map showing the major glaciers and glacial lakes in Sikkim Himalaya. The number on the map indicates the names of glaciers. The names of the glacial lakes are shown on the map itself

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Potentially Vulnerable Glacial Lakes and the Threat of GLOFs

In Sikkim Himalaya, melting glaciers, the formation of proglacial lakes, and the growth of existing glacial lakes are well-known due to climate warming (Basnet et al. 2013; Sharma et al. 2018). Besides, the accelerated rate of glaciers retreat from the last two decades leads to the continuous expansion of glacial lakes. A total of 320 glacial lakes have been reported in the Sikkim Himalaya (Raj et al. 2013). Among them, 14 glacial lakes are potentially vulnerable to lake outbursts (Mool and Bajracharya 2003; Raj et al. 2012). The major glacial lakes in the Sikkim Himalaya are shown in Fig. 8.2. Raj et al. (2013) identified 85 new glacial lakes in their study compared to the previous inventory of glacial lakes prepared by the International Center for Integrated Mountain Development (ICIMOD) (Campbell 2005). Worni et al. (2013) carried out the risk assessment of Shako Cho Glacial Lake in North Sikkim. They have advocated that the lake is highly vulnerable to glacial lake outbursts.

Similarly, Raj et al. (2013) studied the hazard assessment of South Lhonak Lake (SLL) located at the extreme northwest part of Sikkim Himalaya. They also suggested a high outburst probability of SLL. Sharma et al. (2018) carried out the remote sensing- and field-based assessments of SLL and calculated the lake's volume. They have estimated a lake volume of 65.81 million m3 with a maximum depth of 131 m. Their study was the first record of lake bathymetry carried out through a field-based survey in Sikkim Himalaya (Fig. 8.3). They further suggested many mitigation measures that need to be taken up in the SLL. In the remote sensing-based assessment of glacial lakes, Begam and Sen (2019) also identified SLL to have a potentially very high risk of generating GLOF events anytime in the future. Therefore, in Sikkim Himalaya, SLL is considered a highly vulnerable lake with a high probability of outbursts. Sattar et al. (2019) carried out hydrodynamic breach modeling of SLL. They stated that the flood wave could reach the Lachen town located at a distance of 46 km downstream from the lake, at 3 h and 38 min after the breach's initiation, if in case of lake bursts. It would have a peak flood of 3928.16 m3s−1 and a maximum flow velocity of 13.6 ms−1. Similarly, after reaching the Chungthang town located at a distance of 62.35 km from South Lhonak Lake, the flood wave can potentially inundate settlements on the side of the flow channel. The model estimates a peak flood of 3828.08 m3s−1 which is achieved after 4 h of the dam breach as per their simulation.

Fig. 8.3
figure 3

Scientific team from Sikkim State Climate Change Cell carrying out the bathymetric survey of South Lhonak Lake in 2014. Massive calving of ice in the lake can be seen in the photographs

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Shukla et al. (2018) mentioned that glacier melting could lead to the formation of new lakes and expansion of existing lakes in the Sikkim that increased the potential of glacial lake outbursts floods and suggested that persistent attention is required at the earliest level. Further, there are 14 potentially vulnerable glacial lakes in Sikkim Himalaya in terms of glacial lake outbursts. Therefore, climate change impacts are expected to be tangible in other glacial lakes in terms of their expansion of size and volume, if the temperature warming is continuous in the Sikkim Himalayan region.

Observed Climate and People Perceptions

Altitudinal variation with high mountains across Sikkim is the driving factor controlling the climate and weather patterns. Sikkim Himalaya faces the unprecedented consequences of climate change; however, the published records on climatic change and variability are few and fragmented. According to Sharma et al. (2009), the overall increase in temperature is 0.01–0.04 °C annually in the Eastern Himalayan region. Further, Chettri et al. (2010) found that warming rates are the highest in winter in the Eastern Himalayan region. Additionally, Gupta and Das (2006) also reported an increase in mean minimum temperature and climate warming in Sikkim. Telwala et al. (2013) analyzed the historical and recent temperature records. They noted that the warmest and coldest months’ mean temperature had been increased by 0.76 ± 0.25 and 3.65 ± 2 °C, respectively, in Lachen and Lhonak Valleys of North Sikkim Himalaya.

The observed meteorological records in Sikkim indicate no significant change in maximum temperature, but there is an increase in minimum temperature by 2.5 °C during 1957–2009 (SAPCC-Sikkim 2014). The observed records show that the total rainfall has been increased by 250 mm between the periods of 1983–2009. Sharma and Shrestha (2016) analyzed the instrumental meteorological data (1978–2009) of Tadong and Gangtok stations in Sikkim and reported that annual mean minimum temperature and mean minimum winter temperature (DJF) have been significantly increased from the past. More recently, Kumar et al. (2020a) also carried out the meteorological analysis for the Gangtok and Tadong meteorological stations (1961–2017) in Sikkim and found positive increasing trends in minimum temperature. They have noticed accelerated climate warming during the last two decades with an increased probability of extreme temperatures. Therefore, the recent climate warming has had a substantial impact on many developmental sectors like agriculture, forests, water, disaster, etc. People have perceived reduced frost and snowfall, increased hailstorms, warmer winter, and intense rainfall in recent decades (SAPCC-Sikkim 2014). Nowadays, information about regional climate change is growing in demand for an in-depth understanding of climate change impacts on different ecosystems at a regional scale (Liu and Chen 2000). Therefore, community-level perceptions on climate change are equally crucial to developed village-level plans and policies. Sharma and Shrestha (2016) carried out semi-structured interviews on climate change perceptions in 12 villages in Sikkim Himalaya, covering 3–4 villages in a district. They reported a significant increase in temperature and decreased rainfall compared to a decade earlier, warmer winter, water springs that are drying up, and the changes perceived in spring-water recharge phenomenon (locally known as Mul Phutnu). People also perceived the spring season changes, low crop yields, and mosquitoes’ incidences during winter as per their study. The local knowledge-based information on climate can help formulate effective policies and adaptive strategies to cope with climate change (Chaudhary and Bawa 2011).

Climate Change Vulnerability, Adaptation, and Mitigation Programs

As per the IPCC Report (2014), the impacts of climate-related extremes like floods, droughts, heatwaves, cyclones, and wildfires have significant vulnerability and exposure to some ecosystems and many human systems to current climate variability. The Himalayan countries in the HKH region face problems and challenges in meeting the demand for food, water, and energy due to fast socio-economic development, a rise in population, and urbanization (Mukherji et al. 2015). Therefore, it is relatively challenging to minimize and manage climate change impacts and risks through adaptation and mitigation measures. Thus, assessing the risks and vulnerability of a system is essential to prioritize the adaptations and mitigation plans to minimize the climate change impacts. In an early assessment carried out to prepare the climate change action plan in Sikkim, the south district of Sikkim was found highly vulnerable to climate change impacts as most of the district's subtropical areas come under drought-prone zones (Tambe et al. 2011; SAPCC-Sikkim 2014). In a recent vulnerability assessment carried out in IHR using a common framework, the east district of Sikkim was a highly vulnerable district due to its high population density and a high degree of slope (DST-NMSHE2018–19). The methodology framework of vulnerability assessment was based on the guidelines of the Fifth Assessment Report of the IPCC (IPCC 2014).

Owning to the significant adaptation measures for climate change in Sikkim, the Dhara Vikas (springshed development programme), initiated in the year 2008, is an innovative program to revive and maintain drying springs, streams, and lakes (Bhutia 2019). The program has emerged as a robust climate change adaptation strategy for Sikkim's drought-prone districts (west and south). It aimed to enhance water availability in drought-prone areas and was undertaken through the Mahatma Gandhi National Rural Employment Guarantee Act (MGNREGA) to convergence various line departments and non-government organizations (NGOs). The program has succeeded in reviving 55 springs in villages like Kaluk, Rhenock, Ravangla, Sumbuk, Jorethang, Namthang and has recharged 1035 million liters of groundwater annually in the last four years (Bhutia 2019). Sikkim implements the water sector recommendations of the State Action Plan on Climate Change (SAPCC) utilizing the funds from the MGNREGA. However, the other sectoral recommendations of the climate change action plan have not been implemented effectively (Jogesh and Dubash 2015).

In terms of some considerable scientific and mitigation measures in Sikkim, Sikkim State Climate Change Cell (SSCCC) has been actively engaged in climate change-based scientific interventions. SSCCC was established in October 2014 under Sikkim State Council of Science and Technology, an autonomous organization of the State Science and Technology Department, Government of Sikkim. The SSCCC is operational in a project mode under the National Mission for Sustaining the Himalayan Ecosystem (NMSHE), supported by the Department of Science and Technology (DST), Government of India (https://sikkim.gov.in/departments/department-of-science-technology/sikkim-state-climate-change-cell). The SSCCC carried out the first bathymetric survey of potentially vulnerable SLL located in Sikkim Himalaya to know the storage volume of the lake (Sharma et al. 2018). Eventually, GLOF mitigation measures like siphoning of impounded water and debris clearance near the lake outlet were carried out in SLL in collaboration with the Land Revenue and Disaster Management Department (LRDMD), Government of Sikkim. SECMOL-Ladakh technically supported the mitigation measures in SLL. Three (3) number of 8-inch diameter high-density polyethylene (HDPE) pipes have been connected to siphon the impounded water to minimize the threat of GLOF. About 150–180 lit/sec of water has been siphoned with three sets of pipes from SLL (Fig. 8.4).

Fig. 8.4
figure 4

GLOF mitigation (siphoning of impounded water) at South Lhonak Lake in 2016

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In the IHR, the NMSHE and the National Mission on Strategic Knowledge for Climate Change (NMSKCC) under the eight National missions of the National Action Plan on Climate Change (NAPCC) have been coordinated by the Ministry of Science and Technology, Govt. of India from the year 2010. These missions mainly emphasize building capacities, making institutional networks, researching strategic knowledge, and recognizing the knowledge gaps on climate change in the IHR (DST 2010a; DST 2010b). Therefore, identifying central and state-specific climate-related developmental plans and programs is crucial for operationalizing short-term climate change adaptation activities in Sikkim. At the national level, the National Adaptation Fund on Climate Change (NAFCC), established in 2015, has been supporting many states and union territories that are mainly exposed to adverse impacts of climate change in the sectors like agriculture, animal husbandry, water, forestry, tourism. The projects under NAFCC prioritize the requirements that build climate resilience in the sectoral areas identified under the SAPCC. In Sikkim, NAFCC supports the project entitled “Addressing Climate Change vulnerability of Water Sector at Gram Panchayat Level in drought-prone areas of Sikkim,” which has been executed by the Rural Development Department, Government of Sikkim (https://www.nabard.org/content.aspx?id=585).

Gaps and Challenges for Climate and Glaciers in Sikkim Himalaya

Sikkim Himalaya is one of the biological hotspots having varied geographical settings and elevation gradients from 300 to 8586 m AMSL. These diverse geographical areas have distinct microclimatic variations. Therefore, climate warming impacts would be very different in every sector like water, agriculture, forests, health. Consequently, it is important to identify the gaps and challenges that need to be addressed to develop adaptation and mitigation plans to deal with the changing climate. Some of the critical gaps and challenges that require the attention in Sikkim Himalaya are mentioned below:

Limited Instrumental Observatories

Sikkim Himalaya is recognized as a part of India's biodiversity hotspots; however, it is one of the most data-deficit regions of Eastern IHR. There are only two reliable instrumental meteorological observatories located in the Gangtok and Tadong. Broadly, the scarcity of long-term instrumental meteorological datasets in the Himalayas is a major problem as it has impacted the scientific findings (Kumar 2020b). High-altitude meteorological datasets are very minimal in Sikkim that limit the development of climate–glacier relationships and projections. Recently, a few in situ instrumental measurements on glaciohydro-meteorological observations have been made in the East Rathong Glacier (Kumar et al. 2020b; Sharma et al. 2021). Further, there are limited meteorological observatories in the lower reaches of Sikkim.

Institutional Capacity Building

Institutional capacity building is the base for creating a skilled workforce for livelihood upliftments, planning and formulating the developmental plans and policies, and any research and developmental activities. At the state level, the State Institute of Capacity Building (SICB) has been actively working to create a highly skilled workforce empowered with enhanced skills, knowledge and prepared themselves for livelihood upliftments and increased participation of youth, women, and others disadvantaged sections (https://sdedsikkim.in/SICB.aspx#). As a mandate of the NMSHE, DST, the Government of India is supporting the Sikkim for institutional capacity building on climate change adaptation and planning (DST 2010a) in collaboration with the technical partners like the Swiss Agency for Development and Cooperation (SDC), Indian Himalayas Climate Change Adaptation Programme (IHCAP). Further, the German Agency for International Cooperation (GIZ) has been an active technical state partner for Sikkim right from the formulation of the state action plan on climate change (SAPCC-Sikkim 2014). However, capacity building of the nodal officials of the department and sectoral officials is crucial since they can provide vital inputs to climate change plans and policies at the local level.

Absence of Glacier Protection Laws (GPLs) and Glacial Lake Management Plan

It is a widespread fact that climate warming in the Himalayan region is more than the global average. The temperature rise has impacted the glaciers to shrink, and the formation and expansion of proglacial lakes in the Himalayas are evident due to melting glaciers. Similar observations have been made for the Sikkim Himalaya where temperature rise has impacted the glaciers and glacial lakes (Basnet et al. 2013; Sharma and Shrestha 2016; Sharma et al. 2018; Sattar et al. 2019; Kumar et al. 2020b). As compared to Western and Central IHR, the field-based study on glaciers and glacial lakes in Sikkim Himalaya is minimal. Any scientific assessment of glaciers and glacial lakes may highlight the key management plans to help the policy decision. Kumar et al. (2020b) study the hydrometeorology of the East Rathong Glacier in Sikkim Himalaya and have shown the linkages of climate change programs that help build capacities, institutional networks and identify the knowledge gaps in the IHR. Sikkim Himalaya is considered a data-deficit zone on account of the limited study of the freshwater resources in Eastern IHR. As Sikkim caters to many glaciers and snow-dominated zones, Sharma et al. (2021) suggested the decision-makers about the necessity of a dedicated “Regional Centre for Glaciology” for a detailed understanding of the impacts on glacier resources and future changes due to climate change. Through such intervention, they have expected improved glaciological research facilities in the Eastern IHR. Further, such development can be highly beneficial to the policymakers for formulating plans and policies on the management of Himalayan glaciers and potentially vulnerable glacial lakes.

In countries like Argentina and Chile, Glacier Protection Laws (GPLs) have been adopted to protect the cryosphere from harmful activities since the mining activities have damaged glaciers (Anacona et al. 2018). However, by prohibiting activities on glaciated areas, GPLs may limit or even prevent the timely execution of mitigation measures on glacial-related hazards. Therefore, it has overlooked the effect of climate change on the glacial environment that needs to be managed and mitigated. In Sikkim Himalaya, the majority of people are dependent on tourism as it is fast evolving as one of the most critical drivers of the state economy (STP 2018). Adventure tourism (trekking, paragliding, mountaineering, river rafting, etc.) has been substantially increased nowadays in Sikkim. Many communities in the high-altitude areas are yak and sheepherders, and they are also directly or indirectly related to tourism for their livelihoods. Therefore, to protect the glacial environment, it is recommended to have community-friendly regulations or laws and sustainable environmental perspectives. Before enacting the laws for glacier protection or any rules about glaciers and other freshwater resources, it is recommended to have clear communication to the locals and generate climate change awareness regarding the importance of glaciers and glacial hazards to avoid the social pressure in hazard mitigation (Anacona et al. 2018).

Further, many studies confirm 14 potentially vulnerable glacial lakes in Sikkim Himalaya that can bring risk to downstream communities and infrastructures, including hydropower plants. However, there is no glacial lake management/mitigation plans exist in Sikkim Himalaya to date. Therefore, to mitigate the threats of GLOFs in Sikkim Himalaya, a Glacial Lake Management Plan is urgently required with a robust policy for glacial lakes. Sensitization and awareness to the downstream communities regarding the potential GLOFs can help in the prevention of disasters. Further, installing an early warning system (EWS) in the vulnerable glacial lakes is an essential recommendation to tackle the worst hits of floods (Fig. 8.5).

Fig. 8.5
figure 5

Conceptual representation of glacial lake management plan for Sikkim Himalaya

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Climate Science and Media Reporting: Bridging the Gaps

Around the globe, media plays a crucial role in disseminating information and opinions through newspapers, magazines, television, radio, and the Internet. Therefore, media can play a vital role in climate change awareness and target a vast audience, even from social networks. Keller et al. (2019) found that India's climate change coverage in the newspapers has increased significantly in the last 20 years. The report was based on an analysis of 18,224 articles published in the two newspapers.

However, climate change coverage is minimal in the local newspapers in Sikkim. There is significantly less presence of local television media in Sikkim, probably due to the lesser population. Therefore, scientists and researchers may take the platform of social media to raise awareness about recent climate change issues in Sikkim. Boykoff and Rajan (2007) stated that the dearth of training among journalists and a shortage of time to investigate a story and its background could be detrimental in translating science into information. Further, portraying climate change problems based on the perceptions with fabricated stories creates chaos to the audiences. More importantly, the progress and difficulties in translating climate science by the media greatly influence climate adaptation and mitigation actions (Boykoff 2010). Therefore, the media's role is to clearly understand the scientific findings and translate the information to the general public.

Consequently, the capacity building of journalists in climate science is essential in the region to address the gaps in delivering climate change information to the general public. In Sikkim, during 2017, a media workshop on “Climate Change Reporting” was jointly organized by the IHCAP under the SDC, Centre for Media Studies (CMS), and DST, Government of India. The objective of the media workshop was to bring scientists/experts, international agencies, policymakers, and media persons in Sikkim together on the same platform for an in-depth understanding of various components of climate change and its impact on Sikkim and the Indian Himalaya as a whole (a report—media workshop on Climate Change Reporting 2017). Climate change is a global phenomenon with local impacts; therefore, local media still required more capacity building and specialization in climate science reporting.

Need for Maintaining the Science and Policy Linkages

The scientific analysis required the knowledge of observations and interpretations of the results. However, sometimes making plans and policies does not include evidence-based scientific findings in the decision-making process due to various reasons. Pullin et al. (2009) have concluded their study with the following observation: “There is a mismatch between broad holistic questions typically posed in policy formation and narrow reductionist questions that are susceptible to the scientific method. This inhibits the two-way flow of information at the science-policy interface and weakens the impact of applied ecology on environmental policy.” Therefore, it is crucial to make plans and policies supported by scientific analysis and evidence-based scientific observations. In the present era of evidence-based practices, climate policy decisions need to be developed using sectoral priorities supported by scientific evidence. In a nutshell, recent policy decisions may involve the engagement of mainly three major stakeholders—the government (decision maker), the sectoral bureaucrats, and the scientists. Further, policymaking is a complex process, where evidence-based scientific findings act as a vital element along with social, ethical, cultural, legal, economic, and political aspects that are often considered (Montuschi 2017).

Conclusions

In Eastern Himalaya, as discussed earlier, the studies on climate change impacts on glaciers and glacial lakes using field-based observations are scarce, resulting in a limited understanding of glacial melt processes and associated glacial hazards. In Sikkim Himalaya, the little field-based research about glacier retreat and lake formation warrants policymakers’ urgent attention to formulate an effective plan for capacity building to study the glaciers and glacial lakes. Further, due to the risk imposed by harsh weather conditions in the glacier, the field-based observations on glaciers and glacial lakes in Sikkim Himalaya are very few and far. Besides, there are insufficient meteorological observatories to developed climate–glacier relationships and projections. Therefore, the following suggestions have been proposed to have wholesome climate change understanding and effective management of glaciers and glacial lakes in Sikkim Himalaya:

  • Capacity building for the local researchers on the dynamics of the glaciers and glacial lakes.

  • Increase the number of meteorological observatories for in situ-/field-based monitoring of the glacial lakes.

  • Effective mitigation interventions in potentially vulnerable lakes (siphoning of impounded water and installation of early warning system).

  • Build linkages with the nationally coordinated missions like NMSHE, NMSKCC.

  • Capacity building of the media persons for the appropriate translation of climate science to the general masses.

  • Sensitization and awareness about the importance of glaciers, climate risks, and vulnerability, and glacial hazards

  • Linkages need to be built between scientists, bureaucrats, and policymakers (science policy linkages).

  • A dedicated center for climate change adaptation, management, and mitigations.

Studies also show that many glacial lakes are continuously expanding in size and volume. Therefore, both satellite-based monitoring and field-based monitoring of the glacial lakes for assessing hazard potential are needed. Besides, future research lies in the impact assessment and risk modeling for glacial lakes management. Likewise, the high outburst-sensitive lakes need in-depth investigations of the glaciological and geomorphological features for designing sustainable mitigation measures. Also, it is suggested to have continuous monitoring for moderate and low outburst-sensitive lakes. A detailed and comprehensive understanding is necessary to know the lake's formation and evolution since many glacial lakes are still continuously expanding in their size in Sikkim Himalaya.