Mapping of glacial lakes and glacial lake outburst flood in Lahul and Spiti district using remote sensing and GIS

doi:10.21203/rs.3.rs-1402829/v1

Glacial lake outburst floods (GLOFs) refers to the sudden release of water from a glacial lake. This has the potential to endanger human lives as well as cause environmental and economic damage. Climate change is causing glaciers to retreat and subsequent formation of new glacial lakes. GLOFs are one of the most common climate change hazards in India's Himalayan region of Himachal Pradesh. In the present study, GLOFs mapping has been carried out using remote sensing (RS) and geographic information system (GIS). For glacial lake mapping, Landsat-7 and 8 data from 2005, 2010, 2015, and 2019 were employed. Landsat images were employed for classification and change detection using normalized difference water index (NDWI) to identify the temporal variation of Samudra Tapu glacier lake and Geepang Gath glacial lake, which are two major glacial lakes in the Lahul and Spiti district. A 30 m digital elevation model (DEM) was created by the data providers by the shuttle radar topography mission (SRTM) 1arc sec global used for calculating the parameters such as maximum, minimum, mean elevation, slope, and aspect. The lake volume and depth have been calculated using Huggel empirical formulae, and other parameters such as area, slope, aspect, and drainage network have been prepared using ArcGIS 10.8. The maps for land use and land cover (LULC) were produced using the supervised classification technique by considering the maximum likelihood classification (MLC) algorithm. The lake size has increased from 0.542 to 0.929 km 2 for Geepang Gath glacial lake and 0.849 to 1.239 km 2 for Samudra Tapu glacial lake during the time period of 2005-2019. The findings indicate that there is a need to build risk management plans, improve spatial planning in order to be well prepared for future potential GLOF hazards.

Glacial lake outburst floods (GLOFs)

GIS

Remote Sensing

NDWI

LULC

Himachal Pradesh is a mountainous state in Indian Himalayas, covering over 55 thousand square kilometers. The state's peculiar geography results in a diversity of terrain. Snow and ice cover the area above 4,000 meters above mean sea level most of the year. Perpetual glaciers, which are the source of various rivers in the area, generate many glacial lakes. Climate change and variability has shifted dramatically in recent decades that has affected glacier lifecycle in the Himalayan zone. As a result, several extensive glaciers melted quickly, resulting in a huge number of glacial lakes. Such outburst floods also turn into even more damaging rivers of debris when the flow path is steep, the flow velocity is high, and material is available for erosion (Clague et al., 1985; Evans and Clague, 1992; Huggel et al., 2004; Chiarle et al., 2007), threatening tourists and the downstream mountain valley population. In order to know their location, spatial and temporal inventories of glacial lakes are necessary. Changes in their number and area covered, as well as related geo-hydrological properties, are critical to comprehend in order to identify flood-prone zones, reduce flood risk, and the resulting impact on the surrounding population.

The mountain lakes, created by glacial activity, are known by geographers as tarns. Tarns are found mainly in the upper reaches, above 5,500 m, of the Himalayas. The snow-melt, precipitation and springs feed high-altitude lakes. The high elevation Chandratal lake, Chandra valley, Lahaul and Spiti, Himachal Pradesh are largely oligotrophic lakes. Unlike the low altitude lakes, which are in different stages of trophic state index. The high altitude lakes also have an anthropogenic effect and a pristine climate. These glacial lakes can be classified as pro-glacier, en-glacier, sub-glacier, supra-glacier, Ice-dammed lakes and moraine-dammed lakes (Salerno et al., 2012; Zhang et al., 2015). In the Himalayas, there are two types of glacial lakes; one is moraine-dammed lakes and the rest of the ice-dammed reservoirs.

Aggarwal et al. (2016) and Campbell (2005) have respectively mapped 143 and 266 glacial lakes in the Sikkim region, and a rise in the number of glacial lakes creates the prospect of multiple hazardous glacial lake outburst floods (GLOFs) events that occur when a large volume of water is suddenly released from them (Clague and O’Connor, 2015; Veh et al., 2020). There is also high confidence that the number and area of glacier lakes will continue to increase in most regions in the coming decades, and new lakes will develop closer to steep and potentially unstable mountain walls where lake outbursts can be more easily triggered by the impact of landslides (Frey et al., 2010; ICIMOD, 2011; Allen et al., 2016; Linsbauer et al., 2016; Colonia et al., 2017; Haeberli et al., 2017). For instance, many incidents of GLOFs have happened in northern Pakistan, and massive floods have been observed over the last two decades (Amin et al., 2020). Imja Tsho was initially considered to be in the critical condition; however, several new studies categorized Imja Tsho as moderate risk (Budhathoki et al., 2010). Despite the differences on whether or not Imja lake posed an immediate threat, the results of these scientific studies provided a strong foundation for further research on people’s perceptions of GLOF risks and vulnerability.

In high mountains close to established glaciers, moraine-dammed lakes are found. During the Little Ice Age, the moraines impounding these lakes were established. Since the glaciers have then withdrawn, leaving behind closed water-filled basins. When the glacier recedes during the twentieth century, ice melting contributes to the creation of a moraine-dammed glacial lake, leading to the creation of a glacial lake end-moraine accumulation at the front. Many moraine-dammed lakes have drained suddenly, producing floods and debris flows that have caused considerable damage. Usually, failure occurring at the moraine dam is caused by a rockfall or glacier avalanche overhead. Ice core melting, piping, earthquake and other potential failure mechanisms explain the moraine dam failure.

Lakes dammed by glacier ice are referred to as ice-dammed lakes. These lakes are also known as supra-glacial lakes. In general, supra-glacial lakes occur on a glacier surface that is entirely a dense layer of debris covering it. As supra-glacial lakes grow, the ice of the glacier below melts, and moraine-dammed lakes are thus formed. Such lakes are also combined with moraine-dammed lakes or can grow into composite forms occasionally. In glacier ice-dammed lakes, the lakes dammed by glacier ice without lateral moraine is designated as lakes dammed by glacier ice.

Tools and techniques from RS and GIS make it possible to continuously monitor, analyse and track developments and modifications of glacial lakes. The aim of this study is to analyse the temporal variations in glacial lakes using time series lake (2005 - 2019) remote sensing data of Landsat and map major glacial lakes in Lahul & Spiti district.

The study area taken for this study is the Lahul & Spiti district, located in the north- western Indian Himalayan state of Himachal Pradesh (Figure 1). The district occupies location from 31°44'57''N to 32°59'57''N latitude and 76°46'29''E to 78°41'34''E longitude with a geographical area of 13,835 km ². Area wise, it is the largest district of Himachal Pradesh state compared to other districts. Lahul & Spiti is separated in the east from Tibet region of china that forms an international border. Jammu and Kashmir in the north of it and Chamba district to its south-west and west of the study area. Towards, south-east and south it makes boundary with Kullu and Kinnaur districts of the state. The mountains adorn its surrounding with various ice-capped glaciers, and therefore the entire region depicts a terribly rugged parcel of land. Samudra tapu glacial lake and Geepang Gath glacial lakes are two main glacial lakes in Lahul & Spiti district, and they both have shown an increase in their area; therefore, they have been taken under investigation in the present study.

3.1 Satellite data

The remote sensing datasets used for this study is high-resolution satellite imagery and digital elevation model. To carry out the analysis of glacial lakes from 2005 to 2019, Landsat-7 and Landsat-8 data have been used in the research. By comparing all available dataset for this study, images with a maximum 10% cloud cover and least snow cover from the month of October to November has been selected. A total of 12 Landsat images have been downloaded from USGS Website (https://earthexplorer.usgs.gov). The months for which Landsat images have been used are October (11 scenes) and November (1 Scene). A complete description of the dataset along with their specifications is given below.

3.1.1 Datasets specification and details

The specifications and details of various dataset used in the study are summarized in Table 1.

3.1.2 For 2005 (Landsat-7)

3.1.3 For 2010 (Landsat-7)

3.1.4 For 2015 (Landsat-8)

Table 4 Details of Landsat-8 data

3.1.5 For 2019 (Landsat-8)

3.2 Digital elevation model

Digital elevatiom model (DEM) is useful for calculating the parameters such as maximum, minimum, mean elevation, slope and aspect. A 30 m DEM was acquired from the data providers at shuttle radar topography mission (SRTM) 1arc Sec Global download from USGS website (https://earthexplorer.usgs.gov).

4.1 Normalized difference water index

The study of temporal variation in the lake region has been carried out using satellite images. Landsat images have been used classification and change detection using Normalized Difference Water Index (NDWI). The NDWI (McFeeters, 1996) has been calculated as

When applying the NDWI to the spectral bands, the following equation results are obtained,

For Landsat 7,

For Landsat 8,

The highest reflectance is used by NDWI, green with the NIR bands for the extracting bodies of water. The resulting images have been visually examined and associated with google earth imagery. The NDWI values differ from −1 to +1. Much of the characteristics of water are found near the value of +1. McFeeters (1996) defined zero as, for water bodies, the threshold value. Values towards −1 indicate the characteristics of vegetation and bare soil or ground.

5.1 Average slope

One of the essential physiographic elements affecting the slope is the usage of an area's agricultural property. The impact of slopes on farming can be both direct and indirect. The most noticeable direct slope effect is in the form of restrictions on cultivation and availability. The indirect effect of slope manifests itself in pedological and climatic shifts, including the location of the water table, soil growth, air drainage and the relative freedom from frost.

5.2 Drainage network

The study of drainage network provides an idea about the topography, climate, geology, and hydrological features of the region (Figure 4). Much of the runoff is in sculpturing landforms, a major natural agent. It is also linked to settlement patterns in this high altitude arid region. Lahaul & Spiti higher Himalayan and Trans Himalayan regions are inhabited, where there are mainly settlements along the river valleys. There are three main rivers in Lahaul & Spiti Chandra, Bhaga and Spiti and their many tributaries as well. Chandra and Bhaga river after their Chandra-Bhaga, also known as Chenab, is the confluence at Tandi. These are the main drainage basins of the entire region.

5.2.1 Chandra river

It originates from a large snowfield on the base of the southeast of the about Chandra Tal, Baralacha Pass. It flows in the direction of the south-west about the first 48 kms. Then, for sharp northwest and western directions, it takes 64 km further up to Tandi, where it joins the river Bhaga. On the upper left bank of it a lovely glacial lake known as 'Chandra Tal' is located between a low ridge and the Kunzum range. The lake is about a kilometre long and half a kilometre long with an outlet into the river, one kilometre wide.

The river Chandra is fed by a number of around glaciers. The largest is the Shigri and the Samundri on its left bank, Glaciers at Sonapani on the right bank. This reports an average drop of approximately 12.5 metres per kilometre up to its confluence at Tandi with Bhaga.

5.2.2 Bhaga river

The Bhaga river comes from the south western side of the Baralacha river a pass at an altitude of 4800 meters or so. It flows northwest in the direction of nearly 13 km, and then the south-western course. It has an average length of up to Tandi, about 65 km. Barsi, Milang nullah and the major tributaries are Nullah Billing. The valley up to Darcha is barren and rocky. It's got an average fall of 28 meters per kilometres.

5.2.3 Chenab river

Following their confluence at Tandi, the rivers Chandra and Bhaga are called Chandra-Chenab or Bhaga. A number of glaciers are entirely fed by the River from either side, tributaries. Shansha nullah contains the right bank tributaries, Thirot nullah, Miyar nullah, Chokang nullah. Nullah of Lingar, Nullah of Rashil, the Left Bank tributaries are Naida nullah, Ghor nullah, and Galigorh. Among the with a length of about 322, Miyar nullah is the largest tributary for kilometre. For around 75 Kilometre, Chenab runs in the northwest direction. Before its departure into the district of Chamba. There is an average decline of around 6 metres per Kilometres from an altitude of 2800 meters.

5.2.4 Spiti river

From the far north, on the eastern slopes of the Spiti River, the Lahaul & Spiti mountain ranges. At the base of Kunzum, it starts the range of the 'Kunzum La Tagpo' confluence and the Kabzinastreams Pinglung. The deep and flat valleys bordered by elevated vertical cliffs characterize the River Spiti. On the southeast side of Spiti, the total length of the river is around 130 kilometres. In Kinnaur district, it continues up to Khabo, where it joins the river Satluj. The Spiti river on both sides is joined by several tributaries. To the right of it Chiomo, Gyundi, Rahtang, Pin and Sumra are banks. The streams of Shila, Kaza, Lingti, Tabo, and Parechu are joined on the left bank. The Pin river is the Spiti river's most significant right bank tributary. The length of the Pin river is about 50 kilometres.

The Lingti river is about 40 kilometers long, a significant left-hand river bank of the Spiti river tributary. These important tributaries' make valleys suitable for a large number of villages. These are an integral source of for agriculture, irrigation. The entire region is a cold desert, as it only receives scanty rainfall precipitation. A climate barrier is placed by high mountain ranges in the manner of wind-carrying moisture. Thus, due to rain, the entire region remains arid Himalayan ranges' shadow effect. Thus, the function and significance of natural drainage is increased in cold and arid mountain areas, such as Spiti & Lahaul.

The area of the glacial lake has been calculated using the field calculator tool in ArcGIS after digitisation of the lake from the satellite images in sq. km units. No calculation is available for the glacial volume lakes in the Himalayas to reach out from their areas. However, as provided by Huggel et al. (2002) some estimates are available for glacial lakes in the Swiss Alps. In the absence of data on the amount of potentially hazardous, it is considered reasonable to use the same relationships formed for lakes in the Swiss Alps to estimate the amount of water for the lakes in this area. The empirical relationships as available in the analysis by Huggel et al. (2002) are:

The lake volume, V= 0.104A^1.42 (4)

where V is the lake volume in m³ and A is the lake area in m²

The lake depth, D= 0.104A^0.42 (5)

where D is the lake depth in m

The maps for LU/LC of Lahul-Spiti District has been produced using supervised classification techniques on Landsat satellite imagery for 2005, 2010, 2015 and 2019 (Figure 6). The classification process started with the identification of training sets representing different land-use classes. These training sets have been used for supervised classification using maximum likelihood classification (MLC) algorithm. The maximum likelihood classification is the most accurate and reliable classifier (Richards and Jia, 1999; Foody et al., 1992; Saha et al., 2002). The pixels in the unknown class are assigned to a specific land-use class of which it has the greatest likelihood of membership. In this analysis, five major classes of LU/LC are identified: snow/glacier, barren/rocky surface, forest, agriculture/grass, and water. The area of each class can be estimated using the field calculator tool inArcGIS (Figure 5).

Samudratapu glacial lake and Geepang Gath glacial lakes are two main glacial lakes in Lahul & Spiti District. As both show, an increase in their area, the area of interest has been described as coverage. Coverage separately, the inventory of these two lakes has been performed using Landsat-7 and 8 satellite images from 2005, 2010, 2011 and 2019.

8.1 Geepang gath glacial lake

Geepang gath glacier is situated in Chandra basin of Lahaul & Spiti District of Himachal Pradesh. It is located at a longitude of 77° 13' 11.937" E and 32° 31' 38.143" N latitude. The current glacial lake extent measurement analysis is based on a satellite image of 30 m spatial resolution of Landsat-7 and 8. The temporal discrepancies have been satellite data assessments for the years 2005, 2010, 2011 and 2019 (Figure 7). After using the NDWI, digitalization of the result can be extracted. The present result suggests that from the year 2005 to 2019, the lake area is continuously increasing (as shown in Table 7).

8.2 Samudra tapu glacial lake

Samudra tapu glacial lake is situated in Chandra basin of Lahaul & Spiti district of Himachal Pradesh. It is located at a longitude of 77°32'49.18'' E and 32°29'54.13'' N latitude. Satellite data of Landsat-7 and 8 have been used to map the lake extensions. Temporal variations in the area extent of Samudra tapu glacier lake are shown in Table 8. With the help of NDWI, digitalization of the result can be extracted (Figure 8).

In this study, two glacial lakes have been mapped using Geographic Information System (GIS) and Remote Sensing (RS) techniques. Samudra tapu glacial lake and Geepang Gath glacial lakes are two main glacial lakes in Lahul and Spiti District that have been taken as an area of interest. The lake area has increased from 0.542106 to 0.929685 km² for Geepang Gath glacier lake and 0.84923 to 1.23964 for Samudra tapu glacial lake during 2005 – 2019. The lake area in the years 2005, 2010, 2015 and 2019 is given in Tables 7 & 8. Both lakes are situated above 4000 m altitude.

The present results suggest that from the year 2005 to 2019, the lake area is continuously increasing (as shown in Tables 7 & 8). The current lake volume is estimated using equation 4. The values for Geepang gath glacial lake was assessed 3.10506 mm³ and for Samudra Tapu glacier lake it is 1.77628 mm³ for the year 2019. The current lake Depth is estimated using equation 5. For Geepang gath glacial lake depth is measured 34 m and for Samudra tapu glacier lake it is 15 m for the year 2019.

The largest proportion comprising an area of 4619 km² (i.e. 33 %) have a slope of the land more than 30 degree. All of this land is well, over the whole valley of Lahaul-Spiti. There is some portion of this land brought in under cultivation in small terraced fields which are cut closely along the contours. Therefore, a larger part of this land can’t be cultivated due to undulating topographic conditions. The next proportion comprising an area of 3478 km² (i.e. 25%) have a slope of the land between 15 to 30 degree and is evenly distributed in the river valleys. The following fraction, with an area of 3996 km2 (i.e. 29 percent), has a land slope of 5 to 15 degrees, with some sections in the western parts of the Chandra and Chenab valleys and consistently dispersed in smaller areas in Pattan's Lahaul valley. It is distributed uniformly in Spiti valley. A small proportion comprising an area of 1743 km² (i.e. 13%) have slope of the land between 0 to 5 degrees. It covers a large portion of the western Chandra valley and occurs in Lahaul valley along the river and moving south from the great Himalayan range. It is well distributed in the whole of Spiti valley in the northern suburbs south of Zanskar, most of the region covered with snow.

The discussion above clearly indicates that a very significant portion of the land is it falls under a steeply sloping surface and therefore not ideal for agriculture. Most of the sections are either hidden by ice and snowfields or out-crops of rock created by rockfalls and sloping glaciers. The drainage pattern denotes the geometric spatial structure of the in a specific area, streams. It depends on a broad range of considerations; some of the existence of the slope, structural control, lithological control are the essential characteristics, tectonic variables and features of plants. From figure 4, it is apparent that dendritic drainage is the most prominent model pattern. The second theme pattern of the trellis is discernible. Drainage pattern also offers a general overall pattern settlements theory.

Stream ordering (Figure 4) gives an idea of the basin dimension of each tributary and the reach of the discharge of water. Generally, there is a good association between the discharge of water and the width of the valley order for downloading. In other words, the greater the stream order, the narrower the valley would be the discharge of water would be greater and higher. It offers an indirect idea of the area's water supplies.

The Lahul & Spiti district is mainly covered by Barren/Rocky surface (more than 50%). In the last 20 years, snow cover has constantly been increasing, resulting in a decrease in Barren/Rocky surface. The snow cover increased by 44 per cent, while barren surfaces reduced by about 6 per cent during the years 2005-2019 (Table 7). The forest covers in the study area show a large change and have been reduced by about 64 per cent. The area under Agriculture/Grass shows a considerable reduction (47%) during the years 2005-2019. The area under water also reduced by 23 per cent. Distribution of land use/land cover is shown in Table 7. The whole area is mountainous, and agriculture is practised on sloppy lands. Graphs for various land use classes are shown in Figure 5.

The use of GIS and remote sensing technology has enabled mapping of lakes that have evolved at higher altitudes, which would not have been attainable with traditional field research. The results of a comprehensive study of satellite images provide insight into the genesis of these lakes. Monitoring of two glacial lakes, Geepang gath and Samudra tapu, has been carried out to ascertain the depth of the glacial lakes in order to comprehend the change in their location. The monitoring revealed a progressive increase in their size over time, which is supported by primary survey results. It is consequently critical to do in-depth research on such lakes using high-resolution satellite data in order to assess their dangers. This will aid in the assessment of potential risks as well as the mapping of some other new lakes being constructed in the area.

Acknowledgements

The authors are grateful to the NASA for making the Landsat and ASTER GDEM datasets freely available under the umbrella of USGS web server. The present work was financially supported by the National Mission on Himalayan Studies (NMHS), MoES & CC, India under the Himalayan Research Fellowship (HRF) program.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Compliance with ethical standards

The author declares that no copyright norms have been violated, and the study has no conflict of interest.

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Tables 1,2,4,5 are available in the Supplementary Files section.

Table 3. Details of Landsat-7 data

Data	Path	Row	Date of acquisition
Landsat-7	147	38	2010-10-11
Landsat-7	147	37	2010-10-11
Landsat-7	146	38	2010-11-05

Table 6. Percentage of the area under slopes

Slope (in degree)	Area ( )	Area (in hectares)	Percentage of total area
0 - 5	1743	174263	13
5 – 15	3996	399596	29
15 – 30	3478	347800	25
30 – 45	2275	227459	16
More than 45	2344	234381	17
Total area	13835	1383500	100

Table 7. Land use/ Land cover change (2005 - 2019)

	Land use/Land cover Class		Area	(Percent)		Percent Change (2005 - 2019)
	Land use/Land cover Class	2005	2010	2015	2019	Percent Change (2005 - 2019)
1.	Snow/Glacier	27.313	45.491	37.145	39.155	43.357
2.	Barren/Rocky Surface	55.219	47.188	53.762	52.286	-5.312
3.	Forest	4.343	2.528	1.137	1.587	-63.458
4.	Water	0.061	0.062	0.057	0.047	-22.951
5.	Agriculture/Grass	13.064	4.731	7.899	6.925	-46.992
		100.00	100.00	100.00	100.00

Table 7. Temporal variations in the area extent of Geepang gath glacial lake

Year	Area (in ha)	Area (in sq km)	Increase in Per cent
2005	54.2106	0.542106	-
2010	68.1484	0.681484	25.709
2015	78.1553	0.781553	14.684
2019	92.9685	0.929685	18.954

Table 8. Temporal variations in the area extent of Samudra tapu glacier lake

Year	Area (in ha)	Area (in sq km)	Increase in Per cent
2005	84.923	0.84923	-
2010	117.752	1.17752	38.657
2015	121.085	1.21085	2.830
2019	123.964	1.23964	2.379

Mapping of glacial lakes and glacial lake outburst flood in Lahul and Spiti district using remote sensing and GIS

Status:

Version 1

Abstract

Figures

1. Introduction

2. Study Area

3. Material And Datasets

4. Methodology

5. Parameters Incorporated In The Study

6. Lake Area, Volume And Depth

7. Land Use And Land Cover

8. Mapping Of Glacial Lake

9. Results And Discussion

10. Conclusions

Declarations

References

Tables

Supplementary Files

Status:

Version 1