Environmental and Economic Impact of Cloudburst Triggered Debris Flows and Flash Floods in the Himalaya: A Case Study

This paper examines the environmental and economic impact of cloudburst triggered debris ows and ash oods in the Himalaya. A case study of four villages affected by cloudburst calamity was conducted. Data were gathered by a household-level survey of affected villages and households. The authors visited the affected villages immediately after the cloudburst calamity and interviewed the head of all affected households. A total of 143 households were surveyed. First, the damage of houses, cowsheds, bridges, trees (forests and fruits) dislocation, degradation of total land along the streams and arable land in and around the villages were measured with the help of the head of households (environmental impact). The volume of debris, boulders, pebbles, gravels and mud was measured. Economic valuation of all losses was noted (economic impact). This study nds out that a large area of all villages was severely affected by cloudburst triggered debris ow and ash ood, because, they are located in a severely vulnerable landscape. This study reveals that Nirakot village needs to be rehabilitated entirely and in other villages all households, which are severely affected need to be rehabilitated as soon as possible to escape from the future cloudburst catastrophe. Past incidences of cloudbursts triggered calamities in the Uttarakhand Himalaya show that the state suffered tremendously. We gathered data on the major cloudburst incidences in Uttarakhand in the monsoon seasons of 2020 and 2021 from the state disaster relief force (SDRF), Dehradun. In three months of April, July, and August 2020, 13 major and numerous minor cloudburst incidences were noticed in Uttarakhand (Table 1). These incidences resulted in the death of 22 people and 77 animals, and 19 houses were fully damaged. Similarly, in the May and July months of 2021, 10 major and 24 minor cloudburst incidences were occurred in the Uttarakhand Himalaya, resulted in the death of 27 people and 94 animals, and 56 houses were buried. Besides, it caused a huge loss to property and landscape degradation.


Introduction
Cloudburst refers to a sudden and heavy rainfall that takes place within a short time and a particular space (Sati 2013). They are very disruptive events that generally take place in the summer and monsoon seasons.
Cloudburst triggers debris ows, ash oods, landslides, and mass movements in the mountainous regions (Fig. 1). The nature of lands such as precipitous slope and fragile and undulating terrain further accentuate the velocity of debris ows, ash oods, landslides and mass movements. Worldwide, heavy rainfall events have become more intensive and frequent causing intensive cloudburst events (Houghton et  generation. The intensity of rainfall is more than 100mm/hr (Das et al 2006).
The Himalaya is the most fragile landscape in the world. It is prone to geo-hydrological hazards such as cloudbursts, avalanches, and glacier bursts, which triggers devastating debris ows and ash oods. It has been observed that the frequency and intensity of cloudbursts in the Himalaya have been increasing. It is linked with the climate change phenomenon and increasing human-induced activities. Changing monsoon patterns and increasing precipitation in the Himalaya are associated with catastrophic cloudbursts that triggered debris ows and ash oods (Devi 2015). In the meantime, they are the least understood weather systems (Das et al 2006) because they occur in remote areas, does not have rain gauges (Thayyen 2013).
The Indian Central Himalayan Region (ICHR), popularly known as Uttarakhand Himalaya is an integral part of the Himalaya (Sati 2019). The entire region is ecologically fragile and vulnerable to natural hazards. Both atmospheric and terrestrial hazards are common and devastating. Cloudburst triggered landslides, mass movements, debris ows, and ash oods are very common phenomena, which take place every year, mainly during the monsoon season. This causes roadblocks, land degradation, forest and cropland loss, and losses of life and property. The Uttarakhand Himalaya is witnessed to have hundreds of devastating catastrophic events -atmospheric and terrestrial. Kedarnath tragedy, one of the most devastating events in the History of Uttarakhand, which killed more than 10,000 people, was occurred due to cloudburst and glacial lake outburst oods (Upadhyay 2014; Allen et al 2016; Sati 2013). Uttarakhand had received 16 major geo-hydrological and terrestrial hazards within last 50 years (Bhambri et al 2016).
The upper Bhagirathi River basin between Uttarkashi and Gaumukh consists of a highly fragile landscape. It receives heavy rain during the monsoon season. Landslides, mass movements, Debris ows and ash oods are very active in the entire zone. Because of the highly fragile and vulnerable terrain, the Government of India declared a 100 km long belt, which lies between Uttarkashi and Gangotri, as an 'Eco-Sensitive Zone' . Gangotri highland pilgrimage is located on the bank of the Bhagirathi River, where an exodus number of pilgrims visit every year, mainly during the pilgrimage season, which falls in summer and monsoon seasons. Because of landslides, mass movements, debris ows, and ash oods, during the pilgrimage season, roads are often blocked, which leads to human and animal casualties and loss of properties and business avenues. There were many incidences of disasters already taken place during the past decades.
Many studies have been carried out on glacier lake outburst oods and cloudburst triggered debris ows and ash oods in the Himalaya ( Sati 2006Sati , 2007Sati , 2009Sati , 2011Sati , 2014Sati , 2013Sati , 2019Sati , 2020Naithani 2011). These studies were conducted in broader perspectives and most of them were conceptualized. However, the present paper looks into the case study of four villages, severely affected and damaged by cloudburst triggered debris ows and ash oods, which occurred on July 18, 2021. It analyses the environmental impact of cloudburst in terms of forest and fruit trees dislocation, land degradation -arable, forests, and barren land, and damage of houses and cowsheds of affected villages. It also evaluates the economic losses of the affected villages due to the cloudburst catastrophe. The study further suggests policy measures to risk reduction and rehabilitation of vulnerable settlements and villages of disaster-prone areas to safe locations.

Study Area
The cloudburst hit and affected villages are located in Uttarkashi district of Uttarakhand state, India, close to the famous cultural city named Uttarkashi. A National Highway is connecting Haridwar, the valley pilgrimage, and Gangotri, a highland pilgrimage, passing through Uttarkashi town. It is the most travelled area mainly during the summer season because the pilgrims -national and international -visit the Gangotri highland pilgrimage. The four villages -Nirakot, Mando, Kankrari cluster of villages (Sada and Thalan), and Siror, which were affected by cloudburst triggered debris ows and ash oods and located in the Upper Bhagirathi catchment, are severely prone to geo-hydrological disasters. The slope gradient is high, varies from 15 o to 70 o depending upon the location of the villages, which further accentuates the landscape vulnerability. Indravati is a perennial stream, a tributary of the Bhagirathi River that meets Bhagirathi from its left bank. All three Gadheras (streams) -Mando, Diya, and Siror are seasonal but violent during the monsoon season. Nirakot (1530 m) village is located in the middle altitude of Hari Maharaj Parvat (2350 m) in a steep slope, Mando village (1180 m) is located on the left bank of the Bhagirathi River and Mando Gadhera with gentle to a steep slope, Kankrari (1620 m), a cluster of villages, is located on the moderate to the gentle slope on the bank of Diya Gadhera, and Siror village (1280 m) is situated on the left bank of both Bhagirathi and Siror Gadhera with gentle to the steep slope ( Figure 2). There are many human settlements located with small arable land. The people of the villages are involved in practising subsistence agriculture and horticulture on the narrow patches of terraced elds. Crop diversity is high depending on the altitudes of the villages. The main crops grow are paddy, wheat, Mandua, Jhangora, Koni, barely, maize, pulses, oilseeds, apple, peach, pear, plum, apricot, walnut, and citrus fruits -orange, lemon, and Malta. These are both rabi (winter) and kharif (summer) crops grow. Since kharif crops grow during July, therefore, all kharif crops have been damaged due to cloudburst calamity. Forest diversity is rich, mainly temperate forests are found, which vary from pine in the middle altitude (1000 m to 1600 m) to mixed-forests (1600 m -2200 m) and deodar (2200 to 2800 m).

Methodology
This study is based on the collection of household-level data and the participatory observation method. A qualitative and quantitative approach was applied to conduct and elucidate this study. Immediately after the cloudburst hit and affected the four villages -Nirakot, Mando, Kankrari, and Siror on 18 July 2021 at 8.30 pm, the authors visited these villages between 20 and 30 July 2021. The authors constructed a structured questionnaire, which includes detailed questions on the causes and consequences of cloudburst triggered debris ows and ash oods in these villages. A long list of questions was prepared and questions were asked from the head of 143 households, which were severely affected by cloudburst triggered debris ows and ash oods. The questions were mainly related to the loss of lives -humans and animals, environmental impacts such as forestland degradation, dislocation of trees -pine, mixed-oak, deodar, and fruit trees. The perception of the head of households was obtained. The case study villages have rich agro-climate and agro-biodiversity, where the number of crop races/cultivars is grown. The main crops damaged by debris ows were paddy, Mandua, Jhangora, pulses, maize, and Rajma. Further, among fruit trees apple, peach, plum, apricot, Malta, lemon, orange, and walnut trees were own. The data on the area under agriculture/horticulture and forests, which was own due to huge debris ows, were gathered by the household-level survey. Similarly, data on fruit trees, which were washed away, were also gathered by the household-level survey. 'Nali' the unit of measuring land was converted into acres and the value of crops and fruit trees, which were damaged, were noticed at the current price. Valuation of damaged houses, cowsheds, and other economic avenues was noted at current prices. A formula was applied to measure circumference = 2πR and Area = π * R². The volume of debris -boulders, pebbles, sands, and soils was measured by measuring the length, width, and depth of debris. Measurement of degraded forest area was carried out. Based on the slope gradient, accessibility, economy, and climate of the villages, we analysed the vulnerability of villages and ranked them very high vulnerability, high vulnerability, and moderate vulnerability. The maps, graphs, and area photographs support the study.

Major Cloudburst Incidences in the Uttarakhand Himalaya
Past incidences of cloudbursts triggered calamities in the Uttarakhand Himalaya show that the state suffered tremendously. We gathered data on the major cloudburst incidences in Uttarakhand in the monsoon seasons of 2020 and 2021 from the state disaster relief force (SDRF), Dehradun. In three months of April, July, and August 2020, 13 major and numerous minor cloudburst incidences were noticed in Uttarakhand (Table 1). These incidences resulted in the death of 22 people and 77 animals, and 19 houses were fully damaged. Similarly, in the May and July months of 2021, 10 major and 24 minor cloudburst incidences were occurred in the Uttarakhand Himalaya, resulted in the death of 27 people and 94 animals, and 56 houses were buried. Besides, it caused a huge loss to property and landscape degradation. Source: SDRF (2021) *Present case study villages Figure 3 shows economic losses are higher in 2021 than in 2020 due to cloudburst calamities in Uttarakhand. It is because, in 2021, the cloudburst incidences are much more than 2020 even the data of 2021 is only up to July. The gure further shows that animal loss was the highest in both years than houses. It is followed by human loss and then bridges collapsed  (Table 2). At the cloudburst hit area, it formed three gullies, which later on merged into three streams, along which these villages are located. The source of debris and ood was one i.e. Hari Maharaj Parvat and it has equally own in all three directions. Since the cloudburst event occurred at 8:30 pm, the people did not have time to move their household goods, therefore, the damage was enormous. A detailed case study of these villages was conducted and described as follows. This village was also suffered from landslide hazards on 4 th July 1984 at 8:00 pm, which has damaged about 0.5 acres of agricultural land and paddy, pulses, and vegetable crops were damaged fully. A house was buried in debris. year to year. Figure 5 shows four villages -Nirakot, Mando, Kankrari, and Siror, which were severely affected by cloudburst triggered debris ows and ash oods. The volume of debris and boulders can be seen in all the villages. These villages are surrounded by dense temperate forests that vary from pine to mixed-oak and deodar. Kharif crops are growing in the arable land whereas a large cropped land has been washed away.

Environmental Impact
The environmental impact of cloudburst triggered debris ow and ash ood in four villages of Uttarkashi district was analyzed (

Source: by Authors
Economic Impact The economic impact of cloudburst triggered debris ow and the ash ood was tremendous in the forms of a household affected, loss of human and animal life, building loss, forest loss, existing crop loss, loss of fruits, loss of arable land, and loss of bridges (  We calculated the average circumference, area, and volume of boulders in the case study villages used a formula: circumference = 2πR; Area = π * R²; Volume = length x width x depth (Table 5). We noticed that the highest average area of boulders was in Mando village which is 28.3 m 2 followed by Kankrari 19.6 m 2 , Nirakot 12.57 m 2 , and Siror 7.1 m 2 . In terms of the total volume of debris, it was the highest in Kankrari, followed by Mando, Nirakot, and Siror. Source: by Author Figure 6 shows the average diameter of boulders in the cloudburst affected villages. We drew the gure with a scale, 1 cm is equal to 1 m. The average biggest diameter of boulders was found in Mando village (6 m), followed by Kankrari (5 m) and Nirakot (4 m) villages. The average smallest diameter of boulders was found in Siror village (3 m).

Vulnerability Analysis
Based on the above analysis and Table 6, vulnerability analysis of the case study villages was carried out.
The main variables of vulnerability were slope gradient, accessibility of villages, economic conditions of households, and climatic conditions. Based on these variables, Nirakot village has a high vulnerability, Kankrari has a high, and Siror and Mando have a moderate vulnerability. We observed that the cloudbursts incidences in 2020-21 in the Uttarakhand Himalaya occurred mainly in the remote mountainous districts. The plain district did not receive any cloudbursts incidences during the period. It is a fact that mountain districts of Uttarakhand are highly vulnerable to geo-hydrological disasters mainly cloudbursts triggered incidences. The slope gradient is high, the terrain is fragile, and rural settlements and institutions are situated mainly along the perennial streams, which are violent during the monsoon season. There is a long list of catastrophic cloudbursts, which have devastated the entire rural

Conclusion
Cloudburst triggered debris ows and ash oods are natural calamities in mountain regions in general and the Himalaya in particular. They will occur and no one can control them. Subsequently, the environmental losses will be there. However, the economic loss due to their occurrences can be minimized. The study reveals that the economic and human losses of the present calamity were mainly due to the location of four villages. All four villages are located on fragile and precipitous slopes, along the streams, which are violent during the monsoon season. Their settlements and arable land lie on both sides of the streams. Further, the slope gradient is very high and the terrain is fragile. This is the case for the entire Himalayan region. The psychological shocks due to disasters have led to large-scale out-migration. We suggest that the villages -Nirakot and Kankrari need to be fully rehabilitated immediately because they are highly vulnerable and already they were affected by cloudburst calamity. Some settlements of Mando and Siror villages also need to be rehabilitated because their location is in highly vulnerable areas. Mando village was affected twice by cloudburst triggered landslides and debris ow -the present one and in the past July 4, 1984. Suitability analysis of rural areas can be conducted and accordingly, policy for rehabilitation of settlements can be ensured. This will reduce risk and vulnerability, and can minimize economic and human loss. The whole process needs short and long term policies to support the affected families and to rehabilitate them in safe areas. The affected people need immediate compensation (relief package) to restore normalcy in livelihoods and routine work. Early warning system, a rehabilitation centre on the safe side, and plantation of deep-rooted big trees along the stream instead of agriculture or house construction (ecologically-based disaster risk reduction) are the other drivers, which will reduce the risk and vulnerability. Declarations