Dr Baisakhi Sarkar
Deputy Director
National Atlas and Thematic Mapping Organisation
Post disaster analysis of the Uttarakhand disaster in mid-June 2013 reveals the changes to the terrain in the Kedar valley through satellite imagery, and the need for revision of natural hazards map of India with respect to identification of flood prone and drought prone districts
Recent observations show that in the past few years, some north Indian states like Himachal Pradesh, Uttarakhand, Delhi, Jammu & Kashmir, Punjab, Haryana have been receiving plenty of rainfall during southwest monsoon. In east Rajasthan and Gujarat plains, heavy rainfall caused sheet flood. These events can be explained by the hypothesis that summer low pressure trough over the subcontinent has a tendency to get shifted from Rajasthan to elsewhere (farther north northwest) and that the Arabian Sea branch of monsoon has become more powerful with respect to collection of moisture. During June –July, a second low pressure trough forms over central India, delivering plenty of rainfall in Odisha, Chhattisgarh, Vidarbha, Central Maharashtra, Konkan, Goa and coastal Karnataka. Saurashtra, south Rajasthan and Kutch also receive moderate rain. Later, it passes over Sind in Pakistan.
In the last two years, the so-called ‘humid’ state of West Bengal received below normal rainfall as the northern part of Bay of Bengal remained insufficiently hot and thus failed to develop a significant low pressure eye over there. However, this year (2013) West Bengal received plenty of rain. Sohra (Cherapunjee) in Meghalaya known for super humid climate has not received adequate rainfall for a couple of years. This year Uttarakhand received four times more rainfall than normal. All these events indicate a change in the behavioral pattern of monsoon.
Causes of cloud burst
Ascending winds bearing plenty of moisture and attaining condensation level at a rapid rate cause heavy downpour. When an enormous mass of low altitude cloud with significant vertical depth attends saturation level within a short time span, cloud burst and associated thundershower occur over a small pocket. Recent heavy monsoon rainfall in Uttarakhand and Himachal Pradesh could be due to hot summer, heavy snowmelt and rapid evapo-transpiration in middle Himalayan region contributing to formation of fresh rain bearing clouds. Flash flood in Leh on 6th August 2010 could be explained by this hypothesis; south Pakistan got flooded due to heavy rainfall in the Indus catchment area. During summer, hot weather in parts of the Western Himalayas causes fast melting of the Amarnath cave ice (Shiva-ling). By late July, the height of the holy ice mound had dropped significantly. Melting of glaciers and ice fields /snowfields and evaporation contributed in local cloud formation over Uttarakhand, Himachal Pradesh in India as well as over Nepal. Heavy rain in Nepal Himalaya accompanied by melting of glaciers caused flood in northern Uttar Pradesh and north Bihar.
Cloudburst in Uttarakhand
The devastating flood in Uttarakhand in mid-June 2013 was a combined impact of cloud burst in Uttarakhand, quick melting of glacier at high altitude due to beating of ice sheet by raindrops and breaching of natural embankment of Chorabari Tal (north of Kedar) due to accumulation of excess surface runoff. Within 48 hours, 280mm rainfall occurred and about five feet of snow was precipitated at higher altitudes. Apart from Uttarakhand, Himachal Pradesh, northeast Rajasthan and Delhi also received torrential rainfall. For Delhi it was an advent of early monsoon that broke the past record of 150 years. In western India, heavy rainfall occurred during mid-June in Gujarat and southern Rajasthan due to early advent of Arabian Sea branch of monsoon. The monsoon winds were pushed northeastward by an upper air current. On its way towards north northeast, the cloud gathered moisture as a result of evaporation from freshwater bodies and irrigated agricultural fields lying on its way. Over Uttarakhand, it coalesced with the local clouds that formed due to evaporation from water bodies (rivers, lakes), snowfields and glaciers as well as evapo-transpiration from forests. It may be mentioned that expansion of built-up area, auto-emission, emission from aircrafts accelerate formation of brown clouds. A polluted overcast sky hinders temperature radiation and cooling of the earth’s surface. This causes rising of ambient air temperature that in turn increases the rate of evaporation. Uttarakhand and Himachal Pradesh experienced very early monsoon and heavy precipitation that were uncommon at least for past 50 years; the amount of rainfall in Kedar valley was unprecedented since 1925.
Fragile environmental set up
Tectonically, the northeastern part of Uttarakhand is highly fragile and susceptible to earthquake and landslide. The area recorded 10 significant earthquakes during the past 100 years; horizontal seismic coefficient isoline of 0.08 encircles the region. Further, heavy rain causes soil creep and landslide; landslide is aggravated because of deforestation. Much of the casualty in Uttarakhand was due to human interference like construction activities within 100 feet from the river channel disturbing a fragile geological set up (composed of a variety of metamorphic and sedimentary rocks that underwent intense folding and weathering), harnessing of rivers and diverting the discharge for generating hydro electricity.
High velocity of flood water was a result of steep slope – in the affected districts there is a fall of relief from 5000m to 1500m within a short distance. When extra-runoff comes downstream along steep slopes, it denies artificial conduit created for water turbines and tries to follow its original natural course. Hence flooding happens. Since the creation of Uttarakhand, due to development work related to tourism, transport, power generation, etc, natural eco-system has got disturbed. Deforestation, explosion by dynamites for construction of roads, tunnels; building hotels, tourist resorts and parking lot within the catchment area of rivers; construction work related to hydro power projects over Alakananda, Mandakini and Bhagirathi – all contributed in destabilisation of underlying geological structure as well as river/ surface water flow. In many cases, the plinth of the buildings that were demolished by sheet flood did not have sufficient depth. When soil and debris were washed away, the building collapsed. All these factors contributed in landslides, flooding and demolition of structures/ human settlements.
Why flood/disaster in Kedar valley?
The sequence of events in Kedar valley was as follows. On Thursday the 13th June 2013 supercomputer of India Meteorological Department predicted the convergence of two weather systems likely to take place by the weekend and likely to deliver copious rainfall. A low pressure system due to early monsoon advection and an upper air trough from western Asia were about to merge over northwest India. It was expected to cause heavy rainfall in Uttarakhand and adjacent areas. India Meteorological Department’s Delhi office issued a preliminary weather advisory on June 11th and then a second warning of heavy rainfall on June 13th, two days ahead of the torrential precipitation. Around 13,000 pilgrims made their way to Kedarnath alone between 15th and 17th, according to statistics cited by principal secretary to the chief minister of Uttarakhand. For those thousands in the mountains, the forecast did not help.
The low pressure system and the upper air trough had converged over Haryana and Punjab. After their coalescence over Punjab plain, both moved towards Uttarakhand together. It delivered extremely heavy precipitation. According to Shri Singh, Deputy Director General, IMD, convergence of such systems is not unusual during the monsoon season, but the amount of moisture they brought in and the resultant precipitation (280mm in 48 hours) were exceptional. Since the initiation of monsoon season on June 1, Uttarakhand received more than 410 per cent of the normal volume of rain it was expected to receive during this phase. Weather stations across Uttarakhand recorded exceptionally heavy rain between June 15th and 17th, 2013. In Kedar valley on 16th June 2013 at 8-15 AM, sheet-flood transporting large boulders, debris and mud came down the valley when Gandhi Sarovar 3 km up from Kedar temple overflowed due to heavy downpour and consequent melting/breaking of a part of Chorabari Glacier further upstream. About 25m of Chorabari Ridge was demolished under pressure of excess water. This ridge is composed of unconsolidated materials (end moraines); it acted as natural embankment of Chorabari Tal.
The sheet flood generated transported enormous amount of end moraines and fluvial debris. At Kedar, the sheet flood attained about 15 feet height; the discharge was contributed both by the Mandakini (rising from Chorabari Glacier) and Saraswati (rising from Companion Glacier). The northern and southwestern parts of Kedar settlement got more damaged compared to the southeastern part that was least affected as runoff preferred the westernmost route in accordance with gradient, lithology and other geomorphologic factors. Further south, the volume of surface runoff got enhanced due to contribution from Dudhganga and other east flowing streams/ rills debouching in the Mandakini; 14 km stretch of Kedar valley, particularly from Kedar up to Rambara (7 km away from Kedar), was badly damaged. Kedar Temple was not washed away primarily due to mammoth depth of its plinth, its heavy weight and robust structure. Also, the valley slope near the temple is moderately gentle compared to the upper stretch; hence a huge boulder transported as bed load of sheet flood got stand still just behind the temple and protected the rear side of the temple from severe damage.
Up in the mountain, trekkers experienced 7 feet of snowfall in 48 hours near Sweta Peak about 50 km away from Gangotri; their tents got buried under snow. Landslides occurred on ways from Bhujbasa (near Gomukh) to Gangotri and Gangotri to Harsil.
Devastation downstream
An estimated 90 rest houses with 1000 pilgrims sheltered there, were washed away due to flash flood of Mandakini and Alakananda rivers. Several villages of Chamoli and Rudraprayag districts went under water. At least 16 landslides occurred on the road to Uttarkashi. Some affected road routes are Rishikesh-Uttarkashi-Harsil-Gangotri; Rudraprayag-Kedarnath; Joshimath-Badrinath and Dharchhula-Tawaghat in Pithoragarh district.
Due to second successive cloudburst on 24th June over Mular village in Pathani-Kasba valley, Pauri district, landslide occurred on Rudraprayag-Badrinath road, metal railings on roadside were squeezed out by the virulent force of water; trucks carrying relief materials turned upside down. Army helicopter deployed in relief operation was thrashed against the valley side slope.
Changes in Physical Set-up in and around Kedar
The item number 1 in the image is the Mandakini channel, number 2 is Saraswati channel and number 3 is Kedarnath Temple. Due to huge accumulation of debris the river Saraswati lost her downstream track; earlier Saraswati used to meet Mandakini downstream of Kedar; now she meets Mandakini further upstream of Kedar temple. Instead of four hot springs only one hot spring is surviving near Kedar Temple; the hot spring at Gouri Kund is no more traceable.
Global events
It may be mentioned that not only India but some other Asian countries like Philippines experienced flood during 19th-20th August 2013 due to heavy rainfall; South China was flooded due to heavy rainfall. European countries like France experienced heavy rainfall and flood during this summer. A tornado devastated Oklahoma, USA on 21st May 2013. Last year in April, Kenya experienced flood, eastern Australia received abnormally high amount of rainfall during summer. In the past few years, high and mid-latitudinal countries of northern hemisphere have been experiencing very hot summer as well as severely cold winter. This indicates rapid warming in summer and rapid cooling during winter; which might be due to a little more tilting of the earth’s axis. It is interesting to note that this year on July 20th, southern Canada experienced 41º Celsius temperature; New Jersey (USA) recorded 38º Celsius temperature; and it has been happening for past couple of years. On the same day Kolkata, located in the Tropics, was not so hot; it had 37° Celsius temperature.
A tilt in the earth’s axis?
An inference is drawn from recent observations especially after the massive earthquake in Japan on 11th March 2011 and also the frequent earthquakes during the past couple of years, that axis of the earth (which had never been static) might have got tilted. According to Italian and US agencies the quake in Japan has shifted the earth’s axis by 25 cm. Not only in Japan, but frequent earthquakes have occurred elsewhere also. New Zealand experienced massive quake on 22nd February 2011. On 23rd August 2011 an earthquake occurred in the west coast of North America. On 20th September 2011 Sikkim and Darjeeling experienced a massive earthquake. Earlier, on 26th December 2004, Indonesia and adjoining countries were severely affected by earthquake and tsunami. Tilt in the earth’s axis might lead to reception of more insolation by mid-latitude countries during summer. These countries are experiencing more extreme climatic conditions; hot summer and associated depression/cloud burst and very cool winter.
Conclusion
This year (2013), the convergence of upper air trough and low-pressure system pushed the monsoon line across northwest India well ahead of due date – the monsoon covered entire country about a month in advance of the normal date of July the 15th. Climate is changing gradually. The districts of Uttarakhand that experienced flood this year were considered as areas of unpredictable/scanty rainfall 30 years ago. Kheri and adjoining districts of Uttar Pradesh have been facing seasonal floods due to heavy rainfall in Nepal Himalaya; these areas are no more drought-prone, but flood prone. There is a need for revision of natural hazards map of India with respect to identification of flood prone and drought prone districts. Cloud burst, cyclone and tornado are frequent these days. It is imperative that precaution/warning message should be delivered in advance. Tourists might use India Meteorological Department’s weather forecasts that are issued about five days in advance. Keeping in mind the possibility of early monsoon outburst and associated disaster, the period of tourist influx in Uttarakhand could be restricted to the second half of June. Tourists should not be allowed to trek or travel after 10th June if weather satellite shows signs of early monsoon advent and possibility of formation or accumulation of high density low level cloud with significant vertical extension.
