Cloudburst

In recent times extreme rainfall events as cloudbursts are dominant phenomenon trigger large scale mass movement and flash floods in the Himalayan region. Cloudburst is a natural and common phenomenon in the Himalaya, especially in Garhwal and Kumaon region of uttarakhand. Cloudburst and associated disaster affect thousands of people every year and cause loss of life, property, livelihood, infrastructure and environment.

Almost every year several parts of Uttarakhand Himalaya experience cloudburst and associated hazards. Cloudburst during August 1998 at Ukhimath (Rudraprayag) and Malpa (Pithoragarh), August 2001 at Phata (Rudraprayag), August 2002 at Burakedar (Tehri), August, 2012 in Asi Ganga (Uttarkashi), September, 2012 at Ukhimath (Rudraprayag) and June 2013 at Kedarnath (Rudraprayag) are some of the examples of recent cloudburst incidences associated with flash floods and landslides in Uttarakhand Himalaya. The Cloudburst is a natural phenomenon that generally occurs during monsoon period over many regions of the Himalaya. Generally, cloudburst refers to particularly heavy precipitation in a short period of time over limited geographical area. It is often defined as more than 100 mm/hour rainfall within a limited geographical area of a few square kilometres. The landforms of the Uttarakhand Himalaya located above 1200 meter altitude are extremely sensitive for the cloudburst induced landslides during monsoon season.

Cloudburst incidences over many areas of Himalaya often go unnoticed due to the absence of meteorological observatories. Many a times these come to notice only when these are accompanied by losses and casualties. In the absence of losses these can only be identified on the basis of inundation occurring along streams. Mostly upper reach of first order and second order drainages (seasonal streams) have been observed to be overwhelmed by debris flow during these incidences. Slope failures and bank erosion are common during this phenomenon which result sedimentation and sometimes block the river course, turn them into big lake and create flood condition.

Considering extreme rainfall events in Uttarakhand Himalaya, it is suggested that instead of valleys and along abandoned channel of drains people should inhabit on the hard rock or firm ground of slopes for safety reasons. At locations where ground fissures have developed and subsidence has taken place appropriate measures are required for checking infiltration of rainwater as well as surface water. This should precede implementation of permanent treatment measures. People living around these slopes should remain vigilant, particularly during the monsoon period and any physical change in the slope should immediately brought into the notice of authorities. On the basis of information collected from the local people, strong wind and lightning are very common during cloudburst. Even though locals consider it to be a cloudburst event it is hard either to accept or reject their assertion in absence of authentic meteorological data from the proximity of slope failure incidences. Indiscriminate and unscientific construction should be banned especially in landslide affected areas. Besides this safe disposal of rainwater needs to be given due importance. Both surface and subsurface drainage measures should therefore be planned and executed. For this drain pipes could be provided on debris slope. The planned drainage network should be stepped and wide enough to accommodate heavy downpour events. Increasing anthropogenic activities, venturing in unsafe areas due to limited land availability and heavy localized precipitation, these are continuously increasing the landslide vulnerability in Didihat town as well as hilly terrain of Uttarakhand. In case indiscriminate and unscientific construction could not be regulated all mitigation and treatment measures would remain a mere formality and would be of little use. The bioengineering technology can be successfully implemented by using specific and local vegetation along with engineering measures to reduce instability and soil erosion. Although it is difficult to forecast cloudburst events, dense network of rain gauges particularly in the areas identified as being vulnerable to cloudburst is required for better understanding of this phenomenon. Accurate measurement of such events and studies based on different aspects of geology, geomorphology and climatology could help in developing a cloudburst forecasting model. Such studies would at the same time result in efficient landslide risk mitigation. At the same time the awareness about the extreme precipitation events and associated disasters among the dwellers of the area is needed.

Cached at 18/10/2018 09:08:50