As I read the local paper today, another incidence of a cloudburst is reported from the Rajgarh area of Himachal. Unlike tropical cyclones, tornadoes and hurricanes, cloudbursts hardly make it to the news headlines. Perhaps because they affect only a very small area, but their impact however localized is as devastating and lethal as any other natural disaster.
While the local hill folk attribute cloud bursts to the wrath of the local deity, meteorologist are still struggling to figure out what causes them and why the incidences of cloud bursts are on the rise in the western Himalayas.
A cloud burst is a little understood weather phenomenon. The term comes from the earlier notion that clouds were masses of water that burst to cause rainfall. It is a sudden aggressive rainstorm, mostly in desert and mountainous regions, falling for a short period of time limited to a small geographical area. In the mountains, air currents rushing upwards carry a large amount of water and when these currents are blocked by high mountains, the entire load falls on to a small area with catastrophic force. More than 100 mm of rainfall can occur from a cloudburst in an hour and that too over a very small geographical area. Since not much of it can percolate into the soil, it runs off the surface to collect into streams which swell to cause flash floods and mass destruction.
Over the years the frequency of cloudburst has increased in Himachal and adjoining Uttranchal and they have become more violent causing widespread devastation. The increased frequency of cloudburst may be due of natural causes like global warming and climate change but the destruction they cause can be attributed to our own action. Large-scale deforestation of the hills has increased the surface runoff of rainfall causing heavy erosion and flash floods. Similarly, increasing construction of houses, and other structures close to river banks and streams, blocking of rivers courses by dumping debris, and the building of infrastructure such as roads, bridges, dams and even townships without environmental assessment of the area in terms of slope stability and likely debris flow are perhaps the factors that explain why cloudburst are causing so much destruction to life and property in recent years.