The answer should be given in three parts:
The 1st part should clearly bring out the meaning of cloud burst and then explain the process of a cloud burst. Second part should establish the relationship between the cloud burst and flash floods.
Third part should explain how both the occurrence as well as other factors make hilly areas more prone to the problem of cloud burst.
A cloudburst is sudden copious rainfall. It is a sudden aggressive rainstorm falling for a short period of time limited to a small geographical area. Meteorologists say the rain from a cloudburst is usually of the shower type with a fall rate equal to or greater than 100 mm (4.94 inches) per hour.
How does Cloud Burst Happen?
Generally cloudbursts are associated with thunderstorms. The air currents rushing upwards in a rainstorm hold up a large amount of water. If these currents suddenly cease, the entire amount of water descends on to a small area with catastrophic force all of a sudden and causes mass destruction. This is due to a rapid condensation of the clouds. They occur most often in desert and mountainous regions, and in interior regions of continental landmasses.
Flash floods are short-term events, occurring within 6 hours of the causative event (heavy rain, dam break, levee failure, rapid, snow melt and ice jams) and often within 2 hours of the start of high intensity rainfall. A flash flood is characterized by a rapid stream rise with depths of water that can reach well above the banks of the creek.
Relation between Flash Floods and Cloud Burst
• A cloudburst can suddenly dump 72,300 tons of water over one square acre resulting in flash floods. The duration of this phenomenon is short but can cause extensive damage. Thus, cloudbursts are one of the leading causes of flash floods across the world.
Why are Hilly regions more Prone to Cloud Burst?
• The orography of the region plays a dominant role by increasing the convection and hence the intensity of cloud burst. It can occur also over the plain areas, but the frequency of such occurrence is very rare. Thus, it is not necessary that cloudbursts happen only in the mountains or high altitudes as the weather systems have compatibility and criticality in space and time. But the mountainous regions are a favoured location for cloudburst due to undulating geographical features.
• Further, a number of reasons make the mountainous regions more susceptible to the after effects of cloud burst.
• The lashing sheets of rain in mountains make into free flowing mud and slush as the explosive package join the existing river current. Rivers suddenly turn semi-solid and flow with frightening force as liquid mud makes its own path breaking down anything that comes across its way. Such a breach can result in gushing of lake waters down the mountain slopes together with debris, boulders and uprooted trees with a great velocity and damage any structure that comes in the way. There could be a significant loss of life, property and natural habitat in such a scenario.
• Unplanned development in such regions also makes them susceptible to huge destruction.
• The valley regions are one of the most densely populated, which leaves them vulnerable to the after effects of flash floods resulting from cloud burst.