Date: 13/09/2022

Relevance: GS-3: Disaster Management.

Key Phrases: Southwesterly Monsoon Winds, Orographic Lift, India Meteorological Department, Strong Moisture Convergence, Flash Floods, Multiple Doppler Weather Radars, Mapping The Cloudburst-Prone Regions, Automatic Rain Gauges

Why in News?

• The disastrous impact of the cloudbursts causing widespread loss of lives and property is seemingly increasing in a changing climate.
• However, the characteristics of these events remain incomprehensible, with the efforts in monitoring and forecasting them being at an embryonic stage.

What is a cloudburst?

• A cloudburst is a localised phenomenon experiencing an extreme amount of rain concentrated in a short period, sometimes accompanied by hail and thunder.
• The short spells of very heavy rainfall over a small geographical area cause widespread destruction, especially in hilly regions where this phenomenon is the most common.
• According to the India Meteorological Department (IMD), 100 mm of rain in an hour is called a cloudburst.
• Usually, cloudbursts occur over a small geographical region of 20 to 30 sq. km.

How does a cloudburst occur?

• In India, cloudbursts often occur during the monsoon season, when the southwesterly monsoon winds bring in substantive amounts of moisture inland.
• The phenomenon that is responsible for this large amount of precipitation in such a short duration is ‘orographic lift’.
• It is the process by which clouds that are about to rain are pushed up by warm air currents.
• As they reach higher elevations, the water droplets within the clouds become bigger and new ones are formed and these dense clouds eventually burst when unable to hold the large volume of moisture.
• This results in torrential downpours in the geographical region right below and leads to overflowing of water bodies in a very short duration of time.
• Tall cumulonimbus clouds can develop in about half an hour as the moisture updraft happens rapidly, at a pace of 60 to 120 km/hr.
• A single-cell cloud may last for an hour and dump all the rain in the last 20 to 30 minutes, while some of these clouds merge to form multi-cell storms and last for several hours.
• Thus, an orographic lifting together with a strong moisture convergence leads to intense cumulonimbus clouds taking in huge volumes of moisture that is dumped during cloudbursts.

What are the cloudburst prone areas?

• Cloudbursts in India, occur mostly over the rugged terrains of the Himalayas, the Western Ghats, and northeastern hill States of India.
• The heavy spells of rain on the fragile steep slopes trigger landslides, debris flows, and flash floods, causing large-scale destruction and loss of people and property.
• On July 8, 2022, flash floods occurred in the Lidder Valley en route to Amarnath Temple in Jammu and Kashmir, taking the lives of several pilgrims.
• Strong monsoon wind surges along the coast can also result in cloudbursts, as in the case of Mumbai (2005) and Chennai (2015).
• Coastal cities are particularly vulnerable to cloudbursts since the flash floods make the conventional storm water and flood management policies in these cities dysfunctional.

Can cloudbursts be forecasted?

• Weather forecast models face a challenge in simulating the clouds at a high resolution.
• The India Meteorological Department forecasts rainfall events well in advance, but it does not predict the quantum of rainfall.
• The forecasts can be done about light, heavy, or very heavy rainfall, but weather scientists do not have the capability to predict exactly how much rain is likely to fall at any given place.
• Additionally, the forecasts are for a relatively large geographical area, usually a region, a state, a meteorological sub-division, or at best a district.
• As they zoom in over smaller areas, the forecasts get more and more uncertain.
• Moreover, the skillful forecasting of rainfall in hilly regions remains challenging due to the uncertainties in the interaction between the moisture convergence and the hilly terrain, and the heating-cooling mechanisms at different atmospheric levels.
• Theoretically, it is not impossible to forecast rainfall over a very small area as well, but it requires a very dense network of weather instruments and computing capabilities that seem unfeasible with current technologies.
• The IMD’s forecasts, and in general, the weather prediction scenario, have advanced such that widespread extreme rains can be predicted two-three days in advance.
• Cyclones can be predicted about one week in advance.
• However, cloudburst forecasts still remain elusive.

Way Forward:

• Multiple Doppler weather radars can be used to monitor moving cloud droplets and help to provide forecasts for the next three hours.
• This can be a quick measure for providing warnings, but radars are an expensive affair, and installing them across the country may not be practically feasible.
• A long-term measure would be mapping the cloudburst-prone regions using automatic rain gauges.
• If cloudburst-prone regions are co-located with landslide-prone regions, these locations can be designated as hazardous.

Conclusion:

• Climate change is projected to increase the frequency and intensity of cloudbursts worldwide.
• A 1-degree Celsius rise in temperature may correspond to a 7-10% increase in moisture and rainfall.
• As the moisture holding capacity of air increases, it results in prolonged dry periods intermittent with short spells of extreme rains and thus, deeper cumulonimbus clouds form, and the chances of cloudbursts also increase.
• The change in monsoon extremes and cloudbursts which are being witnessed are in response to the 1-degree Celsius rise in global surface temperature.
• As emissions continue to increase and global commitment to reduce emissions proves insufficient, these temperatures are set to hit 1.5 °C during 2020-2040 and 2 °C during 2040-2060.
• Thus, urgent action and policies are needed to protect lives and property from extreme events that will amplify as the global temperature change doubles.

Source: The Hindu

Mains Question:

Q. What is a cloudburst? What is the mechanism behind the occurrence of the cloudbursts? Suggest the way forward for enabling an efficient cloudburst monitoring and forecasting system. (250 words).