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The India Meteorological Department’s weather station in Chinchwad recorded 97 mm of rainfall within an hour on June 23. On June 4, Lohegaon’s weather station reported similar rainfall within a few hours. Such intense to extremely intense rainfall within a span of an hour comes very close to what the IMD calls a cloudburst. Here is a look at why such intense rainfall is becoming common.
The IMD defines a cloudburst as an intense and localised rainfall of 100 mm or more recorded within an hour. Cloudbursts have been recorded in the monsoon season with the Himalayan regions being more prone to such activities.
Anupam Kashyapi, a former head of the IMD’s forecast division in Pune, explained the incidents as the incursion of moisture over highly localised areas. “Given the recorded rainfall was not 100 mm within an hour, technically the two incidents can’t be called cloudbursts. In meteorological terminology, we can call them intense to extremely intense rainfall,” he said.
Kashyapi traced the rainfall to the formation of a cumulonimbus cell, which extends over a certain geographical area. “Radar pictures show us the depth of the clouds, and in areas where the depth of the cloud is around 10-16 km, intense to extremely intense rainfall is reported. Thus if the cloud cover is over Pune, intense to extreme intense rainfall will occur over areas where the cloud depth is more. In areas where the cloud depth is low, light to very light rainfall will occur,” he said
Thus Chinchwad and Lohegaon received intense to extremely intense rainfall due to the depth of clouds in those areas. Such a phenomenon, Kashyapi said, has occurred because of the “non-textbook nature” of the monsoon. With one of the two main currents of the monsoon being weak, rainfall is erratic now. “The present rainfall is more characteristic of pre-monsoon showers: bright daylight followed by evening rainfall. What is missing is the continuous rainfall associated with the monsoon,” he said.
As of Tuesday, Pune has received 13 per cent excess rainfall. Compared with the normal 141.9 mm rain, the district has received 160.1 mm. Most of the rainfall has occurred during the second week of June with the first week and the current week being dry.
Kashyapi said the likely cause of this rainfall is climate change, citing the increased vehicular population, rapid urbanisation and the overproduction of greenhouse gases.
“This intense rainfall comes with its own set of problems. Flooding and damage to property and life can occur with such intense localised rainfall,” he said.
Pune has reported severe flooding when such rainfall occurred. While Mumbai has some sort of infrastructure to deal with localised floods and intense rain, Pune does not have the capacity to deal with such rainfall, according to town planners.
