Prime Minister Narendra Modi has told his fellow Indians that "nature has been testing us" after cloudbursts caused flash flooding that killed hundreds of people across the north of the country, and in neighbouring Pakistan.
What causes cloudbursts? Usually defined as more than 10cm (roughly 4in) of rainfall within an hour over an area less than 30 sq km (11.6 square miles), cloudbursts are more likely to happen in places where warm, moist air is rising upwards in a period of high humidity, low pressure, instability and convective cloud formation.
As the warm, moist air rises, it cools and condenses, creating large, dense clouds that can often get trapped by hills or mountains, instead of moving on. When these clouds cannot contain their moisture any more, they burst, releasing it all at once, effectively like "a rain bomb", said The Associated Press. Cloudbursts "thrive in moisture, monsoons and mountains", all of which are present in India and Pakistan.
Why are they dangerous? The intense rainfall often triggers deadly flooding and landslides, as happened in northern Pakistan and Pakistan-administered Kashmir last week, killing at least 344 people, according to authorities. The death toll included 24 people from the same family, who were swept away on the eve of a wedding. In Indian-administered Kashmir, at least 60 people have been killed in flash flooding, with 200 more missing.
Part of the reason cloudbursts are so dangerous is that there is "no forecasting system anywhere in the world" that can predict exactly where and when they will occur, said Asfandyar Khan Khattak, an official from Pakistan's northwestern Khyber Pakhtunkhwa province.
Are they caused by climate change? Cloudbursts are a natural phenomena but extreme rain events and their related flash-flooding have worsened in recent years as a direct result of climate change. Because a warmer atmosphere holds more moisture, "every tenth of a degree of warming will lead to heavier monsoon rainfall", said Mariam Zachariah, an environmental researcher at Imperial College London.
Khalid Khan, a former special secretary for climate change in Pakistan and chair of climate initiative Planet Pulse, said global warming had "supercharged" the water cycle. "In short, climate change is making rare events more frequent, and frequent events more destructive." |