Sub-daily rainfall refers to extremely heavy rainfall occurring within short time spans, such as within an hour. When this type of rain occurs over urban or poorly drained areas, it overwhelms the drainage systems, leading to flash floods. These sudden floods can cause major damage in a remarkably short time.
There has been a steady increase in the frequency of short-duration, high-intensity rainfall events, particularly in Central India. This rise significantly raises the risk of flash floods, especially in densely populated areas.
The central region of India has seen more frequent short-duration rain events. Meanwhile, long-duration heavy rainfall events have become more common along the northwestern coast. Both patterns increase the risk of floods.
Rain gauge data from 1969 to 2010 indicates that both the intensity and frequency of short-duration rain events have increased in recent decades compared to previous ones. This shift contributes to heightened disaster risk, particularly during the monsoon season.
Global warming has altered atmospheric moisture content and circulation patterns. Warmer air holds more moisture, which increases the chances of intense rainfall. This change is driving the shift in monsoon behavior, leading to more erratic and intense rainfall episodes.
India is witnessing a shift in cloud types during the monsoon. There has been an 8% decline in low-level clouds and an 11% rise in high-level clouds per decade. This alteration is tied to changes in atmospheric temperatures and wind patterns due to global warming.
Low-level clouds tend to be thicker and bring more rainfall. Their decline may reduce overall rain efficiency, even if total rainfall appears high. Additionally, they reflect more sunlight, thus playing a cooling role. Their reduction can diminish surface cooling.
High-level clouds trap heat radiating from the Earth’s surface. Their increase contributes to a warming atmosphere, which can intensify weather extremes and disrupt long-standing weather cycles like the Indian monsoon.
The number of cloudy days during the monsoon season has increased by about 13% per decade. However, the nature and type of clouds matter more than just their presence in determining their impact on rainfall and temperature.
These weather changes demand a rethinking of urban planning, drainage infrastructure, flood forecasting systems, and early warning strategies. Authorities must now prepare for shorter, more intense bursts of rain that can lead to sudden flooding, even in traditionally dry areas.
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