Climate Change

Rain-bearing low cloud cover decreased significantly in last 50 years: study

The study also shows a decline in the number of rainy days in monsoon season

 
By DTE Staff
Last Updated: Monday 12 June 2017
Low cloud cover is responsible for most of the rainfall. Credit: Jimi M/ Flickr
Low cloud cover is responsible for most of the rainfall. Credit: Jimi M/ Flickr Low cloud cover is responsible for most of the rainfall. Credit: Jimi M/ Flickr

There was a decrease in low cloud cover over most regions in India between 1961 and 201, says a study published in the Indian Meteorological Department journal Mausam.

The annual mean low cloud cover, which is responsible for most of the rainfall, shows significant decreasing trend of - 0.45 per cent per decade. The decline is particularly evident in monsoon season, with the cloud cover reducing by 1.22 per cent per decade. Monsoon is responsible for 70 per cent of India’s rainfall and snowfall.

The study also shows a decline in the number of rainy days in the monsoon season at a rate of 0.23 days every decade, which means that India has lost approximately one rainy day in the last 50 years. This is going by the IMD definition of a rainy day: when total precipitation is 2.5 mm or more.

The paper argues that the trend is a cause of “worry” and finds that while the number of rainy days are reducing, the total amount of rainfall does not show much change. This indicates shorter, heavier bursts of rain, which affects crops and result in runoffs, thereby not helping in groundwater recharge.

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  • The all-India southwest monsoon presents 78% of the annual rainfall with 852 mm during 1871-1990. This rainfall clearly showed 60-year cycle. The decadal rainfall [average for ten years] showed as: 850.1, 881.8, 865.9, 822.7, 821.7, 837.6, 871.7, 889.1, 871.7, 844.5, 840.4, 829.7 mm. 1901-70 average is 851.3. Here we must remember the fact that prior to 1957 the measurements were made in inches and from 1957 onwards in millimeters. There are several groups using different data sets and arriving at different means -- for example long-range forecasts refer to those means only. So, one day difference is not a significant but it depends upon the segment of the 60-year cycle. Also, Santacruz rainfall decreased by around 300 mm with the removal of hilluck for the expansion of runway in 70s. But later it recovered with tall buildings with the new international airport terminal.

    Dr. S. Jeevananda Reddy

    Posted by: Dr. S. Jeevananda Reddy | one year ago | Reply