11 days account for 80% of Delhi’s monsoon rainfall this year
Between 8:30am and 5:30pm on Wednesday, Delhi’s five weather stations -- Safdarjung (32mm), Palam (49mm), Lodhi Road (25mm), Ridge (43mm) and Ayanagar (66mm); received an average of 43 mm of rain. The rainfall was the highest in this monsoon season at the Ayanagar station. Safdarjung (68mm), Palam (81mm)and Lodhi road (72mm) recorded the maximum rainfall on July 23, while Ridge (86mm) experienced its highest rainfall so far on July 21.
Wednesday’s rain, apart from causing traffic jams around the city, and water logging in many parts, is likely to skew an interesting trend a bit more: An HT analysis of the India Meteorological Department’s (IMD) gridded dataset up to August 18 shows that Delhi received 80% of its total monsoon rain till Tuesday in just 11 days. The gridded database works with a one day time lag. So, rainfall after 8:30am on August 19 will reflect in the data only on August 20.
This is in keeping with a trend that has become evident even at the national level -- an uneven distribution of the monsoon rainfall, with lots of rain falling on a few days.
Keeping August 19 aside, just four days -- August 13, July 19, July 5 and July 23 -- account for almost half of the monsoon rain this year in the capital. And 19.4% of Delhi’s total monsoon rainfall (till Tuesday) happened on August 13. Once rainfall numbers for August 19 become available, the rainfall distribution might become even more skewed. This data will be available only on Thursday.
The station-wise data cannot be compared with the data in this analysis because the gridded data set calculates average rainfall for Delhi in its entirety, spread over two grids of 0.25 degrees longitude and latitude each, and is not a simple average of the rainfall at individual stations.
Also read: Why Noida handles rain better than Gurugram
See Chart 1: Share on total monsoon rainfall this year in descending order
IMD counts the period from June 1 to September 30 as the monsoon season. This year, 50 days since June 1 have seen rains in Delhi. Due to these recent spells of rain, Delhi’s cumulative rainfall deficit is now within the normal range, according to IMD’s rainfall statistics for August 18. The cumulative monsoon rainfall deficit in Delhi on August 18 was 14%. A departure from the longer period average of -19% to 19% is considered normal.
See Chart 2: Delhi’s rainfall deficit
An analysis of IMD’s gridded rainfall data set shows cumulative rainfall deficit in Delhi has been moving towards the normal range as the monsoon season has progressed. Delhi is approximated by two grids in the gridded data set. A grid is a box bound by two latitudes and longitudes 0.25 degrees apart. The cumulative rainfall deficit was largely in the 30% to 50% range from mid-June to the end of July. In August, the deficit has stayed more in the 20% to 30% range. This will come down after Wednesday’s rainfall statistics are published. To be sure, before June 15, Delhi was less rain deficient than it is now. However, there was a long gap after the early monsoon rains and rainfall picking up again.