Weather Bee | Flood-affected Gujarat, Rajasthan are becoming rainier long-term

So how rainy is this monsoon in Gujarat and Rajasthan? The monsoon season runs officially from June to September. For the period up to August 28, this monsoon is the ninth rainiest since 1901 in Gujarat and the fourth rainiest in Rajasthan. Compared to the 1971-2020 average – currently considered the Long Period Average (LPA) for measuring rain’s performance by the IMD – the departure of this monsoon’s rain is 46.2% in Gujarat and 56.5% in Rajasthan.

As the rank and departure of rain suggest, neither Gujarat nor Rajasthan has experienced a monsoon as rainy as the ongoing one. This could be part of the reason behind the floods in the past week because neither state is the rainiest among states if the metric is the absolute amount of rain. For example, Bihar has received 625 mm rain this monsoon. This amount is somewhere between the amount of rain Rajasthan (542 mm) and Gujarat (815 mm) have received. However, floods have not been reported from Bihar because 625 mm of rain is 20% less rain than the state’s LPA for this part of the season.

To be sure, neither have the two western states experienced floods throughout the season nor have they experienced it for the first time in the past week. This can be understood from the fact that both states had a deficit in June, but a surplus in both July and August. At least anecdotally, the floods appear more widespread or severe in August. This could be because August rain has a bigger departure from LPA than July rain. For example, August rain so far is ranked second highest this year since 1901 in Rajasthan and 13th highest in Gujarat. Gujarat’s situation may have been made worse by the concentration of rain in a few days. Daily rain’s share in total rain this monsoon was 7.3%, 11.3%, and 6.5% in Gujarat from August 26 to August 28. August 27 was, in fact, the eighth wettest day for Gujarat since 1901. As the accompanying chart shows, the temporal distribution of rain has been relatively more even in Rajasthan.

The concentration of rain in a few days is, however, just one way in which rain is concentrated. Rain can also be concentrated in a particular place. An example can make this clear. If a region of 10 equal-area sub-regions receives 100 mm rain in a day in each sub-region, it would average 100 mm rain on the day. The region can also average 100 mm rain in a day in another way: if one sub-region receives 1000 mm rain and other sub-regions receive no rain. Rajasthan and Gujarat have also experienced the latter kind of concentration. This can be seen from the average of heavy or higher intensity rain. This average calculates the average rain for a region only when a sub-region (a grid in IMD’s database) receives at least 35.5 mm rain in a day. Rain of such intensity has an 84.3% surplus in Rajasthan and a 76.7% surplus in Gujarat.

To be sure, while a monsoon as rainy as the ongoing one is rare in Gujarat and Rajasthan, it should not be surprising. For example, of the seven days in Gujarat that were rainier than August 27, 2024; three belong to the 21st century, with two of these three days in 2015 and 2019. Similarly, the 30-year rolling average of June 1-August 28 rain is the highest for the 1995-2024 period in both states. This makes it clear that Rajasthan and Gujarat are getting rainier in the monsoon season, unlike rain averaged at the country level. Both states should, therefore, find ways to cope with the monsoon getting rainier.

Abhishek Jha, HT’s assistant editor-data, analyses one big weather trend in the context of the ongoing climate crisis every week, using weather data from ground and satellite observations spanning decades.