Bengaluru on yellow alert: Why this was the region’s rainiest May in over 60 years

In this Deep Dive, we are talking about the heavy rains in Bengaluru this summer. May 2023 has been the rainiest May in the region since 1957, aggravating Bengaluru’s existing flooding problem. Meteorologists at IMD Bengaluru forecast more rains and thundershowers, in addition to the downpour that has already taken place in the region in the last few days already. To help us analyse the reasons behind this unprecedented rain and Bengaluru’s urban flooding problem, we have with us The Times of India’s Niranjan Kaggere. Niranjan has been covering weather, environment and wildlife in Karnataka for over 15 years. Excerpts…Moyurie: Why did Bengaluru witness this unusually heavy rainfall this time of the year, all of a sudden? Niranjan: This part of the season, which is pre-monsoon season, the situation on the Deccan plateau and the high temperature result in a lot of evaporation and formation of clouds. This is also supported by certain climatological systems that are prevailing over Peninsular India. So, there is an upper air cyclonic circulation from south of Vidarbha, extending up to Telangana region and along with this from south of Chhattisgarh till again Andhra Pradesh there is a trough. Due to this prevailing system and also the high temperature, there has been considerable evaporation of water resulting in formation of clouds. Also listen: Techie drowns in Bengaluru flood: How infrastructure woes ail India’s Silicon ValleyThe oscillation of mercury levels also resulted in convectional rainfall. There is also variability in the Bengaluru terrain itself. So that rainfall varies according to the different topographical locations within Bangalore. For example, if Bengaluru city may have received about 30 mm of rainfall yesterday. The areas which are five kilometres away from Bengaluru city may not have witnessed this much rainfall. So this variability is largely due to the local factors that could largely be the temperature and because of the man-made activities. It could be vehicular emissions and the large built up area. So the temperature also varies. So wherever there is a steep increase in temperature in regions within Bengaluru, they have seen maximum rainfall.Moyurie: Why is Bengaluru so prone to flooding in the event of such heavy rainfall?Niranjan: Local city corporation or the district administration has failed to come up with a solution to address this perennial problem which is plaguing the city for over a decade now. If you look at the very positioning of the city in the Southern Peninsula, you would realise that Bengaluru very comfortably sits on a plateau which is about, say, 3000 feet above sea level or roughly about 920 metres from the sea level. So that means it's quite comfortable for the city to receive a good amount of rainfall all through the year. It’s also advantageous that the city is on a plateau which is surrounded by 3 different valleys. So that means even if it rains, there is less probability for the city of Bengaluru to witness any flooding. But in spite of this geographical and topographical position, Bengaluru is experiencing a lot of flooding during the rainy season or pre-monsoon season. It is largely a man-made disaster. What happened over the years is, with the IT boom, the city exponentially grew in all directions and unlike other metros there is no fixed boundary for the city. If you look at Bengaluru, in all four cardinal directions, there are no limits as such. So the city is growing in every direction haphazardly. Bengaluru, as the world knows, is the city of lakes. There are more than 200 to 300 lakes within the city parameter itself. All these lakes are very well interconnected through stormwater drains which are divided into primary stormwater drain and secondary stormwater drain. So every drop of water that falls on the surface of the plateau has naturally been designed in such a way that it gets into the valley through these drains and then gets drained to a lake. And once it gets filled to the brim, the lake water flows into a river basin. But, due to rapid urbanisation, a lot of these stormwater drains have either been encroached upon or the contours have been altered to meet the needs and desires of the builders and developers. This has resulted in massive blockading of storm water drains. Someone has put pillars into this stormwater drain, somebody has constructed a wall blocking the free flow of water, or in some other cases, the reckless throwing of garbage and the local corporations desilting these drains… al this has resulted in accumulation of water, which has also led to clogging of drains during the pre-monsoon season and the monsoon season. As a result, the rainwater, which is supposed to drain through this stormwater drain and to the lakes, gets blocked phenomenally and refluxed into the underpasses or any low-lying areas. Several low-lying areas have now been converted into residential layouts and gated communities, villas and large housing apartment complexes and all these get flooded. For the full conversation, please listen to the full podcast.Audio production: Prateek Kapoor