While it has rained heavily in certain districts, there has been none in others
The recent heavy rainfall in different parts of India due to western disturbances, associated cyclonic circulations and thunderstorms has the imprint of global warming written over it, experts have told Down To Earth (DTE).
Between March 1 and March 5, 2020, 222 out of the total 683 meteorological districts in the country received large excess rainfall, according to data from the India Meteorological Department (IMD).
Large excess rainfall happens when the rainfall in a particular district is 60 per cent more than normal for that time of the year according to the IMD. In contrast, 265 districts received no rains at all, showing that a large proportion of the country either received too much rainfall or no rainfall.
This has been a pattern that has been observed with rainfall in the country in the past few years across seasons, leading to skewed distribution of rainfall.
During the Southwest monsoon, when most of India receives the majority of its rainfall, it has led to simultaneous floods and droughts in the same region, causing problems for people and their livelihoods.
This is mainly happening due to global warming-induced climate change and making it difficult for meteorological agencies to predict weather, according to experts.
“Our climate, as in tropical climate / weather, are difficult because of two main reasons. The first one is that on a rotating planet, rotational effects are a strong constraint on how quickly winds and ocean currents can move,” Raghu Murtugudde, a climate scientist at the University of Maryland, United States, told DTE.
“This rotational effect is zero on the equator and increases with latitude. Thus, at the tropics, the rotational effects are weak so winds can move fast, especially in the vertical direction which is associated with all our rainfall systems and storms and cyclones,” he added.
The warm tropics lead to a lot of evaporation that provides the energy when it condenses in rising and expanding air. These can organise quickly like in a few minutes to a few hours.
“Convection cells are like popcorn kernels. The entire popcorn kettle can be warm and of the same temperature, but which kernel will pop is very difficult to predict. The situation is very different in mid-latitudes where systems are large and stay for 10 days and can be predicted more easily,” Murtugudde explained.
“Climate change is warming the atmosphere that can hold more water vapour. So it is like a sponge that is getting soaked. Convection is like pressing the soaked sponge which then pours out the water at one or two locations instead of drizzling uniformly. So we get extreme rain,” he said.
“Plus climate change is also warming the land, ie, the popcorn kettle, so more kernels can pop (approximately). The Indian Ocean is like a bathtub with water getting warmer. This supplies huge amounts of moisture to land and creates widespread floods,” Murtugudde noted.
In the past few days, this has been particularly seen in the states of Uttar Pradesh (UP), Madhya Pradesh (MP), Delhi and Karnataka. While in UP, 37 out of the 75 districts had large excess rainfall, 29 of them had no rains at all.
The numbers for MP are 23 (large excess) and 20 (no rain) districts out of the total 51 districts. Karnataka had 20 large excess districts and six no rain districts while Delhi had six large excess districts and three no rain districts.
The northeastern part of the country that is highly vulnerable to climate change, also received heavy rainfall during this period. Three out of four districts of Sikkim received large excess rainfall, as did four out of seven Meghalaya districts.
The rainfall in this region was more uniform, with both states having no districts with no rainfall.
A scientific report titled ‘Climate Vulnerability Assessment for the Indian Himalayan Region Using a Common Framework’, prepared by the Indian Institute of Technology, Guwahati, Indian Institute of Technology, Mandi and Indian Institute of Science, Bengaluru last year had pointed that the northeastern states are particularly vulnerable to climate change owing to the socio-economic conditions.
This is mainly due to factors like poor per capita income, limited crop insurance, few farmers taking loans and poor participation in rural job schemes.
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