North India getting hotter, drier; South wetter: IMD study maps 70 years of climate shift

The IMD study found a clear north–south contrast from 1951-1980 to 1991-2020. Large parts of North India became hotter and drier, while peninsular India became wetter. These changes shifted the boundaries of major climate zones.

In Northwest India, the hot semi-arid zone grew from about 25 per cent to nearly 33 per cent of the region. The temperate zone fell from about a quarter to less than a fifth. In peninsular India, the hot semi-arid zone dropped from around 30 per cent to 16 per cent, with much of that land entering the tropical savannah zone.

The study links the northern shift to rising temperatures and declining rainfall. The drier zone moved eastward from western Uttar Pradesh into eastern Uttar Pradesh. Researchers say this matters especially for agriculture, because farming schedules may need close monitoring as conditions change.

A hot semi-arid climate zone is a region that stays hot but receives low rainfall. In the study, it represents the drier category among the four major zones examined. Its expansion can signal a shift toward hotter, less rainy conditions.

A tropical monsoon climate is different because it is the wettest zone in the study. It receives heavy seasonal rain, rather than the low rainfall associated with a hot semi-arid climate. The two zones therefore differ mainly in their rainfall levels and seasonal rainfall pattern.

The distinction helps researchers track changing climate boundaries. In Northwest India, more land entered the hot semi-arid category. In peninsular India, much of the shrinking hot semi-arid area shifted into the tropical savannah zone, which has warm conditions and a long dry season. The article does not report a major tropical monsoon-area change.

The northern expansion was substantial. In Northwest India, the hot semi-arid zone covered about 25 per cent of the region during 1951-1980. By 1991-2020, it covered nearly 33 per cent, an increase of roughly eight percentage points.

The peninsula moved in the opposite direction. Its hot semi-arid zone covered around 30 per cent during the earlier period but only 16 per cent during 1991-2020. Most of the area that left this category shifted into the tropical savannah zone, which now covers three-fourths of peninsular India.

These figures show that climate-zone change was not uniform across the country. Northwest India became more strongly represented by the hot, dry category. Peninsular India saw that category contract, alongside wetter conditions. The study attributes the northern shift to rising temperatures and declining rainfall.

The study connects the eastward movement to two linked changes: rising temperatures and declining rainfall in northern India. Together, they made parts of the region more like the hot semi-arid zone, which is defined by hot conditions and low rainfall.

Earlier, the dry zone ended around western Uttar Pradesh. In the 1991-2020 climate map, it had pushed farther east into eastern Uttar Pradesh. This was part of a wider expansion in Northwest India, where the zone grew from about 25 per cent of the region’s area to nearly 33 per cent.

The shift matters because Uttar Pradesh is one of India’s most important farming regions. IMD scientist Ananya Karmakar said the timing of sowing and harvesting needs close monitoring. The article identifies the climate drivers, but it does not provide separate temperature or rainfall figures for western and eastern Uttar Pradesh.

Hotter and drier conditions can change the climate conditions farmers use to plan crops. In northern India, the study therefore highlights the timing of sowing and harvesting as something that needs close attention. The concern is especially important in major farming areas.

The clearest example is Uttar Pradesh. The hot, dry zone, once ending around western Uttar Pradesh, has moved east into eastern Uttar Pradesh. This shift reflects rising temperatures and declining rainfall, conditions that can alter the seasonal environment in which crops grow.

The article does not quantify changes in crop yields or prescribe new farming dates. It reports a need for monitoring. Lead author Ananya Karmakar said the timing of sowing and harvesting should be watched closely as the climate map changes. The study therefore points to agricultural scheduling as a key area for attention.

Researchers compare 30-year periods because climate is measured through long-term patterns, not just individual hot, cold, wet, or dry years. A single year or season can be unusual. A longer period gives a steadier picture of typical temperature and rainfall conditions.

The IMD study used successive 30-year climatological periods, from 1951-1980 to 1991-2020. It then compared the climate zones mapped from each period. This approach showed persistent changes, such as the expansion of the hot semi-arid zone in Northwest India and its contraction in the peninsula.

The method matters because climate-zone boundaries should reflect sustained conditions. The study found that the dry zone had moved east into eastern Uttar Pradesh, rather than merely recording one unusual season there. The article does not explain the researchers’ method in detail, but 30-year climate periods are designed to smooth short-term variation.

The article identifies rainfall seasonality as a key feature of India’s climate zones. Tropical monsoon areas are the wettest and receive heavy seasonal rain. Tropical savannah areas are warm year-round but have a long dry season, while hot semi-arid areas have low rainfall.

This means the monsoon helps distinguish wetter and drier regions through the amount and timing of rainfall. When long-term rainfall conditions change, an area may fit a different climate category. The study found more hot semi-arid land in Northwest India and more tropical savannah land in the peninsula.

The article also reports rising temperatures in the north and wetter conditions in peninsular India. Together, temperature and rainfall patterns determine where climate-zone boundaries appear. However, the article does not explain the monsoon’s physical processes or quantify its direct contribution to each regional shift.