Northwest India turned drier, south wetter over 70 years, finds IMD study

The IMD study found a strong regional contrast between 1951 and 2020. Northwest India became warmer and drier, so its hot semi-arid climate zone expanded. The temperate zone also shrank. Southern peninsular India moved in the opposite direction, recording higher overall rainfall and a broader wetter climate zone.

In northwest India, the hot semi-arid zone grew from about a quarter of the region in 1951-1980 to one-third in 1991-2020. The temperate zone fell from about a quarter to less than one-fifth. In the peninsula, the hot semi-arid zone declined from about 30% to 16%, while the tropical savannah zone expanded.

The shift was not only statistical. The dry zone, once ending in western Uttar Pradesh, extended farther east. The study also identified changes in Maharashtra and along the Konkan coast, coastal Karnataka and Kerala. The authors say these trends matter for farming, especially paddy cultivation and agricultural timing in northern India.

The article uses climate-zone labels but does not define them. In established climate science, a hot semi-arid zone is a warm region with relatively low rainfall and a long dry period. It is drier than areas where seasonal rainfall is more reliable, though it is not necessarily a desert.

A temperate zone generally has milder temperatures and stronger seasonal differences than a hot semi-arid zone. A tropical monsoon zone is warm throughout much of the year and receives substantial seasonal rainfall. A tropical savannah zone is also warm, but its rainfall is strongly seasonal and includes a pronounced dry period.

These categories help show long-term environmental change across large areas. In the study, northwest India’s expanding hot semi-arid zone signals declining rainfall and rising temperatures. In peninsular India, increased rainfall helped shrink the hot semi-arid zone and expand the tropical savannah zone, which covered three-quarters of the peninsula.

The study found sizable changes in the share of land assigned to different climate zones. In northwest India, the hot semi-arid zone grew from about a quarter of the region during 1951-1980 to one-third during 1991-2020. The temperate zone declined from about a quarter to less than one-fifth.

The researchers estimated that land equal to roughly 7% of northwest India moved into the drier zone. In peninsular India, the hot semi-arid zone contracted from about 30% of the region to 16%. Most of that area shifted into the tropical savannah zone, which now covers three-quarters of the peninsula.

These figures describe changes in climate-zone coverage, not a simple movement of land. They show how long-term temperature and rainfall patterns altered regional classifications. The study links northwest India’s shift to rising temperatures and declining rainfall, while it connects the peninsula’s wetter classification with increased rainfall.

The study found that India’s climate zones changed location as well as size. In northwest India, the hot, dry zone once ended in western Uttar Pradesh. By the later comparison period, it had extended eastward into the state, bringing a drier classification closer to eastern Uttar Pradesh.

Other shifts appeared across the country. Marathwada and west Vidarbha in Maharashtra moved into the hot semi-arid zone. The tropical monsoon zone extended along the Konkan coast, coastal Karnataka and Kerala. In peninsular India, much of the shrinking hot semi-arid area moved into the tropical savannah zone.

Geographically, the Uttar Pradesh change means the boundary between the dry zone and neighboring climate zones moved east. It does not mean the entire state became uniformly dry. It indicates that long-term local temperature and rainfall patterns increasingly matched the study’s hot semi-arid classification, with possible consequences for farming.

Paddy cultivation in northern India could face greater uncertainty as the region becomes warmer and drier. The study specifically warns that the eastward spread of the dry zone may affect paddy cultivation in Uttar Pradesh. It does not quantify crop losses, but it identifies agriculture as an important concern.

The key mechanism is the combination of rising temperatures and declining rainfall. Together, these changes alter the climate conditions that farmers depend on. If the seasonal pattern becomes less supportive of paddy, farmers may need to watch field conditions and rainfall more carefully when planning operations.

The authors particularly highlight the timing of sowing and harvesting. That does not prove that every farm must immediately change its schedule, but it shows why long-term climate monitoring matters. Farm-sector policymakers could use the findings when assessing agricultural planning in the affected parts of northwest India.

The study was conducted by scientists from the India Meteorological Department and the Indian Institute of Tropical Meteorology. Its findings were published in the IMD’s peer-reviewed journal Mausam. The researchers examined how India’s climate map changed over seven decades, from 1951 to 2020.

For the main comparison, they contrasted the periods 1951-1980 and 1991-2020. They also compared the map decade by decade across 1951-2020. In northwest India, the important signals were rising temperatures and declining rainfall. These trends matched the expansion of the hot semi-arid zone and the shrinkage of the temperate zone.

Southern India showed a different pattern. The study linked the peninsula’s changing classifications to rising overall rainfall. Its findings included a smaller hot semi-arid zone and a larger tropical savannah zone. The researchers also identified local shifts in Maharashtra and along parts of the western and southern coasts.

Climate zones summarize long-term patterns rather than one unusual season. A region can move into another classification when its sustained temperature and rainfall conditions increasingly resemble that zone. The article links northwest India’s change to rising temperatures and declining rainfall, and the peninsula’s change to rising overall rainfall.

The mechanism works through the balance between warmth and moisture. More heat combined with less rainfall supports a drier classification, such as hot semi-arid. Greater rainfall can support a wetter classification, even where temperatures remain warm. The study used these broad patterns to track shifts in India’s climate map over seven decades.

The article does not provide the exact thresholds or formula used for each classification. It does show the observed outcome: northwest India’s hot semi-arid area expanded, while peninsular India’s contracted. The authors’ decade-by-decade comparison indicates that these were long-term regional trends, not isolated weather events.