Rising temperatures and falling rainfall driven by a lesser-known oceanic phenomenon are causing climatic shifts in several parts of India, says a research paper by scientists at the India Meteorological Department (IMD) and the Indian Institute of Tropical Meteorology (IITM), published this month.
For the analysis, the team sorted India into climate types based on temperature and rainfall thresholds. The steppe zone’s eastern edge moved from west Uttar Pradesh to eastern part of the State. While the Indian subcontinent is used to the effects of El Niño — a warming of the Central Pacific and linked to the shrinking of the southwest monsoon — previous studies have found that most VM events were followed by El Niño events. The MAUSAM study, however, doesn’t explicitly link the VM to El Niño.
The study found that in north-west India, the hot, semi-arid steppe zone grew from 25.7% of the region’s area in 1951-80 to 33.1% in 1991-2020, while the milder temperate zone shrank from 25.8% to 18.7%. In peninsular India, the hot semi-arid steppe zone fell from 30.3% of the region’s area in 1951-80 to 16.4% in 1991-2020. Tropical savannah rose from 61.6% to 75.7%.
Konkan and Goa, coastal Karnataka, and Kerala and Mahe saw their tropical monsoon zones expand, according to the paper published in the latest edition of MAUSAM , the in-house journal of the IMD.
The Pacific Decadal Oscillation (PDO) correlates negatively with Indian monsoon rainfall, like the El Nino-La Nina cycle. Studies have shown that when the El Niño Southern Oscillation and the PDO are in phase, they reinforce the usual El Niño-monsoon link, and when out of phase, they offset each other. The globe is currently in the grip of one of the strongest El Niños in history and it has shrunk India’s monsoon rainfall this year by 12%. For the study, the scientists first sorted India into climate types, applied them to the IMD’s gridded records on 0.25-degree squares, roughly 25 km across. They repeated this for five 30-year windows, each starting a decade after the last, and tracked how the map changed.
