The North Eastern region continues to reel under heavy rainfall triggered by remnants of Cyclone Remal. While the hilly state of Mizoram has witnessed multiple landslides, Manipur's Imphal has experienced one of the worst floods in recent times. Notably, the heavy rainfall came just days after various parts of the North East experienced their hottest day ever with maximum temperatures crossing 40 degrees Celsius last week. Much like the rest of the world, the North East is also witnessing a rise in annual temperatures over the years. Here is a look at how the temperatures have risen, why they have been rising, and what can happen in the future. But first, how hot did it get last week in the North East? While temperatures were hitting highs throughout the week, they reached their peak on May 25 when the India Meteorological Department (IMD) reported that four out of its 18 stations in the North Eastern region recorded their highest-ever maximum temperatures: Lumding in Assam at 43 degree Celsius, Silchar in Assam at 40 degree Celsius, Itanagar in Arunachal Pradesh at 40.5 degree Celsius, and Passighat in Arunachal Pradesh at 39.6 degree Celsius. Four other stations across Assam and Arunachal Pradesh recorded their highest-ever maximum temperatures for the month of May. What was even more striking was how steep the departure of these temperatures from the normal temperature at this time of the year was. It was more than 6 degrees hotter than normal in 12 of these stations. In Passighat, the departure was 9.3 degrees; in Guwahati, Dibrugarh, Tezpur, Silchar and North Lakhimpur in Assam, the departure was over 8 degrees Celsius. The anomalies – or differences between actual maximum temperatures and normal temperatures – were far steeper in this region than in other parts of India. According to Dr Partha Pratim Gogoi, Assistant Professor in Geology at Assam’s Dimoria College and climate researcher, the entire North Eastern region is showing a higher rate of rise in temperature compared to the rest of the country. How have temperatures gradually increased in the North East over the years? Last week’s spike in temperatures is in line with how mercury has been rising across the region over the years. In the eight states of the North East — Arunachal Pradesh, Assam, Manipur, Meghalaya, Mizoram, Nagaland, Sikkim, and Tripura — average annual mean temperatures have increased by between 0.67 and 1.06 degree Celsius during the period 1901-2023, according to the IMD data. Nagaland has seen the highest rise in annual mean temperatures — 1.06 degree Celsius — and Meghalaya has seen the lowest — 0.67 degree Celsius — for the period. There has also been a moderate warming of summer maximum and winter minimum temperatures between 1990 and 2019, according to the 2022 study, ‘District-Level Changes in Climate: Historical Climate and Climate Change Projections for the North-Eastern States of India, by Vidya S and Indu K Murthy of the Center for Study of Science, Technology and Policy (CSTEP), an Indian think-tank based in Bengaluru. For instance, Arunachal Pradesh has experienced a warming of 0.16 degree Celsius to 0.27 degree Celsius in the summer maximum temperature and 0.15 degree Celsius to 0.33 degree Celsius in the winter minimum temperature during the period. The region saw record-breaking temperatures in 2023 as well. The worst affected state was Sikkim — the average annual temperature (24.75 degree Celsius) during 2023 was 1.77 degree Celsius warmer than its Long Period Average (LPA) for the period 1981-2010, making it the warmest year on record for the state since 1901. Last year was also the warmest year ever for Manipur, Meghalaya, Mizoram, and Tripura. Why are temperatures increasing? The primary reason for the increase in temperatures is the rise of greenhouse gas (GHG) emissions across the world. Since the Industrial Revolution, human activities like burning fossil fuels have been releasing heat-trapping GHGs such as carbon dioxide and methane at unprecedented levels, leading to global warming. The planet as a whole has become at least 1.1 degree Celsius warmer than the average of the 1850-1900 period. The Indian subcontinent has witnessed a spike of 0.7 degree Celsius in the annual mean temperatures since 1900. El Niño — an abnormal warming of surface waters in the equatorial Pacific Ocean — also contributed to the record-breaking temperatures seen last week, according to Dr Rahula Mahanta, director of the Interdisciplinary Climate Research Center in Assam’s Cotton University. The weather pattern is known for triggering extreme heat in many parts of the world and the ocean. A decrease in the tree cover across the region could have also played a role. Gogoi said, “Other local factors could be related to land use, land cover change which results in changes in the surface characteristics. For example, if there is a wetland and we have eradicated it and built buildings and infrastructure on it, we are feeling the heat more because absorption is more”. What happens next? The situation is expected to get worse. Researchers believe that if GHG emissions are not radically and quickly curbed, temperatures will soon breach the 1.5 degree Celsius threshold, which was established in the 2015 Paris Agreement. In the North East, temperatures can reach 1.5 to 2 degrees above the pre-industrial levels by 2035-2040, according to Dr NH Ravindranath, retired Professor from Indian Institute of Science Bangalore’s Centre for Sustainable Technologies. The rise in temperatures would lead to an increase in rainfall. Higher temperatures cause evaporation of water not only from land but also oceans and other water bodies, meaning a warmer atmosphere holds more moisture. Experts suggest for every 1 degree Celsius rise in average temperature, the atmosphere can hold about 7% more moisture. This makes storms more dangerous as it leads to an increase in precipitation intensity, duration and/or frequency, which ultimately can cause severe flooding. “Rainfall could increase by 15 to 20-25% even in the next 15-20 years… More rain is always good if it is evenly distributed over June July August September. But our studies show high intensity rainfall events of more than 50 mm per day or 100 mm per day will increase. That means that there will be high intensity, flood, damage causing rain events more and more in the coming years,” Dr Ravindranath said. Some of the region’s states are already facing increased rainfall and floods. For example, Manipur is currently witnessing its worst flooding in about a decade, Dr Ravindranath said. Mizoram, Assam and Arunachal Pradesh are amongst the most “vulnerable” to climate risks. The 2019 Government of India study, ‘Climate Vulnerability Assessment for Adaptation Planning in India Using a Common Framework’ carried out by IIT Mandi and Guwahati and IISc Bangalore stated that “vulnerability” “represents the propensity or predisposition of the system to be adversely affected, independent of hazard and exposure.”
