Heatwaves will intensify four-fold by 2100 - govt report

The average temperature over India is projected to rise by approximately 4.4°C relative to the recent past (1976-2005 average) by the end of this century, in the worst-case scenario, says the first-ever climate change assessment report for India.

This would be four times the rise of around 0.7°C in average temperature during 1901–2018. The report, titled “Assessment of Climate Change over the Indian Region”, published by the Ministry of Earth Sciences, says that the rise in temperature is largely on account of GHG (greenhouse gas) induced warming, partially offset by forcing due to anthropogenic aerosols and changes in Land Use and Land Cover (LULC).

In the recent 30-year period (1986–2015), temperatures of the warmest day and the coldest night of the year have risen by about 0.63°C and 0.4°C, respectively. By the end of the 21st century, these temperatures are projected to rise by approximately 4.7°C and 5.5°C, respectively, relative to the corresponding temperatures in the recent past (1976–2005 average). By 2100, the frequencies of occurrence of warm days and warm nights are projected to increase by 55% and 70%, respectively, relative to the reference period 1976-2005.

The frequency of summer (April–June) heat waves over India is projected to be 3 to 4 times higher by the end of the 21st century, as compared to the 1976–2005 baseline period. The average duration of heat wave events is also projected to approximately double, but with a substantial spread among models.

In response to the combined rise in surface temperature and humidity, amplification of heat stress is expected across India, particularly over the Indo-Gangetic and Indus river basins.

Indian ocean warming

Sea surface temperature (SST) of the tropical Indian Ocean has risen by 1°C on average during 1951–2015, markedly higher than the global average SST warming of 0.7°C, over the same period. Ocean heat content in the upper 700 m (OHC700) of the tropical Indian Ocean has also exhibited an increasing trend over the past six decades (1955–2015), with the past two decades (1998–2015) having witnessed a notably abrupt rise. During the 21st century, SST and ocean heat content in the tropical Indian Ocean are projected to continue to rise.

Changes in rainfall

The summer monsoon precipitation (June to September) over India has declined by around 6% from 1951 to 2015, with notable decreases over the Indo-Gangetic Plains and the Western Ghats. There is an emerging consensus, based on multiple datasets and climate model simulations, that the radiative effects of anthropogenic aerosol forcing over the Northern Hemisphere have considerably offset the expected precipitation increase from GHG warming and contributed to the observed decline in summer monsoon precipitation. There has been a shift in the recent period toward more frequent dry spells (27% higher during 1981–2011 relative to 1951–1980) and more intense wet spells during the summer monsoon season.

Over central India, the frequency of daily precipitation extremes with rainfall intensities exceeding 150 mm per day increased by about 75% during 1950–2015. With continued global warming and anticipated reductions in anthropogenic aerosol emissions in the future, models project an increase in the mean and variability of monsoon precipitation by the end of the 21st century, together with substantial increases in daily precipitation extremes.

Drought

The overall decrease of seasonal summer monsoon rainfall during the last 6–7 decades has led to an increased propensity for drought over India. Both the frequency and spatial extent of droughts have increased significantly during 1951–2016. In particular, areas over central India, southwest coast, southern peninsula and north-eastern India have experienced more than two droughts per decade, on average, during this period.

The area affected by drought has also increased by 1.3% per decade over the same period. Climate model projections indicate a high likelihood of increase in the frequency (> two events per decade), intensity and area under drought conditions in India by the end of the 21st century under the worst case scenario, resulting from the increased variability of monsoon precipitation and increased water vapour demand in a warmer atmosphere.

Sea level rise

Sea levels have risen globally because of the continental ice melt and thermal expansion of ocean water in response to global warming. Sea-level rise in the North Indian Ocean (NIO) occurred at a rate of 1.06–1.75 mm per year during 1874–2004 and has accelerated to 3.3 mm per year in the last two and a half decades (1993–2017), which is comparable to the current rate of global mean sea-level rise.

Tropical cyclones

There has been a significant reduction in the annual frequency of tropical cyclones over the NIO basin since the middle of the 20th century (1951–2018). In contrast, the frequency of very severe cyclonic storms during the post-monsoon season has increased significantly (+1 event per decade) during the last two decades (2000–2018). However, a clear signal of anthropogenic warming on these trends has not yet emerged. Climate models project a rise in the intensity of tropical cyclones in the NIO basin during the 21st century.

Changes in the Himalayas

The Hindu Kush Himalayas (HKH) experienced a temperature rise of about 1.3°C during 1951–2014. Several areas of HKH have experienced a declining trend in snowfall and also retreat of glaciers in recent decades. In contrast, the high-elevation Karakoram Himalayas have experienced higher winter snowfall that has shielded the region from glacier shrinkage. By the end of the 21st century, the annual mean surface temperature over HKH is projected to increase by about 5.2°C. Projections indicate an increase in annual precipitation, but decrease in snowfall over the HKH region by the end of the 21st century, with large spread across models.

Source: Asia Insurance Review