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
twenty-first 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), under the RCP8.5 scenario.
By the end of the twenty-first century, the frequencies of occurrence of warm days and
warm nights
4 are projected to increase by 55% and 70%, respectively, relative to the reference
period 1976-2005, under the RCP8.5 scenario.
The frequency of summer (April–June) heat waves over India is projected to be 3 to 4 times
higher by the end of the twenty-first century under the RCP8.5 scenario, 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 twenty-first century, SST (Fig. 1) 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. The frequency of localized heavy precipitation occurrences has increased
worldwide in response to increased atmospheric moisture content. 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, CMIP5 models project an increase in the mean (Fig. 1) and variability
of monsoon precipitation by the end of the twenty-first century, together with substantial
increases in daily precipitation extremes.
Droughts
The overall decrease of seasonal summer monsoon rainfall during the last 6–7 decades has led
to an increased propensity for droughts over India. Both the frequency and spatial extent of
droughts have increased significantly during 1951–2016. In particular, areas over central India,
4
Warm days (nights) correspond to cases when the maximum (minimum) temperature exceeds the 90th
percentile.
Executive Summary
xv
night of the year have risen by about 0.63°C and 0.4°C, respectively. By the end of the
twenty-first 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), under the RCP8.5 scenario.
By the end of the twenty-first century, the frequencies of occurrence of warm days and
warm nights
4 are projected to increase by 55% and 70%, respectively, relative to the reference
period 1976-2005, under the RCP8.5 scenario.
The frequency of summer (April–June) heat waves over India is projected to be 3 to 4 times
higher by the end of the twenty-first century under the RCP8.5 scenario, 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 twenty-first century, SST (Fig. 1) 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. The frequency of localized heavy precipitation occurrences has increased
worldwide in response to increased atmospheric moisture content. 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, CMIP5 models project an increase in the mean (Fig. 1) and variability
of monsoon precipitation by the end of the twenty-first century, together with substantial
increases in daily precipitation extremes.
Droughts
The overall decrease of seasonal summer monsoon rainfall during the last 6–7 decades has led
to an increased propensity for droughts over India. Both the frequency and spatial extent of
droughts have increased significantly during 1951–2016. In particular, areas over central India,
4
Warm days (nights) correspond to cases when the maximum (minimum) temperature exceeds the 90th
percentile.
Executive Summary
xv