southwest coast, southern peninsula and north-eastern India have experienced more than 2
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
(>2 events per decade), intensity and area under drought conditions in India by the end of the
twenty-first century under the RCP8.5 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.
At the end of the twenty-first century, steric sea level
5 in the NIO is projected to rise by
approximately 300 mm relative to the average over 1986–2005 under the RCP4.5 scenario,
with the corresponding projection for the global mean rise being approximately 180 mm.
Tropical Cyclones
There has been a significant reduction in the annual frequency of tropical cyclones over the
NIO basin since the middle of the twentieth century (1951–2018). In contrast, the frequency of
very severe cyclonic storms (VSCSs) 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 twenty-first 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 twenty-first century, the annual mean surface temperature over HKH is
projected to increase by about 5.2°C under the RCP8.5 scenario (Fig. 1). The CMIP5 projections under the RCP8.5 scenario indicate an increase in annual precipitation (Fig. 1), but
decrease in snowfall over the HKH region by the end of the twenty-first century, with large
spread across models.
Conclusions
Since the middle of the twentieth century, India has witnessed a rise in average temperature; a
decrease in monsoon precipitation; a rise in extreme temperature and rainfall events, droughts,
and sea levels; and an increase in the intensity of severe cyclones, alongside other changes in
the monsoon system. There is compelling scientific evidence that human activities have
influenced these changes in regional climate.
Human-induced climate change is expected to continue apace during the twenty-first
century. To improve the accuracy of future climate projections, particularly in the context of
5
Steric sea-level variations refer to changes arising from ocean thermal expansion and salinity variations.
xvi
Executive Summary
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
(>2 events per decade), intensity and area under drought conditions in India by the end of the
twenty-first century under the RCP8.5 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.
At the end of the twenty-first century, steric sea level
5 in the NIO is projected to rise by
approximately 300 mm relative to the average over 1986–2005 under the RCP4.5 scenario,
with the corresponding projection for the global mean rise being approximately 180 mm.
Tropical Cyclones
There has been a significant reduction in the annual frequency of tropical cyclones over the
NIO basin since the middle of the twentieth century (1951–2018). In contrast, the frequency of
very severe cyclonic storms (VSCSs) 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 twenty-first 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 twenty-first century, the annual mean surface temperature over HKH is
projected to increase by about 5.2°C under the RCP8.5 scenario (Fig. 1). The CMIP5 projections under the RCP8.5 scenario indicate an increase in annual precipitation (Fig. 1), but
decrease in snowfall over the HKH region by the end of the twenty-first century, with large
spread across models.
Conclusions
Since the middle of the twentieth century, India has witnessed a rise in average temperature; a
decrease in monsoon precipitation; a rise in extreme temperature and rainfall events, droughts,
and sea levels; and an increase in the intensity of severe cyclones, alongside other changes in
the monsoon system. There is compelling scientific evidence that human activities have
influenced these changes in regional climate.
Human-induced climate change is expected to continue apace during the twenty-first
century. To improve the accuracy of future climate projections, particularly in the context of
5
Steric sea-level variations refer to changes arising from ocean thermal expansion and salinity variations.
xvi
Executive Summary