Increasing risks and challenges of compounding floods in a changing climate
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Increasing risks and challenges
of compounding floods
in a changing climate
International Conference
on Flood Management
Roxy Mathew Koll
Centre for Climate Change Research
Indian Institute of Tropical Meteorology
Ministry of Earth Sciences
People on the coastal flood plain Neumann et al. 2015; LECZ = low-elevation coastal zone
May 2021 — cyclone rains that caused floods IMD rain map merged with Cyclone Tracks
Compound events during a Cyclone
Cyclone Tauktae
220 km/hr
Compound Flood
= storm surge/waves + rain water + river water
+
sea level rise + high tide
Cyclone Yaas
110 km/hr
Number of cyclones are increasing in the Arabian Sea
1982-2000 2001-2019
50% more
Deshpande et al. 2021
Compound events during a Cyclone — Waves and storm surges
Mumbai
NIOT/INCOIS
Compound events during a Cyclone — Rainfall
100% more
Harikrishnan, Roxy et al. 2021
Monsoon Extremes/Floods are also increasing
While the total monsoon rainfall is
decreasing, number of extreme rains
(above 150 mm/day) are increasing
225 0. 8
E xtreme R ain E vents
n ts
Mean R ainfall
195 E ve
0. 4
R ai n
m e
tr e
165 Ex
0. 0
Mea
135 n Ra
i nf a l
l
(mm day -1)
-0. 4
105
Roxy et al. 2017
75 -0. 8
1950 1970 1990 2010
Roxy, Ghosh et al. 2017
Sea Level Rise Collins et al. IPCC SROCC 2019; Beal et al. BAMS 2019
Sea Level Rise
During the 20th century, the global Rate of
mean sea level rose by about 15cm. Sea Level Rise
Sea level is currently rising
more than twice as fast and
will further accelerate
reaching up to 1.10 m in 2100
if emissions are not sharply
reduced.
Many low-lying coastal cities and small Sea Level Rise at 3-6 cm per decade
islands will be exposed to risks of
flooding and land loss annually by 2050, Sea level changes are not uniform,
especially without strong adaptation. some regions show more sea level rise
than others.
Reason: Non-uniform ocean warming.
Sea level changes happen due to
melting ice/glaciers and ocean
warming.
Water expands as it warms
Panickal et al. Climate Change Report 2020; Collins et al. IPCC SROCC 2019; Beal et al. BAMS 2019Compound Events
Sea level rise, storm surge, heavy
rains, and a flooded river can overlap
and damage a city and its outlying
regions
Collins et al. IPCC SROCC 2019; AGU/EosPopulation rise is a threat multiplier
We always forget to add that the
population of coastal cities is
increasing.
Increasing exposure due to the rising
population is one of the most important
causes for losses due to increased
vulnerability to climate change.
Mumbai population
= 21 Million in 2021 and 42 million in
2050.
Collins et al. IPCC SROCC 2019; AGU/EosPopulation is a threat multiplier Neumann et al. 2015
Way forward
§ The Indian Ocean will continue to warm in the future churning off
more cyclones and floods along the west coast.
§ We can't wait for these forecasts to evacuate people every year.
§ We can't evacuate ecosystems, infrastructure, houses, and cars.
§ We need a long-term vision. We need a coastal risk assessment
considering the compound extremes and risks.How do we monitor and forecast these changes? Beal et al. BAMS 2020; Hermes et al. Frontiers in Marine Science 2019
Regional Partnership There is a need for increased investment and stronger partnerships with Indian Ocean rim countries and end-users, along with improved data sharing and commitments to best practices. Beal et al. BAMS 2020; Hermes et al. Frontiers in Marine Science 2019
Some of the collaborators in this work
Climate Research Lab @ IITM Indian Ocean Network
IPCC Team
UN Decade of Ocean
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