Talk Structure
1. Natural Disasters: human and
economic costs
2. Loss of wetlands
3. Mitigating physical impacts of floods,
droughts and storms
4. Coping with the aftermath
5. Nature Based Solutions/Green
engineering
6. Conclusion
The Toll of Natural Disasters
Between 1998 and 2017
• 1.3 million people killed
• 4.4 billion people injured,
homeless, displaced or in
need of assistance
• 91% of disasters due to
floods/storms
/droughts & other
extreme weather
events
The Economic Cost
Population growth and
economic development
means increasing nos. of
people and infrastructure are
exposed to hazards.
Early warning systems and
timely evacuations have
reduced loss of life but
economic losses continue to
grow.
Extreme weather events increasing in
intensity and frequency
Climate change and complexity of
disasters is creating “deep uncertainty”
More complex disasters are occurring
– induced by confluence of multiple
causes
Increasingly difficult to determine
which areas should prepare for what
kind of disaster
Climate Change
Disaster events in Asia-Pacific Region – average per decade
One of the strongest defences against
natural disasters are healthy ecosystems.
Ecosystem services are critical for
helping to achieve DRR.
This is recognized by Sendai framework
for Disaster Risk Reduction as well as the
Paris Agreement on climate change.
Environmental Degradation
Role of wetlands in mitigation
Wetlands can help mitigate natural
disasters in two ways:
• Reduce the immediate physical
impacts
• Help people survive and recover in the
aftermath
Ecosystem-based Disaster Risk Reduction (Eco-DRR)
the sustainable management, conservation, and restoration of ecosystems to reduce disaster risk, with the aim of achieving sustainable and resilient development (Estrella and Saalismaa 2013:30).
-
Wetland loss and
degradation
AFP – US Coast Guard
ABC Aust
Wetland loss and degradation continues ... an examination of the
extent and rates of loss and degradation provides cause for
concern … under global change it is likely to get more
difficult….
Review of wetland loss data
Davidson 2015. Marine and Freshwater Res
Widely reported that 50% of world’s wetlands had been lost (or
lost since 1900), but the origin of this figure was obscure
- came from USA in 1950s based on limited data;
widely used as a global figure without an evidence base
Davidson (2015): long-term loss averaged 54–57%, may have
been as high as 87% since 1700, where we have data
3.7 times faster rate of loss during the 20th & early 21st
centuries, with 64–71% loss since 1900, where we have data.
Loss has slowed in Europe & N America, still high in Asia
Wetland Extent Index
Approx 40% decline in wetland sites across the world in the
extent of both marine/coastal and inland wetlands over 40 years
Based on data from more than 1000 wetland sites globally
between 1970 and 2008. Regions and individual sites vary a lot
“Human-made” wetlands have increased, especially in southern
Asia due to conversion of natural wetlands into rice paddies, but
does not offset the losses in natural wetland area
Global Biodiversity Outlook-4 technical report 2014 & Dixon 2015
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Populations of many wetland- dependent
species are declining
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Friess et al 2019. Annual Review of Environment and Resources
Top 10 countries with mangrove loss between 2000 and 2012
By the 1980s land-use change was the predominant cause of mangrove loss. Suggested deforestation rates as high as 35% lost in the 1980s and 1990s. Cited rates of loss varied from 1 to 8% per year, although the accuracy is unknown due to lack of consistent methods.
Mangrove loss – 20th and early 21st Century
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Bunting et al 2018. Remote Sensing
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Wetlands play a critical role in providing ecosystem services
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Wetlands play a critical role in providing ecosystem services – trade-offs occur
between food and coastal protection and ….
H
Bunting et al 2018. Remote Sensing
Wetlands for Flood Protection
Role of wetlands in flooding varies
depending on location in the
catchment, antecedent conditions,
rainfall amount, distribution and
intensity and biophysical
characteristics of the catchment.
In many cases floodplains (provide
space for flood water) thereby
reducing downstream flow peaks and
attenuating flows.
Other (e.g. headwater wetlands) are
runoff generating areas and increase
flood peaks and flow
TEEB – inland wetlands provide regulating services of US$ 23,018 per year
Cherwell – Oxfordshire UK
97/98 Easter 98 Oct 2000
Current 20.7 59.5 25.0
Restored 18.6 (-10%) 52.3 (-12%) 20.9 (-16%)
Embanked 32.0 (+54%) 90.5(+52%) 63.3 (+153%)
floodplain restoration… can be
a valuable part of a
catchment’s flood
management strategy.
Easter 1998
Zambezi – Southern AfricaLuswishi Floodplain
0
20
40
60
80
100
120
1-O
ct-8
0
1-N
ov-
80
1-D
ec-
80
1-Ja
n-8
1
1-Fe
b-8
1
1-M
ar-8
1
1-A
pr-
81
1-M
ay-8
1
1-Ju
n-8
1
1-Ju
l-81
1-A
ug-
81
1-Se
p-8
1
1-O
ct-8
1
1-N
ov-
81
1-D
ec-
81
1-Ja
n-8
2
1-Fe
b-8
2
1-M
ar-8
2
1-A
pr-
82
1-M
ay-8
2
1-Ju
n-8
2
1-Ju
l-82
1-A
ug-
82
1-Se
p-8
2
Flo
w (m
3s-1
)
Daily flow with and without floodplain: HY1984-1985
Without floodplain (simulated) With floodplain (observed)
0
20
40
60
80
100
120
140
1 10 100
Pe
ak fl
oo
d f
low
(m
3s-1
)
Return period (yrs)
Flood Frequency
With floodplain (observed) Without floodplain (simulated)
Extrapolated
Return
Period (yrs)
Flood peak (m3s-1)
With
floodplain
Without
floodplain
2 47 73
10 65 105
25 71 115
50 75 122
100 79 128
200 82 133
Colombo’s Wetlands
• Colombo is a city built around wetlands
(Colombo Wetland Complex)
• Hydrological catchment is 227 km2
• Wetlands cover of 20 km2 in the CMR
but declining due to landfill and waste
disposal
• Reduce urban flooding – store 39% of
flood waters.
• 232,000 people - greater flood
protection
• Save 1% of the CMR’s GDP loss
Precipitation
P E
QO
QI
Interfluve
Clay
Evapotranspiration
OUTFLOW
INFLOW
DAMBO
Upland wetlands Dambo flood function varies
seasonally:
• reduce runoff (attenuate floods)
prior to saturation
• promote runoff (enhance
floods) once saturated
Andes – runoff from high alpine
grassland wetlands increases with
areal extent of wetlands
Event Rainfall (mm)
Total flowQtot (mm)
Old water (Qo) (mm)
New water (QN) (mm)
QN/P(%)
QN/Qtot(%)
26/01/96 35.1 10.63 3.17 7.46 21.3 70.2
09/02/96 18.6 2.66 1.74 0.92 4.95 34.7
Isotope analyses from a dambo in Zimbabwe
Wetlands for drought mitigation
Flow maintenance during dry
seasons and droughts
Many wetlands perceived to act as
“sponges” filling in the wet season
and releasing water slowly in the
dry season.
Many wetlands perceived to
recharge groundwater
Dambos, Southern Africa
Zimbabwe legislation to prevent their
use for agriculture because they are
the “source” of dry season flow.
Considerable volumes of water
stored in the wetland at the end of
the wet season but only small
proportion (12%) converted to flow.
Depletion is primarily through
evapotranspiration.
BFI 1-day minimum (m3s-1)
10-day minimum(m3s-1)
With wetlands 0.284 0.12 0.13
Without wetlands 0.444 0.24 0.27
Muchindamu River in Zambia (area of wetlands = 10% of the catchment)
GaMampa, South Africa
Perception – the wetland is the source of very
important dry season river flow.
Reality – the wetland itself contributes little to
the dry season river flow. The flow is
maintained by groundwater from the
undisturbed upper catchment.
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
22
-Ju
n-0
6
2-J
ul-0
6
12
-Ju
l-06
22
-Ju
l-06
1-A
ug-
06
11
-Au
g-0
6
21
-Au
g-0
6
31
-Au
g-0
6
Flo
w (
m3s-1
)
Flow measured upstream of the wetland Flow measured at B7H013
Max – slides on coastal wetlands for coastline protection (4 slides?)
Urban development – mangrove coastlines
Wetlands and coastline protection
Wetlands and coastline protection
Industrial / port development – salt marsh and reedbeds
Max – slides on coastal wetlands for coastline protection (4 slides?)
Wetlands and coastline protection
Port & urban development – estuaries and deltas
Max – slides on coastal wetlands for coastline protection (4 slides?)
Water flows - Barrages & drought – coastal lakes and lagoons
Wetlands and coastline protection
Mangroves and Climatic Fluctuations
Dieback of mangroves along northern
Australian coastline in 2015/2016 ca.
10,000 ha
Concerns about the impact of climate-
related phenomena on the long-term
integrity and viability of this ecosystem
Primary drivers of change are:
fluctuations in sea level, rising
temperatures, changes in rainfall &
inundation
Wetlands role in coping with the aftermath of natural disasters
• Importance of social capital to post disaster
recovery is widely recognized but there is much
less recognition of the role of environmental
capital.
• When roads and communication networks are
disrupted and government services are
overstretched, wetlands can provide food, water
and building materials in the immediate aftermath
(survival stage) of natural disasters.
• Long term recovery is also assisted by healthy
ecosystems.
• Natural capital is a “pillar” in the recovery process
Principals:
• Protect/restore the full hydraulic response of
landscapes/catchments damaged by farming and other human
activities – increase infiltration, reduce rapid runoff, increase water
storage (above and below ground).
• Re-establish and restore the natural functions of rivers, floodplain,
mangroves and other wetland environments but with full
(quantified) understanding of the implications for hydrology.
• Engineer “naturalistic” DRR measures with an emphasis on small-
scale, locally managed features as an alternative, or in tandem
with, built infrastructure (e.g. dams and walls).
Nature Based Solutions/Green engineering
Making Space for the River Instead of ever-increasing the height of
dikes, remove them and reconnect
floodplains.
Really a form of improved spatial
planning – a return to a more natural
river system
Netherlands – USD 2.85 billion to
manage water in a “different way”
Not just a technical innovation – often
requires new legislation, new forms of
inter-organizational collaboration, new
forms of public-public and public-
private coordination and new forms of
governance
Wallingford, UK
Mississippi, USA
Harvesting floods
well
recharge structure
irrigation
city+ +
++++
+
++++
+
flood prone
sea
+
diversions
Wet Season – without UTFI
Dry Season – with UTFIWet Season – with UTFI
Plan View– with UTFI
Hybrid approaches for coastal defense
Hybrid engineering approaches:
link 'soft' ecosystem-based approaches
(green) with 'hard' infrastructure approaches
(gray) to enhance the resiliency of coastal communities/shorelines.
Conclusions
• As a consequence of climate change, the frequency of natural disasters
(droughts, floods, storms) is likely to increase in the future
• Wetlands are not a panacea for mitigating the human impacts of these
disasters. Sometimes they help mitigate impacts, but sometimes they do not.
• For any location we need to understand the context specific role that
wetlands play. Much more research is needed including the trade-offs that
are occurring in coastal zones with the conversion of wetlands such as
mangroves in favour of other land uses.
• Often the best solutions for mitigating the impacts of disasters are through a
mix of soft (green) and hard (grey) engineering also often in conjunction with
non-physical interventions (awareness, warning systems, insurance,
managed retreats etc.)
Thank you