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 ….

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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

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0

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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

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Flo

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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