Impacts of severe weather: Chasing resilience for NZ

Submission to the Economic Development, Science and Innovation Select Committee, Parliament

November 2018

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Prepared by: R.G. Bell

For any information regarding this report please contact:

Rob Bell Programme Leader Hazard Impacts and Risk +64-7-856 1742 rob.bell@niwa.co.nz

National Institute of Water & Atmospheric Research Ltd

PO Box 11115

Hamilton 3251

Phone +64 7 856 7026

NIWA CLIENT REPORT No: 2018315HN Report date: November 2018 NIWA Project: CANC1902, CAVA1904

Quality Assurance Statement

Reviewed by:

Dr Sam Dean, Chief Scientist for Climate and Weather Hazards

Formatting checked by: Alison Bartley

Approved for release by:

Dr Sam Dean, Chief Scientist for Climate and Weather Hazards

Front cover: Foxton flooding, February 2004. [Alan Blacklock, NIWA]

Contents

1 NIWA and its role in severe weather impacts .............................................................. 5

1.1 Statement of Core Purpose ...................................................................................... 5

1.2 NIWA’s mission ......................................................................................................... 5

1.3 Qualifications (Dr Rob Bell) ....................................................................................... 6

2 Aotearoa-New Zealand: Context for severe weather events ........................................ 7

2.1 Severe weather hazards ........................................................................................... 7

2.2 Geographic context ................................................................................................... 7

2.3 Economic activities sensitive to severe weather and health & safety ..................... 7

3 Risk from severe weather events ................................................................................ 8

3.1 Risk ............................................................................................................................ 8

3.2 Historical development ............................................................................................. 8

3.3 Civil Defence and Emergency Management context ................................................ 9

4 Weather-related civil-defence declarations and insurance costs .................................. 9

4.1 Civil defence declarations since 1967 ....................................................................... 9

4.2 Insured costs since 1967 ......................................................................................... 10

5 Historic Weather Events catalogue (HWE) ................................................................ 11

5.1 Background ............................................................................................................. 11

5.2 Snapshot of results ................................................................................................. 12

6 RiskScape ................................................................................................................ 14

7 National coastal risk exposure study (2015) .............................................................. 16

8 Looking forward....................................................................................................... 16

8.1 Changing climate and weather ............................................................................... 16

8.2 Climate change attribution for recent severe weather events .............................. 17

8.3 Paradigm shift needed to reduce future risks to severe weather .......................... 17

Figures

Figure 4-1: Number of weather-related emergency declarations across regions in NZ since 1967 (52 years) with main causes categorised as flooding or “other” contributing hazard. 10

Figure 4-2: Annualised insured costs (bars) for weather-related events in NZ since 1968 (ex TC Gisele) in terms of 2018 NZ$. 11

Figure 5-1: The main contributing hazard to the number of severe weather events in the NIWA HWE catalogue by region. 13

Figure 5-2: Time series of the number of severe weather events that are classified as predominantly floods in the NIWA HWE catalogue per region each year. 14

Figure 6-1: The RiskScape framework overlays hazard exposure layers on various assets with different vulnerabilities to derive impacts, people affected, damage and some categories of economic losses. 15

Figure 7-1: Nation-wide coastal risk exposure for low-lying land no higher than 0.5 metres above spring high tide. 16

Severe weather: Damage and economic losses 5

1 NIWA and its role in severe weather impacts The National Institute of Water & Atmospheric Research (NIWA) – Taihoro Nukurangi is a Crown

Research Institute (CRI) wholly owned by the Crown equally through two shareholding cabinet

ministers appointed by the New Zealand Government and governed by a Crown-appointed Board of

Directors.

CRIs are subject to the Crown Entities Act 2004, the Crown Research Institutes Act 1992, and the

Companies Act 1993.

The Shareholders' expectations of NIWA are contained in the Statement of Core Purpose that defines

our purpose, expected outcomes, scope of operation, and operating principles. This Statement of

Corporate Intent (SCI) sets out NIWA's strategy for delivering against this core purpose over the next

five years. The SCI is reviewable annually.

NIWA has 679 staff and revenue (2018) of $151M.

1.1 Statement of Core Purpose

NIWA will fulfil its purpose through the provision of research and transfer of technology and

knowledge in partnership with key stakeholders including industry, government and Māori:

• Increase economic growth through the sustainable management and use of aquatic

resources.

• Grow renewable energy production through developing a greater understanding of

renewable aquatic and atmospheric energy resources.

• Increase the resilience of New Zealand and South-West Pacific islands to tsunami and

weather and climate hazards, including drought, floods and sea-level change.

• Enable New Zealand to adapt to the impacts and exploit the opportunities of climate

variability and change and mitigate changes in atmospheric composition from greenhouse

gases and air pollutants.

• Enhance the stewardship of New Zealand’s freshwater and marine ecosystems and

biodiversity.

• Increase understanding of the Antarctic and Southern Ocean climate, cryosphere, oceans

and ecosystems and their longer-term impact on New Zealand.

The relevant core purposes in relation to severe weather impacts and risk are outlined above in bold.

1.2 NIWA’s mission

NIWA’s mission is to conduct leading environmental science to enable the sustainable management

of natural resources for New Zealand and the planet.

To accomplish that mission, NIWA operates its research and consultancy activities and outreach

primarily through three key platforms:

1. Climate and Weather Hazards.

6 Severe weather: Damage and economic losses

2. Marine Environment.

3. Freshwater Environment.

Most of the research and consultancy projects addressing the analysis, prediction and forecasting of

severe-weather exposure and risk are undertaken within the Climate and Weather Hazards platform

at NIWA.

I present this submission on behalf of colleagues from within NIWA who have contributed material

and developed databases, methodologies, tools and forecasting systems to assist in understanding

past events and predicting future impacts and forecasting weather exposure (e.g., RiskScape, NIWA-

Weather, Historic Weather Events catalogue, NZ Climate Database).

1.3 Qualifications (Dr Rob Bell)

I hold the position of Programme Leader: Hazard Impacts & Risk at NIWA, which I have held since

2012. I have also held a range of coastal-related positions at NIWA since 1992, and former

Government agencies, DSIR and Ministry of Works & Development, since 1980.

In 1980 I was awarded a Doctor of Philosophy (PhD) degree in Civil Engineering from the University of

Canterbury, focused on river sediment transport during floods.

I have 38 years’ experience in the field of coastal and environmental engineering and natural hazards

and risk, focusing in the last decade, on coastal climate-change risks and adaptation.

As founding co-leader of RiskScape over a decade ago, I managed the development of both the

RiskScape system and the Historic Weather Events (HWE) catalogue, which I draw on for this

submission.

Severe weather: Damage and economic losses 7

2 Aotearoa-New Zealand: Context for severe weather events

2.1 Severe weather hazards

Severe weather impacts can arise as a single contributing weather-related hazard (e.g., hail) through

to compound hazard events, where several hazards may combine to generate adverse impacts (e.g.

hail and flash flooding).

The main types of severe weather events are:

• High or intense rainfall leading to urban flash flooding or river floods and can trigger

landslides.

• Storms (mid-Tasman lows, Southern Ocean fronts, ex tropical cyclones, localised convective

systems) that generate compound hazards such as rainfall, high winds, tornadoes, lightening,

hail storm surge and waves/swell.

• Extended periods of drought where evapotranspiration exceeds rainfall through persistent

hot weather and winds.

• Snow falls and subsequent flooding or freeze-overs.

The varying time scales, intensities and presence of compound hazards in the make-up of a severe

weather event makes it difficult to consistently quantify damage and financial losses from weather-

related events and therefore predict the risk ahead of time.

2.2 Geographic context

Aotearoa-New Zealand (A-NZ) straddles a wide of latitudes from north to south ranging from the

sub-tropics (34°S) to the roaring forties and the sub-Antarctic islands of the Southern Ocean (53°S).

Our country is enveloped by wide expanses of the SW Pacific Ocean, creating a strong maritime

influence on our weather and exposure to storms, tropical cyclones, wind and swell from long

fetches. On the other hand, the wide-open expanse of ocean around New Zealand with Cook Strait

providing a safety valve between the main Islands means storm surges from wind setup and low-

pressure systems seldom reach above 1 m around the open coast. Cook Strait also acts as a wind

funnel contributing to severe weather in the Wellington, Wairarapa and Marlborough regions.

The steeply rising Southern Alps along the spine of the South Island (Te Wai Pounamu) also

significantly influence weather patterns including the foehn lee-wind effect from the predominant

south-westerly airstream. The Alps also contribute to severe weather through intense rainfall

(windward slope and headwaters of Canterbury/Otago rivers), extended periods of dry conditions on

the lee side, strong turbulent lee-slope winds (westerly or SE winds) and heat waves in

Canterbury/Otago.

2.3 Economic activities sensitive to severe weather and health & safety

New Zealand’s main economic sectors, such as primary production (agriculture, horticulture,

viticulture, fisheries, aquaculture, forestry) and tourism are moderately to highly sensitive to severe

weather, including prolonged droughts for the primary sector. The Māori economy, which relies

substantially on the primary production, is similarly susceptible to severe weather events.

8 Severe weather: Damage and economic losses

Transport is another sector that is susceptible to risk from severe weather events e.g., ferry services,

flight disruptions, and landslips, flooding or bridge failure causing road impassibility.

In general, most infrastructure and utility services, especially on or above ground, have inherent

criticalities that are often triggered by severe weather events e.g., wind-blown trees or snow/ice that

brings down power transmission lines.

By global standards, New Zealand has a high rate of insurance penetration both from the private

sector and EQC, which covers landslides and flood damage to land (not buildings and contents)

subject to certain conditions. In particular, floods are generally covered under comprehensive private

insurance for building owners (compared with, for example, UK and Australia).

While casualties and injuries from severe weather events has diminished substantially over the

climate record with much improved warning systems and weather forecasts, the impacts on health

and safety for people remains an issue for most events e.g., heatwaves, lightening, wild fires, hail,

winds, floods, landslides etc.

3 Risk from severe weather events

3.1 Risk

Risk is the combination of:

▪ hazard exposure (single or compound hazards)

▪ the vulnerability of the receptors (people or assets) exposed (= consequences)

▪ and the likelihood of that hazard combination.

For example, a street may be flooded occasionally from a coastal storm-tide event, causing transport

disruption, some vehicle corrosion and other losses with minor consequences. But the risk can be

much greater for a higher storm-tide event, even though infrequent, when houses and businesses

are flooded and damaged requiring a lengthy recovery period.

Consequences increase markedly when flood levels exceed critical levels that impact assets such as

the floor levels of buildings, electrical control systems or cause flooding of vehicles. Similarly, there

are critical thresholds for risks from other weather-related hazards.

Risk in its broadest sense is the effect of uncertainty on objectives – with the objective in this case a

more resilient New Zealand that reduces risk to avoid adverse consequences.

3.2 Historical development

Settlers in New Zealand commonly chose to live next to rivers and lakes, as these were a source of

fresh water, and the adjacent plains usually had fertile soil. The rapid housing and infrastructure

development of 1900–1950s also gave little regard to the risks of severe weather, likely due to the

limited monitoring data available and partial knowledge on severe weather and the risks.

Even to the present, there has been continuing development on flood and coastal plains, which is

significantly increasing risk exposure – particularly as seas rise and more intense rainfall occurs.

Severe weather: Damage and economic losses 9

Valuations of private assets (buildings, contents, vehicles etc.,) and public infrastructure and service

utilities have increased markedly – often at a higher rate than the Consumer Price Index, which also

increases risk from severe weather.

River and coastal flood control stop-banks were extensively developed from the early 1900s

onwards. Following the enactment of the Soil Conservation and Rivers Control Act in 1941, this

process accelerated through subsidized projects by the then Ministry of Works & Development

(MWD). This reduced the magnitude of flooding by “taming” some of the larger rivers, although it

does raise the “residual risk”, which could be realised if the structure breaches (e.g., Edgecumbe) or

is overtopped. Following the dissolution of MWD in 1988, the Soil Conservation and Rivers Control

Amendment Act 1988 and the Resource Management Act 1991, natural hazard management and

control was devolved to regional or unitary councils to avoid, reduce or manage the risks from

natural hazards.

3.3 Civil Defence and Emergency Management context

Under the Civil Defence Emergency Management Act 2002 (CDEMA) and associated National Civil

Defence Emergency Management Plan, CDEM Groups and the Ministry for Civil Defence and

Emergency Management (MCDEM) have roles and responsibilities managing risk across the 4 R’s

(Reduction, Readiness, Response and Recovery).

Under Section 16.5 of the National Plan, NIWA has a role as a science and research provider to

provide public information on:

▪ climatic and seasonal risks (including drought)

▪ marine geological, seafloor and coastal hazard and processes,

and provide scientific advice to the National Crisis Management Centre, agencies and CDEM Groups

as needed.

Through the RiskScape project (in collaboration with GNS Science), NIWA is also proactively assisting

councils and CDEM Groups to assess risk from weather-related and tsunami impacts to better inform

decision making on reducing unacceptable risk (1st R).

NIWA is also assisting councils with readiness through flood and storm-tide forecasting services, to

complement Met Service’s official severe-weather warning service.

NIWA maintains the New Zealand drought monitor system and provides advice to the Ministry of

Primary Industries when a significant drought is emerging.

4 Weather-related civil-defence declarations and insurance costs

4.1 Civil defence declarations since 1967

Figure 4-1 shows the main cause of emergency declarations by MCDEM or CDEM Groups since 1967

in relation to severe weather events, based on information from MCDEM.1

1 https://www.civildefence.govt.nz/resources/historical-emergencies/

10 Severe weather: Damage and economic losses

72% of the weather-related civil defence emergencies across the regions were mainly related to

flooding from rivers, intense rainfall or sea flooding in coastal areas. The regions with most flood

declarations in descending order are the West Coast, Otago, Horizons-Manawatu and Taranaki.

1988 was a busy year for emergencies, particularly from ex TC Bola that affected several regions. Last

year and to date this year (2018) have also seen several declarations made across different regions.

This data only provides an indication on the potential or perceived severity of weather-related events

in declaring, usually before the magnitude of consequences is fully known – rather than a direct

proxy for damage and economic losses.

Figure 4-1: Number of weather-related emergency declarations across regions in NZ since 1967 (52 years) with main causes categorised as flooding or “other” contributing hazard. Note: Flooding includes rivers, urban flash flooding, and coastal sea flooding. “Other” includes wild-fire events.

4.2 Insured costs since 1967

The Insurance Council of NZ (ICNZ) publishes summarised data on the estimated insured costs in NZ

from natural hazards.2

Figure 4-2 shows the insured costs (translated to NZ$2018) from weather-related events (including

wild-fire and rain-induced landslides) since 1967. It doesn’t include commercial buildings,

infrastructure or private assets that have been covered by offshore insurers, nor by EQC.

Annual insured costs for weather-related events have exceeded $200M both last year (2017) and to

date this year and came close in 2013 and 2004.

The largest insured costs for a single event has exceeded $100M twice – in the January 1984

Southland floods ($148M–2018) and the same equivalent costs for the February 2004 Lower North

Island floods and storm.

2 https://www.icnz.org.nz/natural-disasters/cost-of-natural-disasters/

Severe weather: Damage and economic losses 11

Qualitatively, the trend in the published insured costs (excluding offshore insurers and EQC) has seen

increase in the annual insured costs in the last two decades. This is mainly reflected by the increasing

number of “insurance events” (up to 10 pa) and the increasing risk from ongoing development and

asset valuation. Isolating the effect of climate change on the trend will require more analysis – but

recent work on the % attribution in recent events to climate change influences is summarised later.

Figure 4-2: Annualised insured costs (bars) for weather-related events in NZ since 1968 (ex TC Gisele) in terms of 2018 NZ$. The circles show the number of “insurance events”, which generally apply at threshold costs of ~$1M. Note: some of the early years appear to have missing data, as indicated by the proxy for those years (open circle) using the number of declared emergencies.

5 Historic Weather Events catalogue (HWE)

5.1 Background

In the early stage of the research programme to develop RiskScape (a multi-hazard risk modelling

tool), it was recognised that there was no national consistent database for past weather events and

the impacts for NZ.

From 2005 to 2012, the Historic Weather Events (HWE) catalogue was set up, populated (a few 1000

hours) and developed into a searchable web service on the NIWA web site.3 Since then, HWE has

been updated when a severe weather event exceeds a specific threshold.

Of particular note is that HWE only contains weather events that have exceeded a moderately high

bar if one of the following criterion is reached:

o Loss of life or > 5 injuries.

o > 50 evacuees.

o 10+ properties damaged.

3 https://hwe.niwa.co.nz/

12 Severe weather: Damage and economic losses

o Significant crop and/or stock damage.

o Declaration of an emergency by CDEM.

o Major disruption or damage to engineering lifelines.

o General damage >$1M or likelihood (probability) of event of < 1 in 10 years.

The structure of the entries in HWE are focused on regional impacts from events to ensure it was

relevant for regional management of hazards including emergency declarations. Therefore, the year-

by-year counts include the occurrences of the hazard across the regions – even though it was a single

overall weather event that caused it.

Entries in HWE date back to 1840, relying on several sources of information including newspaper

reports, books, reports and government agency and council databases. Key agencies holding this

information and images were the National Library, Alexander Turnbull Library, Papers Past, Met

Service (Mark Pascoe, Erick Brenstrum), Ministry of Works Water & Soil Division archives, Hocken

Library (University of Otago) and coastal databases (Waikato University and Amber Dunn).

At this stage images (including weather maps) are not currently incorporated.

5.2 Snapshot of results

While the HWE catalogue contains a wealth of information, I have selected two analyses of the

records to illustrate the contributing weather hazards to events (by region) and the time series of the

number of flood-event occurrences per region each year since 1840.

Figure 5-1 shows the proportion of nine contributory hazards that primarily caused the events that

are recorded in the catalogue by region.

The main natural hazards that contribute to severe weather are: flooding, high winds (including

tornadoes), rain-induced landslides, and in southern regions, snowfalls. Maritime and coastal hazards

also feature for northern areas and Wellington but are predominantly the result of frequent

shipwrecks and loss of life from weather events in the 1800s and early 1900s, which seldom occur

now due to accurate weather forecasts, safe harbour approaches and maritime safety systems.

Over 400 occurrences of severe weather have occurred in Auckland, Waikato and Wellington/Hutt

regions, followed closely by Canterbury, Northland and Otago.

The number of recorded floods were highest in Waikato, Northland, Wellington/Hutt and Canterbury

regions. Numbers of wind hazard events were greatest in Auckland, followed by Wellington/Hutt and

Waikato. The higher number of events in the northern regions is partly related to exposure to ex-

tropical cyclones.

Severe weather: Damage and economic losses 13

Figure 5-1: The main contributing hazard to the number of severe weather events in the NIWA HWE catalogue by region.

Figure 5-2 displays a time series of the number of severe weather events that are classified as

predominantly floods in the NIWA HWE catalogue across regions, each year. Annotations show some

of the features or milestones in the series. Early in the record, there is a paucity of information on

events but also the population and development were much smaller, meaning fewer events reached

the HWE threshold, although casualties were more common.

The first Hutt River stop-bank was built from 1901–1906 and extended north through Upper Hutt

between 1956 and 1972.4 A severe flood in the Esk River in Hawke’s Bay in 1938 deposited metres of

silt downstream and was the catalyst for enacting the Soil Conservation and Rivers Control Act in

1941. By the 1970’s most of large river-control schemes had been completed, including Hauraki-

Waihou scheme.

The lull in the number of flood events by region in the 1970s to 1908s (Figure 5-2) is probably a

combination of the completion of stop-banks for the high-risk areas and the positive phase of the 20

to 30-year Interdecadal Pacific Oscillation (IPO) – a Pacific-wide climate cycle that alternately

enhances the strength of El Niño or La Niña episodes. The IPO switched phases in 1999 and may

partially explain the upsurge in flood events in the following first decade of this century. While

human-induced climate change may be expected to have increased the likelihood of flooding in

recent years, the number of factors just outlined means it is not yet possible to say how much of the

increasing trend visible in Figure 5-2 may be attributable to climate change.

4 http://www.gw.govt.nz/assets/Our-Services/Flood-Protection/Hutt/FP-Hutt-River-FMP.pdf

14 Severe weather: Damage and economic losses

Figure 5-2: Time series of the number of severe weather events that are classified as predominantly floods in the NIWA HWE catalogue per region each year. Note: this is not the number of flood events to affect NZ but counts the number of regions where flooding occurred during an event that triggered the criteria.

By far the highest number of flood events by region was recorded in 2008, when multiple flood

events affected several regions, with for example 13 occurrences of flooding in Wellington that year.

The cumulative insured cost for the 2008 year for NZ (Figure 4-2) was $100M (2018).

These results only relate to the number or composition of severe weather events – but further

detailed analysis of impacts, damage and economic losses are needed. Met Service and NZIER will

provide a summary of more in-depth costs and losses for a few recent events in their submission to

the Committee, which includes information from the HWE catalogue.

6 RiskScape RiskScape5 is a quantitative multi-hazard risk software package that has been developed for over a

decade by NIWA and GNS Science collaborating on this joint programme.

RiskScape provides the framework for users to model the risk (impacts and losses) from hazard

exposure generated by:

▪ geological hazards (earthquakes, volcanoes, landslides or tsunami) and

▪ weather-related hazards (floods, wind/tornadoes, coastal flooding and landslides).

Figure 6-1 shows a schematic of the RiskScape framework, which overlays hazard exposure layers

(e.g., flood map from a dynamic flood model) onto a spatial map of the various assets and people

(e.g., buildings, cars, contents, where people live or work), connected using accurate LiDAR

topography.

5 https://riskscape.org.nz/

Severe weather: Damage and economic losses 15

Figure 6-1: The RiskScape framework overlays hazard exposure layers on various assets with different vulnerabilities to derive impacts, people affected, damage and some categories of economic losses.

Each of the assets have listed characteristics e.g., floor level, house floor area, building age, number

of storeys, road or bridge height. These are used in vulnerability functions to calculate the degree of

damage or number of people affected from the hazard exposure and accumulated over a suburb, city

or region and even nationally.

For example, if the flood level from the hazard model is below the floor level of any house, then only

minimal damage or disruption is calculated for that asset, whereas flood heights above the floor level

cause a % damage relative to the depth of flooding inside.

RiskScape is under continual improvement with increasing flexibility for users to convert hazard

exposure into risk to better inform choices on where and how to best reduce the risk (given limited

budgets to address risk) and how many people could be affected by a hazard including estimates of

how long they might be displaced.

Crucial to obtaining plausible estimates of damage and economic losses, is the ongoing need to

develop a national asset inventory to sit alongside the Census demographic data. At present

RiskScape is providing some informal coordination of national asset data and attributes.

Topographic databases are also an essential ingredient in estimating risk, requiring LiDAR6 scanned

topography (accurate to 0.1 m in vertical) to represent the land surface in coastal and river flood

models. A 2015 report by NIWA7 for the Parliamentary Commissioner for the Environment on the risk

exposure from rising seas found that using the best available national topography would generate

risk estimates that were only 50% of those calculated using accurate LiDAR.

The holy grail NIWA is working towards is to combine weather and “downstream” hazard forecasting

with RiskScape to eventually provide councils and CDEM Groups with the ability to forecast risk

ahead of the event e.g., how many people should we prepare to evacuate, or what damage and costs

are we likely to incur during this event to start mobilising resources.

6 Light Detection And Ranging – aerial laser scanning of the land surface 7 https://www.pce.parliament.nz/media/1384/national-and-regional-risk-exposure-in-low-lying-coastal-areas-niwa-2015.pdf

16 Severe weather: Damage and economic losses

7 National coastal risk exposure study (2015) NIWA used RiskScape, the asset database and LiDAR topography (where available) to undertake for

the first time a nation-wide assessment of risk exposure in low-lying coastal areas of NZ. Essentially a

“risk census”, normally-resident populations and various assets (e.g., kilometres of road and rail,

airports, numbers of buildings and their replacement value) were enumerated in bands of land

elevation from 0 to 3 metres above mean spring high tide.

Figure 7-1 outlines the more critically exposed areas to coastal hazards and ongoing sea-level rise for

land that is no higher than 0.5 metre above mean spring high tide.

Figure 7-1: Nation-wide coastal risk exposure for low-lying land no higher than 0.5 metres above spring high tide. Data source: NIWA (2015) report for the Parliamentary Commissioner for the Environment.

8 Looking forward

8.1 Changing climate and weather

The changing climate means the past record of weather-related events and their impacts will

increasingly become less informative to estimate future damage and losses generated by severe

weather and when the time is right to adapt, reduce risk and move to a more sustainable option. I

provide a few examples.

Ongoing sea-level rise will increasingly affect flooding of coastal areas. Only modest rises in sea level

(e.g. 30 cm for Wellington) are required for an infrequent 1-in 100-year present-day sea-flood to

become an event that happens on average once a year, along with more frequent nuisance flooding.8

8 https://www.pce.parliament.nz/publications/preparing-new-zealand-for-rising-seas-certainty-and-uncertainty

Severe weather: Damage and economic losses 17

NIWA’s projections for the Ministry for the Environment’s guidance for local government (2016,

updated 2018)9 show that:

▪ Summers will become drier in the North Island, and wetter in the west and south of

the South Island is winter.

▪ Droughts are projected to increase in eastern and northern areas of NZ

▪ Rainfall will become more intense, particularly for short-sharp duration events, with a

projected 13-18% increase in the 1-hour duration rainfall for every 1°C rise in

temperature. This will have a substantial impact on urban flooding or where low-lying

coastal areas have rising groundwater levels from sea-level rise.

8.2 Climate change attribution for recent severe weather events

NIWA’s Weather @ Home project utilizes private PC’s to crunch lots of simulations of specific severe

weather events, with two subsets of simulations. Those that do not include the changes in climate

and greenhouse gases to date and those that do have climate change included.

By comparing these two sets of simulations for the same rainfall or drought event, it is possible to

estimate the fraction of attributable risk (FAR) for the event that is due to the influence of climate

change. While described as attributable risk, in this context it is simply the change in the probability

of an event that is being referred to.

A recent report, Frame et al. (2018) for Treasury,10 analysed 12 rainfall events from 2007 to 2017 and

two drought events in the summers of 2007/08 and 2012/13. The FAR for the rainfall events ranged

from 5 to 40% with mostly around 30% for the influence of climate change on these severe events.

For the two drought events, the FAR was lower at 15-20% factor for attribution of climate change.

In summary, the report proposed that these FARs can be used to estimate that climate change-

related floods and droughts have cost the NZ economy at least $120M for insured damages for

floods and $720M for economic losses from droughts over the last decade. This prototype report is

likely to be used for ongoing development of comprehensive methodologies to quantify the

increasing economic costs for weather-related hazards.

8.3 Paradigm shift needed to reduce future risks to severe weather

With the increasing trend in insured costs (and by inference non-insured costs, disruption and

economic losses) as development on hazard-prone areas intensifies and increased asset

appreciation, along with the emergence of a growing climate-change signal, a renewed focus on the

1st R (risk reduction) is required.

A new paradigm is needed to manage risk to severe weather and the growing climate-change

influence on extreme events. Do we continually react, clean up & stay put? If we continue to pursue

flood and erosion hazard protection measures (e.g. more stop-banks or seawalls), what are the limits

9 http://www.mfe.govt.nz/publications/climate-change/climate-change-projections-new-zealand 10 Frame, Rosier, Carey-Smith, Harrington, Dean, Noy (2018). Estimating financial costs of climate change in New Zealand. Report for Treasury by the NZ Climate Change Research Institute and NIWA. URL: https://treasury.govt.nz/sites/default/files/2018-08/LSF-estimating-financial-cost-of-climate-change-in-nz.pdf

18 Severe weather: Damage and economic losses

to this strategy of containment (up to a design level), and the increased residual risk (e.g., if the

protection structure is breached or overtopped).

An emerging paradigm internationally and in NZ, is how can we better anticipate, adapt and work

with nature to manage the impacts of severe weather, especially flooding, as the influence of

climate-change increases the risk e.g., rather than a hold-the-line approach designed using historic

events, giving room for the river, sea or potential landslide and adopting water-sensitive urban

design that works with stormwater, groundwater and floods – rather than fighting the influx of

water.

Central to this emerging paradigm is the use of adaptive pathways planning or robust decision-

making approaches (e.g., the Ministry for the Environment coastal guidance for local government

released last year). These provide a framework that accommodates future uncertainties and changes

in hazard exposure and risk along with changes in social and economic situations.

An adaptive planning approach, working collaboratively with communities, enables a future suite of

short-term actions and long-term options (pathways) to be pre-planned to reduce natural-hazard risk

with agreed thresholds to be avoided.

By monitoring changes in risk and frequency of events, a switch to the next option or pathway can be

triggered when the agreed threshold is reached e.g., number of floods in a decade. Having a long-

term adaptive plan could also inform the recovery phase (4th R) of a severe-weather event through

“building back better or somewhere else” – or in the case of frequent droughts, adjusting the type of

primary production or change practices. Adaptive planning also enables timely investment in risk

reduction – not too early and not too late.

The other key ingredient of reducing risk to severe weather, especially flooding and landslides, is the

need to effectively implement land-use planning policies and rules that better align the type of

development or reduced intensification on coastal and flood plains that sustainably “lives with

water” rather than fights or contains water (e.g., Ericksen, 1986 report from 30 years ago).11

11 Ericksen, N. (1986). Creating flood disasters? New Zealand's need for a new approach to urban flood hazard. Water & Soil Miscellaneous Publication No. 77. Publisher: Wellington, NZ: Water and Soil Directorate, Ministry of Works and Development.