Related - Floodplain Manager April 2021

March Floods Create Records but Not Unprecedented

Record rain fell across NSW in March 2021 and flooding reached record heights according to a special climate statement released by the Bureau of Meteorology (BoM).

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The report summarises the rainfall and flooding experienced in NSW and Queensland in March 2021 (FM March).

It reports that a blocking high pressure system in the Tasman Sea combined with a low pressure system on north west Australia to feed moist tropical air into eastern Australia between 17 and 26 March.  March rainfall overall for New South Wales was 136.3 mm, which was 153% above the 1961−1990 average, making it the state’s second-wettest March on record after 1956, and the wettest month since January 1995.  It also experienced its second wettest day and third wettest weeks since records began in 1900.

Several rivers reached major flood levels across NSW including the Hastings and Manning Rivers which reached their highest recorded levels.  The Hawkesbury-Nepean River at Penrith reached its highest peak since 1961 and at Windsor its highest peak since 1990.

However, despite a major flood not occurring on the Hawkesbury Nepean since 1990, the cyclic long-term rainfall pattern of the region points to this not being an unusual or singular occurrence. Research into the flood periods of the Hawkesbury-Nepean River suggest that a pattern of 40 to 50 years of dry weather with infrequent small floods are followed by 40 to 50 years of wet weather with frequent major floods. For instance, the last wet-weather period saw one major flood occur every four years between 1950 and 1990.  It is possible that the March 2021 flood could be ushering in another prolonged wet period with several major floods.

(Read here, here, and here).

Insure or Relocate?

Rising insurance bills and increasing disaster frequency and costs predicted under a changed climate has prompted experts to urge Government to buy-back flood prone and uninsurable homes.

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The Insurance Council of Australia (ICA) has declared an insurance catastrophe following the recent extreme rain and flooding across Sydney and broader New South Wales (FM March, 2021). As of 10 April 2021, the insurance bill for the floods had risen to $537 million from 35,845 claims, as affected residents continue to lodge claims with their insurers. Meanwhile, a NSW Treasury study on climate change risk predicts rising sea levels will expose between 39,000 and 46,000 properties in the state to coastal erosion or inundation, and cost between $15.8 and $17.2 billion a year in damages by 2061. To combat this, the Committee for Sydney has called for buy-backs of thousands of homes in flood-prone areas of western Sydney by the federal government. The Committee’s resilience director, Sam Kernaghan states that “If nothing is done to address this escalating risk from extreme weather and climate change, by 2100 Sydney will have a projected 91,000 “uninsurable” addresses”. An Infrastructure NSW spokesperson said the government had considered buybacks to mitigate flood risk, including in its Hawkesbury-Nepean flood strategy released in 2018. However, this idea was largely dispelled as having “very significant social and economic costs”. (Read here and here).

Floods Good News for Some

Floods in March 2021 (FM March) have brought much needed flows to parts of the Barwon, Namoi and Darling rivers which have not seen substantial flows since 2016.

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The BoM reported that in inland areas of northern New South Wales and southern Queensland water storage levels in the northern Murray–Darling Basin increased from 27.9% on 17 March to 46.0% on 28 March, reaching 47.1% of capacity at the end of March. This included the highest and third highest daily increases in combined storage volumes since 1993. Farmers have rejoiced at the river replenishment after years of drought and many are hopeful for their first major harvest in years. (Read here).

More Rain Further South Under Changed Climate

Climate change will lead to fewer cyclones overall, but they won’t be any less severe and may be experienced further south over time.

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Observations of tropical cyclones passing within 400 km of Geraldton, WA have shown that where cyclones form, as well as where they reach their maximum intensity, has been moving away from the equator in recent decades. If current trends continue then areas such as south-east Queensland and northern New South Wales could become more prone to tropical cyclones bringing increased rainfall. This has implications for the overall impact on these communities as the population density is much higher in these areas than the equivalent regions on the west coast (Read more here).

Coastal Floods to Increase in Coastal WA

Researchers from the University of Western Australia have found that a combination of rising sea levels and climate cycle factors unique to WA may accelerate coastal flooding risks in the future.

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The study analysed 50 years of coastal data and found that while sea levels had been rising steadily at 3 to 5 millimetres per year in recent decades, on par with global averages, sea levels along the WA coastline were also strongly affected by El Nino and La Nina conditions. Results showed that during La Nina, sea levels can be elevated by up to 30 cm in coastal WA. The research findings have implications for planned protection of coastal populations and infrastructure, particularly in low lying areas. Lead researcher Professor Ryan Lowe emphasised that: “We must develop and implement new solutions for large-scale coastal protection, as our reliance on conventional ways of protecting the coastline such as sea walls and breakwaters may become increasingly unsustainable to address the scale of the problem” (Read more here).

Community-maintained Flood Defence Keeps Town Protected from Riverine Flooding

A levee built in 1956 continually protects Goondiwindi, Qld from flooding that once saw the town inundated three times in one year.

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The town which sits on the banks of the Macintyre River, was frequently subject to major flooding until local Council members Bill McNulty and Vern Redmond took action by building a 21 km levee at a cost of 57,000 pounds. Excluding a swiftly repaired breach in 2011, the levee has successfully protected the town from major floods ever since. University of New England river scientist Professor Martin Thoms says that while the levee is suitable for current floods, increased flood frequency and intensity predicted under a changed climate could cause the barrier to be exceeded. For instance, the 2011 flood saw water levels reach 10.4 metres which is just 60 cm shy of the top of the levee. (Read more here).

Floods Worse for People with a Disability

Research by the University of Sydney’s University Centre for Rural Health has found that flooding can worsen social inequalities for people with a disability.

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The research surveyed people with a disability and their carers after a major flood in the Northern Rivers region of New South Wales in 2017. The results showed that disabled people were more likely to have their homes flooded and need to be evacuated; remain displaced for longer than those without a disability; experience disruptions in access to food and support essentials; and be at higher risk of post-traumatic stress disorder six months after the flood. Issues commonly experience by those surveyed included lack of mobility affecting ability to evacuate in timely manner and difficulty comprehending warning messages. This research has prompted a push for more inclusive disaster action tailored for those living with a disability such as developing person-centred preparedness plans(Read more here).

Lismore Flood Stories

Flood Stories is an immersive audio walk and storytelling experience for the victims of the 2017 Lismore floods.

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Flood Stories curator Jeanti St Clair created the project to allow flood survivors and her broader audience to “reflect on what we learned as a flood town, and what we need to remember for the future”. The project sees visitors don a raincoat and gumboots and listen to headsets with stories of those who survived the flood or were part of the rescue and recovery teams. The audience takes a tour from the Quad into the Lismore CBD streets all the while listening to stories of survival and reflection on preparedness for future floods and climate emergencies (Read more here).

Is Sea-Level Rise Overestimated?

Scientists from Utrecht University have published an article in the Science Advances Journal which concludes that projected sea-level rise in 100 years is about 25% lower than expected from the current simulations.

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Current estimates for future sea-level rise are based on a large ensemble of climate model simulations. In this study, researchers have used a new high-resolution model which takes into account ocean eddy processes and projects a smaller mass loss as a result of iceshelf melt than current climate models. By adding ocean eddies into the simulation, the researchers were able to create a more realistic representation of the ocean temperatures surrounding Antarctica, which is key for determining the mass loss of the Antarctic ice sheet (Read more here).

Indicator‐Based Methodology to Assess Building Vulnerability to Flash Floods

This study proposes a physical vulnerability index that combines intrinsic vulnerability of buildings and flash flood intensity in order to better assess building damages caused by flash floods.

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This innovative approach involves integrating the characteristics of exposed buildings with the potential damage that could be caused by flash floods through the inclusion of flash flood parameters. Intrinsic vulnerability measures the amount of potential damage based on building properties, such as building materials, age, number of floors, and condition. Flash flood intensity takes into account flooding parameters such as average flow velocity and depth. This allows for a more thorough assessment of building vulnerability, a key component of risk assessments (Read more here).

Slum Dwellers Identify Alternative Flood Solution

Residents of Manzoor Colony, a slum in Karachi, Pakistan, have mapped flood risk from blocked drains to successfully stop government plans to demolish thousands of homes.

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While the government said that slum settlements would need to be removed to allow for drain widening in the city, community members believed the flooding was caused by drains being blocked with rubbish and sludge. However, the government insisted that the drains are cleaned out every year before the monsoon, and that blockages were caused by illegal construction. To provide evidence, a team from the non-profit Technical Training Resource Centre worked with residents to photograph and map blockages across the settlement. This work showed that only 40 homes would need to be removed in order to clear the drains, as opposed to the thousands of homes that were originally intended to be demolished. The mapping provides valuable information on the key areas for flood risk and can be an empowering tool for community members to address flood issues (Read more here).

20% More Floods in 2020

In comparison to the past two previous decades, 2020 experienced 23% more floods, 26% more storms, and 18% more flood deaths than the annual averages.

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While 2020 may have been defined by the ongoing COVID-19 pandemic, the year was also dominated by disasters, with higher-than-average number of events and economic losses. However, there were fewer total deaths from disasters compared to the average from previous decades, due to the absence of mass casualty events. Floods were the most common disaster in 2020, with 201 worldwide events. Storms affected a total of 45.5 million people and caused $92.7 billion in economic losses, making it the most expensive disaster. Flood impacts were felt most heavily in East Africa, South Asia and China. Heatwaves and floods caused the majority of disaster-related deaths in 2020. (Read more here and here).

Battle Flood Basilica

As sea levels rise, Venice’s iconic 900-year-old St. Mark’s bBasilica faces a growing risk from tidal flooding with damaging saltwater.

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In November 2019, a particularly high tide of almost two metres above mean sea level left much of the subsiding Italian city inundated for weeks. The basilica, located in St Mark’s Square which is one of the lowest parts of the city, had tiles torn away, windows broken by floodwaters, and extensive damage to marble columns, floors and mosaics from corrosive saltwater. Inflatable barriers in the tunnels beneath the church can only withstand water levels of under one metre, which is insufficient to defend the church against increasingly high tidal flood levels. The network of flood barriers designed to protect all of Venice are insufficient to protect the basilica from the low flood depths it is impacted by. New independent flood defences have been proposed, including physical barriers outside of the church and manually operated valves inserted into the drainage tunnels beneath the church to block approaching waters. However, these designs are yet to be implemented due to their high costs (Read more here).

Geomojis – A Universal Disaster Warning Language

A Geomoji glossary of geoscience-related pictograms is proposed as a cross-cultural tool to improve geohazard communication.

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The goal of this effort is to create a set of easily understood symbols to represent common geological themes, in order to bridge the gap between pictures and words from specific languages. It is hoped that the project will grow from crowdsourced contributions, with adaptations for local context and requirements. It can be used in a variety of settings, from tourist sites to school textbooks(Read more here).

Resilient City or Resilient Citizens?

Jakarta’s flood resilience is largely due to its residents, who have learnt from past flood experience and taken measures to reduce future risk.

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While the government focuses on reactive measures such as flood evacuation, the residents of Jakarta have learnt to take proactive measures at the household-scale such as storing electronics above the reaches of flood waters. Additionally, flood water pumps, drains, local water level monitoring and early warning systems have been established at the community-level in neighbourhoods that regularly flood. (Read more here).

International Floods

There were 19 international floods reported across 18 countries in April 2021. At least 200 people died and more than 125,000 were displaced.

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Internationally significant floods included:

Indonesia and East Timor

Torrential rainfall from Tropical Cyclone Serojia triggered floods and landslides in Indonesia and East Timor killing more than 150 people and displacing more than 10,000. Approximately 2,000 buildings were damaged or destroyed. Six cargo helicopters were deployed to deliver much needed aid to communities cut-off by mudslides and floodwater. Authorities struggled to provide temporary accommodation for the thousands displaced by the floods as the countries continue to struggle with surging COVID-19 cases. (Read here, here and here).

Philippines

Two people have died and over 65,000 people were pre-emptively evacuated from the Bicol and Eastern Visayas regions of the Philippines. Typhoon Surigae brought damaging winds and rainfall of 214 mm in 24 hours to 19 April in Northern Samar. Flooding was reported in 22 barangays in Eastern Samar province. Roads were blocked and 52 houses were totally destroyed. (Read here and here).

Angola

Heavy rain and flash floods in Angola’s capital Luanda caused 24 fatalities and displaced as many as 8,000 people. As many as 2,289 homes were damaged and 60 destroyed, affecting 11,000 people. Other damages included 14 schools, four health centres and four bridges. (Read here)

Diary

Flood and Coast 2020 Conference and Exhibition
Where: Online and Telford International Centre, UK
When: Multiple online and in person between December 2020 to June 2021
For more information visit here

International Conference on Urban Flood Control and River Flood Management
Where: Singapore
When: 03 to 04 May 2021
For more information visit here

Association of State Floodplain Managers 45th Annual National Conference
Where: Raleigh Convention Center, North Carolina
When: 9 to 12 May 2021
For more information visit here

Floodplain Management Australia National Conference 2021
Where: Virtual conference
When: 25 to 28 May 2021
For more information visit here

FLOODrisk 2020 European Conference on Flood Risk Management
Where: Budapest, Hungary
When: 21 to 25 June 2021
For more information visit here

46th Annual Natural Hazards Research and Applications Workshop
Where: Natural Hazards Center at the University of Colorado Boulder
When: 11- 14 July 2021
For more information visit here

Eighth International Conference on Flood Management
Where: The University of Iowa, USA
When: 9 to 11 August 2021
For more information visit here

Australian Disaster Resilience Conference 2021
Where: International Convention Centre, Sydney, NSW
When: 18 to 19 August 2021
For more information visit here

Flood Expo
Where: Birmingham, UK
When: 22 to 23 September 2021
For more information visit here

Resources

Debate Over Land Use in NSW After Multiple Natural Disasters
An ABC Radio debate discusses whether to salvage resources or leave land alone which has been devastated by significant natural disasters. (Read here)

Improving Public Messaging for Evacuation and Shelter-in-Place
The US Federal Emergency Management Agency (FEMA) has released a report of findings and recommendations for improving public messaging for evacuation and shelter‐in‐place.(Read here)

NSW Flood Kids
ABC’s Behind the News (BTN) has released a short video documenting the difference experiences of NSW children during the recent March Floods. (Watch here)

Flood Resources for Schools
A series of flood resources targeted at primary school children have been released as part of the Flood:ED Program in the USA (Read here)