Double trouble: floods and COVID-19 have merged to pose great danger for Timor-Leste

Posted on April 16, 2021 by particularkev

Mark Quigley, The University of Melbourne; Andrew King, The University of Melbourne; Brendan Duffy, The University of Melbourne; Claire Vincent, The University of Melbourne; Ian Rutherfurd, The University of Melbourne; Januka Attanayake, The University of Melbourne, and Lisa Palmer, The University of MelbourneTimor-Leste is reeling after heavy rain caused severe floods and landslides over the Easter weekend, killing at least 42 people. Rates of COVID-19 in Timor-Leste are also on the rise. Together, these hazards threaten to interact with deadly consequences.

Our research has assessed the likelihood of natural hazards coinciding with, and influencing, the COVID-19 pandemic. Unsurprisingly, we found temporary relaxations of COVID-19 restrictions during natural disasters are likely to cause large spikes in infection rates.

In Timor-Leste’s capital Dili, the floods and the pandemic have combined to form a dangerous dynamic. Flood damage prompted authorities to temporarily lift COVID-19 restrictions. Evacuees are gathered in group shelters where social distancing may be challenging. Flooding cut power to some COVID treatment centres and put extra pressure on Timor-Leste’s health system.

The situation offers lessons for other populated, flood-prone cites battling the COVID-19 pandemic. Natural hazards will, of course, persist throughout the pandemic. Better understanding the complex interactions between double disasters will help societies and systems become more resilient.

A boy undergoes a COVID test in Timor-Leste, where the pandemic response has been complicated by flooding.
Antonio Dasiparu/EPA

Dili: a recipe for disaster

On April 3 and 4, more than 400mm of rain was recorded in Dili. Floodwater and debris washed into populated areas. Recent reports indicate at least 42 people died and 13,554 were displaced. Nearby Indonesian islands were also hit and at least 130 deaths were reported.

Several natural and human factors combine to make Timor Leste vulnerable to flooding.

The country’s mountainous topography (see image below) encourages rainfall and creates steep stream systems that rapidly transfer floodwater into adjacent populated areas. Weak rocks and steep catchments are highly susceptible to landslides.

Flowing water interacts with the mountains, causing sediment to accumulate in the shape of a fan or cone. This directs flood waters and sediment into central Dili. Also, rampant deforestation and development has increased soil erosion and stream discharge during heavy rain.

Rapid and largely uncoordinated population growth, particularly in Dili, has concentrated vulnerable populations into flood plains and low-elevation coastal areas highly exposed to flooding.

Other factors increasing the flood risk in Dili include:

concrete structures that don’t allow water to sink into the ground
multi-pylon concrete bridges that trap flood debris
urban drainage channels choked with sediment and urban waste.

More broadly in the region, three climate features combined to create ideal conditions for the recent high rainfall and tropical storms: the West Pacific Monsoon, the Madden Julian Oscillation and a La Niña

The top image shows modelled rainfall from April 1 to 5 across Timor-Leste. Inset images show the total daily rain (top left) and maximum hourly rain over a 24-hour period (bottom right) recorded at Dili. The bottom image shows the topography of northern Timor-Leste, where high-elevation catchments exit into low-elevation populations centres of Dili and Laclo.

The COVID combination

Dili is frequently hit by large floods – most recently in March 2020. But this time, the disaster coincided with an escalation in Timor Leste’s COVID-19 infection rate.

In late March this year, the number of new daily cases in Timor-Leste was rising quickly. On April 10, there were 70 new daily cases, bringing the total confirmed cases to more than 1,000.

Even without these twin disasters, many in Timor-Leste already lacked access to medical services and lived below the poverty line. COVID-19 restrictions exacerbated food shortages and poverty.

Then the floods hit. They left thousands homeless with severely restricted access to food and clean water. Roads and bridges collapsed. Crops were destroyed and firewood collection – essential for cooking – has been difficult in some areas.

The floods disrupted a COVID-19 lockdown in Dili, and forced people into crammed refuge centres. Flooding of a national medical storage facility damaged supplies. The national laboratory also flooded and a COVID-19 isolation facility was temporarily evacuated.

During floods, the risks of waterborne and vector-borne disease outbreaks increases. Should this occur, Timor-Leste’s fragile health system would be under even greater pressure.

The first batch of COVID-19 vaccines arrived in Timor Leste on April 5 and the vaccination program has managed to operate despite the flood-related challenges.

A road collapsed after floods — Floods in Timor-Leste caused roads to collapse.
Antonio Dasiparu/EPA

A global problem

Many global cities are vulnerable to multiple interacting hazards like those now faced by Timor-Leste. Our analysis suggests 16 of the world’s 20 most populous cities, comprising 5% of the world’s population, have similar geology, population density and/or land use to Dili and could face similar multiple disasters. These cities include Jakarta, Tokyo and Manila.

In emergency situations, the need for disaster response and recovery may justify temporarily lifting COVID-19 restrictions. But pandemic measures must be reinstated as soon as possible. Our modelling, pictured below, suggests when COVID restrictions are lifted in response to a disaster, infection rates ascend rapidly.

Blue line shows confirmed daily COVID-19 infections, which have increased since mid-March. The red and green lines are modelled forecasts for daily infection rates assuming relaxation of COVID-19 restrictions for two weeks (green) and three weeks (red). Testing delays may produce a time-lag between our forecast scenarios and the real-world data.

What can be done?

Potential solutions are more likely to be effective when they involve multiple groups working together. This includes international and local experts, diverse support agencies and affected communities.

Our research identifies ways to improve disaster preparedness and response in a COVID-19 world. They include:

developing scenarios and forecasts to deal with the interaction of multiple hazards, including COVID-19
using centrally operating disaster coordination platforms to assist and empower local disaster responders
evacuation centres that allow for social distancing
storing supplies of personal protective gear and medical equipment in areas less exposed to natural hazards
mobile teams of humanitarian workers, volunteers and medical staff that can respond to natural disasters in COVID-affected regions.

Dili residents clean up after flooding — Widespread change is needed to protect vulnerable Dili residents from future disasters.
Antonio Dasiparu/EPA

Finally, measures must be taken to reduce the risks posed by future disasters. This must be done in culturally informed ways and includes:

improving land and water management
land-use planning that considers disaster risk
urban clean-up after events such as floods.

Such actions are crucial in developing nations such as Timor-Leste, where urban development can amplify natural hazards with tragic results.

Oktoviano Tilman de Jesus, Demetrio Amaral Carvalho and Josh Trindade contributed invaluable expertise to this work.

This article is part of Conversation series on the nexus between disaster, disadvantage and resilience. Read the rest of the stories here.

Mark Quigley, Associate Professor of Earthquake Science, The University of Melbourne; Andrew King, ARC DECRA fellow, The University of Melbourne; Brendan Duffy, Fellow in Structural Geology and Tectonics, The University of Melbourne; Claire Vincent, Lecturer in Atmospheric Science, The University of Melbourne; Ian Rutherfurd, Professor in Geography, The University of Melbourne; Januka Attanayake, Research Fellow, The University of Melbourne, and Lisa Palmer, Associate Professor, School of Geography, The University of Melbourne

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Australia: New South Wales Flood Crisis Continues Into Fifth Day

Posted on March 22, 2021 by particularkev

Australia: Extreme Weather Continues

Posted on February 12, 2020 by particularkev

Queensland’s floods are so huge the only way to track them is from space

Posted on February 9, 2019 by particularkev

Linlin Ge, UNSW

Many parts of Queensland have been declared disaster zones and thousands of residents evacuated due to a 1-in-100-year flood. Townsville is at the epicentre of the “unprecedented” monsoonal downpour that brought more than a year’s worth of rain in just a few days, and the emergency is far from over with yet more torrential rain expected.

Such monumental disruption calls for emergency work to safeguard crucial infrastructure such as bridges, dams, motorways, railways, power substations, power lines and telecommunications cables. In turn, that requires accurate, timely mapping of flood waters.

For the first time in Australia, our research team has been monitoring the floods closely using a new technique involving European satellites, which allows us to “see” beneath the cloud cover and map developments on the ground.

Given that the flooding currently covers a 700km stretch of coast from Cairns to Mackay, it would take days to piece together the big picture of the flood using airborne mapping. What’s more, conventional optical imaging satellites are easily “blinded” by cloud cover.

But a radar satellite can fly over the entire state in a matter of
seconds, and an accurate and comprehensive flood map can be produced in less than an hour.

Eyes above the skies

Our new method uses an imaging technology called “synthetic aperture radar” (SAR), which can observe the ground day or night, through cloud cover or smoke. By combining and comparing SAR images, we can determine the progress of an unfolding disaster such as a flood.

In simple terms, if an area is not flooded on the first image but is inundated on the second image, the resulting discrepancy between the two images can help to reveal the flood’s extent and identify the advancing flood front.

To automate this process and make it more accurate, we use two pairs of images: a “pre-event pair” taken before the flood, and a “co-event pair” made up of one image before the flood, and another later image during the flooding.

The European satellites have been operated strategically to collect images globally once every 12 days, making it possible for us to test this new technique in Townsville as soon as flooding occurs.

To monitor the current floods in Townsville, we took the pre-event images on January 6 and January 18, 2019. The co-event pair was collected on January 18 and January 30. These sets of images were then used to generate the accurate and detailed flood map shown below.

The image comparisons can all be done algorithmically, without a human having to scrutinise the images themselves. Then we can just look out for image pairs with significant discrepancies, and then concentrate our attention on those.

Satellite flood mapping along the Queensland coast, compiled using images from the European radar satellite Sentinel-1A.
European Space Agency/Smart Spatial Technology Development Laborator (SSTD), UNSW, Author provided

Our technique potentially avoids the need to monitor floods from airborne reconnaissance planes – a dangerous or even impossible task amid heavy rains, strong wind, thick cloud and lightning.

This timely flood intelligence from satellites can be used to switch off critical infrastructure such as power substations before flood water reaches them.

Linlin Ge, Professor, UNSW

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Yes, a tsunami could hit Sydney – causing flooding and dangerous currents

Posted on October 29, 2018 by particularkev

File 20181014 109207 1cee72t.jpg?ixlib=rb 1.1 — Manly’s The Corso pedestrian area could be flooded if a large tsunami arrived at Sydney Harbour.
from www.shutterstock.com

Kaya Wilson, University of Newcastle and Hannah Power, University of Newcastle

Sulawesi’s recent tsunami is a striking reminder of the devastating, deadly effects that the sudden arrival of a large volume of water can have.

Published today, our new research shows what might happen if a tsunami hit Sydney Harbour. A large tsunami could cause significant flooding in Manly. Even very small waves might result in dangerous currents in the entrance of the Harbour and in narrow channels such as at the Spit Bridge.

Beyond Sydney, large areas of the east coast of Australia would also be affected.

Our study considered a range of tsunamis, with heights ranging from just 5cm to nearly 1.5m when measured outside the Heads of Sydney Harbour. These wave heights sound small, but because the wavelengths of tsunami are so long (tens to hundreds of kilometres), these waves contain a very large mass of water and can be incredibly powerful and destructive. Wave heights also increase as the tsunami encounters shallower water.

A tsunami generated by an earthquake off Chile in 1960 created waves that reached Australia..
NSW Office of Environment and Heritage holdings

How a tsunami might happen

Most tsunamis are caused by earthquakes at sea, where a shift in the sea floor creates the sudden movement of a large volume of water.

Our study approach involved modelling the likely effects of different-sized tsunamis generated by earthquakes on the New Hebrides trench to the northeast (in line with the Vanuatu islands) and the Puysegur trench (south of New Zealand).

For each event we assigned Average Recurrence Intervals (ARI), which provide an average indication of how often tsunamis of different sizes are likely to occur.

The tsunamis we studied range from an ARI of 25 years to 4,700 years. The tsunami with an ARI of 4,700 had a wave height of 1.4m outside the Heads and is the largest tsunami we could reasonably expect in Sydney Harbour. An event with an ARI of 4,700 can also be considered as an event with a 1.5% chance of occurring over a 70-year lifetime.

What would the tsunami look like?

The tsunamis we’d expect to see in Sydney Harbour would be a sequence of waves with about 15-40 minutes on average between each peak. Some waves might break, and others might appear as a rapid rising and falling of the water level.

The highest water levels would depend on the tide and the size of the event – the largest events could raise the water level up to several metres higher than the predicted tide levels.

The visualisation below represents a tsunami in a fictional location, and shows the rise and fall of water levels (with time sped up).

Tsunami visualisation in a fictitious location (created by the IT Innovation team at the University of Newcastle).

What area is at highest risk?

A tsunami is not just one single wave, but generally a sequence of waves, lasting hours to days. Within the Harbour, larger waves are most likely to breach land, and high tide increases the risk.

The narrow part of Manly – where The Corso part-pedestrian mall is located – is one of the most exposed locations. The largest tsunamis we could expect may flood the entire stretch of The Corso between the open ocean and the Harbour.

The low-lying bays on the southern side of the Harbour could also be affected. A tsunami large enough to flood right across Manly is estimated to have a minimum ARI of 550 years, or at most a 12% chance of occurring over an average lifetime.

Maximum inundation estimated to occur for a tsunami sourced from a 9.0Mw earthquake at the Puysegur trench.
Kaya Wilson, Author provided

Examining these worst-case scenarios over time shows how this flooding across Manly may occur from both the ocean side and the harbour side, isolating North Head.

Maximum inundation estimated to occur for a tsunami sourced from a 9.0Mw earthquake at the Puysegur trench and an animation showing the arrival of this tsunami at high tide. Each frame of the animation represents a two minute time interval.

How fast would a tsunami move?

Even though the smaller tsunamis may not flood the land, they could be very destructive within the Harbour itself. Our modelling shows the current speeds caused by smaller tsunamis have the potential to be both damaging and dangerous.

The map below shows the maximum tsunami current speeds that could occur within the Harbour for the largest event we could reasonably expect.

Maximum current speeds estimated to occur for a tsunami sourced from a 9.0 magnitude earthquake at the Puysegur trench.
Kaya Wilson, Author provided

Areas exposed to the open ocean and locations with a narrow, shallow channel – such as those near the Spit Bridge or Anzac Bridge – would experience the fastest current speeds. A closer look at the area around the Spit Bridge, shows how even smaller tsunamis could cause high current speeds.

The animation below shows a comparison between the current speeds experienced during a regular spring high tide and those that may occur if a tsunami generated by a 8.5 magnitude earthquake on the New Hebrides trench coincided with a spring high tide. A tsunami of this size (0.5m when outside the Harbour) has been estimated to occur once, on average, every 110 years (a 47% chance of occurring over a lifetime).

Current Speed animation and maximum current speeds expected to occur at the Spit Bridge for a tsunami sourced from a 8.5MW earthquake at the New Hebrides trench. Each frame of the animation represents a 2 minute time interval.

This video below shows similar current speeds (7m/s based on video analysis) when the Japanese tsunami of 2011 arrived in the marina in Santa Cruz, California, and caused US$28 million of damage.

A small, fast-moving wave can have a huge impact.

Historical records show us what happened when a tsunami generated by an earthquake off Chile reached Sydney Harbour in 1960. We didn’t have any instruments measuring current speeds then, but we have witness accounts and we know that many ships were ripped from their moorings.

Fort Denison tide gauge records of the 1960 Chilean tsunami in Sydney Harbour.
NSW Office of Environment and Heritage holdings

A whirlpool and significant erosion was also reported in the Spit Bridge area. Photographs from the time show just how much sand was washed away at Clontarf Beach.

Clontarf beach erosion: (Left) 2014 in usual sediment conditions and (right) 1960 post tsunami.
Northern Beaches Council holdings

How to stay safe

A large tsunami affecting Australia is unlikely but possible. Remember that tsunamis are a sequence of waves that may occur over hours to days, and the biggest wave in the sequence could occur at any time.

The Joint Australian Tsunami Warning Centre (JATWC), jointly operated by Geoscience Australian and the Bureau of Meteorology, provides a tsunami warning system for all of Australia.

Warnings when issued are broadcast on radio and television, through the Bureau of Meteorology Tsunami warning centre and on twitter (@BOM_au).

State Emergency Services are trained to respond to a tsunami emergency and there are online resources that can help communities with awareness and preparation.

The bathymetry compilations used by this research are publicly available and can be viewed as a publication with links for free download.

Kaya Wilson, PhD Candidate, University of Newcastle and Hannah Power, Senior Lecturer in Coastal Science, University of Newcastle

This article is republished from The Conversation under a Creative Commons license. Read the original article.