Hong Kong Is Tracking Worst-Case Scenario Impacts – 8 Reasons To Act Now
By Chien Tat Low, Debra Tan 24 September, 2021
With this summer of rising climate risks, don’t get caught out. We run through 8 reasons why HK must to act now – from hot weather, strong winds to flash floods – be prepared!
This summer was a new wake-up call, changing our understanding of new extremes. As if the numerous droughts, fires and floods around the world were not enough of a signal that we must pay attention to climate change, it even hailed in Hong Kong in mid-September!
Falling ice in a hot day with over 30°C is certainly unusual for Hong Kong. But actually, as the climate is changing, we are now seeing more extreme and record-breaking weather events in Hong Kong that are tracking impacts under the worst-case emission scenario of 3-5°C, when we are only at 1.1-1.2°C of warming today. Given that we’ve underestimated impacts, it is likely that our adaptation planning is inadequate and needs to be revisited to ensure that we are safe and properly protected against climate threats ahead.
Here are 8 reasons why we need to step up protection and safeguard Hong Kong…
1. Hong Kong has already warmed by 1.8°C compared to the global average of 1.1-1.2°C
We have been sweating through the summer and it is getting hotter and hotter each year. Indeed, the temperature in our city has been steadily rising as shown in the chart below. The HKO projects that by 2030 the temperature will rise by 0.6-1.4°C (relative to 1986-2005) under the worst-case scenario or RCP8.5. However, today Hong Kong is already 1.8°C hotter. This is much worse than the worst-case projection for 2030 and is closer to the projection for 2040. So we are 20 years ahead of time in terms of warming – clearly, we have underestimated how hot this city could be in the future.
2. Record breaking “Very Hot Days” & “Hot Nights” in 2020 – worse than 2040’s RCP8.5
As temperatures rise, the annual number of “Very Hot Days” (daily maximum temperature >= 33°C) in Hong Kong is on the rise too. As shown in the chart below, the annual average “Very Hot Days” in 2011-2020 has more than doubled relative to the previous decade. In 2020, Hong Kong hit a record-breaking 47 “Very Hot Days”, which again far exceeded both the high-end of the worst-case scenario projections for 2030 of 40 days and 2040 of 46 days. Again, we have seriously underestimated climate impacts.
In 2020, Hong Kong broke records with 47 “Very Hot Days” & 50 “Hot-Nights” – tracking worst-case projections
Not surprisingly, it’s also getting hotter at night in Hong Kong. The “Hot Nights” (daily minimum temperature >=28°C) in 2020 reached a record-breaking 50 days in 2020, tracking the worst-case projection for 2030 of 25-56 days. Over the last 10 years, the annual average “Hot Nights” has also increased nearly 60% compared to the previous decade.
It appears that “Very Hot Days” and “Hot Nights” will only increase in the future. Already in 2021, we have had 38 “Very Hot Days”, and 46 “Hot Nights” so far (up to 31 August). Since a reprieve is unlikely, we should start developing a greener plan to keep our city cool. Singapore already has the world’s largest underground district cooling system and started the “Cooling Singapore” project to develop solutions to address the city’s excess heat. These seem like smart moves for Hong Kong to follow, especially as our city urban landscape is even more compact than Singapore’s and will trap more heat as temperatures rise.
3. Less and less “Cold Days” ahead
On the other hand, we are experiencing fewer “Cold Days” (daily minimum temperature <= 12°C) in Hong Kong. As shown in the chart below, the average number of “Cold Days” has been gradually decreasing since 1961. But don’t throw away your winter clothes just yet because there still will be cold days ahead, just fewer of them.
4. Sea level rise (SLR) jumped 20cm in the 1990s & could jump again after around 2060 to 2.47m by 2100 – we are not prepared!
Rising temperatures also cause higher and faster sea level rise (SLR). Not only because mountain glaciers and polar ice sheets are melting, but oceans are also warming and expanding causing seas to rise. Did you know that thermal expansion from ocean warming has caused 50% of SLR so far according to the IPCC AR6?
SLR rose steeply by ~20cm during 1990-2020…
…so seas do not rise in a straight line but could exhibit an abrupt jump over time
So where are we on SLR in Hong Kong? According to the HKO, the mean sea level in Hong Kong (Victoria Harbour) rose at a rate of 3.1cm per decade during 1954-2020. This doesn’t sound like a lot and could be misleading because when we look closely, SLR rose steeply by ~20cm during 1990-2020. This means that after 1990, seas have risen at a rate of 6.7cm per decade – see chart below:
Scientists warn that projected sea level rise could face an abrupt jump after around 2060 if we don’t decarbonise sooner to keep within 1.5-2°C
The key point to take away here is that seas do not rise in a straight line but could exhibit an abrupt jump over time. Now, scientists warn that projected sea level rise could face an abrupt jump after around 2060 if we don’t decarbonise sooner to keep within 1.5-2°C. Such observations and research led the IPCC AR6 to warn that SLR of “2m by 2100 and 5m by 2150 under a very high GHG emissions scenario cannot be ruled out due to deep uncertainty in ice sheet process”.
These numbers may sound surreal and unimaginable, but they could become our reality. Some governments are revisiting their adaptation planning for these new levels – Copenhagen is building a new island to protect the city, Singapore has already announced it will adapt to 3m of SLR by 2100, and London is considering bringing forward the raising of the embankment along the River Thames.
HK could face >2m SLR by 2100 yet DSD’s plans just protect against 0.49m SLR
The almost 100 Central Banks in NGFS are also recommending stress testing for physical risks under the “Current Policies” scenario (+3°C by 2100). This mean the highest SLR for Hong Kong could be 2.47m according to Climate Analytic, a non-profit organisation that developed NGFS’s Climate Impact Explorer tool. Note that this is not far off our worst-case stress test recommendation of 2.9m by 2100.
Meanwhile, Hong Kong’s Drainage Services Department (DSD) has plans to only protect against 0.49m of SLR by 2100.
In light of the latest science, surely we should be upgrading our adaptation plans to ensure that they are up to date and will protect us from climate scenarios which “cannot be ruled-out”. If we do not act…
Hong Kong could look like this in your lifetime.
5. More thunderstorms & record-breaking rains ahead…
It also feels like there’ve been more thunderstorms recently. Indeed, there are increasingly more thunderstorm days since 1961 – please see the chart on the right.
With thunderstorms on the rise, we are seeing more extreme rains too…
According to the HKO, extreme rain records are being broken in a shorter period of time – the hourly rainfall recorded at HKO’s headquarters has been broken several times in the last few decades, whereas it used to take several decades to break the record in the past – please see the chart below:More specifically, the HKO also warn that the frequency of an extreme 3-hour rainfall event of >200mm used to be once in 41 years back in 1900; but has now increased to once in 21 years in 2000.
Can our drainage system cope with more increasingly extreme rainfalls ahead?
Going forward, can Hong Kong’s current drainage system cope with increasingly record-breaking extreme rainfalls? We must be prepared for the worst; after all, Zhengzhou experienced a 1,000-year rain event this July. On this front, we are worried because it appears that Hong Kong has underestimated future rainfall projections, which brings us to the next point…
6. Current rainfall is tracking the worst-case projections for 2030; we need to prepare for more rain
Currently Hong Kong has 1,400mm to 3,000mm total rainfall per year depending on location. But looking forward, Hong Kong is projected to receive more and more rain in the future as can be seen in the chart below. According to the HKO, Hong Kong could have +317mm more rainfall than the yearly average under the worst-case scenario projections for 2030, but this was already exceeded in late 1990’s with +343mm more rainfall than the yearly average.
The level of projected worst-case rainfall excess by 2100 is 2x higher than what the DSD is protecting for…
So we are likely tracking worst-case projections for rainfall; and we are only at 1.8°C warming in Hong Kong. Imagine what will happen when we reach 3°C of warming. By 2100 +806mm or a 27% increase in rainfall could be a reality. Unfortunately, these levels are almost 2x higher than what the DSD is protecting for, a 13.8% increase in rainfall by 2100.Surely it’s time for Hong Kong to revisit the adequacy of our drainage system and ensure that they are resilient to the new climate extremes. It’s not just Hong Kong, Singapore is also experiencing new rain records this year – see what the CEO of Singapore’s National Water Agency has to say about preparing for more rain ahead.
And Singapore doesn’t even have typhoons like Hong Kong. These could bring even more extreme rainfalls as well as storm surges which will increase the risk of flooding.
7. More T8-T10 typhoons ahead
T10- Mangkhut in 2018 was a wake-up call for Hong Kong. Over the years, Hong Kong has been hit by more and stronger typhoons. Between 2011-2020, the number of typhoons was up from 48 to 58. Among these typhoons, T8-T10 also increased from 14 to 19. It is in line with scientists’ prediction that typhoons will become stronger and possibly more frequent because of climate change.But Hong Kong has been lucky so far as we have not had any Mangkhut-like T10 typhoons since 2018. However, devastating typhoons did hit our neighbours – Typhoon Hagibis and Faxai in Japan (2019), Typhoon Molave and Typhoon Goni in South East Asia (2020), and Typhoon In-fa in China (2021). All these typhoons resulted in the loss of lives and caused billions of economic damages.
So, we must not be complacent. Besides storm surges, which we will discuss in the next point, we must also start talking about wind speed.
Mangkhut put Hong Kong’s building resilience to the test…should we be rethinking skyscrapers?
Mangkhut’s high winds caused at least 500 reports of smashed windows or glass curtain walls across Hong Kong. In fact, the maximum sustained wind speed of Mangkhut reached 250km/h and its wind gusts even reached 256km/h. Luckily this was for short periods with the majority of Hong Kong experiencing gusts of 150km/h as buildings in Hong Kong are only built to withstand winds of 250km/h according to Hong Kong’s Buildings Ordinance.
This clearly raises questions around Hong Kong’s resilience to wind speeds. Is the Code strong enough to protect Hong Kong given that Mangkhut’s sustained wind speeds were already at 250km/h? Should we be rethinking skyscrapers?
We may well need to take action sooner than we think as the IPCC warned that by 2050 a 1-in-100 year storm could be an annual occurrence for most low-lying cities like Hong Kong; since Mangkhut was a 1-in-50 year storm, Hong Kong better be prepared
8. Storm surges of 2m+ are here today & could cause 5-7m of storm tides
In 2018, Mangkhut brought record breaking storm surges of 2-3m across Hong Kong. With tides, Hong Kong was hit with maximum sea levels or storm tides of 3.88m in Quarry Bay and 4.71m in Tai Po Kau. If Mangkhut hit Hong Kong directly at astronomical high tide, the storm tides could have reached 5-7m and caused large swathes of low-lying reclaimed land to flood.
Evidently, adapting to multi-meter SLR is not going to be enough as we will also have multi-meter storm surges to deal with. Recent typhoons in the region have already resulted in storm surges of 2m-5m as shown in the chart below:
By 2100, we may well have to protect against 10m of coastal flooding – 2.47m of SLR + 2.5m of maximum high tides + 5m of storm surges
Please note that the above numbers denote storm surges and not storm tides as the latter will depend on tide levels at the time of the storm. So by 2100, we may well have to protect against 10m of coastal flooding – 2.47m of SLR + 2.5m of maximum high tides + 5m of storm surges. It is clear that by 2100, with multi-meter SLR, even a 1m+ storm surge will be a challenge.
And that’s not even including overtopping waves which can already be multi-meter high – such as 3.4m during Typhoons Faxai and 15m during Hagibis that swept Japan in 2019.
This could put Hong Kong at high coastal flooding risks as 27% of its population and 70% economic activities are packed into just 6% of low-lying coastal reclaimed land. Nearly 70% of commercial activities as well as key infrastructure including the airport and ports are also clustered in coastal areas.
Hong Kong should embrace the risks now & adapt to thrive
The worst-case scenario impacts are already being felt in Hong Kong today and these are likely to get a lot worse if we do not rein in global emissions. Hong Kong must fast-track decarbonisation to 2030-2040 but given the current state of global decarbonisation, Hong Kong should follow Singapore and place more emphasis on adaptation.
We must learn to live with deep uncertainties ahead by putting in place no-regret adaptation planning
We are entering an era of fast-evolving new climate risks. We must learn to live with deep uncertainties ahead by putting in place no-regret adaptation planning.
Perhaps we need to start a grand redesign of all Hong Kong buildings – one that takes into consideration higher wind speeds from typhoons that would occur yearly from 2050, hotter and sweatier days ahead, and flash floods from record-breaking rains. This climate-ready and resilient Hong Kong must also survive rapid multi-meter SLR, which could permanent submerge low-lying areas and must be net zero or even carbon positive. It’s time to Re-IMAGINE HK – join us to adapt and thrive.
We will be running a series of Re-IMAGINE HK labs to brainstorm outcomes so email us if you would like to participate!
Check out how Hong Kong could look like by 2100 and 2150 if left unprotected…
|Re-IMAGINE HK 2100 Coastal Threat Snapshot||Re-IMAGINE HK 2150 Coastal Threat Snapshot|
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