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!

HK’s tracking worst-case scenario impacts for Very Hot Days & Hot Nights + we’ve already warmed by 1.8°C. Less cold days but heavier & more frequent rains lie ahead
HK's coastal defence, drainage & building codes work for now but may not cope with future of multi-meter SLR, record-breaking rains + typhoon storm surges/ wind speeds
HK’s been lucky with typhoons as neighbours face 5m storm surges. Advancing climate threats demand no-regret adaptation; like Singapore, HK must go all-in on adaptation

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 


Further Reading

  • Code Red: 8 things you need to know about water in IPCC AR6 IPCC AR6 is a code red for water too! CWR’s Debra Tan shares 8 things you may have missed on water and urges to delay no more
  • 8 Asia Water Risks: Here Today & Here To Stay In Asia – Damaging typhoons, life & business disrupting water outages and threatening sea level rise… China Water Risk review’s 8 water threats too great to miss in Asia from just the past 3 years
  • No-Sense Climate Strategies: From DSD To HSBC – Hong Kong’s shortsighted & unrealistic climate plans will leave key assets & infrastructure exposed that mean the government, companies, investors and the public are even more exposed. China Water Risk’s Dharisha Mirando & Debra Tan expand
  • HK Submerged? Is This Map For Real? – Rising sea level is a catastrophe waiting to happen but we have to avoid alarmism & choose the right map to visualise the risks. Getting the right scenarios also matter. Find out more in our review
  • Sea Level Rise – What The Science Tells Us – What’s the latest on sea level rise projections? HKU’s Dr. Nicole Khan shares key findings from her survey of 100+ sea level experts, as well as talks risks to Hong Kong and what we should take away from COVID-19
  • Future SLR Projections & Biggest Worries – In this follow up interview, HKU’s Dr. Nicole Khan shares her biggest concerns on how future SLR projections are rising higher & faster than thought & shares the best approach for building realistic scenarios
More on Latest
  • 2021 World Water Week: 3 Key Action Takeaways to Build Resilience Faster – 2021 World Water Week gives 3 important action takeaways for us to charge forward & build resilience faster – CWR’s Soomin Park breaks them down
  • Sponge City Is Transforming Urban Flood Management – Sponge city was launched to combat urban flood risks yet public has doubts over its effectiveness. What does the Chinese govt do to promote the policy? What role does social media play? Dr. Faith Chan, Dr. Dimple Thadani & Lei Li break it down
  • Not Just a Drop in the Ocean – Global water guru Professor Asit Biswas & Singapore PUB’s CEO Peter Joohee Ng share how the country is setting the example on climate change & water mgmt by formulating long-term plans despite only accounting for 0.1% of global GHG emissions
  • 3 First Steps To Protect HK From Rising Seas – The IPCC AR6 warnings on rising seas bring bad tidings for Hong Kong. If you are 20 & younger, HK could become the new Atlantis in your lifetime unless we take action now. See 3D maps of areas submerged and get on top of what you need to do to survive, adapt & thrive
  • Designing Resilience – 2 Architectural Students’ Take on Coastal Threats – Shocked by HK’s coastal threat, HKU’s Fergal Tse & Oscar Wong became CWR’s interns to re-design Victoria Harbour. We sit down with them to understand what local youths think about climate change and & their projects with CWR changed their perspective
Chien Tat Low
Author: Chien Tat Low
Low has extensive inter-disciplinary research experience, which although wide-ranging, focuses on identifying hotspots to facilitate better planning. At CWR, Low uses spatial modelling and statistical analysis as well as remote sensing, cartography, and geo-statistics to map and assess water risks. In addition, he helps manage CWR’s extensive network of contributors and partners. CWR is Low’s first foray outside academia and he hopes to apply his 12 years of scientific know-how toward enhancing the understanding of water risk in Asia, including spatial temporal variabilities of anthropogenic and natural factors on water resources. Previously, Low was a postdoctoral fellow at the University of Hong Kong where he devised methodologies to measure and benchmark the quality of urban life in an Asian context. As a certified GIS Professional, he also taught GIS and spatial analysis modules there. Low’s research on urban, human and environmental health is published in 11 prominent international peer-reviewed journals; he has also written a chapter in a book on managing environmental hazards. His PhD thesis on place effect on human well-being was prize-winning. Low is currently the reviewer editor for the journal “Frontiers in Environmental Informatics” and also reviews other international journals such as “Applied Geography”.
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Debra Tan
Author: Debra Tan
Debra heads the CWR team and has steered the CWR brand from idea to a leader in the water risk conversation globally. Reports she has written for and with financial institutions analyzing the impact of water risks on the Power, Mining, Agricultural and Textiles industries have been considered groundbreaking and instrumental in understanding not just China’s but future global water challenges. One of these led the fashion industry to nominate CWR as a finalist for the Global Leadership Awards in Sustainable Apparel; another is helping to build consensus toward water risk valuation. Debra is a prolific speaker on water risk delivering keynotes, participating in panel discussions at water prize seminars, numerous investor & industry conferences as well as G2G and academic forums. Before venturing into “water”, she worked in finance, spending over a decade as a chartered accountant and investment banker specializing in M&A and strategic advisory. Debra left banking to pursue her interest in photography and also ran and organized philanthropic and luxury holidays for a small but global private members travel network She has lived and worked in Beijing, HK, KL, London, New York and Singapore and spends her spare time exploring glaciers in Asia.
Read more from Debra Tan →