Recent days of heavy rainfall show the kind of weather Hong Kong must prepare for in an era of accelerating climate change The past week has seen four incidences of black rain. On Tuesday, two separate warnings were issued before 9am, so parents were all working from home as kindergarten and holiday activities were cancelled, leaving the city much quieter than usual.
This quiet prompted me to ask three questions. Is this the usual bad weather or driven by climate change? If it is long-term change, what are the impacts and costs? And what are we doing about it?
According to the Hong Kong Observatory, annual rainfall is increasing slowly but occurring in much more intense periods. Black rainstorms are more frequent and intense, meaning more intense run-off. The most recent black rain warning was the second-longest on record, with the longest coming in 2023. Meanwhile, typhoons have increased noticeably in strength.
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Why is this? There is a general agreement that the Earth's climate is changing because of a combination of natural and human factors, including variation in sunlight, Earth's orbital changes and volcanic activity. However, natural effects have been overshadowed by the increasing atmospheric concentration of greenhouse gases from human activity since the Industrial Revolution.
The Intergovernmental Panel on Climate Change (IPCC) has produced six assessment reports since 1990. As the science becomes clearer, each report is more certain, urgent and strident than the last. Human-induced climate change has become a major challenge of our time, and now it is on the streets of Hong Kong.
The Observatory has recorded sea surface temperatures increasing at 0.2 degrees Celsius per decade since 1975. Air temperatures are increasing, too, at a rate of 0.37 degrees per decade since 1995, a rate more than twice as fast as the trend from 1885 to 2024.
The number of hot nights - with a minimum temperature of 28 degrees - and very hot days - with a high of 33 degrees or more - has surged in the past century. At the same time, the number of cold days - with a temperature of 12 degrees or lower - has fallen by nearly half.
Hotter air has more energy, meaning it can carry and deposit more rain. More energy in the climate also means stronger winds. Warmer oceans expand in volume and glacial melt adds to the volume, so we are at risk from a combination of heat, more rainfall, sea level rise and stronger storm surges.
More intense rain and wind, interspersed with hotter, drier periods, affect ecosystems and human systems. They can affect human health and disease, water supply, agricultural production, supply chains and transport systems such as the MTR and harbour tunnels. They can also affect real estate, a fact of which insurance companies are well aware.
The insurance industry is the canary in the coal mine of climate. Insurance costs are rising, to the point some assets are becoming uninsurable. Without insurance, lending and mortgages are impossible. Without lending, property values collapse.
One civil engineer I know has complained that the historical climate data they use for infrastructure design is based on a climate that no longer exists. Weather is exceeding all known norms. So what standards do engineers design to, and who is liable if something goes wrong?
In 2022, the Drainage Services Department laid out new flood management standards for civil engineers. But what is equally important is whether the city's infrastructure, which substantially predates that 2022 update, can meet those new standards. Upgrading drainage systems can take years and is a massive technical and financial undertaking, especially in a climate of increased scrutiny of government spending.
So far, Hong Kong's infrastructure has proven to be remarkably resilient - arguably world-class - when compared to other cities facing similar rainfall intensity. But how long will that be the case?
Every nation which is a signatory to the Paris Agreement has to show how it will achieve net zero carbon emissions by 2050. China is expected to publish its latest five-year plan to reduce carbon emissions later this year, and Hong Kong is likely to be part of that plan. Next year, the city will revise its own Climate Action Plan.
In 2015, the Financial Stability Board set up the Taskforce on Climate-Related Financial Disclosure with the goal of recommending the types of information that companies should disclose regarding risks related to climate change. Since then, stock exchanges around the world - including the Hong Kong stock exchange - have started requiring annual reporting on climate impacts, risks and opportunities for listed companies.
There is no equivalent obligation for cities as an entity. However, our listed companies and communities are dependent on city assets - transport, power, water, supply chains, schools and hospitals - which are largely outside corporate control but can be influenced or controlled by the city.
The Legislative Council has discussed plans to enhance forecasting. Meanwhile, the business community has long asked for a cross-departmental platform on all climate-related information, including a risk map with projections aligned with the latest IPCC assessment, similar to the London Climate Risk Map or the European Climate Risk Assessment. There is also a need for a more detailed and actionable plan than we have now to reach Paris Agreement targets.
Meanwhile, global carbon emissions continue to increase. The temperature rises. Rainy days will continue to get rainier. The typhoons get more powerful. The valuable assets of Hong Kong are more at risk from intense rain, stronger typhoons, sea level rise and lost days like Tuesday.
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