Most road and rail infrastructure on the planet is “inevitably” exposed to extreme weather due to climate change, finds a new study, with its international team of analysts urging policy-makers to prepare in advance and minimize losses.

Just published in the journal Earth Futures, the analysis by researchers from China, the Netherlands, and the United States combines global data on 18.9 million kilometres of rail and road infrastructure with the latest in sustainable development and climate forcing models to investigate the change in the exposure of this infrastructure to eight meteorological hazards: maximum temperature, thaw-freezing index ratio, annual temperature difference, annual freeze-thaw cycles, annual precipitation, maximum daily precipitation, annual torrential rain days, and annual drought + heavy rain compound events.

Defined as “heavy rain with more than 25 millimetres per day occurring in the same month as a drought event,” the compound event indicator is new. The study team included it to “highlight a previously overlooked aspect in meteorological analysis—the potentially hazardous state of slope and subgrade (the roadbed over which asphalt is laid, for example) when heavy rainfall occurs on dry or cracked soil.”

The analysis is based on the understanding that transport infrastructure built to “design standards based on historical observation” will not be adequate to weather future extreme weather events brought on by global heating. The authors cite the case of a train track catching fire on a bridge in London in July, 2022, when a searing heat wave raised temperatures in the United Kingdom capital beyond 40°C. Designed for “traditional cool summers,” UK railways are not prepared for the record-breaking heat that is coming down the track.

And as an example of the dangers posed by extreme precipitation, the authors point to the record-breaking rainfall which pounded Zhengzhou, the capital of east-central China’s Henan province, in mid-July, 2021. Lasting roughly three days, the deluge included a peak period which saw rain hammering down at 201.9 millimetres per hour.

11 Months to Fix a Road

The severe rainfall “damaged tens of thousands of roads” across the capital, “causing direct economic losses of at least US$1.6 billion,” the researchers write. “Most of the damaged roads required months to rebuild or repair, with the longest repair period for severely damaged roads reaching 11 months.” 

But still, overall, extreme temperatures (especially heat) pose a bigger threat than extreme rainfall, they note.

The team used a range of shared socioeconomic pathways (SSPs) and future climate change scenarios, ranging from the most to least optimistic combinations of future social development and greenhouse gas emissions.

“Our findings indicated that global extreme heat and permafrost thawing pose particularly severe threats,” the authors write. Under an “extreme” climate scenario “which we may be on track for under current global efforts,” 78.4% of global rail and road infrastructure assets totalling about14.8 million kilometres will be exposed to extreme temperature changes by the late 21st century.

Under that same scenario, “record-breaking extreme heat occurs with extremely high probability around the globe, with greater than 90% annual record-breaking probability of maximum temperature in the late 21st century,” the authors warn. That means “record-breaking extreme heat would become the common state,” particularly in equatorial countries, southern Europe, and western North America.”

That choice of future also carries “increased risk of heavy rain events occurring in dry months, especially in the late 21st century under the scenarios of rapid development and high radiative forcing, and more infrastructure is expected to be impacted.” Rail and road assets in West Africa, South Africa, central South America, India, southeastern North America, and Southeast Asia face particular exposure to such compound events.

Emission Cuts Can Reduce Exposure

Aggressive emission reductions still offer considerable protection, the authors note. In the more optimistic future scenarios, “we anticipate a consistent reduction in cumulative [expected annual exposure, or EAE] to 37% and 89% of total assets, respectively.” East North America stands to “gain significantly”, with cumulative exposure reduced from 157% in the most dire scenario to 38% in the most hopeful one.

In the Western Indian Ocean, cumulative EAE falls from 162 to 39%. “Of particular significance is the potential reduction in extreme heat exposure, decreasing from near-total exposure (98%) to 24% and 79%, respectively” across three different scenarios, the authors write.

The study recommends a range of adaptive and preparatory measures, including “enhanced standards for technical testing and facility retrofitting or reinforcement, improved early warning and forecasting systems, and adjusted design safety factors when planning new infrastructure projects.” And they urge all responsible parties to “work closely with communities and local governments to develop climate change adaptation strategies.”

“Even if global efforts to reduce emissions bring benefits, exposure is inevitable,” the authors say. So “these efforts are key to fortifying future infrastructures against the projected rise in extreme weather events, ensuring their resilience and ability to respond effectively.”