Star Guest at Hong Kong Rain Summit Highlights Threat to Cities
Blind Spot
Hong Kong’s record-breaking deluge provided a fitting backdrop to a scientific conference on extreme rain last week. Too perfect, perhaps, with the downpour forcing the first day of the gathering online.
The irony was not lost on the conference crowd. Organizers called the rain “our star and self-invited participant,” and several presenters changed their slides to directly address the torrent that flooded roads, stranded cars, and triggered landslides. A Danish climate scientist quipped that he was grateful for the opportunity to “see convective precipitation first hand.”
The intense downpour was also a reminder of the real and growing threat posed by extreme rain worldwide, something that’s particularly acute in cities. Complex topography in urban areas can stump weather forecasters, and higher population density puts more lives at risk.
Traditional climate models struggle to simulate sudden and intense rain, said Andreas Prein, a professor at ETH Zurich who specializes in high-resolution weather modeling. That creates a huge blind spot for city planners and policymakers, because it’s those detailed projections that can help stress-test urban infrastructure and game-out emergency response plans, he added, speaking at the conference after it had returned to an in-person gathering.
Scientists are tackling this problem with what’s known as convection permitting climate models, a relatively young field that takes a physics-based approach to presenting a finer view of small-scale processes such as localized convective rain. Put simply, it enables better simulations of thunderstorms, hailstorms, and extreme precipitation, and how they might evolve in the future.
Those insights are key to assessing and planning for emerging weather and climate risks in places such as Hong Kong, which recorded its heaviest daily August precipitation since 1884 last week. Other cities such as Valencia in Spain and Guangzhou in China have in recent years also seen extreme rainfall.
For now, there’s a lingering question mark over the complexities of urban physics. For example, changing land use patterns and temperature contrasts between downtown and suburban areas can affect weather conditions in a city, which can in turn influence regional weather and climate systems.
“Cities are not only recipients of weather,” said Fei Chen, a professor at the environment and sustainability division at the Hong Kong University of Science and Technology. “They are actually making their own weather.” — Mary Hui
The Week Ahead
AMERICAS
Most of the US, including the Rocky Mountains from Wyoming to northern Arizona and east to Nebraska, will likely experience warmer than normal temperatures through Aug. 18 to 24, the US Climate Prediction Center said. Parts of the Pacific Northwest and northern New England will be closer to seasonal, with northern Maine actually cooler than normal. Rain will be close to seasonal across large parts of the US, but the Midwest from Iowa to Illinois, and parts of the US West will see below normal rainfall, the agency said.
EMEA
A high-pressure pattern amplified by former tropical storm Dexter is spreading a heat wave across Europe this week, driving up temperatures in France, Spain and the Mediterranean. Temperatures could reach 43C (109F) in parts of southwestern France, with forecasters expecting the heat to linger through much of the week. Heat and wildfire warnings have been issued across a wide swath of the continent, from the UK and Germany to Italy and Greece.
APAC
Tropical Storm Podul is tracking toward Taiwan, where it’s set to make landfall as a typhoon on the east coast on Wednesday. The system is expected to weaken as it moves across the island and reemerges into cooler waters on track for China’s Fujian province. A quasi-stationary rain band that has stalled over Japan since Sunday will start clearing on Tuesday, and temperatures will climb much above normal from the weekend.
Weather Explained
Researchers say tsunami warnings have improved dramatically since the 1960s due to better data on earthquakes, volcanoes and submarine landslides, along with advances in computer modeling and sea floor mapping.
Two million people were ordered to evacuate across the Pacific late last month after an 8.8-magnitude earthquake near Russia’s Kamchatka Peninsula sent tsunami waves rippling toward Japan, Chile, Indonesia, Hawaii and the west coast of the US.
Thirteen people in Japan were reportedly injured in the tsunami, and one person died during the evacuation, according to data from NOAA’s National Centers for Environmental Information Center. Five-meter high waves flooded the port in Severo-Kurilsk, 1.2-meter waves were recorded in Hawaii and smaller waves hit coastal areas of California and Indonesia.
Despite improvements, modeling tsunami waves and their potential effect on populated areas thousands of miles away is an ongoing challenge for researchers and emergency authorities.
The potential sources of deadly or damaging tsunamis are well-known and closely monitored, said Lisa McNeil, a professor of tectonics at the University of Southampton. The specific location and timing of tsunami-triggering events, however, is harder to pin down.
“What we don’t know, usually, is exactly which part of a fault will move,” she said. “We have an idea on a longer time scale of the probability, but not in the sense of next week or even next month.”
The height and location of potential waves are also determined by bathymetry — the depth, shape and structure of the ocean floor, which is a major factor on a tsunami’s destructive potential. McNeil says sea floor data near coastlines is particularly tricky to assemble due to challenges collecting accurate sonar data in shallow water.
McNeil says the response to the July 29 tsunami highlights lessons learned during the 2004 tsunami in the Indian Ocean, which sent 30-meter (98-foot) waves rippling across the region at more than 500 miles (805 kilometers) per hour. Poor data and an inadequate warning system were blamed for many of the 230,000 deaths. — Joe Wertz