Climate change brings earlier arrival of intense hurricanes

Intense tropical cyclones are one of the most devastating natural disasters in the world due to torrential rains, flooding, destructive winds, and coastal storm surges. New research co-authored by a University of Hawai'i at Manoa atmospheric scientist revealed that since the 1980s, Category 4 and 5 hurricanes (maximum wind speed greater than 131 miles per hour) have been arriving three to four days earlier with each passing decade of climate change. Their findings were published recently in Nature.

"When intense tropical cyclones occur earlier than usual, they cause unexpected problems for communities," said Pao-Shin Chu, atmospheric sciences professor in the UH Manoa School of Ocean and Earth Science and Technology and Hawai'i State Climatologist. "Moreover, the earlier advance of these storms will overlap with other weather systems, for example local thunderstorms or seasonal monsoon rainfall, and can produce compounding extreme events and strain the emergency response."

Changes in many characteristics of intense hurricanes under a warming climate, for example, the number, intensity, and lifespan, are fairly well-studied. However, little is known about changes in the seasonal cycle of these intense events.

Using satellite data, historical tropical cyclone tracks, NOAA rainfall records, and various statistical methods, Chu and co-authors found that there has been a significant shift of these intense tropical cyclones from autumn to summer months since the 1980s in most tropical oceans. The effect was particularly observed in the eastern North Pacific off the coast of Mexico, where most hurricanes near Hawai'i come from; the western North Pacific; the South Pacific; the Gulf of Mexico; and the Atlantic coast of Florida and the Caribbean.

"It was surprising to consistently see earlier arrivals when we independently assessed satellite data and conventional ground-based observations of intense tropical cyclones," said Chu.

In August 2017, for example, Hurricane Harvey, a Category 4 hurricane, made landfall on Texas and Louisiana and inflicted catastrophic flooding and more than 100 deaths.

Using simulations from multiple global climate models (e.g., high-resolution CMIP6 models), the team detected warmer oceanic conditions developed earlier, which favored the earlier onset of intense tropical cyclones. Further, they found that the warming was primarily driven by greenhouse gas forcing.

"In a future with high carbon dioxide emissions, the earlier shifting trend is projected to be amplified," said Chu.

In South China and the Gulf of Mexico, the earlier onset of intense tropical cyclones contributes significantly to an earlier onset of extreme rainfall.

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When natural disasters strike locally, urban networks spread the damage globally

When cyclones and other natural disasters strike a city or town, the social and economic impacts locally can be devastating. But these events also have ripple effects that can be felt in distant cities and regions -- even globally -- due to the interconnectedness of the world's urban trade networks.

In fact, a new study by researchers at the Yale School of Forestry & Environmental Studies finds that local economic impacts -- such as damage to factories and production facilities -- can trigger secondary impacts across the city's production and trade network. For the largest storms, they report, these impacts can account for as much as three-fourths of the total damage.

According to their findings, published in the journal Nature Sustainability, the extent of these secondary costs depends more on the structure of the production and supply networks for a particular city than on its geographic location. Regional cities that are dependent on their urban network for industrial supplies -- and that have access to relatively few suppliers -- are most vulnerable to these secondary impacts. Larger, global cities such as New York and Beijing, meanwhile, are more insulated from risks.

"Cities are strongly connected by flows of people, of energy, and ideas -- but also by the flows of trade and materials," said Chris Shughrue '18 Ph.D., lead author of the study which is based on his dissertation work at Yale. He is now a data scientist at StreetCred Labs in New York. "These connections have implications for vulnerability, particularly as we anticipate cyclones and other natural hazards to become more intense and frequent as a result of climate change over the coming decades."

The paper was co-authored by Karen Seto, a professor of geography and urbanization science at F&ES, and B.T. Werner, a professor from the Scripps Institution of Oceanography.

"This study is especially important in the context of climate impacts on urban areas," Seto said. "Whereas we tend to consider a city's vulnerability to climate change as limited to local events, this study shows that we need to rethink this conceptualization. It shows that disasters have a domino effect through urban networks."

Using a simulation coupled with a global urban trade network model -- which maps the interdependencies of cities worldwide -- the researchers show how simulated disasters in one location can trigger a catastrophic domino effect.

The global spread of damage was particularly acute when cyclones occurred in cities of North America and East Asia, largely because of their outsize role in global trade networks -- as purchasers and suppliers, respectively -- and because these regions are particularly susceptible to cyclone events.

Often, adverse impacts are primarily caused by a spike in material prices, followed by production losses to purchasers. These production losses eventually can cause industrial shortages, which can then induce additional cycles of price spikes and shortages throughout the production chain.

Similar outcomes have been borne out following real world disasters. For instance, when catastrophic flooding occurred in Queensland, Australia, the impact on coking coal production prompted a 25-percent spike in the global costs. And the economic impacts of Hurricane Katrina extended far beyond New Orleans for several years after the historic storm.

While the example of cyclones can act as a proxy for other isolated disasters -- such as the 2011 tsunami in Japan which caused global economic disruptions, particularly in the auto sector -- the researchers say the findings are particularly relevant in terms of climate-related natural events.

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