by Daniel Brouse
Most climate change models forecast rising sea levels as the predominant threat of a warming climate to flood risks. Though sea level rise is of great concern, so should be extreme rainfall.
Both the sea and air temperatures are rising. Warm air can hold more moisture than cool air. Warmer sea temperatures result in more evaporation. Warmer air can hold more moisture. The increased moisture in the air moves over land causing inland deluges.
Hurricane Ida in the summer of 2021 is a good example. Because of the 85 degrees Fahrenheit Gulf of Mexico ocean temperature, Ida rapidly gained strength right before it made landfall jumping from a Category 1 to a Category 4 storm. The warm air allowed more moisture to be carried as rain. The storm was so large that it was able to pick up more moisture from the Atlantic Ocean. The ocean moisture was carried inland and dumped over places like Pennsylvania and New York. Ida caused record flood damage in parts of Pennsylvania. The Philadelphia Inquirer reported, “The remnants of Hurricane Ida destroyed or damaged hundreds of homes in Southeastern Pennsylvania and caused more than $100 million in public infrastructure damage across the state.” There were more deaths in the Northeastern USA than where the storm made landfall in Louisiana. The New York Times reported, “The remnants of Hurricane Ida caused flash flooding and a number of deaths and disrupted transit across parts of New York and New Jersey. The storm killed at least 43 people in New York, New Jersey, Pennsylvania and Connecticut and left more than 150,000 homes without power.”
The Journal Nature published the study Tropical cyclone climatology change greatly exacerbates US extreme rainfall–surge hazard examining how current models underestimate the risk of Rainfall–surge Hazard. “Tropical cyclones (TCs) are drivers of extreme rainfall and surge, but the current and future TC rainfall–surge joint hazard has not been well quantified. Using a physics-based approach to simulate TC rainfall and storm tides, we show drastic increases in the joint hazard from historical to projected future (SSP5–8.5) conditions. The frequency of joint extreme events (exceeding both hazards’ historical 100-year levels) may increase by 7–36-fold in the southern US and 30–195-fold in the Northeast by 2100. This increase in joint hazard is induced by sea-level rise and TC climatology change; the relative contribution of TC climatology change is higher than that of sea-level rise for 96% of the coast, largely due to rainfall increases. Increasing storm intensity and decreasing translation speed are the main TC change factors that cause higher rainfall and storm tides and up to 25% increase in their dependence.”
From the article Rising Temperatures Bringing Bigger Floods published in the Journal Science, “CO2 emissions have boosted risk of intense precipitation and consequent flooding. To determine how rising temperatures have altered flood risk, atmospheric scientist Pardeep Pall of the University of Oxford in the United Kingdom and his colleagues ran thousands of climate simulations. In roughly half of them, they reduced atmospheric concentrations of carbon dioxide to levels measured in the year 1900, and they adjusted ocean temperatures and the amount of Arctic sea ice—which affects high-latitude weather patterns—accordingly. In the other simulations, they modeled modern conditions. Then they compared the rainfall amounts generated in both types of simulations. Finally, they fed the rainfall values into a model that assesses the potential for flooding. In 90% of the simulations, results suggested that the flood risk in England and Wales in autumn 2000 was at least 20% higher than it would have been in 1900.”
As the Earth warms, the air will hold more moisture. More moisture-laden air moves over land and creates atmospheric rivers (Pineapple Express). The Journal EOS in the article Atmospheric Rivers Spur High-Tide Floods on U.S. West Coast said, “Atmospheric rivers are narrow bands of moisture that travel across the lower troposphere, generally at the leading edges of massive low-pressure systems. At their peak, they can carry as much water through the sky as the Amazon River does on land. They unleash intense winds and heavy rain as they surge across the Pacific Ocean, eventually making landfall on the U.S. West Coast, contributing to many high-tide flooding events.”
The atmospheric rivers also bring heavy rainfall inland causing extreme flooding. In October of 2021 NOAA said, “a convergence of storms brought more than half a foot of rain to parts of the Bay area in addition to strong winds, flash floods, and mud/landslides. They also bring the potential for heavy snow to higher elevations in the Sierra Nevada mountain range.” (Atmospheric River Hits the West Coast)
More articles on Flood Insurance, Extreme Weather Events, Rising Sea Levels and Global Warming
