The Effects of Hurricane Season on the Chesapeake
Floodwaters in Houston after Hurricane Harvey. (photo: David J. Phillip/Associated Press)
Agnes, Hugo, Floyd, Andrew, Katrina, and Sandy turned out to be dastardly souls. This year, we also had the misfortune of meeting those vile beings called Harvey, Irma, and Maria. These infamous characters are none other than the hurricanes that have had damaging impacts on the landscape of the United States in recent years.
As global temperatures increase, scientists have been warning that hurricanes will occur more often and be more intense. In May 2017, NOAA predicted an above-average hurricane season with anywhere between two and four major hurricanes (categories 3-5). NOAA updated this prediction in August 2017, suggesting that as many as five major hurricanes could impact the United States.The storms that make landfall are more intense due to rising global temperatures. Warm air can hold more water vapor, therefore allowing storms to hold and drop more precipitation when they make landfall.
Graphic: CNN
The 2017 hurricane season may go down in history for the unparalleled destruction caused by the frequent and intense storms. Hurricane Irma destroyed 25% of the homes in the Florida Keys and resulted in 65% of the homes having major damage. Hurricane Maria was the strongest storm to ever hit Puerto Rico. The damage from Maria decimated the energy grid and it will likely take months to restore power to the island. Hurricane Harvey, however, claims the precipitation title. The storm set the record for the most rainfall ever from a tropical cyclone in the continental United States, dropping 51 inches of rain. It is estimated that the storm dumped 27 trillion gallons of rain over Texas and Louisiana.
While the Bay region has been relatively untouched by severe weather this hurricane season, we should be mindful that severe weather events could derail improvements made to the Bay. Hurricane season overlaps at least partially with the crop harvest season. Croplands are more susceptible to erosion when the crops have been harvested and the land is barren. Additionally, strong winds and flooding events virtually eliminate the benefit of soil capturing best management practices like vegetated buffers. Strong storms also have the power to churn up and flush out legacy sediment that has been holding nutrients in place for centuries.
This photo (courtesy of Google) depicts the sediment clouds in the Susquehanna River leading into the Chesapeake Bay following Tropical Storm Lee.
The effects on the Chesapeake Bay of Tropical Storm Lee, which is by comparison a much smaller storm than either Irma, Maria, or Harvey, are well documented and informative. In September 2011, Tropical Storm Lee generated between 4 and 7 inches of rain throughout much of the Susquehanna River Basin, with some areas getting over 12 inches of rainfall and many areas experiencing flooding. The release of sediment, and therefore nutrients, from the Susquehanna River past the Conowingo Dam produced a 100-mile plume that was visible by satellite for several days. It was widely acknowledged that the nutrient releases to the Bay from this event were significant.
Multiple storms making landfall over the Chesapeake Bay in the same hurricane season could have compounded impacts. We can look to the events in the Pamlico Sound of North Carolina in 1999 as illustrative. That year, three hurricanes hit the area and dumped approximately 1 meter of rainfall, which created 50-500 year flooding events. It was estimated that the combined floodwaters from these three storms decreased salinity in the estuary by 75% and delivered at least half of the annual nitrogen load. Other effects from these three storms on the estuary were: a creation of conditions within the water body that are not conducive for aquatic life, an increase in algae which exacerbates the poor conditions for aquatic life, the displacement of marine organisms, and an increase in diseases in fish.
With two months remaining in hurricane season, the Bay Watershed is still at risk of experiencing a major storm event. Unanticipated releases of nutrients and sediment to the Bay could throw a monkey wrench in the progress that has been made to date. With Nate lurking around in the Caribbean and models suggesting a path over the Bay Watershed, threats posed to the Bay’s improvement by severe weather should not be discounted or ignored.
Kim Snell-Zarcone is the agriculture contractor at the Choose Clean Water Coalition