Along with the destruction they cause for human civilization, tropical cyclones play a vital role in nourishing onshore ecosystems with freshwater. As a tropical storm tracks inland, it creates thunderstorms via a common convective process. In the southeast United States especially, these storms can represent a large fraction of the total rainfall during hurricane season, which extends from 1 June through 30 November. Here Lowman and Barros use the Duke Coupled Hydrology Model with Vegetation in two different scenarios—with and without the influence of tropical cyclones—to assess how such storms impact gross primary productivity in the southeast United States.
The model includes a large number of variables, such as soil characteristics and vegetation type, to track the movement of water through a region as realistically as possible. Using the scientific understanding of plant physiology, specifically how processes in light and photosynthetic reactions scale with carbon assimilation, the researchers could also calculate the total amount of photosynthesis occurring in the region using the same model.
To understand the effect of the storms, the researchers ran the model with retrospective data from 2002 to 2012 and compared the real-world results with a second simulation in which all tropical cyclones had been removed and replaced with average weather. Many variables proved to be important in determining how much influence a cyclone would have on gross primary production, but the timing and trajectory of cyclones proved to be especially important.
In wet years with more tropical cyclones than average, such as 2004 and 2005, the storms increased gross primary productivity by up to 9%—the equivalent of 3–5 million grams of carbon per square meter across the study region. In dry years the cyclones increased carbon uptake by 4%–8% relative to the simulations where the storms had been replaced with average weather.
Under the current climate trends, tropical cyclones are expected to increase in the future, and thus, the authors argue that understanding how they impact vegetation, carbon fixation, and drought will become only more important with time. (Journal of Geophysical Research: Biogeosciences, doi:10.1002/2015JG003279, 2016)
—David Shultz, Freelance Writer