CESD research scientist Christina Patricola weighed in this summer on new research indicating a global slowdown in the rate at which tropical cyclones move over a region. Because the amount of tropical-cyclone-related rainfall that any local area might experience is inversely proportional to this translation speed, these findings could have important implications for regional rainfall rates.

Commenting on the study findings by James P. Kossin in a piece for the News & Views section of Nature, Patricola drew upon knowledge from her own studies of the impact of climate warming on tropical cyclone, or hurricane intensity and rainfall.

Kossin analyzed 68 years of observations of global trends in tropical-cyclone translation speed, and regional trends over individual ocean basins and adjacent land. Kossin found that translation speeds — the speed at which a cyclone moves over a region — have decreased globally over the period from 1949-2016.  Since regional rainfall from tropical cyclones is inversely proportional to translation speed (and proportional to rainfall rate), Kossin’s work suggests that the total amount of regional rainfall from tropical cyclones might have increased.

“Hurricane Harvey is an extreme example of how slowly a cyclone can move over land, and of how that slow translation speed can be accompanied by extremely heavy rainfall,” Patricola explains. “Scientists have begun to understand that as the climate warms, there’s an expectation that global-scale circulation — or winds — in the Tropics will slow.

“Hurricane Harvey is an extreme example of how slowly a cyclone can move over land, and of how that slow translation speed can be accompanied by extremely heavy rainfall.” — Christina Patricola

“The direction and speed at which a tropical cyclone travels is guided by the winds in the surrounding environment. Kossin’s work is novel in that he hypothesized how changes in overall atmospheric circulation can influence one of the tropical-cyclone characteristics — translation speed — important for rainfall,” Patricola says.

For her own studies of tropical cyclones, Patricola uses high-resolution numerical climate models and observations to understand connections between changes in climate and extreme events such as tropical cyclones, floods, and drought.

Her previous research indicates that climatological Atlantic hurricane frequency can be maintained in the absence of the typical hurricane precursor, African Easterly waves; that the spatial pattern of El Nino’s ocean warming is important for the magnitude of Atlantic hurricane reductions; and that favorable temperatures in the Atlantic and Pacific Ocean basins concurrently can lead to extremely active hurricane seasons.

Patricola also participates on the research team engaged in DOE’s Calibrated and Systematic Characterization, Attribution and Detection of Extremes (CASCADE) Scientific Focus Area (SFA). Led by William Collins and Travis O’Brien in CESD, the CASCADE SFA is developing new ways to simulate and detect extreme events using software capable of processing vast amounts of climate model and observational data on the world’s fastest and most computationally efficient computers.

Climate Models

Climate Models: Horizontal Resolution, Simulation Quality (cascade.lbl.gov)

“The ability to use climate models as we do here at Berkeley Lab allows us to simulate changes in both the probabilities of extreme event occurrence, and the magnitude of extreme events,” Patricola says.

“Because we can simulate the tropical cyclones at regional scale, we are able to represent the intensities of the strongest types of cyclones. This ability gives us a clear pathway forward towards identifying the extent to which rainfall rates could increase as the climate warms.”