12 January 2024

A new method for measuring flash drought in the Caribbean


Drought is increasingly threatening Caribbean islands. If we want to measure, anticipate and mitigate its effects, a U.S. study notes, we need to rely on a new index

by Matteo Cavallito


Caribbean islands are particularly prone to flash drought, the phenomenon of sudden water shortage that is made increasingly common by climate change. Preventing and measuring this kind of event, however, requires the use of a peculiar method based on a new indicator, a U.S. study says.

“The tropics have extremely intense solar radiation, so atmospheric processes tend to be expedited,” Craig Ramseyer, a professor at the same polytechnic institute and co-author of the study with colleague Paul Miller of the Department of Oceanography at Louisiana State University, said in a note published by Virginia Tech. “Despite often receiving daily rainfall, island ecosystems are particularly vulnerable to drought conditions.”

A new index to measure drought

In the study. published in the Journal of Hydrometeorology, the authors used a new index to measure atmospheric moisture demand to identify hazardous conditions. So-called evaporative demand, said Miller quoted in the statement, “is a measure of how thirsty the atmosphere is and how much moisture it can collect from soil or plant matter.”

The indicator, called EDDI or Evaporative demand drought index, is an alternative to traditional measurements of soil moisture. Which, the authors note, are poorly suited to conditions on Caribbean islands.

“A lot of drought observation is based on soil moisture, but in tropical environments, a decline in soil moisture is a response to other things that have already happened so you’re further down in the chain of events,” Ramseyer said. “We can mitigate a lot of losses in, say, agriculture, by being able to forecast sudden, anomalous increases in evaporative demand.”

The research

The study analyzed 40 years of data highlighting the high frequency of flash drought that has historically occurred at different times of the year, not just during typical dry seasons. With the new index, the study notes, “a high-resolution spatiotemporal analysis of flash drought can be performed across the entire Caribbean region, no longer being constrained to coarser gridded datasets and/or the sparsely distributed long-term observation datasets in the region.”

EDDI, in particular, identified 46 ‘outbreaks’ of flash drought during which “significant fractions of the pan-Caribbean encounter rapid drying over 15 days and then maintain this condition for another 15 days.”

The data set, moreover, “reveals a tendency for flash drought to assume recurring typologies concentrated in one of the Central American, South American, or Greater Antilles coastlines, although a simultaneous, Caribbean-wide drought is never observed within the period examined.”

Preventing damage to agriculture and more

The results of the study, the research concludes, “indicate that flash droughts occur with regular periodicity in the Caribbean. Expansive flash droughts tend to occur in coherent subregional clusters. Future studies will further investigate the drivers of these flash droughts to create early warning systems for flash drought.” This may make it possible to more effectively prevent these phenomena.

The increasing frequency of flood and drought events linked to climate change makes the ability to take action to limit their consequences even more important. The impact of drought, the authors remind, obviously affects agriculture but also tropical ecosystems. Moreover, access to fresh water is a necessity for both residents and the tourism industry, which remains a key element of the local economy.