NOAA MAPP University of Georgia

Understanding the Mechanisms Leading to Early Warning of Meteorological and Hydrological Drought in the U.S. Caribbean

This project will create a multiproduct assessment of drought, including flash drought, and then evaluate climate mechanisms, with a focus on the role of the SAL, that are critical in improving drought early warning in the U.S. Caribbean.

Introduction to the project: In groundwater-limited settings, such as the U.S. Caribbean, societal, ecological, and agricultural water needs are largely supplied by regular rainfall. Consequently, these islands, Puerto Rico and the U.S. Virgin Islands, are vulnerable to even short, rapid-onset, dry spells, known as “flash drought,” and drought early warning is immensely valuable for civil authorities on the islands. In the wake of the 2015 drought, precipitation deficits were linked to the early arrival of an elevated hot, dry, dust-laden feature, termed the Saharan air layer (SAL). The SAL increased static stability, largely suppressing convective precipitation during a typically rainy time of year. The SAL is a precursor of Caribbean drought.

Project Goal: This project will first examine and diagnose drought through a suite of hydrometeorological variables, drought indices, and drought definitions, such as the Palmer Drought Severity Index, Standardized Precipitation Evaporation Index, etc. Episodes of low drought metrics will be compared to in-situ hydrologic measurements, such as USDA Soil Climate Analysis Network data, in the U.S. Caribbean to infer their ability to capture flash drought onset. Next, concurrent meteorological fields from renanalysis products will be examined during the flash drought periods to identify the local meteorological conditions driving flash drought and how these differ from conventional drought. Third, drought frequency will be characterized as a function of SAL activity over the U.S. Caribbean. Self-organizing maps, a machine learning technique, will mine historical 2D fields of the Galvez-Davison Index, a recently developed tool well-suited for detecting SAL outbreaks, to determine common historical SAL behavior during the hydrologically critical early rainfall season in the U.S. Caribbean. Teleconnection indices and seasonal numerical weather forecasts will be analyzed for their ability to provide early warning of SAL, and therefore drought, in the U.S. Caribbean.

Drought in the Carribbean: The U.S. Caribbean (Purto Rico and US Virgin Islands), including the San Juan metropolitan area, suffered a major drought in 2015 that caused severe water shortages and water rationing for hundreds of thousands of residents. Only three of the 77 municipalities in PR were not included in the drought at the peak of the event in August 2015, and the island experienced its first “extreme drought” recorded by the Drought Monitor (NDMC 2019). The percentage of the island classified as “moderate to severe drought” reached nearly 45% of the island, while more than 20% had moved into the more intense rating of “extreme drought” by early August (Fig. 1). Agricultural sector losses exceeded $12 million by early August and cost the Puerto Rico Aqueduct and Sewer Authority as much as $15 million a month (USDA 2015), exacerbating ongoing economic hardship on the island for more than a decade.

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