Abstract:
Puerto Rico experienced an unusually rapid transition from drought in just a few months. From the beginning of the year, there were almost no signs of drought, to the end of August, large areas fell into severe or even extreme drought. Local rainfall plummeted, water resources continued to decrease, and some communities had to implement water supply rationing. Faced with the deteriorating situation, the Governor of Puerto Rico declared a state of emergency at the end of July, and the U.S. government subsequently approved a drought disaster declaration at the end of August, covering more than 20 local cities and towns.
Puerto Rico usually enters its wet season in May each year, but the situation in 2026 is completely different. Seasonal rains that were supposed to arrive have yet to arrive, and this unusually dry weather lasted until the end of August, gradually plunging much of Puerto Rico into drought.
The assessment released by the U.S. Drought Monitoring System on August 25 showed that about three-quarters of Puerto Rico was already in at least a moderate drought state at that time. The areas classified as extreme drought were mainly concentrated in the east and southwest of the main island, and the scope continued to expand in the previous week, covering about 44% of the entire Puerto Rico.
The speed of this change is particularly alarming. Just three months ago, no area of Puerto Rico was officially classified as drought, with less than 20% of the land considered abnormally dry at the time. In fact, during the late winter and early spring of 2026, the weather in the Caribbean region of the United States was even wetter than normal for a time, and then the situation quickly turned abnormally dry.
Data from the U.S. National Integrated Drought Information System shows that from mid-May to mid-July, much of Puerto Rico received less than 60% of normal precipitation. The situation is more serious in the south and southwest, with rainfall even less than 20% of normal levels, and the cumulative precipitation deficit reaches 3 to 6 inches, which is about 76 to 152 millimeters.
Abnormally high temperatures further exacerbated water loss. San Juan, the capital of Puerto Rico, experienced one of the hottest Julys on record. The combination of high temperatures and continued lack of rain quickly dried up soil and surface water resources. Rivers are also clearly affected, with flows in some including the Fajardo River in northeastern Puerto Rico falling to record lows.
David Mocco, senior research scientist at the Hydrological Sciences Laboratory at NASA's Goddard Space Flight Center, said a variety of satellite data and ground observations clearly show the high temperatures and dry conditions Puerto Rico is experiencing. Satellite estimates of soil moisture have been particularly important in recent drought assessments, along with ground observations such as meteorological data, river flows, and groundwater well conditions.
Moko was responsible for writing the U.S. Drought Monitor Weekly Report released on August 18, 2026. He and Jonathan Case of NASA's Marshall Space Flight Center were among the first NASA scientists to participate in producing the U.S. Drought Monitoring System's weekly drought maps.
The worsening drought has begun to directly affect local residents, farmers and ranchers. Since early August, water supply rationing has been implemented in many municipalities in Puerto Rico, and residents are facing increasing water pressure. Some observers also point out that problems with local water infrastructure also make water shortages more difficult to deal with.
The impact on agriculture is equally obvious. Persistently dry soil has disrupted the growth of fruit trees, cocoa, bananas, coffee and other crops and caused agricultural losses. The livestock industry is also taking a hit, with ranchers having dwindling reserves of hay used to feed their livestock.
In this rapidly developing drought crisis, the maps released by the U.S. Drought Monitoring System have become an important tool for the government to judge the situation and allocate relief resources. The system has released weekly drought maps since 1999 and is a joint effort by the National Drought Mitigation Center at the University of Nebraska-Lincoln, the U.S. Department of Agriculture, the National Oceanic and Atmospheric Administration, and NASA. NASA has supported the project with Earth observation data and scientific expertise for years, and starting in 2026, two NASA scientists will officially join the team responsible for weekly drought assessments.
These drought assessments are not only used to document climate and water conditions, but are also directly relevant to disaster relief policy. The USDA can initiate a rapid disaster determination process based on drought monitoring results to release emergency assistance resources for communities, farmers and other groups affected by severe drought.
The changes Puerto Rico has experienced this time also show once again that drought is not necessarily a slow development process. When there is a drastic transition between normal rainfall and sustained high temperature and lack of rainfall, an area with previously normal water resources may quickly cross multiple drought levels in just a few months and evolve into a serious water crisis affecting residents' water supply, agricultural production, and ecosystems.
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