Quantifying the role of forested lands in providing surface drinking water supply for Puerto Rico
The Forest Service, U.S. Department of Agriculture published a General Technical Report (GTR-SRS-197) in 2014 that quantified the role that water originating on National Forest System lands contributed to the drinking water supply and determined what population and communities were being served in the 13 Southern States of Region 8 of the Forest Service. The Commonwealth of Puerto Rico is included in Region 8, but it was not included in the results of GTR-SRS-197 because at the time of that report the Water Supply Stress Index (WaSSI) model used for the assessment was not parameterized for Puerto Rico. The goal of this project was to implement the same methodology used in GTR-SRS-197 for the mainland of Puerto Rico. WaSSI is a monthly water balance and flow routing model that can quantify the amount of water at a watershed outlet. Water intake location data from the U.S. Geological Survey (USGS) and population served data from the Puerto Rico Aqueduct and Sewer Authority were used to quantify the amount of population being served by water originating on forested land. Puerto Rico has a total land area of 8,900 km2, and 38 percent of that land area is forested with 1.2 percent in National Forest System land and 37.1 percent in commonwealth and private forest land. We estimated that all lands in mainland Puerto Rico produced 6.5 billion m3/year of water. Of that total, National Forest System lands provided 219 million m3/year of water (3.3 percent of total land), and commonwealth and private forest lands provided 2.6 billion m3/year of water (40 percent of total land). A population of 3.6 million people was served by 113 intakes located downstream of commonwealth and private forest land, and 13 of those intakes were also located downstream of El Yunque National Forest and served a population of 780,000. National Forest System land and commonwealth and private forest land play an unequal role in providing water for the people of Puerto Rico. More than 2.1 million people receive at least 30 percent of their water from commonwealth and private forest land. In comparison, more than 139,000 people receive at least 30 percent of their water from National Forest System land. Our analysis provides quantitative information on water yield from forest lands and sources of water supply in Puerto Rico. This study is an addendum to GTR-SRS-197.