Hydrology and Climate of Four Watersheds in Eastern Puerto Rico By Sheila F. Murphy and Robert F. Stallard Chapter C of Water Quality and Landscape Processes of Four Watersheds in Eastern Puerto Rico Edited by Sheila F. Murphy and Robert F. Stallard Professional Paper 1789–C U.S. Department of the Interior U.S. Geological Survey Contents Abstract .........................................................................................................................................................47 Introduction...................................................................................................................................................47 Climate and Hydrology of Eastern Puerto Rico ..............................................................................49 Climate Variability and Change .........................................................................................................53 Relation of Land Cover to Climate and Hydrology ........................................................................54 Cloud Forest .........................................................................................................................................54 Interpretive Approach .................................................................................................................................56 Precipitation.........................................................................................................................................56 Regression Model of Precipitation Based on Elevation ......................................................57 Spatially Based Precipitation Model ......................................................................................57 Precipitation Based on Land Cover ........................................................................................57 Cloud Drip .............................................................................................................................................57 Runoff ....................................................................................................................................................59 Groundwater and Storage .................................................................................................................60 Water-Supply Inputs and Outputs ....................................................................................................60 Evapotranspiration..............................................................................................................................60 Error Estimation for Water Budgets .................................................................................................61 Precipitation and Runoff in Eastern Puerto Rico ....................................................................................62 Water Budgets for Study Watersheds .....................................................................................................75 Summary........................................................................................................................................................77 Acknowledgments .......................................................................................................................................78 References ....................................................................................................................................................78 Figures 1. Maps of Caribbean showing Puerto Rico and study watersheds ......................................48 2. Map of hurricane tracks over or near Puerto Rico since 1850 ...........................................50 3. Digital elevation model of elevation and relief of Puerto Rico ............................................51 4. Map of mean annual precipitation of Puerto Rico ................................................................51 5. Map of eastern Puerto Rico showing location of sites, Luquillo Experimental Forest, and El Toro Wilderness ..............................................................................................................52 6–15. Diagrams of the following: 6. Indices of oscillations that affected Puerto Rico, 1950–2010 .......................................55 7. Elevation versus mean annual precipitation (1991–2005) at stations in or near study watersheds, eastern Puerto Rico ..........................................................................62 8. Mean daily precipitation by year at stations in or near study watersheds, eastern Puerto Rico ............................................................................................................64 9. Mean daily runoff by year at U.S. Geological Survey stream-gaging stations, eastern Puerto Rico ............................................................................................................66 10. Distribution of log of mean annual runoff from study watersheds and Río Fajardo for periods of record .............................................................................................69 11. Mean daily precipitation by month at stations in or near study watersheds ............70 12. Mean daily runoff per month at U.S. Geological Survey stream-gaging stations, eastern Puerto Rico ............................................................................................................71 13. Percent occurrence of hourly precipitation intensity at U.S. Geological Survey stream-gaging stations (1991–2005), eastern Puerto Rico ..............................72 14. Percent occurrence of hourly runoff intensity at U.S. Geological Survey stream-gaging stations (1991–2005), eastern Puerto Rico ...........................................73 15. Runoff and precipitation at U.S. Geological Survey stream-gaging stations during and after Tropical Storm Dean, August 2001 ......................................................74 Tables 1. Temperature statistics for 1991–2005 at meteorological stations in or near study watersheds, eastern Puerto Rico ............................................................................................50 2. Stream-gaging and precipitation stations, eastern Puerto Rico ........................................53 3. Precipitation and evapotranspiration rates reported in literature, eastern Puerto Rico ..................................................................................................................................58 4. Total annual precipitation at stations in or near study watersheds, 1991–2005 ..............63 5. Annual runoff, stream statistics, and stream characteristics study of watersheds ..................................................................................................................................65 6. Statistical properties of annual runoff of study watersheds and Río Fajardo, 1991–2005 .....................................................................................................................................67 7. Summaries of successive regressions of annual runoff and precipitation in eastern Puerto Rico ..................................................................................................................................68 8. Rainfall intensity at U.S. Geological Survey stations during major storms in eastern Puerto Rico, 1991–2005 ..............................................................................................................72 9. Runoff rates from study watersheds and percentage of time that hourly runoff is below those rates, at percentiles of annual runoff volume .................................................73 10. Modeled recessions of study watersheds after storm events ...........................................76 11. Annual precipitation estimated by various methods ............................................................77 12. Annual water budgets of study watersheds ..........................................................................77 Abbreviations Used in This Report km kilometer km2 square kilometer m meter mm millimeter mm day−1 millimeters per day mm h−1 millimeters per hour mm yr−1 millimeters per year m s−1 meters per second m3 s–1 cubic meters per second yr year AR autoregressive BP before present ENSO El Niño–Southern Oscillation ET evapotranspiration IMA integrated-moving-average LTER Long-Term Ecological Research NOAA National Oceanographic and Atmospheric Administration PRISM parameter-elevation regressions independent slopes model USGS U.S. Geological Survey WEBB Water, Energy, and Biogeochemical Budgets Conversion Factors Multiply By To obtain Length millimeter (mm) 0.03937 inch (in.) meter (m) 3.281 foot (ft) kilometer (km) 0.6214 mile (mi) Area square kilometer (km2) 0.3861 square mile (mi2) Flow rate meter per second (m s−1) 3.281 feet per second (ft s−1) cubic meters per second (m3 s−1) 35.31 cubic feet per second (ft3 s−1) millimeters per hour (mm h−1) 0.03937 inches per hour (in. h−1) millimeters per day (mm h−1) 0.03937 inches per day (in. h−1) millimeters per year (mm yr−1) 0.03937 inches per year (in. yr−1) Hydrology and Climate of Four Watersheds in Eastern Puerto Rico By Sheila F. Murphy and Robert F. Stallard Abstract Introduction Puerto Rico lies directly in the path of the easterly trade Five field sites throughout the United States have been winds, which deliver steady rainfall to the mountains and monitored since 1991 as part of the U.S. Geological Surveyʼs steer tropical wave systems toward the island. Hurricanes and (USGS) Water,