A Land-Atmospheric Interaction Study in the Coastal Tropical City of San Juan, Puerto Rico

This paper focuses on the surface-atmospheric interaction in a tropical coastal city including the validation of an atmospheric modeling and an impact study of land-cover and land-use (LCLU) changes. The Regional Atmospheric Modeling System (RAMS), driven with regional reanalysis data for a 10-day simulation, is used to perform the study in the San Juan metropolitan area (SJMA), one of the largest urban conglomerations in the Caribbean, which is located in the island of Puerto Rico and taken as the test case. The model's surface characteristics were updated using airborne high-resolution remote sensing information to obtain a more accurate and detailed configuration of the SJMA. Surface and rawinsonde data from the San Juan Airborne Thermal and Land Applications Sensor (ATLAS) Mission are used to validate the modeling system, yielding satisfactory results in surface/canopy temperature, near-surface air temperatures, and vertical profiles. The impact analysis, performed with the updated SJMA configuration and a potential natural vegetation (PNV) scenario, showed that the simulation with specified urban LCLU indexes in the bottom boundary produced higher air temperatures over the area occupied by the city, with positive values of up to 2.5 degrees C. The same analysis showed changes in the surface radiative balance in the urban case attributed to modifications in the LCLU. This additional heat seems to motivate additional vertical convection that may be leading to possible urban-induced precipitation downwind of the SJMA. This was evident in a precipitation disturbance when the city is present (similar to 0.9 mm, 22.5% increase) captured by the model that was accompanied by increases in cloud formation and vertical motions mainly downwind of the city.