Climate/Hydrometeorology
The Luquillo Mountains have steep slopes and rise abruptly from the coast to peaks nearly 1100 m asl over the course of 10 km (González et al. 2013). Average annual temperatures range from 20 to 25o C (Harris et al. 2012). Average annual rainfall ranges from approximately 2500 to 5000 mm varying primarily with elevation, but patterns of rainfall shadowing depending on wind direction also have a strong influence on annual rainfall (Murphy et al. 2017). Hurricanes occur frequently at the site, with direct hits to the Luquillo Mountains by Category 3 or higher storms thought to occur about every 60 years, based on historic records of several hundred years duration (Scatena and Larsen 1991, López-Marrero et al. 2019). Interception rates decline following hurricane defoliation and canopy damage; rates return to background levels once canopy cover has been re-established (Heartsill-Scalley et al. 2007). Interception loss is high at the site, and has been attributed to the rainfall pattern, with many small storms that wet the canopy but generate relatively little throughfall (Scatena 1990).
Atmospheric inputs to LM catchments include large amounts of marine aerosols (Gioda et al. 2013, Medina et al. 2013, McDowell et al. 1990). Transport of dust from North African deserts occurs frequently and affects both rain and throughfall chemistry (Heartsill-Scalley et al. 2007; McClintock et al. 2019). Clouds and fog inputs are large relative to many sites (Eugster et al. 2006) but represent a small proportion of total precipitation input on the highest peaks. Although previous studies reported cloud base level starts at 600 m, Van Beusekom et al. (2017) showed that the lowest cloud base most frequently occurs at 702 to 915 m. Weekly measurements of throughfall volume and chemistry have been made since 1988, providing the only published record of long-term variation in throughfall volume and chemistry in a tropical forest (McDowell 2017a). Throughfall in the Luquillo Mountains is particularly enriched in potassium (K+) relative to rainfall, as is observed globally (McDowell et al. 2020). Annual fluxes of K+ in throughfall are twice as high as litterfall K+ fluxes, and proportionally much higher than those of any other element (McDowell 1998). Hydrologic infrastructure includes 4 meteorological stations, an NADP station (PR 20), 3 bulk precipitation collectors, a network of throughfall collectors, 12 stream gages, 3 walk-up canopy towers, 3 deep observation wells, several dozen riparian wells, and 3 lysimeter nests.