Shifting climate in Caribbean tropical forests: Long-term trends at La Selva (Costa Rica) and El Verde (Puerto Rico)

Abstract

Climate change is altering ecosystems worldwide, but long-term, site-level hydroclimatic responses remain comparatively under-documented in many tropical regions. We analyzed long-term air and water temperature, precipitation, and stream water level data from two active Caribbean research sites: La Selva Research Station, Costa Rica, and El Verde Field Station, Puerto Rico. Our goal was to assess long-term hydroclimatic trends and changes in extreme events using continuous monitoring from automatic and manual sensors. Long-term records show a mean daily temperature of 25.1°C (1992–2024, range: 19.5-29.6°C) at La Selva and 23.6°C (2000–2024, range: 17.7-28.2°C) at El Verde. Mean annual precipitation is 4166 mm at La Selva (1983–2024) and 3635.8 mm at El Verde (1975–2024). We found a decadal warming trend of 0.29°C at both locations. The El Niño Southern Oscillation (ENSO) influenced air temperature at El Verde, where La Niña (+0.02°C day −1 , 95% CI: 0.002–0.042) phase was associated with higher daily temperatures, but had no detectable effect on air temperature at La Selva. A significant increase in the frequency of extreme temperature events (defined as exceeding the 95 th , 97 th , and 99 th percentiles) was observed at both sites. Using the 95 th percentile and a fitted generalized linear model, both locations had ~8 extreme temperature events per year in the beginning and increased to ~35 events per year in 2024. Changes in precipitation extremes were site-specific and differed between wet and dry metrics. La Selva showed an increase in wet extremes (heavy precipitation), with 99 th percentile rainfall exceedances rising from ~1 event per year (1983–1985) to 6 per year in 2024. In contrast, El Verde showed no significant increase in heavy-precipitation events, but exhibited an increase in dry extremes (dry days <1.4 mm, increasing from 152 to 170 days per year). Stream water temperature had a moderate but significant increase. At La Selva, water temperature increased by 0.2°C, and at El Verde, by 0.9°C. An increasing tendency in high-water-level conditions was observed at both locations, though with marginal statistical support (p = 0.08 for the 99 th percentile at La Selva and 95 th percentile at El Verde), with estimated durations above these extreme thresholds roughly doubling over the study period. Overall, our study shows an increasing frequency of extreme events, both wet and dry, at these two Caribbean protected locations. These findings suggest important and distinct regional changes in climate over the region, with important consequences for ecosystem conservation and management.