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

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 95th, 97th, and 99th percentiles) was observed at both sites. Using the 95th 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 99th 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