资源环境科技发展态势分析平台

The tropical forests of northeast Puerto Rico (NE PR) and the Luquillo Mountains (LM) are a large repository for biodiversity and have an important role in regional biogeochemical processes. Precipitation is a key driver of the productivity of these sensitive ecosystems. This study analyses historical precipitation variability from 1985 to 2014 at El Verde Field Station (EVFS) at 380m on the north facing slope of the LM. The primary objective of this study is to identify atmospheric states that lead to extreme wet/dry conditions at EVFS. This study also investigates how those wet/dry atmospheric states change over the study period through an epoch approach on annual and seasonal timescales.

Self-organizing maps (SOMs) are used to produce atmospheric states from ERA-Interim low-tropospheric moisture and circulation variables. These atmospheric states are downscaled to precipitation at the EVFS rain gauge. A probability density function of observed precipitation is calculated for each atmospheric state. Changes in node frequency, which is the number of days mapping to a particular node compared to the total number of days in the temporal period, are used to evaluate changes in wet/dry atmospheric states at EVFS.

Results indicate that low-precipitation days at EVFS are associated with atmospheric states with high 1000-700hPa bulk wind shear and decreased 700hPa moisture. Wet days in the study region are associated with moist low-tropospheric environments with low wind shear. Our results indicate an increased frequency of dry season atmospheric states with lower 700hPa moisture. Over the study period, the dry season has a decrease in median and extreme precipitation during rainy days (days >0mm). A decrease in early rainfall season median precipitation on rainy days is observed despite an increase in days with measurable precipitation, likely driven by an increase in light rainfall days (<5mm).