The response of drought and precipitation variability to regional climate forcing in northeast Puerto Rico
Ramseyer, Craig Allen
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Northeast Puerto Rico is home to a wide range of terrestrial and aquatic climate-sensitive ecosystems. Climate disturbances such as extreme events (e.g. hurricanes) and drought have cascading impacts on the biota. The biota responds to changes in precipitation variability on daily and sub-daily time scales. As a result, high temporal and spatial resolution climate data are needed to adequately assess climate impacts on the ecological process occurring in the region. This dissertation analyzes past, present, and future precipitation variability at a highly localized scale in northeast Puerto Rico. Additionally, a more comprehensive understanding of the regional climate forcing on precipitation variability is achieved. Artificial neural networks are used to downscale synoptic scale atmospheric variables to precipitation. These tools allow for modeling precipitation and determining the atmospheric processes driving precipitation variability This dissertation finds that precipitation throughout Puerto Rico is driven primarily by variability in specific humidity and wind shear in the low-troposphere. The driest daily precipitation in northeast Puerto Rico is observed in synoptic environments with high wind shear and low moisture at 700 hPa. Both of these atmospheric variables are driven by changes in the north Atlantic sea-surface temperature, the Saharan Air Layer, and the North Atlantic Subtropical High. The historical record shows little linear trend in total precipitation, however, precipitation variability is shown to be changing especially during the early rainfall season. It is posited that this increase in variability could be in part due to changes in the mechanisms driving the Caribbean Mid-Summer Drought. Future precipitation in northeast Puerto Rico is likely to be more variable with an overall drying trend. The highest magnitude changes are expected to occur in the early rainfall season as the trade wind inversion strengthens and wind shear across the region increases. These changes will cause disruptions to precipitation processes across several scales of motion, from tropical storm development to deep, moist convection. These trends in precipitation will likely cause significant impacts to the ecosystems of northeast Puerto Rico.