However, the weather and climate of tropical islands is also affected by strong maritime influences as well as synoptic scale phenomena, such as El Niño and the North Atlantic Oscillation.įortunately, the existence of long-term databases and a relatively high density of observation stations in Puerto Rico may provide unique opportunities to assess climate variations on a small tropical island and to detect and isolate any regional drivers of local climate conditions. However, LULCC may be an important component of climate change on small tropical islands, particularly given widespread historical vegetation changes associated with agricultural transitions and rapid urbanization, including coastal development related to tourism. Further, the traditional coarse resolution grids designed for climate assessment in continental settings, including generalized assumptions of similar vegetation and land cover types, are not well suited for studying the scale and heterogeneity of small regions. Such work is particularly challenging because of a typical scarcity of long-term data and low data densities. There is comparatively little climate research in tropical settings and on small tropical islands. Further, it is known that similar land cover changes induce different climate feedbacks at different latitudes. However, the complex dynamics of LULCC-climate mechanisms vary from place to place and between land-cover classes. Much of the existing work examining the impacts of LULCC on local climates has focused on mid-latitude continental sites. This reinforces the importance of studying climate responses to LULCC in a variety of environmental settings. On the other hand, afforestation (the creation of forests in places where they did not previously exist), although considered desirable in some respects, may lead to unintended results depending on local conditions and processes. Such changes resulting from deforestation have been linked to reductions in cloud cover and cloud formation height that could reduce precipitation. Deforestation can result in albedo increases, reduction of evapotranspiration (which changes sensible and latent heat partitioning), and rainfall interception. Although there has been considerable interest in evaluating temperature differences between urban areas and their rural surroundings, studies of variations in long-term precipitation due to urbanization or other changes in land use and land cover (LULC), such as deforestation/afforestation, are limited. The effects of urbanization on local climate were first observed in Europe centuries ago (as cited in ) leading to the recognition of what is now known as the Urban Heat Island (UHI) effect. However, precipitation trends at particular stations contradict synoptic-scale long-term trends, which suggests that local land use/land cover effects are driving precipitation variability at local scales. Precipitation in Puerto Rico has been decreasing over the past century as a result of a decrease in precipitation during periods (months or years) of low rain. We found no statistical evidence for significant differences between average monthly precipitation in urban and non-urban areas directly from surface stations, but, after subdividing by Holdridge Ecological Life Zones (HELZs) in a GIS, there were statistically significant differences (α = 0.05) in yearly average total precipitation between urban and non-urban areas in most HELZs. Particular focus was given to detecting impacts from the urban landscape on mesoscale climates across Puerto Rico. For the small tropical island of Puerto Rico, where maritime climate is dominant, we used long-term precipitation and land use and land cover data to assess whether there were any detectable impacts of LULCC on monthly and yearly precipitation patterns and trends over the past century. To understand controls on long-term changes in precipitation for scientific and environmental management applications it is necessary to examine whether local land use and land cover change (LULCC) has played a significant role in changing historical precipitation patterns and trends. Water is critical for sustaining natural and managed ecosystems, and precipitation is a key component in the water cycle.
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