High‐resolution dynamically downscaled rainfall and temperature projections for ecological life zones within Puerto Rico and for the U.S. Virgin Islands

Abstract

The weather research and forecasting (WRF) model and a combination of the regional spectral model (RSM) and the Japanese Meteorological Agency Non‐Hydrostatic Model (NHM) were used to dynamically downscale selected CMIP5 global climate models to provide 2‐km projections with hourly model output for Puerto Rico and the U.S. Virgin Islands. Two 20‐year time slices were downscaled for historical (1986–2005) and future (2041–2060) periods following RCP8.5. Projected changes to mean and extreme temperature and precipitation were quantified for Holdridge life zones within Puerto Rico and for the U.S. Virgin Islands. The evaluation reveals a persistent cold bias for all islands in the U.S. Caribbean, a dry bias across Puerto Rico, and a wet bias on the windward side of mountains within the U.S. Virgin Islands. Despite these biases, model simulations show a robust drying pattern for all islands that is generally larger for Puerto Rico (25% annual rainfall reduction for some life zones) than the U.S. Virgin Islands (12% island average). The largest precipitation reductions are found during the more convectively active afternoon and evening hours. Within Puerto Rico, the model uncertainty increases for the wetter life zones, especially for precipitation. Across the life zones, both models project unprecedented maximum and minimum temperatures that may exceed 200 days annually above the historical baseline with only small changes to the frequency of extreme rainfall. By contrast, in the U.S. Virgin Islands, there is no consensus on the location of the largest drying relative to the windward and leeward side of the islands. However, the models project the largest increases in maximum temperature on the southern side of St. Croix and in higher elevations of St. Thomas and St. John.

Modeling general circulation model bias via a combination of localized regression and quantile mapping methods

“…The majority of literature agrees that the Caribbean will see reduced rainfall in its future climate (Bowden et al, 2021;He and Soden, 2017). Within the RCP4.5 forcing scenario, our methods tend to be consistent with those of the literature.…”

“…Historical max 11.11 25.00 27.78 28.89 29.98 30.56 31.11 31.67 32.22 32.78 41.11 RCP4.5 max 11.86 25.97 29.02 30.20 30.98 31.63 32.23 32.77 33.34 34.00 41.81 RCP8.5 max 11.62 26.29 29.35 30.59 31.36 32.03 32.62 33.17 33.73 34.44 Within the Caribbean, recent literature tends to favor drying conditions, although some literature does provide conflicting opinions. Bowden et al (2021), Campbell et al (2011), and He and Soden (2017 all note a general drying pattern for Puerto Rico and its surrounding islands. Biasutti et al (2012) note a 30 % decrease specific to spring and summer rainfall.…”

“…Many studies have utilized dynamic downscaling (DD) and statistical downscaling (SD) techniques in an effort to accurately model Puerto Rico's future climate. Bhardwaj et al (2018) and Bowden et al (2021) employ highresolution regional climate models (RCMs) to develop dy-namically downscaled climate estimates across a 2 km grid in Puerto Rico. Ramseyer and Mote (2016) and Ramseyer et al ( , 2019 examine the utility of neural networks as a method for downscaling precipitation within Puerto Rico, while other studies (Khalyani et al, 2016;Van Beusekom et al, 2016;Miller et al, 2019) focus on the impacts of climate change on water availability in Puerto Rico using several downscaled products.…”

To be policy-relevant, future climate research must include the noncontiguous United States

“…Although global climate models have historically lacked the fine resolution needed to inform mitigation and adaptation planning for small islands, scientific advancements and increases in computing power have improved the geographic resolution of climate projections ( 9 ). Yet, modeling future climate in places like Hawai’i, US-Affiliated Pacific Islands, and the US Caribbean is still complicated because islands have more land–sea interactions than many contiguous states with coastlines, and they may have complex terrain or experience unique climate phenomena ( 10 , 11 ). The physical landscape of Alaska has also proved challenging, with its tall mountains, seasonally varying sea ice, and large seasonal swings in temperature ( 12 ).…”

Drought stress and hurricane defoliation influence mountain clouds and moisture recycling in a tropical forest

“…The subtropics are projected to become drier over the 21st century, and minimum temperatures are increasing (54,55). In this study, drought-driven rise in cloud altitude was mitigated by high-elevation temperatures cool enough for condensation, but our results indicate that compounded effects of drought with warmer minimum temperatures due to forest loss or regional warming present a significant risk for decrease in orographic precipitation.…”