As cities are increasing technological efficacy on greenhouse gas (GH) emission reduction efforts, the surrounding urban ecosystems and natural resources may be affected by these measures. In this research, climate indicators such as heat index, extreme heat events, intensified urban heat islands (UHIs), and sea breeze are projected for the middle and end of the 21st century to understand the climate change signal on these variables with and without building energy mitigation measures. Cities amplify extreme heat and UHI impacts by concentrating large populations and critical infrastructure in relatively small areas. Here, we evaluate the combined climate and building energy mitigation impacts on localized climate metrics throughout the 21st century across extreme emission scenarios (RCP8.5) for the tropical coastal city of San Juan. The analysis of statistically downscaled global circulation model outputs shows underestimation for uncorrected summer daily maximum temperatures, leading to lower extreme heat intensity and duration projections from the present time which are corrected using bias-corrected techniques. High-resolution dynamic downscaling simulations reveal a strong dependency of changes in extreme heat events in urban settings, however, the intensities shift to lower-level grasslands and croplands with energy mitigation measures (combination of white roof, tilted photovoltaic roof, and efficient heating ventilation and air conditioning systems). The building energy mitigation measures have the potential of reducing the UHI intensities to 1 °C and 0.5 °C for the 2050 and 2100 climate periods, respectively.

To determine potential changes in the frequency and intensity of future storm events due to climate change in New York City (NYC), a statistical downscaling technique is proposed. First, a historical benchmark was determined using weather station data from the John F. Kennedy (JFK) and La Guardia (LGA) airports for the period 1973–2017. This historical information was used to perform the bias-correction exercise of near-future (2011–2050) global circulation model (GCM) output (ORNL RegCM4; RCP 8.5). Results show that NYC is projected to experience higher wind gusts under a warming climate for the period 2017–2050 in comparison with the historical data period, with the most extreme event projected to produce a maximum wind gust of approximately 110 mph, a significant increase over the past maximum of 80 mph. The historical 700-year return period event was estimated at 115 mph, while the overall 700-year event (historical and projected) is estimated at 124 mph. The most extreme cases of maximum daily wind gusts are projected to occur during the winter and early spring seasons. No increase in the number of projected tropical storms was observed, but the intensity of the storms is projected to be higher than during the historical period. These changes in extreme wind events could have serious implications for NYC in terms of urban planning, potential power outages, transportation disruptions, impacts on building structures, and public safety.

Understanding the interactions between large-scale atmospheric and oceanic circulation patterns and changes in land cover and land use (LCLU) due to urbanization is a relevant subject in many coastal climates. Recent studies by Lebassi et al. found that the average maximum air temperatures during the summer in two populated California coastal areas decreased at low-elevation areas open to marine air penetration during the period of 1970-2005. This coastal cooling was attributed to an increase in sea-breeze activity.The aims of this work are to better understand the coastal flow patterns and sea-land thermal gradient by improving the land-cover classification scheme in the region using updated airborne remote sensing data and to assess the suitability of the updated regional atmospheric modeling system for representing maritime flows in this region. This study uses high-resolution airborne data from the NASA Hyperspectral Infrared Imager (HyspIRI) mission preparatory flight campaign over Southern California and surface ground stations to compare observations against model estimations.Five new urban land classes were created using broadband albedo derived from the Airborne Visible and Infrared Imaging Spectrometer (AVIRIS) sensor and then assimilated into the Weather Research and Forecasting (WRF) Model. The updated model captures the diurnal spatial and temporal sea-breeze patterns in the region. Results show notable improvements of simulated daytime surface temperature and coastal winds using the HyspIRI-derived products in the model against the default land classification, reaffirming the importance of accounting for heterogeneity of urban surface properties.

Global climate change manifests in the Caribbean basin as increased SSTs, precipitation anomalies, and changes in atmospheric moisture content, among other effects. These regional climate changes have a profound impact on the local human, flora, and fauna populations. Such is the case of the Enriquillo basin, a highly sensitive ecosystem located in the southwestern region of the Caribbean island of Hispaniola. The major bodies of water in the basin, Lake Enriquillo and Lake Azuei, show a shrinking and expanding pattern since the early 1980s. The surface area of Lake Enriquillo was observed to reach minimum values in 2004 (170 km(2)), shifting to a rapid expansion to its current levels (>350 km(2) as of late 2013). Lake Azuei is observed to grow at similar rates. This lake expansion could be attributed to regional climate change. Long-term regional climate data reflect increasing SSTs (~1 degrees C), air temperatures (~0.37 degrees C decade(-1)), dewpoint (~0.66 degrees C decade(-1)), and precipitation (~30%); no reliable local precipitation records were found. Furthermore, local governments are being forced to issue evacuations, prompting one of the first cases of environmental refugees not caused by an extreme event (e.g., a hurricane or tsunami). The hypothesis of lake expansion in the Enriquillo basin as a regional response to climate change is further investigated with the use of an integrated regional atmospheric modeling system. Model results from simulations performed for years during the lakes' lowest water levels (2003-04) and during their continued growth (2012-13) show increased total accumulated surface precipitation, atmospheric liquid water content, and an enhanced positive feedback system that produces orographic cloud cover in the surrounding tropical montane cloud forests as a consequence of the changing atmospheric and oceanic conditions.

We show a sea surface temperature (SST) warming trend for the Caribbean and surrounding region over 1982–2012. Using an optimum interpolated SST product, a 30 year climatological analysis was generated to observe annual, monthly, and seasonal trends. Results show that SSTs are increasing annually for the region. For the two Caribbean rainy seasons, the Early Rainfall Season (ERS) and the Late Rainfall Season (LRS), estimated trends at 0.0161°C yr−1 and 0.0209°C yr−1 were observed, with high statistical significance. Subregional analysis revealed that warming is greatest in the Gulf of Mexico and north of South America during the ERS and LRS. Additionally, LRS averages for 1998–2012 reflect an increase in magnitude and intensity of the Atlantic Warm Pool (AWP) since the 1983–1997 period reflected in the AWP Area Index. Extreme increases/decreases in the time series show potential correlation with El Niño and the Southern Oscillation.

California near‐surface air temperatures are influenced by large‐scale, regional and local factors. In that sense, a numerical model experiment was carried out to analyze the contribution of large‐scale (changes in atmospheric and oceanic conditions) and regional (increased urbanization) factors on the observed California South Coast Air Basin regional summer daily maximum temperature warming pattern from 1950 to 2013. The simulations were performed with past (1950–1954) and present (2009–2013) land cover and climate conditions. The past land cover was derived from historical digital maps, and the present land cover was updated with high‐resolution airborne remote sensing data. Results show that both factors contribute to the total change in daily maximum temperatures. Changes due to large‐scale climate conditions dominate in coastal (due to warming sea surface temperatures) and nonurban regions, while changes due to urbanization have an impact mainly in urban areas, especially inland where large‐scale warming weakens. Increased urbanization has also reduced sea‐breeze intensity due to changes in surface roughness. The model was able to reproduce the regional observed warming pattern, as it incorporates urban heat island effects, otherwise underestimated by large‐scale climate change only.

Urbanization, along with other cases of land cover and land use changes, has significant climate impacts in tropical regions with the added complexity of occurring within the context of global warming (GW). The individual and combined effects of these two factors on the surface energy balance of a tropical city are investigated by the use of an integrated atmospheric modeling approach, taking the San Juan Metropolitan Area (SJMA), Puerto Rico, as the test case. To achieve this goal, an ensemble of climate and weather simulations is performed, with climate scenarios combining urban development and sprawl with regional climate change over the past 50 years and the short-term simulations designed to test the sensitivity to different urban vegetation configurations as mitigating alternatives. As indicator of change, we use the thermal response number (TRN), which is a measure of the sensible heating to the thermal storage of a surface or region, and the Bowen ratio, which is defined as the ratio of sensible to latent heat fluxes. The TRN of the area occupied by the SJMA has decreased as a consequence of replacing the lowland coastal plain vegetation with man-made materials, indicating that it takes less energy to raise the surface temperature of the urban area, whereas the TRN of forested regions has remained virtually unchanged. The GW signal also has effects on the thermal response of the SJMA, where dryer current conditions generate lower TRN values. Differences owing to GW are more evident in the Bowen ratio pattern, mostly associated with the drier present conditions observed and its effects on sensible and latent heat fluxes. In terms of testing different mitigation strategies, the short-term simulations show that the urban area is more efficient in partitioning surface energy balance terms when green roofs are specified, as opposed to including vegetation inside the urban core.

The additional heating of the air over the city is the result of the replacement of naturally vegetated surfaces with those composed of asphalt, concrete, rooftops and other manmade materials. The temperatures of these artificial surfaces can be 20 to 40 C higher than vegetated surfaces. This produces a dome of elevated air temperatures 5 to 8 C greater over the city, compared to the air temperatures over adjacent rural areas. This effect is called the heat island. Urban landscapes are a complex mixture of vegetated and non-vegetated surfaces. It is difficult to take enough temperature measurements over a large city area to. The use of remotely sensed data from airborne scanners is ideal to characterize the complexity of urban albedo and radiant surface temperatures. The National Aeronautics and Space Administration (NASA) Airborne Thermal and Land Applications Sensor (ATLAS) operates in the visual and IR bands was used to collect data from Salt Lake City, UT, Sacramento, CA, Baton Rouge, LA. And San Juan, Puerto Rico with the main objective of investigating the Urban Heat Island (UHI). In this presentation we will examine the techniques of analyzing remotely sensed data for measuring the effect of various urban surfaces on their contribution to the urban heat island effect.

Large-scale climate data for the north tropical Atlantic (NTA) region show that air temperatures have increased during the past 50 years (1955-1959 to 2000-2004) with moderate warming near the Caribbean islands to considerable heating in the northern region. This pattern may be driven by sea surface temperature anomalies in the same region of study that follow relatively small changes in the Caribbean basin to stronger anomalies in the northeast. These changes might be associated with changes in the long-term pattern of the NTA high-pressure system that drives climate in the region. A series of mesoscale numerical experiments were designed to study the regional impacts these large-scale changes have on the hydrological cycle of the island of Puerto Rico. Results indicate that increased easterly surface winds for the 1950-2000 time frame disrupts a pattern of inland moisture advection and convergence zone, increasing cloud base heights and reducing the total column liquid water content over high elevations. This combination of factors produces a reduction in precipitation over the central and eastern mountains of Puerto Rico.

Land-cover and land-use (LCLU) changes have significant climate impacts in tropical coastal regions with the added complexity of occurring within the context of a warming climate. The individual and combined effects of these two factors in tropical islands are investigated by use of an integrated mesoscale atmospheric modeling approach, taking the northeastern region of Puerto Rico as the test case. To achieve this goal, an ensemble of climate simulations is performed, combining two LCLU and global warming scenarios. Reconstructed agricultural maps and sea surface temperatures form the past (1955-59) scenario, while the present (2000-04) scenario is supported with high-resolution remote sensing LCLU data. Here, the authors show that LCLU changes produced the largest near-surface (2-m AGL) air temperature differences over heavily urbanized regions and that these changes do not penetrate the boundary layer. The influence of the global warming signal induces a positive inland gradient of maximum temperature, possibly because of increased trade winds in the present climatology. These increased winds also generate convergence zones and convection that transport heat and moisture into the boundary layer. In terms of minimum temperatures, the global warming signal induces temperature increases along the coastal plains and inland lowlands.

This paper focuses on the surface-atmospheric interaction in a tropical coastal city including the validation of an atmospheric modeling and an impact study of land-cover and land-use (LCLU) changes. The Regional Atmospheric Modeling System (RAMS), driven with regional reanalysis data for a 10-day simulation, is used to perform the study in the San Juan metropolitan area (SJMA), one of the largest urban conglomerations in the Caribbean, which is located in the island of Puerto Rico and taken as the test case. The model's surface characteristics were updated using airborne high-resolution remote sensing information to obtain a more accurate and detailed configuration of the SJMA. Surface and rawinsonde data from the San Juan Airborne Thermal and Land Applications Sensor (ATLAS) Mission are used to validate the modeling system, yielding satisfactory results in surface/canopy temperature, near-surface air temperatures, and vertical profiles. The impact analysis, performed with the updated SJMA configuration and a potential natural vegetation (PNV) scenario, showed that the simulation with specified urban LCLU indexes in the bottom boundary produced higher air temperatures over the area occupied by the city, with positive values of up to 2.5 degrees C. The same analysis showed changes in the surface radiative balance in the urban case attributed to modifications in the LCLU. This additional heat seems to motivate additional vertical convection that may be leading to possible urban-induced precipitation downwind of the SJMA. This was evident in a precipitation disturbance when the city is present (similar to 0.9 mm, 22.5% increase) captured by the model that was accompanied by increases in cloud formation and vertical motions mainly downwind of the city.

The annual precipitation pattern in the Caribbean basin shows a distinct bimodal behavior, where the first mode is called the Early Rainfall Season (April–July), and the second mode the Late Rainfall Season (August–November). The brief, relatively dry, period in July is usually referred to as the midsummer drought (MSD). It has been hypothesized that the migration through the Caribbean basin of the Intertropical Convergence Zone (ITCZ) and increases in aerosols due to the passing of Saharan Dust across the Caribbean in the summer months may result in the observed precipitation pattern. This paper focuses on determining the origins of the Caribbean MSD. Multiple regression analysis was carried‐out to determine if the ITCZ, the North Atlantic Oscillation (NAO) index, the Vertical Wind Shear (VWS), and different atmospheric particle (AP) concentrations transported from northern Africa correlate with the Caribbean MSD. It is shown that the ITCZ and NAO are weakly correlated with the Caribbean precipitation variability; however, the VWS and aerosol particles revealed an important contribution to rainfall during the summer months. Numerical experiments were then performed to quantify the influence of different VWS scenarios and different AP concentrations on the Caribbean precipitation bimodal behavior. The numerical approach uses the Regional Atmospheric Modeling System coupled with a new cloud microphysics module that allows discrimination between small and giant particles, as well as Cloud Concentration Nuclei (CCN) and Giant CCN activation. These numerical experiments support the statistical result that the VWS and the AP influence the rainfall production and pattern during the MSD. Results indicate that cloud microphysics play an important role in producing the observed climatological bimodal pattern, while variations in large‐scale atmospheric dynamics (like the VWS) help explain variations in the strength and pattern of the bimodal events and behavior.

Quantification of total climate changes due to the combined effects of land cover and land use (LCLU) and green house gases (GHG) is becoming essential. This research has the high level goal of improving our understanding of these combined climate effects (LCLU + GHG) in tropical coastal areas, taking Puerto Rico as testing case. The research uses an integrated approach of high-resolution remote sensing and climatological data, linked to a numerical atmospheric model (RAMS) employed to perform ensembles of climate simulations (combining 2-LCLU and 2-global climate scenarios). Reconstructed agricultural maps (1951 & 2000) are used to define past and present LCLU, complementing the present with RS data. Direct and cross comparison of the results is allowing quantifying single, combined, and competitive effects. Results indicate that global GHG have dominant effects on minimum temperatures (following regional tendencies), while urban sprawl dominates maximum temperatures. Forestation of past agricultural areas have an overwhelmingly mitigation effect on temperatures.