Search for: All records

Appropriately characterizing future changes in regional-scale precipitation requires assessment of the interactive effect owing to greenhouse gas-induced climate change and the physical growth of the built environment. Here we use a suite of medium resolution (20 km grid spacing) decadal scale simulations conducted with the Weather Research and Forecasting model coupled to an urban canopy parameterization to examine the interplay between end-of-century long-lived greenhouse gas (LLGHG) forcing and urban expansion on continental US (CONUS) precipitation. Our results show that projected changes in extreme precipitation are at least one order of magnitude greater than projected changes in mean precipitation; this finding is geographically consistent over the seven CONUS National Climate Assessment (NCA) regions and between the pair of dynamically downscaled global climate model (GCM) forcings. We show that dynamical downscaling of the Geophysical Fluid Dynamics Laboratory GCM leads to projected end-of-century changes in extreme precipitation that are consistently greater compared to dynamical downscaling of the Community Earth System Model GCM for all regions except the Southeast NCA region. Our results demonstrate that the physical growth of the built environment can either enhance or suppress extreme precipitation across CONUS metropolitan regions. Incorporation of LLGHGs indicates compensating effects between urban environments and greenhouse gases, shifting the probability spectrum toward broad enhancement of extreme precipitation across future CONUS metropolitan areas. Our results emphasize the need for development of management policies that address flooding challenges exacerbated by the twin forcing agents of urban- and greenhouse gas-induced climate change.

The air temperature cooling impacts of infrastructure-based adaptation measures in expanding urban areas and under changing climatic conditions are not well understood. We present simulations conducted with the Weather Research and Forecasting (WRF) model, coupled to a multi-layer urban model that explicitly resolves pedestrian-level conditions. Our simulations dynamically downscale global climate projections, account for projected urban growth, and examine cooling impacts of extensive cool roof deployment in Atlanta, Detroit, and Phoenix (USA). The simulations focus on heatwave events that are representative of start-, middle-, and end-of-century climatic conditions. Extensive cool roof implementation is projected to cause a maximum city-averaged daytime air temperature cooling of 0.38 °C in Atlanta; 0.42 °C in Detroit; and 0.66 °C in Phoenix. We propose a means for practitioners to estimate the impact of cool roof treatments on pedestrian-level air temperature, for a chosen roof reflectivity, with a new metric called the Albedo Cooling Effectiveness (ACE). The ACE metric reveals that, on average, cool roofs in Phoenix are 11% more effective at lowering pedestrian-level air temperature than in Atlanta, and 30% more effective than in Detroit. Cool roofs remain similarly effective under future heatwaves relative to contemporary heatwaves for Atlanta and Detroit, with some indication of increased effectiveness under future heatwaves for Phoenix. By highlighting the underlying factors that drive cooling effectiveness in a trio of cities located in different climatic regions, we demonstrate a robust framework for estimating the pedestrian-level cooling impacts associated with reflective roofs without the need for computationally demanding simulations.

In the US, more than 80% of fatal cases of heat exposure are reported in urban areas. Notably, indoor exposure is implicated in nearly half of such cases, and lack of functioning air conditioning (AC) is the predominant cause of overheating. For residents with limited capacity to purchase, maintain, and operate an AC system, or during summertime power outages, the ability of buildings to maintain safe thermal conditions without mechanical cooling is the primary protective factor against heat. In this paper, we use whole-building energy simulations to compare indoor air temperature inside archetypical single-family residential buildings without AC at the start and middle of the century in eight US cities. We ran the models using hourly output from 10 year regional climate simulations that explicitly include heating from mid-century projections of urban development and climate change under a ‘business-as-usual’ emissions scenario. Moreover, to identify the impacts from evolving construction practices, we compare different versions of building energy standards. Our analysis shows that summertime overheat time may increase by up to 25% by the middle of century. Moreover, we find that, while newer building energy codes reduce thermal comfort under moderate outdoor weather, they perform better under extreme heat.