Abstract
We examine the joint contribution of urban expansion and climate change on heat stress over the Sydney region. A Regional Climate Model was used to downscale present (1990–2009) and future (2040–2059) simulations from a Global Climate Model. The effects of urban surfaces on local temperature and vapor pressure were included. The role of urban expansion in modulating the climate change signal at local scales was investigated using a human heat-stress index combining temperature and vapor pressure. Urban expansion and climate change leads to increased risk of heat-stress conditions in the Sydney region, with substantially more frequent adverse conditions in urban areas. Impacts are particularly obvious in extreme values; daytime heat-stress impacts are more noticeable in the higher percentiles than in the mean values and the impact at night is more obvious in the lower percentiles than in the mean. Urban expansion enhances heat-stress increases due to climate change at night, but partly compensates its effects during the day. These differences are due to a stronger contribution from vapor pressure deficit during the day and from temperature increases during the night induced by urban surfaces. Our results highlight the inappropriateness of assessing human comfort determined using temperature changes alone and point to the likelihood that impacts of climate change assessed using models that lack urban surfaces probably underestimate future changes in terms of human comfort.
Highlights
Cities create an environment that is clearly distinct from their surrounding areas
The combined contrasts of temperature and vapor pressure between urban and rural areas shown in Fig. 3 lead to relative humidity values at night 10–15% drier in the urban environment than in the rural one, which is consistent with previous finding using Global Climate Models (GCMs) [26]
The effects of urban areas on local temperature and vapor pressure from the simulations are in agreement with previous results [4, 23] and with the theoretical basis of energy partitioning in the urban environment [21]
Summary
Cities create an environment that is clearly distinct from their surrounding areas. Urban structures alter the surface energy budget [1], modify the vertical profile of various atmospheric properties, interact with both local and regional circulation, and introduce additional sources of heat (e.g. anthropogenic heat). The climate conditions in the urban environment significantly differ from their rural counterparts. The study of the urban climate has attracted considerable attention from a broad range of researchers in the last few decades with considerable effort devoted to understanding the urban-atmosphere interactions under present climate [2,3,4,5]. The effect of urban areas is confined in spatial extent and relatively small in global terms [6, 7] it has implications for most of the world’s population. Over half of PLOS ONE | DOI:10.1371/journal.pone.0117066 February 10, 2015
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