A modeling study of the sensitivity of urban heat islands to precipitation at climate scales

Gu, Yaofeng; Li, Dan

doi:10.1016/j.uclim.2017.12.001

Cited by 42 publications

(32 citation statements)

References 39 publications

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“…1 and results in SI Appendix). As previously reported, annual and summer averages of ∆Ts increase with increasing mean annual rainfall (15,17,18), and while Nicosia and Madrid show summer ∆Ts values that are lower than the annual mean, the opposite is observed in cities characterized by a wet climate (Fig. 2D).…”

Section: Resultssupporting

confidence: 84%

“…These results are consistent with the hysteretic patterns analyzed and explained here using a coarse-grained model. In general, the intensity of UHIs (both in terms of air and surface temperatures) is directly linked to local precipitation (15,17,18,28), and urban cool islands generally occur in seasonally dry climates (15,16,73,75) where sparse natural vegetation generates barren surfaces that have lower ET , sometimes lower albedo, and are less efficient in dissipating heat than 3D urban fabrics (15,73,76). Urban irrigation can significantly contribute to cooling during summertime (73), but model results here suggest that urban oasis effects exist because of a combination of urban-rural characteristics rather than urban ET alone (75).…”

Section: Broader Impactmentioning

confidence: 99%

“…Given their implications for energy demand (2), climate adaptation policies (3), public health (4), and heat-related mortality (5,6), UHIs have been widely studied over the past decades considering both air and surface temperature observations (e.g., refs. [7][8][9][10][11][12][13][14][15][16][17][18]. Air UHIs are most intense during nighttime, based on air temperature measurements above or below the roof level, whereas surface UHIs (SUHIs), as derived from remotely sensed skin surface temperatures, generally reach peak values during daytime (19)(20)(21)(22).…”

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confidence: 99%

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Seasonal hysteresis of surface urban heat islands

Manoli

Fatichi

Bou‐Zeid

et al. 2020

Proc. Natl. Acad. Sci. U.S.A.

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Temporal dynamics of urban warming have been extensively studied at the diurnal scale, but the impact of background climate on the observed seasonality of surface urban heat islands (SUHIs) remains largely unexplored. On seasonal time scales, the intensity of urban–rural surface temperature differences (ΔTs) exhibits distinctive hysteretic cycles whose shape and looping direction vary across climatic zones. These observations highlight possible delays underlying the dynamics of the coupled urban–biosphere system. However, a general argument explaining the observed hysteretic patterns remains elusive. A coarse-grained model of SUHI coupled with a stochastic soil water balance is developed to demonstrate that the time lags between radiation forcing, air temperature, and rainfall generate a rate-dependent hysteresis, explaining the observed seasonal variations of ΔTs. If solar radiation is in phase with water availability, summer conditions cause strong SUHI intensities due to high rural evaporative cooling. Conversely, cities in seasonally dry regions where evapotranspiration is out of phase with radiation show a summertime oasis effect controlled by background climate and vegetation properties. These seasonal patterns of warming and cooling have significant implications for heat mitigation strategies as urban green spaces can reduce ΔTs during summertime, while potentially negative effects of albedo management during winter are mitigated by the seasonality of solar radiation.

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Section: Resultssupporting

confidence: 84%

Section: Broader Impactmentioning

confidence: 99%

mentioning

confidence: 99%

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Seasonal hysteresis of surface urban heat islands

Manoli

Fatichi

Bou‐Zeid

et al. 2020

Proc. Natl. Acad. Sci. U.S.A.

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“…Local hydroclimatic conditions also contribute to the intensity of UHIs 2,14 , with rising mean annual precipitation causing an increase in urban to rural surface temperature differences (∆T s ), a proxy for urban warming with respect to the more efficient cooling of the surrounding rural surfaces. Given the complexity of urban systems, identifying and isolating the causes of UHIs remains challenging 3,15 and the factors contributing to the observed changes in ∆T s across city sizes and hydroclimatic conditions continue to be a subject of inquiry and debate 2,13,14,16 .…”

Section: Mainmentioning

confidence: 99%

Magnitude of urban heat islands largely explained by climate and population

Manoli

Fatichi

Schläpfer

et al. 2019

Nature

682

352

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Urban heat islands (UHIs) exacerbate the risk of heat-related mortality associated with global climate change. The intensity of UHIs is known to vary with population size and mean annual precipitation but a unifying argument is missing, and geographically targeted guidelines for heat mitigation remain elusive. Here we analyze urban-rural surface temperature differences (∆T s) worldwide and find a nonlinear increase of ∆T s with precipitation that is controlled by water/energy limitations on evapotranspiration and that modulates the scaling of ∆T s with city size. We introduce a coarse-grained model linking population, background climate, and UHI intensity and we show that urban-rural changes in evapotranspiration and convection efficiency are the main determinants for warming. The direct implication of these nonlinearities is that mitigation strategies aimed at increasing green cover and albedo are more efficient in dry regions, while cooling tropical cities is a challenge that will require innovative solutions.

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“…In regard to city expansion, a key question is how UHII can be released efficiently or how its negative effects can be mitigated. In this respect, natural ventilation performance and heat loss/gain are linked to the urban morphological layout which may increase UHII [18][19][20][21]. Also, the buildings' energy consumption can increase due to the impact of UHII.…”

Section: Introductionmentioning

confidence: 99%

The Interactive Impact of Building Diversity on the Thermal Balance and Micro-Climate Change under the Influence of Rapid Urbanization

Makvandi

Elsadek

et al. 2019

Sustainability

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Numerous cities face the serious problems of rapid urbanization and climate change, especially in recent years. Among all cities, Wuhan is one of the most affected by these changes, accompanied by the transformation of water surfaces into urban lands and the decline of natural ventilation. This study investigated the impact of surface urban heat island enlargement (SUHI) and block morphology changes in heat balance. Accordingly, the interactive impact of building diversity with major building forms (low-rise, mid-rise, and high-rise) on thermal balance and microclimate changes under the influence of urban land expansion at the residential block scale was studied. To investigate the heat balance changes by air temperature intensification and air movement reduction, a long-term and field observational analysis (1980–2018) coupled with computational fluid dynamic simulation (CFD) was used to evaluate the impact of building diversity on thermal balance. Outcomes show that urban heat island intensity (UHII) increased by 2 ℃ when water surfaces in urban areas decreased; consequently, there was a deterioration in the air movement to alleviate UHII. Thus, the air movement declined substantially with UHII and SUHI enlargement, which, through increased urban surfaces and roughness length, will become worse by 2020. Furthermore, the decline in air movement caused by the transformation of urban water bodies cannot contribute to the heat balance unless reinforced by the morphology of the urban blocks. In the design of inner-city blocks, morphological indicators have a significant impact on microclimate and heat balance, where increasing building density and plot ratio will increase UHII, and increasing water surfaces will result in an increase in urban ventilation. Lastly, a substantial correlation between air temperature and relative humidity was found, which, together with the block indicators, can help control the air temperature and adjust the urban microclimate.

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A modeling study of the sensitivity of urban heat islands to precipitation at climate scales

Cited by 42 publications

References 39 publications

Seasonal hysteresis of surface urban heat islands

Seasonal hysteresis of surface urban heat islands

Magnitude of urban heat islands largely explained by climate and population

The Interactive Impact of Building Diversity on the Thermal Balance and Micro-Climate Change under the Influence of Rapid Urbanization

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