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Land surface albedo is a significant regulator of climate. Changes in land use worldwide have greatly reshaped landscapes in the recent decades. Deforestation, agricultural development, and urban expansion alter land surface albedo, each with unique influences on shortwave radiative forcing and global warming impact (GWI). Here, we characterize the changes in landscape albedo-induced GWI (GWIΔα) at multiple temporal scales, with a special focus on the seasonal and monthly GWIΔα over a 19-year period for different land cover types in five ecoregions within a watershed in the upper Midwest USA. The results show that land cover changes from the original forest exhibited a net cooling effect, with contributions of annual GWIΔα varying by cover type and ecoregion. Seasonal and monthly variations of the GWIΔα showed unique trends over the 19-year period and contributed differently to the total GWIΔα. Cropland contributed most to cooling the local climate, with seasonal and monthly offsets of 18% and 83%, respectively, of the annual greenhouse gas emissions of maize fields in the same area. Urban areas exhibited both cooling and warming effects. Cropland and urban areas showed significantly different seasonal GWIΔα at some ecoregions. The landscape composition of the five ecoregions could cause different net landscape GWIΔα.
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Urban Land Expansion Amplifies Surface Warming More in Dry Climate than in Wet Climate: A Global Sensitivity Study
Abstract Urbanization changes Earth's climate by contributing to the buildup of atmospheric greenhouse gases and altering surface biophysical properties. In climate models, the greenhouse aspect is prescribed with urbanization and emission trajectories embedded in socioeconomic pathways (SSPs). However, the biophysical aspect is omitted because no models currently simulate spatially explicit urban land transition. Urban land is typically warmer than adjacent natural land due to a large urban‐versus‐natural land contrast in biophysical properties. The lack of biophysical representation of urbanization in climate models raises the possibility that model projection of future warming may be biased low, especially in areas with intense urban land expansion. Here, we conduct a global sensitivity study using a dynamic urban scheme in the Community Earth System Model to quantify the biophysical effect of urban land expansion under the SSP5‐RCP8.5 scenario. Constant urban radiative, thermal, and morphological properties are used. We find that the biophysical effect depends on land aridity. In climate zones where surface evaporation is water‐limited, the biophysical effect causes a significant increase in air temperature (0.28 ± 0.19 K; mean ± one standard deviation of nine ensemble pairs;p < 0.01) in areas where urban expansion exceeds 5% by 2070. The majority of this warming signal is attributed to an indirect effect associated with atmospheric and land feedback, with the direct effect of land replacement playing a minor role. These atmospheric feedback processes, including solar brightening, soil drying, and stomatal closure, act to enhance the warming initiated by surface property changes of urban land replacement.
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- Award ID(s):
- 2145362
- PAR ID:
- 10659666
- Publisher / Repository:
- Wiley Online Library
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Atmospheres
- Volume:
- 130
- Issue:
- 4
- ISSN:
- 2169-897X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1029/2024JD041696
