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Title: Urbanization-induced urban heat island and aerosol effects on climate extremes in the Yangtze River Delta region of China

The WRF-Chem model coupled with a single-layer urban canopy model (UCM) is integrated for 5 years at convection-permitting scale to investigate the individual and combined impacts of urbanization-induced changes in land cover and pollutant emissions on regional climate in the Yangtze River Delta (YRD) region in eastern China. Simulations with the urbanization effects reasonably reproduced the observed features of temperature and precipitation in the YRD region. Urbanization over the YRD induces an urban heat island (UHI) effect, which increases the surface temperature by 0.53 °C in summer and increases the annual heat wave days at a rate of 3.7 d yr −1 in the major megacities in the YRD, accompanied by intensified heat stress. In winter, the near-surface air temperature increases by approximately 0.7 °C over commercial areas in the cities but decreases in the surrounding areas. Radiative effects of aerosols tend to cool the surface air by reducing net shortwave radiation at the surface. Compared to the more localized UHI effect, aerosol effects on solar radiation and temperature influence a much larger area, especially downwind of the city cluster in the YRD. Results also show that the UHI increases the frequency of extreme summer precipitation by strengthening the convergence and updrafts over urbanized areasmore » in the afternoon, which favor the development of deep convection. In contrast, the radiative forcing of aerosols results in a surface cooling and upper-atmospheric heating, which enhances atmospheric stability and suppresses convection. The combined effects of the UHI and aerosols on precipitation depend on synoptic conditions. Two rainfall events under two typical but different synoptic weather patterns are further analyzed. It is shown that the impact of urban land cover and aerosols on precipitation is not only determined by their influence on local convergence but also modulated by large-scale weather systems. For the case with a strong synoptic forcing associated with stronger winds and larger spatial convergence, the UHI and aerosol effects are relatively weak. When the synoptic forcing is weak, however, the UHI and aerosol effects on local convergence dominate. This suggests that synoptic forcing plays a significant role in modulating the urbanization-induced land-cover and aerosol effects on individual rainfall event. Hence precipitation changes due to urbanization effects may offset each other under different synoptic conditions, resulting in little changes in mean precipitation at longer timescales.« less
Authors:
 [1] ;  [2] ;  [3] ;  [2] ;  [2] ;  [4] ;  [2] ;  [5] ;  [6] ;  [7]
  1. Hohai University, Nanjing (China). State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Center for Global Change and Water Cycle; Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
  2. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
  3. Pacific Northwest National Lab. (PNNL), Richland, WA (United States); University of Science and Technology of China, Hefei (China)
  4. Nanjing University (China). School of Atmospheric Sciences; Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
  5. Nanjing University of Information and Technology, Nanjing (China). College of Atmospheric Science; Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
  6. Nanjing University (China). School of Atmospheric Sciences
  7. Nanjing Meteorological Bureau, Nanjing (China)
Publication Date:
Report Number(s):
PNNL-SA-125598
Journal ID: ISSN 1680-7324; KP1701000; KP1703010
Grant/Contract Number:
AC05-76RL01830
Type:
Published Article
Journal Name:
Atmospheric Chemistry and Physics (Online)
Additional Journal Information:
Journal Name: Atmospheric Chemistry and Physics (Online); Journal Volume: 17; Journal Issue: 8; Journal ID: ISSN 1680-7324
Publisher:
European Geosciences Union
Research Org:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; WRF-Chem; urban canopy model; UCM; Yangtze River Delta; YRD
OSTI Identifier:
1353305
Alternate Identifier(s):
OSTI ID: 1356506