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Nanjing University of Information Science and Technology (2022)

Effects of Ecohydrological Changes on “Urban Dry Islands” Across China

黄萧霖

Titre : Effects of Ecohydrological Changes on “Urban Dry Islands” Across China

Auteur : 黄萧霖

Grade : Doctoral Dissertation 2022

Université : Nanjing University of Information Science and Technology

Résumé partiel
Urbanization leads to differences in near-surface atmospheric humidity between cities and surrounding suburbs,creating an urban dry island/wet island effect.Changes in atmospheric humidity associated with urbanization have important implications for climate change prediction and impact assessment,such as cloud formation,rainfall intensity,human thermal comfort,and wildfires at the urban-forest interface.In this paper,we use various techniques and methods such as ground-based comparative observation,remote sensing monitoring technology,mesoscale numerical simulation,statistical analysis,and based energy balance contribution splitting to finely characterize the urban hydrothermal change process at multiple scales.Using vapor pressure deficit and specific humidity as atmospheric dry / humidity indicators,the spatial and temporal distribution patterns and change characteristics of urban dry islands in five typical urban agglomerations in four climate zones of China in the past four decades are examined,including the Pearl River Delta in the humid zone,the Yangtze River Delta in the semi-humid zone,the Chengdu-Chongqing in the semi-arid region,the Beijing-Tianjin-Hebei in the semiarid region,and the northern Tianshan in the arid region.Regional land cover changes(e.g.,leaf area index),hydrological changes(e.g.,reduced evapotranspiration due to urbanization)and urban climate change(temperature and humidity)are coupled to quantitatively characterize the hydroclimatic feedbacks of cover changes in urban agglomeration and to elucidate the chain reaction mechanism of ‘land cover pattern → ecohydrological processes → coupled hydrothermal balance → urban dry island effect’.The specific findings are as follows.(1)The five large urban agglomerations in China have experienced aggravated atmospheric drying during the past 30 years.The UDI effects were significantly enhanced and more pronounced during daytime and growing seasons.Based on empirical data,this study revealed a plausible connection between land-use change and an urban atmospheric moisture drying phenomenon,or UDI effect across a large climatic gradient.We show that the five large urban agglomerations in China have experienced aggravated atmospheric drying during the past 30 years.During 1980-2018,the urban near-surface atmosphere became drier than the surrounding suburbs in the five major urban agglomerations with different climate gradients,and the urban dry island effect(ΔVPD > 0 or Δq < 0)appeared around 2000.The urban dry island effect was stronger and occurred more frequently during daytime ;the intensity and frequency of urban dry island were more pronounced in the growing season than in other seasons.Although nighttime UWI partially offset the daily UDI effect and made daily UDI underestimated during 2000–2010,after 2010,it weakened or disappeared in humid and semihumid areas,resulting in a significant increase in daily UDI.

Mots clés : urban dry island (UDI) effect ;land use/cover change ;land surface evapotranspiration ;vapor pressure deficit ;specific humidity ;attribution analysis ;numerical simulation ;

Présentation (CNKI)

Page publiée le 17 octobre 2022