Abstract
Previous studies on the impact of urbanization on the diurnal temperature range (DTR) have mainly concentrated on the intra-seasonal and interannual–decadal scales, while relatively fewer studies have considered synoptic scales. In particular, the modulation of DTR by different synoptic weather patterns (SWPs) is not yet fully understood. Taking the urban agglomeration of the Yangtze River Delta region (YRDUA) in eastern China as an example, and by using random forest machine learning and objective weather classification methods, this paper analyzes the characteristics of DTR and its urban–rural differences (DTRU–R) in summer from 2013 to 2016, based on surface meteorological observations, satellite remote sensing, and reanalysis data. Ultimately, the influences of urbanization-related factors and different large-scale SWPs on DTR and DTRU–R are explored. Results show that YRDUA is controlled by four SWPs in the 850-hPa geopotential height field in summer, and the DTRs in three sub-regions are significantly different under the four SWPs, indicating that they play a role in regulating the DTR in YRDUA. In terms of the average DTR for each SWP, the southern sub-region of the YRDUA is the highest, followed by the northern sub-region, and the middle sub-region is the lowest, which is most significantly affected by high-level urbanization and high anthropogenic heat emission. The DTRU–R is negative and differs under the four different SWPs with variation in sunshine and rainfall. The difference in anthropogenic heat flux between urban and rural areas is one of the potentially important urbanization-related drivers for DTRU–R. Our findings help towards furthering our understanding of the response of DTR in urban agglomerations to different SWPs via the modulation of local meteorological conditions.
Highlights
The results show that the probability density distribution of DTRU–R under the four weather types tends to be negative on the whole, and the peak values are concentrated within −1–0°C
The main conclusions are as follows: The YRDUA region is mainly controlled by four synoptic weather patterns (SWPs) in the 850-hPa geopotential height field
The lower Diurnal temperature range (DTR) in the middle sub-region is mainly affected by its high levels of urbanization and anthropogenic heat emissions
Summary
Diurnal temperature range (DTR) is the difference between the maximum surface air temperature and the minimum surface air temperature in a whole day, which can reflect the global and regional characteristics of temperature change (Easterling, 1997; Braganza et al, 2004; Vose et al, 2005), and has an important impact on human health (Kan et al, 2007; Lim et al, 2012; Yang et al, 2013; Zhang et al, 2018) and crop yield (Lobell, 2007; Tao et al, 2008). The intensification of urbanization across the globe has contributed to the decline in DTR since the 1950s (Gallo et al, 1996; Kalnay and Cai, 2003; Feddema 2005; Mohan and Kandya, 2015). This is mainly because the underlying impervious surfaces of cities increases the nighttime temperature by absorbing a large amount of energy in the daytime and releasing it at night (Forster and Solomon, 2003; Zhou et al, 2007; Yang et al, 2020a; Zong et al, 2021). Due to the radiative cooling effect of aerosol pollution over cities, the daytime temperature decreases (Zheng et al, 2018; Yang et al, 2020b), and the DTR decreases in cities owing to the asymmetry in the changes of maximum and minimum temperature
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