Knowledge of the day-to-day dynamics of surface urban heat island (SUHI) as well as their underlying determinants is crucial to a better design of effective heat mitigation. However, there remains a lack of a globally comprehensive investigation of the responsiveness of SUHI variations to meteorological variables. Based on the MODIS LSTs and auxiliary data in 2017, here we investigated 10,000+ cities worldwide to reveal day-to-day SUHI intensity (SUHII) variations (termed as SUHIIdv) in response to meteorological variables using Google Earth Engine. We found that: (1) meteorological variables related to the thermal admittance, e.g., precipitation, specific humidity and soil moisture (represented by daily temperature range in rural area, DTRr), reveal a larger regulation on SUHIIdv than those related to the air conditions (e.g., wind speed and near-surface air temperature) over a global scale. (2) Meteorological regulations on SUHIIdv can differ greatly by background climates. The control of specific humidity on SUHIIdv is significantly strengthened in arid zones, while that of wind speed is weakened prominently in equatorial zones. SUHIIdv is more sensitive to soil moisture in cities with higher background temperatures. (3) All meteorological variables, except that related to soil moisture (DTRr), show larger impact on SUHIIdv with antecedent precipitation over the global scale. Precipitation is observed to mitigate the SUHIIdv globally, and such effects are even more pronounced in equatorial and arid zones. We consider that our findings should be helpful in enriching the knowledge of SUHI dynamics on multiple timescales.
Variations in the surface urban heat island intensity (SUHII) are regulated mainly by three types of control: surface property, background climate (or weather) conditions, and overall urban metric. However, intensive debates arise over the relative importance of these three control types. Here, over 896 Chinese city clusters, we reconcile these debates by showing that the priorities of the three SUHII control types depend closely on the scale and sampling criteria, although they are all crucial in regulating SUHII variations. With increasing temporal scale, the contributions from climate (or weather) conditions decrease, while those from surface property and overall urban metric increase. We find no consistent ranking in the relative importance of these three control types on various spatial scales. The sampling style of city cluster also contributes to disagreements regarding SUHII controls. Our findings potentially help resolve the long‐standing debate on the relative importance of SUHII controls.
A comprehensive comparison of the trends and drivers of global surface and canopy urban heat islands (termed Is and Ic trends, respectively) is critical for better designing urban heat mitigation strategies. However, such a global comparison remains largely absent. Using spatially continuous land surface temperatures and surface air temperatures (2003–2020), here we find that the magnitude of the global mean Is trend (0.19 ± 0.006°C/decade, mean ± SE) for 5,643 cities worldwide is nearly six‐times the corresponding Ic trend (0.03 ± 0.002°C/decade) during the day, while the former (0.06 ± 0.004°C/decade) is double the latter (0.03 ± 0.002°C/decade) at night. Variable importance scores indicate that global daytime Is trend is slightly more controlled by surface property, while background climate plays a more dominant role in regulating global daytime Ic trend. At night, both global Is and Ic trends are mainly controlled by background climate.
Westerlies-dominated arid central Asia (ACA) has a very fragile ecological environment that highly depends on the available moisture sources. However, the moisture history of this region during the Holocene has been a controversial topic for several decades. Here, we performed optically stimulated luminescence (OSL) dating and grain-size analysis of aeolian sediments from the eastern Balikun Basin. Our results demonstrated that the early Holocene climate in the Balikun Basin was dry (beforẽ 6.5 ka) and then became wetter during the mid-late Holocene. This Holocene climate pattern correlates well with other climatic inferences from various proxies acquired at various ACA locations, further supporting an earlier view that the Holocene climate in ACA was out of phase with that of the East Asia summer monsoon. Furthermore, an extremely dry event at 4.3-2.6 ka correlated well with pollen records and a decrease of~4°C in temperature in the western Balikun Lake, but this event was not evident in other ACA regions. Finally, Mingsha Shan Sand Dunes in the eastern Balikun Basin initially accumulated in the earliest Holocene. We suggest that the early Holocene dry climate in the ACA region and the local geomorphology are responsible for the formation of the Mingsha Shan Sand Dunes.
Large‐scale human activity changes in megacities during Chinese New Year (CNY) are believed to significantly affect urban heat islands (UHIs). However, the urban‐rural gradient in UHI variations responsive to human activity changes in cities remains largely unclear. Using in‐situ surface air temperature obtained from a meteorological network that includes 3000‐plus stations, we show that the mean UHI intensity (UHII) in 31 Chinese capitals is 0.52 ± 0.23 K during the CNY holiday and 0.77 ± 0.29 K in the reference period, indicating a UHII reduction of 0.25 ± 0.20 K during the holiday. The reduced UHII decreased more from city core (0.54 K) to city periphery (0.071 K). We find that these UHII reductions were larger at night than during the day and were larger in northern subtropical and warm temperate climates than in other climates. These UHII reductions were mainly attributable to the decline in anthropogenic heat release.
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