Non-linear effects of meteorological variables on cooling efficiency of African urban trees. (November 2022)

• Record Type: Journal Article
• Authors: Cheng, Xueyan; Peng, Jian; Dong, Jianquan; Liu, Yanxu; Wang, Yanglin
• Is Part Of: Environment international. Volume 169(2022)
• Publication Date: 2022-11
• Subjects: Urban tree cooling efficiency -- Non-linear effects -- Generalized additive model -- Meteorological variables -- African cities; Environmental protection -- Periodicals; Environmental health -- Periodicals; Environmental monitoring -- Periodicals; Environmental Monitoring -- Periodicals; Environnement -- Protection -- Périodiques; Hygiène du milieu -- Périodiques; Environnement -- Surveillance -- Périodiques; Environmental health; Environmental monitoring; Environmental protection; Periodicals; 333.705
• DOI: 10.1016/j.envint.2022.107489
• Languages: English
• ISSNs: 0160-4120

Abstract

Highlights: Arid cities among 40 African cities had greater urban tree CE. CE increased and then decreased as AT/TDPD increased, with turning point of 34 °C/26 °C. Sahel cities couldn't cool only by trees since they would have more days over 34 ℃. Abstract: Urban tree cover is widely regarded as an environmentally-friendly and effective urban cooling approach. Meteorological variables, including air temperature, wind speed, and humidity, have complex impacts on the cooling efficiency (CE) of urban trees (i.e., the negative ratio of the land surface temperature change to the tree cover percentage change). This means that increasing the urban tree cover to alleviate heat stress is not necessarily suitable for cities with different climates. African cities are confronted with larger heat risks but lack considerations for the effectiveness of urban tree cooling in urban planning. In this study, 40 African major cities with population greater than 500, 000 in different climatic regions were selected, and 1459 CEs during each city's corresponding warmest 3 consecutive months were calculated combined with the availability of meteorological data. The generalized additive models revealed the non-linear impacts of air temperature/temperature dew point difference on CE, which were more evident in arid cities. The CE of urban trees actually increased and then decreased along with the increase of air temperature/temperature dew point difference, and the turning point were 34 °C/26 °C, respectively. African cities would have different frequencies of warm days with an air temperature over 34 °C under different Shared Socioeconomic Pathways within the next 30 years. Specially, the cities around Sahel would suffer up to 40–60% days over 34 °C, which meant their urban tree CE would decrease along with air temperature increase. This study highlighted that in African cities, especially those with arid climate, it was unadvisable to only count on increasing tree cover to alleviate urban heat stress in the warming future, which called for other combined cooling strategies.