Urban Forests as Main Regulator of the Evaporative Cooling Effect in Cities

Tc Chakraborty,Simone Fatichi,Naika Meili,Athanasios Paschalis,Gabriele Manoli

doi:10.1029/2020av000303

Abstract

AbstractHigher temperatures in urban areas expose a large fraction of the human population to potentially dangerous heat stress. Green spaces are promoted worldwide as local and city‐scale cooling strategies but the amount, type, and functioning of vegetation in cities lack quantification and their interaction with urban climate in different settings remains a matter of debate. Here we use state‐of‐the‐art remote sensing data from 145 city clusters to disentangle the drivers of surface urban heat islands (SUHI) intensity and quantify urban‐rural differences in vegetation cover, species composition, and evaporative cooling. We show that nighttime SUHIs are affected mostly by abiotic factors, while daytime SUHIs are highly correlated with vegetation characteristics and the wetness of the background climate. Magnitude and seasonality of daytime SUHIs are controlled by urban‐rural differences in plant transpiration and leaf area, which explain the dependence of SUHIs on wetness conditions. Leaf area differences are caused primarily by changes in vegetation type and a loss of in‐city forested areas, highlighting the importance of maintaining “natural reserves” as a sustainable heat mitigation policy.

Highlights

With the global population increasingly living in cities (e.g., Seto et al, 2011), urban vegetation can provide critical ecosystem services for human and ecological well-being (Endreny, 2018) for a large fraction of the global population
The Dominant Role of Evaporative Cooling. Both SUHId and SUHIn in the northern hemisphere have distinct seasonal patterns that change with the wetness index of the background climate (Figure 2)
We exploited the potential of state-of-the-art remote sensing data to provide a mechanistic understanding of vegetation-climate interactions in complex urban settings and to quantify the links between urban fabric, green spaces, vegetation types, and surface urban heat islands (SUHI)

Summary

Introduction

With the global population increasingly living in cities (e.g., Seto et al, 2011), urban vegetation can provide critical ecosystem services for human and ecological well-being (Endreny, 2018) for a large fraction of the global population. Urban green spaces, such as parks, gardens, and street trees, represent such a “natural capital” for cities (Willis & Petrokofsky, 2017). The spatial extent of vegetated surfaces clearly plays a role in reducing urban temperatures (e.g., Manoli et al, 2019; Winbourne et al, 2020), but the different amount and type of green spaces in existing cities and the various interactions among vegetation type, phenology, and UHI intensity remain largely unexplored

Methods

Results

Conclusion