Quantifying the impact of land cover composition on intra-urban air temperature variations at a mid-latitude city.

Hai Yan,Chenxiao Guo,Li Dong,Jie Hu,Shuxin Fan,Zoe G Davies

doi:10.1371/journal.pone.0102124

Abstract

The effects of land cover on urban-rural and intra-urban temperature differences have been extensively documented. However, few studies have quantitatively related air temperature to land cover composition at a local scale which may be useful to guide landscape planning and design. In this study, the quantitative relationships between air temperature and land cover composition at a neighborhood scale in Beijing were investigated through a field measurement campaign and statistical analysis. The results showed that the air temperature had a significant positive correlation with the coverage of man-made surfaces, but the degree of correlation varied among different times and seasons. The different land cover types had different effects on air temperature, and also had very different spatial extent dependence: with increasing buffer zone size (from 20 to 300 m in radius), the correlation coefficient of different land cover types varied differently, and their relative impacts also varied among different times and seasons. At noon in summer, ∼37% of the variations in temperature were explained by the percentage tree cover, while ∼87% of the variations in temperature were explained by the percentage of building area and the percentage tree cover on summer night. The results emphasize the key role of tree cover in attenuating urban air temperature during daytime and nighttime in summer, further highlighting that increasing vegetation cover could be one effective way to ameliorate the urban thermal environment.

Highlights

We aim to elucidate: 1) To what extent does the conversion of land cover from rural natural surfaces to man-made surfaces affect the urban air temperature variations, and the seasonal and diurnal variation of the relationship; 2) what spatial extent is air temperature at a point affected by the composition of land cover conditions around that location; and 3) if the relative importance of different land cover types in explaining air temperature difference varies with time and extent expansion
Effects of man-made surfaces on urban air temperature Figure 3 shows the relationships between air temperatures and the percentage of man-made surfaces (PerMS) at different temporal and spatial scales
The results showed that the increase of man-made surfaces due to urbanization has a significant positive effect on the magnitude of intra-urban air temperature variation, the effect varied among different times and seasons

Summary

Introduction

One of the most important causal factors is the conversion of land cover from rural to urban covers, mainly the replacement of natural vegetation covers by impervious manmade surfaces [3]. The composition and arrangement of natural and man-made surfaces, including impervious surfaces, vegetation areas and water body, as well as the local weather conditions influence near surface energy flux partitioning, resulting in variable local climates [5]. Using a variety of image data, these studies found that land cover characteristics, such as vegetation indices measured by NDVI (normalized difference vegetation index), and the relative amounts of other land cover types (building area, impervious surface, water body) significantly affect the urban temperature distribution patterns and UHI intensity [13,14,15,16,17,18,19,20]

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