Temporal consistency between gross primary production and solar-induced chlorophyll fluorescence in the ten most populous megacity areas over years

Yaoping Cui,Berrien Moore,Joanna Joiner,Yaochen Qin,Xiaocui Wu,Xiangming Xiao,Shenghui Zhou,Yuanwei Qin,Jinwei Dong,Russell B Doughty,Jie Wang,Geli Zhang,Yao Zhang

doi:10.1038/s41598-017-13783-5

Abstract

The gross primary production (GPP) of vegetation in urban areas plays an important role in the study of urban ecology. It is difficult however, to accurately estimate GPP in urban areas, mostly due to the complexity of impervious land surfaces, buildings, vegetation, and management. Recently, we used the Vegetation Photosynthesis Model (VPM), climate data, and satellite images to estimate the GPP of terrestrial ecosystems including urban areas. Here, we report VPM-based GPP (GPPvpm) estimates for the world’s ten most populous megacities during 2000–2014. The seasonal dynamics of GPPvpm during 2007–2014 in the ten megacities track well that of the solar-induced chlorophyll fluorescence (SIF) data from GOME-2 at 0.5° × 0.5° resolution. Annual GPPvpm during 2000–2014 also shows substantial variation among the ten megacities, and year-to-year trends show increases, no change, and decreases. Urban expansion and vegetation collectively impact GPP variations in these megacities. The results of this study demonstrate the potential of a satellite-based vegetation photosynthesis model for diagnostic studies of GPP and the terrestrial carbon cycle in urban areas.

Highlights

At present 54% of the world’s population resides in urban areas[1]
Three datasets (GPPvpm, GPPmod[17], and Global Ozone Monitoring Instrument 2 (GOME-2) solar-induced chlorophyll fluorescence (SIF)) generated from various data resources and methods are used to examine the seasonal dynamics of urban gross primary production (GPP) and SIF
We investigate to what degree vegetation phenology, physiology, and greenness (using mean Enhanced Vegetation Index (EVI) of growing season as a proxy) affected the dynamics of annual GPP during 2000–2014 (Figs 4 and 5, and Fig. S4)

Summary

Introduction

At present 54% of the world’s population resides in urban areas[1]. Most cities are experiencing an acceleration of urbanization in terms of both population growth and area expansion[1,2]. The gross primary production (GPP) of vegetation is an important variable in the terrestrial carbon cycle. GPPvpm has not yet been evaluated in urban areas because there is no appropriate observation data available for validation. A number of studies have used SIF data to evaluate the phenology of forests, grasslands, and croplands. A few other studies have evaluated the relationship between SIF and GPP in different regions[20,23,27,32]. Until this study, the relationship between SIF and GPP in urban areas has not been evaluated. One challenge in evaluating the relationship between GPP and SIF in urban area is related to the coarse spatial resolution of the GOME-2 SIF data (0.5° × 0.5°). This study describes the urban and surrounding areas as an “urban” gridcell comprising urban, sub-urban, as well as any adjacent rural areas that usually have a high degree of socioeconomic and functional integration with neighboring urban areas

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Results

Conclusion