A review of methods for quantifying urban ecosystem services

Many methods have been applied to quantify urban ecosystem services (UESs) in the past two decades. Timely reviews of UES assessment methods are necessary for tracking the methodological progress and identifying research gaps. In this study, we systematically analyzed 862 to reveal the overall trend of quantitative studies of UESs, the types of ecological structures and UESs assessed in those studies, and the main equations and parameters used. We found a rising trend of quantitative studies of UESs, accelerating after 2015. Large-size and publicly-owned ecological structures and regulating services were assessed the most frequently. We identified 1,130 equations and 1,190 parameters. Simple methods and equations were used more regularly than complex ones. Values for around 30% of parameters were taken from published papers, while the sources or the values were not specified for about 40% and 20% of all parameters, respectively. The remaining 10% were derived from field measurements and other sources. Based on our findings, we recommend building an open database of quantitative methods, testing the suitability of existing methods for urban environments, developing new methods specifically designed for urban areas, and increasing the transparency of reported methods.