Quantitative assessment of demand and supply of urban ecosystem services in different seasons: a case study on air purification in a temperate city

Context: For policy makers and scientists to understand patterns of ecosystem services demand (ESd) and supply (ESs) that show a paradox of a compact city, information regarding the balance between ESd and ESs is needed. However, as evaluation of the ESd–ESs balance based on averaged yearly data would minimize the impact of extreme values, the analysis based on seasonal data is important. Objectives: To elucidate seasonal changes of and mismatches between ESd and ESs, we investigated (1) whether seasonal variations of ESs and ESd for PM and SO removal were synchronous; (2) in which season ESs could most/least satisfy ESd; (3) whether seasonal imbalance existed, although ESs might apparently satisfy ESd based on annual data; and (4) how spatial patterns of seasonal mismatches varied. Methods: Deficit ratio and supply–demand ratio were utilized to assessed the risk of ESd–ESs mismatch for air purification and analyzed the extent to which ESs meets ESd respectively, on seasonal and annual timescales in Shenyang. Results: The ESd and ESs of air purification ecosystem services for PM and SO are asynchronous. Inconsistency in the seasonal pattern between ESs and ESd induces severe mismatch between ESs and ESd in some seasons, e.g., winter. Assessment based on annual data could result in overoptimistic evaluations of ecosystem services. Conclusions: The ESs–ESd balance isn't only spatially heterogeneous but also temporally heterogeneous. Therefore, explicit spatiotemporal analysis of ecosystem services would provide additional information that could help policy makers develop and implement effective targeted strategies.