How Do Urban Green Spaces Influence Land Surface Temperature Dynamics in Urbanizing Areas?

Urbanization induces complex interactions between socioeconomic activities and environmental changes, as reflected in the increase of Night-Time Light (NTL) and the decline of Fractional Vegetation Cover (FVC). While NTL is a key indicator of economic growth and infrastructure expansion, its concurrent association with vegetation loss exacerbates urban heat island (UHI) effects. Although substantial progress has been achieved in examining the individual impact of urbanization on land surface temperature (LST), studies investigating the simultaneous trends of NTL and FVC and their combined effect on LST remain limited.

This study utilized a 20-year (2000–2020) remote-sensed dataset to investigate the spatial and temporal interactions among NTL, FVC, and LST anomalies in East Asian megacities, especially Seoul, Tokyo, Beijing, Shanghai, and Hong Kong. Trends in NTL and FVC were analyzed using the Mann-Kendall test and Sen’s slope methods, while LST anomalies were examined to evaluate relationships with NTL and FVC. The analysis specifically focused on summer months to comprehensively evaluate urban heat island effects. Furthermore, NSGA-II optimization was employed to identify the optimal NTL and FVC ranges that best capture LST trends and explore city-specific urban green space planning patterns.

The results reveal distinct nonlinear relationships between night-time light, fractional vegetation cover, and land surface temperature. LST responses varied depending on the increased balance between NTL and FVC. LST showed a more moderated response in regions where NTL and FVC increased proportionally, suggesting that vegetation can partially mitigate urbanization's thermal impacts through a synergistic effect. Conversely, areas with disproportionately high NTL increases and limited FVC growth exhibited heightened LST sensitivity, reflecting the restricted capacity of vegetation to offset the thermal stress caused by rapid urban expansion.

In Shanghai, rapid urbanization has resulted in a substantial increase in land surface temperature (LST), underscoring the city's heightened vulnerability to urban development. In contrast, both Seoul and Shanghai exhibited more moderate declines in LST in areas where urban green space initiatives were implemented. However, despite Shanghai's extensive urbanization, the expansion of urban green spaces, as quantified by the rate of change in the Fraction of Vegetation Cover (FVC), has been comparatively limited relative to other cities. Furthermore, over the past 20 years, the frequency of FVC and NTL increases demonstrated a more substantial correlation with LST increases than the intensity. These findings highlight the pronounced spatiotemporal heterogeneity in urban environments, emphasizing disparities in environmental stress and recovery potential driven by varying interactions between NTL and FVC.

This research suggests key indicators, such as the balance between NTL and FVC, to guide the development of cooling strategies in urban planning. The findings highlight the potential of integrating vegetation restoration into urban planning as a critical approach to achieving global sustainability goals, particularly SDG 11 (sustainable cities and communities) and SDG 13 (climate action).