[Comparison of methods for exploring spatiotemporal variations of urban heat island effect: With Wuhan Metropolitan...

In the context of global climate change, the urban heat island effect (UHI) poses a severe threat to the health and life quality of residents. Explorations of the spatiotemporal variations of intra-urban heat island effect present as a key foundation for identifying the impacts of diversified and differential construction modes on the thermal environment, as well as testing the implementation effect of relevant planning interventions. However, the spatio-temporal variability of UHI manifests as highly dynamic and stochastic, governed by the nonlinear coupling between built environment and climate system. Such intrinsic volatility poses a critical challenge for precise diagnostic assessment in urban planning. To distill actionable insights from this complexity, two classes of "sequential reduction" strategies have emerged. The "time-space" approach prioritizes temporal trend extraction before spatial partitioning based on trend similarity, while the "space-time" approach clusters spatial units by trajectory similarity prior to trend analysis. Yet, despite their proliferation, a systematic critique regarding their core rationales, methodological protocols, and distinct domains of applicability remains conspicuously absent. To fill this gap, we utilized 11 periods of land surface temperature data by Landsat satellites for Wuhan from 2000 to 2024 to systematically compare the two methods in terms of analytical capabilities and applicability in planning evaluations. Results showed that the "time-space" method, relying on the trend test of independent pixels, identified 10 types of spatial zones, which could be further summarized into three major patterns, including persistent warming pattern, significantly mitigated pattern, and balanced-stable pattern. Among them, persistent warming pattern accounted for 21.9% of the area, while significant mitigation pattern accounted for 0.1%. Those results indicated that this method was highly sensitive to local subtle changes and was therefore more suitable for meso-micro assessment oriented to urban detailed planning and urban renewal. The "space-time" method was based on temporal clustering to preferentially identify homogeneous spatial units. It identified 13 types of spatial zones with consistent upward trends, which could be further summarized into three major patterns, including persistent warming pattern, stable high-temperature pattern, and stable low-temperature pattern. Among them, persistent warming pattern accounted for 26.6% of the area. This method emphasized the identification of the overall continuous spatial pattern and was hence more suitable for city-level assessment through master plans for improved spatial patterns of urban thermal environments. Overall, both categories of methods revealed a shared pattern in the spatiotemporal variations of the UHI in Wuhan's metropolitan development area: "overall intensification and core shift". However, distinct differences in the logic and strategies used to handle spatiotemporal complexity had led to significant discrepancies in the assessment results, indicating an urgent need for further methodological innovation.