Mapping Urban Heat Drivers and Cooling Priorities in Topographically Enclosed Districts: A Remote Sensing Framework Applied to Crater District, Aden, Yemen

Topographically enclosed urban districts, set within valleys, basins, or volcanic craters inside larger cities, may experience intensified surface heat, as the surrounding terrain restricts ventilation and traps warm air. This intra-urban form remains poorly characterized in data-scarce semi-arid and arid regions. We present a remote sensing framework to diagnose surface urban heat drivers and map cooling-priority zones, applied to Crater District, Aden, Yemen, inside an extinct volcanic caldera in an arid coastal climate.

Cloud-free Landsat 8/9 thermal imagery for the 2023-2025 hot season (43 scenes) was processed in Google Earth Engine to retrieve land surface temperature (LST) data, using the single-channel method with NDVI-based emissivity. A topographic enclosure index was derived from SRTM elevation data, calculated as the difference between the mean elevation of a 500 m neighborhood and each pixel's elevation, representing relative terrain depression and vegetation cover from NDVI. Surface Urban Heat Island Intensity (SUHII) was computed relative to the periphery, and the influence of enclosure and vegetation on LST was assessed via pixel-wise correlation (n = 2967) and Getis-Ord Gi* hot-spot analysis. Hot spots were overlaid with high-enclosure, low-vegetation zones to generate a cooling-priority map.

The mean district-interior LST reached 46.5C, which is marginally below the periphery (46.7C; SUHII ~ -0.2C). This modest district-wide SUHII reflects that the surrounding periphery is itself a hot, arid landscape rather than a cool baseline. Within the district, LST correlated positively with topographic enclosure (r = 0.235, p < 0.001) and weakly with vegetation cover (r = 0.101, p < 0.001), showing that more enclosed sub-areas experience elevated surface heat independent of the district's overall SUHII. Hot-spot analysis identified significant heat clusters covering approximately 0.14 km2, concentrated in the most enclosed, least vegetated sectors; these were flagged as the highest-priority zones for cooling intervention (~0.11 km2).

These findings indicate that topographic enclosure is a statistically significant driver of intra-urban surface heat variation in arid urban settings. The framework translates these drivers into a spatial cooling-priority map, offering a low-cost, transferable planning tool for topographically constrained districts in semi-arid and arid cities where ground data are limited.