Linking urban expansion to thermal stress: assessing land use transitions, spectral dynamics, and surface temperature in Burewala

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Abstract
Land Use and Land Cover (LULC) transformations driven by human activities significantly influence the thermal behavior and ecological function of urban environments. This study investigates the spatiotemporal dynamics of LULC, land surface temperature (LST), and key spectral indices—including the Normalized Difference Built-up Index (NDBI, for mapping impervious surfaces), the Normalized Difference Vegetation Index (NDVI, for assessing vegetation health and density), and the Normalized Difference Water Index (NDWI, for detecting surface water and moisture)—in Burewala City, Pakistan. Using multi-temporal Landsat imagery (2003, 2014, 2023), supervised classification and transition matrix analysis revealed quantitatively modest but environmentally significant urban expansion, with built-up areas increasing from 11.44% to 12.71% (a net gain of 19.05 km2), primarily through the conversion of 53.57 km2 of bare soil. Although the classified area of vegetation slightly increased, NDVI values demonstrated a significant decline in vegetative health. Concurrently, mean LST rose substantially from 26.87 °C to 36.76 °C. Zonal analysis quantified a distinct thermal hierarchy among LULC classes, with built-up areas exhibiting the highest mean LST—exceeding vegetated surfaces by 3.6 °C in 2023. The spatiotemporal pattern of the Urban Thermal Field Variance Index (UTFVI, a measure of ecological thermal comfort) showed a marked expansion of areas experiencing strong heat island stress. Statistical analysis revealed strong correlations, most notably a robust and consistent negative relationship between LST and NDVI (R2 = 0.82 to 0.76). The findings reveal that urban growth, coupled with the degradation of vegetation quality and loss of surface moisture, is a primary driver of elevated surface temperatures and worsening thermal comfort. These results underscore that effective mitigation of urban heat requires policies focused on enhancing vegetative health, restoring urban water cycles, and implementing targeted interventions in zones of high thermal stress, moving beyond conventional land-use planning.

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