Unravelling the impact of land use transformation on thermal environment across seasons: A comprehensive study of rapidly urbanizing Patna Planning Area, India.

The impact of Land Use Land Cover (LULC) alterations on the spatial distribution of surface temperature and the resulting urban thermal conditions across seasons remain poorly understood, especially in medium-sized cities predominantly located on natural riverine levees. This study reveals the intricate relationship between LULC changes and Land Surface Temperature (LST) and the degradation of urban ecology across pre- and post-monsoons using multi-temporal Landsat imagery for 1993, 2009, and 2021. Here, an ecological assessment of the Patna Planning Area (PPA) has been carried out using the Urban Thermal Field Variance Index (UTFVI), particularly employing spatial lag models (SLM), Moran's I, and bivariate Local Indicators of Spatial Association (LISA) maps. The result shows that built-up area in PPA has increased by 128.09%, whereas agricultural land has decreased by 15.36% from 1993 to 2021. These excessive changes in LULC significantly impacted the spatial distribution of LST in both seasons. The mean pre-monsoon LST has increased by 4.31 °C, whereas the mean post-monsoon LST has shown a rise of 1.36 °C in the last 28 years. In addition, within each LULC category, the LST and UTFVI during the pre-monsoon were higher in the surrounding agricultural land compared to the PPA's primary built-up areas, which signifies the presence of the urban cool island effect. The possible reason for this effect is the presence of moisture due to the mighty Ganges along the northern extremity and the "Jalla" area (back swamp) in and around the core city region. On the contrary, during post-monsoon, the LST and UTFVI of built-up land have displayed inconsistent changing patterns, such as from a trivial random existence of heat patches in the year 1993 to a full-phase urban heat island in the year 2021; meanwhile, there was the presence of an urban cool effect in the year 2009.