Effects of rapid urbanization on the urban heat island and its spatial characteristics in Delhi, India

Rapid urbanization and changes in land use and land cover have led to uncontrolled and unsustainable expansion of Indian cities. This growth has brought with it several environmental challenges, including a significant increase in the intensity of urban heat islands (UHIs) in these urban areas. This study investigates the profound impact of rapid urbanization on changes in land use and land cover (LULC), land surface temperature (LST), and urban heat island (UHI) intensity in the National Capital Territory (NCT) of Delhi, India. Using Landsat satellite images from 1990, 2000, and 2020, we conducted a comprehensive analysis using random forest (RF) algorithms for LULC classification and the Mono-Window algorithm for LST detection. Additionally, a mixed linear modeling (MLM) approach was employed to analyze the statistical relationship between LULC types and LST dynamics across three time periods (2001, 2011, and 2021), accounting for inter-annual variability and fixed effects of land cover categories. The results show a significant expansion of built-up areas from 479.66 km² (32.32%) in 2001 to 719.64 km² (48.49%) in 2021, with a corresponding decrease in open areas by over 17% and water bodies from 16.09 km² (1.08%) to 12.34 km² (0.83%). The mixed linear model revealed built-up areas as the primary contributors to rising LST, with an annual increase of 0.262 °C/year, while water bodies exhibited the strongest cooling effect, reducing LST by 5.87 °C relative to dense vegetation. Year-specific random effects showed a net increase of 3.81 °C in 2021 compared to 2001. This urban expansion was directly related to an increase in LST, where the average temperature increased by about 3–5 °C, and a significant amplification of UHI effects, with urban areas warming by up to 7 °C compared to rural areas. Spatial analysis of UHI morphology using landscape metrics demonstrates increasing fragmentation and spatial expansion of heat-affected areas over time, with the number of SUHI patches rising by approximately 50% during the study period. These findings emphasize the escalating thermal stress in rapidly urbanizing areas and highlight the urgent need for climate-sensitive urban planning and targeted green infrastructure interventions to mitigate adverse heat impacts.