Urban areas in arid regions face escalating heat stress from the synergistic impacts of climate change and urbanization. While many studies focus on predictive modeling, a critical gap exists in understanding the long-term historical degradation of urban cooling ecosystem services. This research addresses this gap by conducting a 40-year assessment in Yazd (Iran), integrating a future projection to formulate a sustainable heat mitigation model. A multi-method approach was employed: climatic records (1965-2020) for heatwave analysis; Landsat imagery (1983, 2003, 2023) for land use/land cover (LULC) dynamics; the CA-Markov model for a 2035 LULC projection; and the InVEST Urban Cooling Model (UCM) for quantifying cooling services. Findings revealed a disproportionate increase in nighttime temperatures, with heatwave frequency surging from five to fifty days over five decades. Historically, built-up areas expanded from 12.2% to 41.8% while tree cover shrank from 18.4% to 7.3%. This led to a decline in Cooling Capacity (CC) from 0.81 to 0.60, reducing the average UHI mitigation effect from 1.87 degrees C in 1983 to 0.83 degrees C in 2023. Projections indicate these trends will persist, with continued urban expansion further compromising the city's thermal resilience by 2035. This study provides quantitative evidence of a critical decline in urban climate resilience. The findings serve as an urgent call for proactive urban planning and offer an evidence-based framework for policymakers to design and prioritize nature-based interventions-such as strategic greening and blue infrastructure-to counteract the projected intensification of thermal stress and build a more sustainable future for arid cities.Graphical AbstractThis graphical abstract illustrates the combined impact of global warming and rapid urbanisation on the thermal resilience of Yazd, a historic city located in an arid region of Iran. The workflow begins by identifying the key challenges and leads to a multi-decadal analysis of LULC changes (1983-2023). This analysis reveals a significant increase in built-up areas at the expense of vital tree cover. Concurrently, a trend analysis of heatwave metrics (1965-2020) reveals a notable intensification of thermal stress, particularly an increase in the frequency and severity of nocturnal heatwaves. The direct consequence of these interacting pressures is quantified spatially through the Heat Mitigation Index (HMI), which shows a significant reduction in the urban ecosystem's cooling capacity over the 41-year period. In response to this escalating vulnerability, the abstract proposes a dual-pronged mitigation strategy integrating modern nature-based solutions with the city's vernacular architectural wisdom. This includes leveraging traditional passive cooling systems such as 'badgirs' (windcatchers) and 'ab-anbars' (water reservoirs), as well as establishing ecological corridors. Finally, the key findings are synthesised into actionable policy recommendations emphasising the necessity of integrated blue-green infrastructure, the prioritisation of native vegetation and the vital role of traditional knowledge in fostering adaptive, climate-resilient urban design. The graphic encapsulates the study's narrative, from diagnosing the problem to conducting a data-driven analysis, and ultimately proposing holistic, context-specific solutions.