The aim of this study is to investigate the role of climate change and urban heat islands on the climatic elements of Iranian cities. Climate change is recognized as the greatest threat to modern humanity. The climatic elements of Iran, particularly temperature and evapotranspiration, have undergone significant changes over the past five decades, resulting in increased crop water requirements. The research methodology was based on regression analysis and linear trend coefficients. The findings indicate that over the past 41 years, daytime and nighttime temperatures have increased at rates of 0.0245 and 0.0265 °C yr⁻¹, respectively, which are twice the global average. Annual evapotranspiration increased by 5.36 mm, while annual precipitation decreased by 1.1 mm. Precipitation variability has increased, and the drought index has remained negative over the past 19 years. The combined effects of global warming and urban heat islands have increased air temperature by up to 4 °C in some selected cities. Overall, the intensification of unfavorable climatic conditions and the interaction of these two phenomena have exacerbated environmental crises in Iranian cities and threatened ecological sustainability. This situation has reduced urban livability. Water resource management should be reconsidered in response to these changes. These findings highlight the necessity of urban management and adaptation to climate change