Rising temperatures that occur in cities resulted in the urban heat island (UHI) which could also amplify the thermal heat stress, leading to climate-related human mortality. Our study investigated the UHI effect and thermal heat stress of heat index (HI) in the U.S. cities of arid, continental, temperate, and tropical climate zones. A long-term simulation of the UHI and HI was conducted using Community Land Model version 5.0 from 1990 to 2014. The relationship between UHI and HI with climate and energy flux variables are analyzed with divided study periods (1990-2000 and 2001-2014) for the urban impact assessment. Higher sensible heat was reported, particularly in the arid and tropical cities. Further, temperate climate showed increasing annual trends for UHI and Delta HI (urban-rural difference of HIs). The later period (2001-2014) demonstrated greater UHI and Delta HI trends, implying a notable change in climate and urban expansion. The UHI, ranging from 0.73 degrees C to 2.07 degrees C, was more intense compared with Delta HI, at 0.14 degrees C to 1.23 degrees C. The UHI was positively correlated with temperatures in hot cities, while precipitation is the main driver in the continental city. For Delta HI, the relationship with temperatures were dominant in all climate zones.