What can cause the big city to be warmer than the surrounding counrtyside?

The phenomenon of urban areas being warmer than their surrounding countryside is known as the "urban heat island" effect. This is primarily caused by human activities, dense construction materials like asphalt and concrete that absorb and retain heat, and reduced vegetation. Additionally, heat generated from vehicles, buildings, and industrial processes contributes to the elevated temperatures in cities. The lack of green spaces and natural land cover further exacerbates the temperature difference.