The hottest spring in eastern China in 2018 was caused by a combination of factors, including a strong El Niño and a blocking high pressure system. The El Niño, which is a warming of the Pacific Ocean, brought warm, moist air to eastern China, which led to increased precipitation and higher temperatures. The blocking high pressure system, which was located over Mongolia and Siberia, prevented the cold air from the north from reaching eastern China, further contributing to the warmer temperatures. In addition, the urban heat island effect, which is the phenomenon of higher temperatures in urban areas than in rural areas, also played a role in raising the temperature in eastern China.