Changnon’s contributions in hydroclimatology falls into three general categories: surveys of severe rainstorms, rainfall frequencies, and urban effects on precipitation. Many of these activities started in the 1950s and continue on to the present. Changnon has produced numerous publications on heavy rainfall events in Illinois and elsewhere, based on regular NWS networks, special Water Survey high-density networks, and field surveys. His contributions under rainfall frequencies include the examination of urban effects and climate change on rainfall frequencies that led to recent updates to those numbers. But perhaps his most well-known contributions in hydroclimatology are in the arena of the urban effects on precipitation. By 1960, he and Floyd Huff had begun to document the urban influence on the overlying precipitation field. However, it was an interesting exchange in the scientific literature over the La Porte, Indiana, precipitation anomaly and its causes that spurred interest in the subject. Under his leadership, a large field project was embarked upon in St. Louis in the mid-1970s (METROMEX), perhaps the definitive study on the urban effect on precipitation. This work continues today with published work on the recent heavy precipitation in the Chicago area using a high-density network.