Lismore is characterized by a humid subtropical climate, with mild to warm temperatures throughout the year. The region enjoys ample rainfall, with an annual average of 1,343 mm. Summers in Lismore are typically warm, with temperatures ranging between 20°C (68°F) and 35°C (95°F). Due to its geographical location, Lismore experiences high levels of humidity, often reaching 100% during the summer months, making it more humid than surrounding areas. The city enjoys 109.6 clear days annually, providing residents with occasional breaks in the often wet weather.

The climate's impact on Lismore is not limited to heat and humidity, however. The area is known for its susceptibility to flooding, particularly from the Wilsons River and Leycester Creek. The city has experienced a history of significant flood events, the most notable being the 2022 flood, which reached an unprecedented height of 14.4 metres (47 feet). This record-breaking flood was the largest in modern history, surpassing previous major floods in 1954 and 1974, both of which saw waters rise to 12.1 metres (40 feet). These events often exceeded the height of the city's levee wall, leading to widespread damage in low-lying areas.

Flood mitigation efforts have been underway for several years. In 1999, a government-funded scheme aimed to protect the Central Business District (CBD) and South Lismore from a 1-in-10-year flood event was approved. The scheme was designed to prevent smaller floods from entering the central area, thus improving evacuation time in the event of larger floods. However, in 2005, around 3,000 residents had to be evacuated following a flood that affected much of the city. Fortunately, the newly completed levee wall at the time prevented further damage to the CBD.

In 2017, Cyclone Debbie caused significant flooding in Lismore, with Wilsons River reaching 11.6 metres (38 feet), overtopping the levee for the first time since its completion. This flooding caused extensive damage to CBD businesses and highlighted the ongoing flood risks for the area. In response, an additional $8.2 million was allocated in 2018 for flood mitigation works.

The 2022 floods were particularly devastating, as the Wilsons River reached its peak of 14.37 metres. This flood caused extensive damage to both the CBD and nearby residential areas. Reconstruction efforts have been ongoing for years, with some areas still in the process of rebuilding. The floods not only disrupted daily life but also highlighted the vulnerability of the region to extreme weather events.

Lismore's climate and flood history underscore the challenges faced by residents and officials in managing the natural risks of the region. Despite these challenges, ongoing mitigation efforts aim to reduce the impact of future flood events on the community.