Throughout history, three quarters of China's floods have been caused by the Yangtze River. Usually the Yangtze floods occur during most non-drought years. During monsoon season, which occurs from June to September, flooding and mudslides have consequently been perennial problems as they typically lead to several hundred deaths annually. In the case of the 1935 flood, the mudslides occurring as a result of the 1931 China Floods significantly eroded the natural flood barriers which existed previously making the consequences of this flood more severe.