In winter, occasional waves of cold front form a high-pressure zone centered over Mongolia sweep southward, damaging tea bushes and fruit trees in northern Hunan. The average minimum temperature in December and January is 6 degrees Centigrade. Summer is usually long and humid, and temperatures are slightly higher in the north. The average maximum temperature in July and August is 30 degrees Centigrade. The north has an average of 260 frost-free days a year, while the south has 300 days.
Rainfall is ample, with the maximum precipitation occurring between spring and summer.
The total annual rainfall of 1,602 millimeters decreases from south to north. Hunan lies in the path of cyclones that pass from west to east along the Yangtze Basin in summer, bringing with them at times long periods of heavy rain, resulting in extensive flooding of low-lying lands around the Dongting Lake. In the hilly regions of central and southern Hunan, the soils are for the most part lateritic heavy clays that are strongly acidic and poor in organic material. These regions are subject to soil erosion, especially when deforestation has occurred and plant coverage is low. Despite vast deforestation to make way for cultivation over the past centuries, however, large woods of pine, cedar, bamboo, and camphor are found in the western highlands.