Zhongshan is located in the south of  “Tropic of Cancer” and “northern border of tropical zone”, characterized by warm climate, adequate sunshine and heat. The annual amount of solar radiation is 105.3 kcal / cm2 out of which the scattering solar radiation is 57.7 kcal / cm2 , and direct sunshine solar radiation is 45.5 kcal / cm2 on average. Out of 12 months in a year, July sees the strongest solar radiation, as high as 12 kcal / cm2; and February has the weakest, as low as only 5.6 kcal / cm2. With abundant sunshine, the city has a potential capability of utilizing solar energy. There are 1843.5 hours of sunshine per year on average. From July to October, days are longest with 6.7 hours of sunshine per day on average. From February to April, days are shortest with only 2.8 hours. The annual average temperature is 21.8℃, with little changes by years. Among the 12 months in a year, July is the hottest one with the daily average temperature as 28.4℃; and January, the coldest one, 13.2℃. As many as 361.5 days per year are frost-free.

Relative Humidity & Evaporation 

Relative humidity in Zhongshan is 83 per cent on an average. 86 per cent in 1957 as the highest, and 81 per cent in 1967 and 1977 as the lowest. Among the year, May and June has the highest relative humidity while December and January the lowest. Evaporation is 1448.1 mm on average 1605.1 mm in 1971 as the highest, and 1279.9 mm in 1965 as the lowest.

Extreme weather in Zhongshan can be classified into several types, as the severe moist winter in winter and spring, typhoons, rainstorms, floods in summer, autumn and winter. Extreme climate here are of two sub-types, dry cold and wet cold. Affected by the northern cold wind, January and December might witness over 10℃of sudden drop of temperature within 24 hours, even frost. Even though there are only seven days of severe chilling days every year, this weather does harm to winter harvest of photos, bananas, pond fishes and early seedling. The chilling rainy days happen in January and early March, and the cold spell in an otherwise warm early spring happens in the middle of March or later. Typhoons are the most disastrous weather from July to September, and according to the statistics, those causing damages happen three to seven times per year on average. 90% of the rainstorms in a year fall in the period from April to September. The floods in rainy season reach over 1443.5 mm, taking up 82 percent of the total rain fall.

(source – internet)