Botswana has predominantly sub-tropical climate. As a result the country is largely arid to semi-arid. The rainfall season is in the summer months which start from October to march of the following year. The peak of the rains is January which seems to have shifted to February in the recent years. About 99% of the rains occur in localized thunderstorms, which tend to be erratic and unpredictable could be destructive in nature. The average annual rainfall is about 500mm per annum in the extreme northeast, to less than 250mm per annum in the other parts of the country.
The average daily maximum temperature in summer is about 32degrees Celsius in January while the extreme can reach about 42 degrees Celsius. The average daily minimum temperature is about 18 degrees Celsius in January while the extreme can fall to about 7 degrees Celsius. September and April are the transition months.
The winter months are from May to August. The winter is dry with peak of the winds in August. The average daily maximum temperature in winter is about 21degrees Celsius in July while the extreme can fall to less than negative 5 degrees Celsius. The lowest temperature occurs over the southern and southwestern parts of the country. Occasionally, the country experiences early morning frost during winter season.
Botswana's Climate - General Facts
Botswana lies between latitude 18S and 27S and longitudes 20E and 29E with area 582,000 square kilometers. It is a land-locked country about 675 km inland form the Indian ocean and 1025 km form the Atlantic. It has an average elevation of 1000 m but lower than that of the plateaus of Zambia to the North, Zimbabwe in northwest, South Africa in the southeast, and South Namibia to the west. Highest hill being the Kanye Hill at 1491 m with no barriers of the low of mountain. Botswana enjoys a warm and dry tropical climate with semi-ari lands.
Mean annual rainfall varies from maximum of 650 mm in Kasane to a minimum of less than 250 mm is the Kgalagadi (Tsabong).
In all seasons, two high pressure systems in the Atlantic and one over the Indean ocean cause subsidence over Botswana and Southern Africa resulting in an arid to semi-arid climate.
Botswana suffers drought in some years with one of the worst drought in the year 1981-1987.
Since Botswana has a large desert area known as Kgalagadi, the diurnal (daily) variation of temperature is large with hot day temperature and cooler nights.
Relative Humidity is maximum in the early morning with about 70% and minimum in the afternoon with 30-40%.
On the average there were 75 thunderstorm days a year in Gaborone with a higher frequency from October to January and decreased from February to April.
At the old Gaborone Airport, a ground squall with maximum wind of 70 knots (130 km/p.h.) occured at 17:10 local time on 28 December 1980. At Sir Seretse Khama Airport, a gust speed over 80 knots (148 km/p.h.) was recorded on 26 Dec. 1985.
Winds and Pressure
In Botswana surface wind are predominently easterly to north easterly except in the south west of the country, in Tshane and Tsabong where northerly winds are dominant Calm conditions are also observed in a large number of occations. Forenoon pressure is higher than afternoon pressure at all stations.
Mean annual sunshine hour varies from 8.2 to 9.7 hours/day or 75 to 81% at all stations which means each station receives a large amount of sunshine per day.