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Although Zambia lies within the tropics, its climate is modified by the altitude of the country and is generally favourable to human settlement and comfort. The marked seasonal pattern of precipitation is caused by the north and south movement of the intertropical convergence zone (ITCZ), which shifts with the Sun. In January the ITCZ is in its southernmost position, and the rainy season is at its peak; by June it has moved north, and the weather is dry. Summer rains reduce the high temperatures that might be expected at this time.
Precipitation (concentrated in just five months) varies according to agroecological region but generally comes in storms with heavy raindrops that lead to a hard soil surface and surface erosion. The driest region receives annual precipitation of less than 30 inches (800 mm), while precipitation in the wettest region normally exceeds 40 inches (1,000 mm); precipitation occasionally exceeds 55 inches (1,400 mm) in the northeast.
Temperature is modified by elevation, with the highest mean daily maximum temperatures occurring in the Luangwa valley and the southwest. The coolest area overall is the high Nyika plateau, in the northeast on the border with Malawi. During the cold months (June and July), the area west of the Line of Rail is coolest, with mean minimum temperatures mostly below the mid-40s F (about 7 °C). Sesheke, in the southwest, has frost on an average of 10 days per year.
Average annual hours of sunshine range from more than 3,000 in the southwest to less than 2,600 on the eastern border. Winds are predominantly easterly-southeasterly, although in the rainy season winds blow from the northwest and north. Wind speeds are rarely strong enough to cause damage.
Although the major contrast is between the rainy season and the drier months, three seasons may be identified. The warm wet season lasts from November until April, when temperatures range between the high 60s and low 80s F (low to mid-20s C) and during which time the country receives the vast majority of its annual precipitation. The movement into Zambia of the moist Congo air mass from the northwest heralds the start of the rains, in the north usually in early November and toward the end of the month around Lusaka. The change from dry to wet conditions is transitional rather than abrupt. December and January are the wettest months. Cloud cover lowers maximum temperatures but also limits radiative heat loss at night, so that minimum temperatures are kept relatively high. Relative humidity values are high, typically 95 percent in early morning but declining to 60–70 percent by midafternoon. Sunshine is surprisingly frequent; Lusaka averages six hours of sunshine per day in January. Precipitation declines rapidly in April with the northward movement of the ITCZ.
The cool dry season lasts from May until August, with maximum temperatures ranging from the high 50s F (mid-10s C) to the low 80s F (mid-20s C); morning and evening temperatures may be significantly lower. The Sun is overhead in the Northern Hemisphere, so temperatures are low; July is usually the coldest month. Clear skies allow maximum heat radiation and result in especially low temperatures on calm nights, with occasional ground frost occurring in sheltered valleys.
The hot dry season lasts from September until October, when maximum temperatures range from the low 80s F (mid-20s C) to the mid-90s F (mid-30s C). This is a period of rapidly rising temperatures; just two months separate July, the coldest month, and October, usually the hottest (although if the rains are delayed November can be hotter). Usually by mid-October cooler oceanic air moves in, leading to increasing humidity and cloud formation. High temperatures and increasing humidity make this one of the least comfortable times of the year, although the first rains wash away dry-season dust.
Plant and animal life
On the plateau, miombo woodland is characteristic: a semicontinuous tree cover dominated by small leguminous trees of the Brachystegia and Julbernardia genera but with a significant grassy undergrowth. Burning of the grasses in the dry season causes the trees to develop a corky, fire-resistant bark. Mopane woodland, in which Colophospermum mopane dominates but in which the baobab is distinctive, occurs in the drier and hotter valleys of the Zambezi in the south and in the Luangwa valley. Zambezi teak (Baikiea plurijuga) occurs in the southern fringe of the area covered by the Kalahari Sands. Mukwa (Pterocarpus angolensis), a good furniture timber, is found in the Lake Bangweulu area. More than one-tenth of the country has been set aside as forest reserve or protected forest areas; in all, some two-fifths of the country’s land is under protection.
Where there is seasonal flooding—in swamps and on floodplains, notably in the Bangweulu and Lukanga regions, in the upper Zambezi, and on the Kafue Flats—open grasslands are characteristic. On the plateau the tree cover is broken by grass-covered dambos: shallow saucer-shaped valleys, often lacking a surface watercourse.
The variety of Zambia’s mammals is notable, and there are large concentrations on the major floodplains, particularly in the national parks of the Luangwa and Kafue valleys. Depletion of wildlife has occurred because of the spread of human activities outside the parks, while poaching is a serious threat within. The illegal trade in rhino horn has been responsible for the virtual elimination of the rhinoceros from Zambia, and poaching of elephants for their tusks has greatly reduced their numbers, despite government measures to deter the practice. There is a large range of smaller mammals and varied and numerous birdlife. The fish eagle, Zambia’s national emblem, is common on large stretches of open water.
Reptiles include crocodiles, tortoises, terrapins, a variety of lizards, and many poisonous and nonpoisonous snakes. Insects of most orders are prevalent. Termite mounds, often large and sometimes pinnacled, are a landscape feature of some areas and can hinder farming operations.
Wildlife is protected in a number of national parks and game-management areas, which together constitute some one-third of the country. Some national parks have tourist facilities; these include South and North Luangwa, Kafue, Lochinvar, Blue Lagoon, Sumbu, Nyika, and Mosi-oa-Tunya. Kafue, the oldest and largest of these parks (8,650 square miles [22,400 square km]), is on the plateau and has generally low game concentrations, although it is noted for the variety of species of antelope it hosts. Lake Itezhi-Tezhi, a reservoir behind a regulating dam on the Kafue, has flooded part of the park. South Luangwa (3,500 square miles [9,100 square km]) has one of Africa’s largest (but declining) elephant concentrations. North Luangwa offers true wilderness adventure: walking safaris. Thornicroft’s giraffe is unique to the Luangwa valley. The other parks are much smaller. Lochinvar, on the Kafue Flats, is of particular interest to bird-watchers, with more than 400 species recorded. The Kafue lechwe is unique to the flats. The Mosi-oa-Tunya National Park protects the environs of Victoria Falls and is recognized by UNESCO as a World Heritage site. Nyika National Park was established to preserve remnant patches of montane forest. Sumbu, on the shores of Lake Tanganyika, is renowned for easy sightings of the rare sitatunga, a type of aquatic antelope.