Saul Gwakuba Ndlovu
THE month of October in Zimbabwe is usually associated with the first rains in the region that covers the western part of the country, Botswana, Zambia’s Western Province, western parts of Mozambique, the northern districts of the Transvaal, Masvingo Province and the Midlands.
It may fall from about the 17th, 18th or 19th of that calendar month. However, that is not invariably the case every year as each rainy season has its own more or less unique meteorological characteristics.
People from the countries listed above attach vital importance to rain so much that Botswana’s national slogan is “pula”, a Tswana word which means “rain”. The word also now refers to that country’s national currency.
The cultural attitude to the region’s weather conditions can be divided into three categories: the traditional religious community, Christian community and the meteorological community. The traditional religious community’s belief is that weather conditions are created and controlled by Mwali (uNgwali, Mwari), a god whose places of abode are rocky shrines, the main one being at Njelele in the Matopo Hills, the second at Manyangwa in the Tjehnaga area of the Bulilima District, and the third being at Ntogwa’s Village in Chief Habangana’s territory in northern Botswana.
The second, the meteorological cultural community, are Christians whose belief is that rain is a gift from God, and that prayers to God will be answered with adequate rains that avert droughts.
The third group comprises those who believe that meteorological patterns are natural occurrences that are beyond the wish and control of human beings. These people are geographers, meteorologists, hydrologists and climatologists. These are generally called scientists.
We shall discuss the rain patterns of some parts of Africa and why they take that form.
Rain is actually drops of water vapour found in the air which accumulate as clouds, condense and come down as drops.
The water vapour may have been carried by the wind across an ocean, a lake or from a large man-made water reservoir such as Lake Kariba or Lake Nasser in Egypt.
That wind may be deflected upwards where it is cooled and the water vapour condenses into millions of tiny droplets that accumulate to form clouds.
The wind will pick up water vapour if it passes over a warm ocean current. Rain-bearing clouds form more easily along the Equator than further south or north away from the Equator. In fact from zero to 10 degrees south and north of the Equator it is virtually always raining, and the region is called the doldrum belt.
That is a latitudinal factor we must take into consideration when we are talking about rainfall. The further a region is from the equator, the more likely it is to have less rain.
Altitude is another factor to consider because condensation resulting in rainfall occurs more on higher than on lower altitudes. That is why in Zimbabwe there is usually more rainfall on the high than on the low veld.
More condensation occurs at higher than at lower altitudes because it is colder higher up than lower down. This is because there is less air to hold the sun’s heat higher up than lower down.
It is because of that altitudinal factor that snow is found high up on Mount Kilimanjaro in spite of the fact that it is much closer to the equator than Umfazi Omithiyo in Matabeleland North or Malinda Badzimu in Matabeleland South, mountains situated thousands of kilometres south of the equator.
We have made reference to ocean currents in this article. Seas and oceans greatly influence rainfall in various parts of the world because about four-fifths of the earth’s surface is covered with water, and only about a fifth is hard land – terra firma.
It is because of this fact that meteorologists sometimes talk about the El Nino and the La Nina maritime phenomena. A pronounced occurrence of the El Nino phenomenon portends a drought in Southern Africa. That is what our meteorologists have told us in their weather forecasting.
In this modern world, it is quite possible to use some instruments to see what the weather will be like a day or two or even a couple of months ahead.
That is what is called weather forecasting, a form of very intelligent guesswork using various information and scientific knowledge.
The information and knowledge are supplied to a central location station by smaller ones strategically situated in the region being covered.
Instruments found virtually at every meteorological station are a rain gauge, a sunshine recorder, a wind vane, a Stevenson screen, a cup anemometer, a grass minimum thermometer and a soil thermometer. These are the barest instruments that the least equipped meteorological station may need.
Additional instruments will include an aneroid barometer with which to measure pressure, a thermograph with which to record temperature changes, and a mercury barometer to record more accurately atmospheric pressure as it changes during the course of the day.
Some meteorological stations have what are known as dry bulb thermometers to measure relative humidity. Wind direction and speed are recorded by anemometers.
It is by means of these various instruments that meteorologists are able to say with more or less a high degree of accuracy what tomorrow’s, next week’s, next month’s and even next year’s weather is likely to be.
The reader will by now have noticed that the scientific meteorologists collect and interpret data unlike our traditional weather people who claim to have power to influence the weather in their own favour.
We will remember too that some of the world’s deserts, the Kgalahari and the Namib, are in Southern Africa, our region. The largest world’s desert, the Sahara, is in our continent. If we had the power to influence the weather there would be no deserts in the world.
However, people live by their various beliefs to criticise which would be to criticise those people’s very existence. While we dance and pray for rain, we must heed the predictions of the meteorologists by preparing for the worst. Wisdom is in getting fore – armed since we have been forewarned.
In our next article, we will deal with fog, mist, hurricanes, lightning and thunder.
- Saul Gwakuba Ndlovu is a retired, Bulawayo – based journalist. He can be contacted on cell 0734 328 136 or through email. [email protected]