The Regional Climate

The starting point for any design project is an understanding of the brief, the site and the context. This includes the microclimate - not only now but in the future. This understanding is crucial to the creation of sustainable buildings that can provide comfort even in extreme weather conditions.

The data in this section is taken from the online resource Weather Spark, which provides weather data for 150,165 locations worldwide. While there is an array of climate resources available online, data is often associated with 'virtual weather data'; typically an interpolation of real existing weather stations further away. The reliability of this weather data should be understood, in particular as data related to wind directionality may be locally variable. Prevailing winds should be checked against local experience on site, taking local topography into account. Learning from locals, and if possible, installing a weather station at an early stage can help to identify the very local climate characteristics relevant for building orientation

Temperature

The climate of East Africa is rather atypical of equatorial regions and weather conditions can vary considerably over only a short distance.

The graph below shows the daily average high and low air temperatures throughout the year for four selected cities in Uganda. This data can be broken down into monthly averages through the online resource weatherspark.com.

Temperatures can be seen to be highest in the north and coolest in the south at Kabale, where the altitude is higher. It is noticeable that there is a reasonable temperature difference throughout of around 10°C between day and night. This means that buildings with high levels of thermal mass and permanent ventilation openings will benefit from night-flushing and stay cool into the next day.

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Average high and low temperatures throughout the year for four different cities in Uganda.

Solar Radiation

East Africa receives a great deal of sunshine each month, which is useful for providing continuous energy supply through solar PV and solar thermal collectors.

In temperate climates direct solar radiation helps improve comfort conditions when air temperatures are too low. Buildings can act as solar collectors to attract and store heat from the sun. In East Africa, however, temperatures are generally comfortable, while the graph below shows that solar energy is consistently high throughout the year at 5-7 kWhs/sqm. This means it is more relevant for buildings to provide shading from the sun so that direct solar radiation isn’t translated into overheating. The abundant sunshine can however, be beneficial in terms of providing a continuous energy supply both for solar photovoltaic systems and solar thermal collectors.

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Average daily incident solar energy throughout the year for four different cities in Uganda.

Precipitation

Much of East Africa has typically two rainy seasons through the year which is great for growing plants but not so good for providing continuous water supply.

The graphs show that in Kampala and southern Uganda there are generally two rainy seasons in March to May and September to December. Further north the rainfall tends to be greater from April to December. Rainfall brings with it higher humidity, the graph showing the incidence where the relative humidity is above 65% shows that in the central region around Kampala and on the shore of Lake Victoria, excessive humidity is a problem in the early summer, requiring buildings to be designed to maximise air movement.

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Average monthly precipitation

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Chance of muggy conditions

Graphs showing prevalence and severity of rain and humidity throughout the year for four different cities in Uganda.

Wind

Wind data can provide a starting point for locating ventilation openings but should be considered alongside local experience on-site.

The graph of windspeed gives an idea of the comparative difference between Gulu and particularly Kotido, where wind speeds are relatively high and can be used to counteract overheating, and Kampala and Kabale where wind speeds are quite modest. A wind rose describes both the wind speed and direction and therefore gives an idea of the cooling potential of natural ventilation. The illustration below shows the predominant wind direction in Kampala is from the south and indicates the number of hours per year that the wind blows from each direction.

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Wind Rose Kampala Meteoblue

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Average wind speed

Meteoblue. Climate (modelled) Kampala. URL https://www.meteoblue.com/en/weather/historyclimate/climatemodelled/kampala_uganda_232422. Visited on 26.07.2019.

Comfort Conditions

While some areas of East Arica are consistently comfortable, others require the benefit of thermal modification that a well-designed building affords.

These graphs show at a glance what time of year and time of day you are likely to encounter uncomfortable climatic conditions at each of the four locations, with uncomfortable air temperatures shown in red. It is evident that whereas in Kabale the air temperatures are tolerable throughout the year, in Gulu one would be looking for shade and air movement to provide natural cooling from December through to April, while in Kotido this would be desired from mid-September to April. Fortunately in both these areas windspeed is relatively high at that time of year.

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Comfort levels Gulu

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Comfort levels Kampala

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Comfort levels Kotido

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Comfort levels Kabale

Comfort conditions throughout the year for four different cities in Uganda.

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