In fact, some locations experience over twice as much fog as others. Regional variability is shown to be strongly related to the mesoscale influences of urbanization and the North Sea. Within the country, a comprehensive in-depth analysis of regional differences between fog occurrence is made, together with an assessment of local physical factors which could bias fog formation in one location over another. On a national scale, interannual variability is linked to changes in synoptic pressure-gradient forcing. Using observations from a dense network of weather stations throughout the country, the climatology of fog in the Netherlands is assessed over a period of 45 years. Devoid of significant topography, it is an excellent location for assessing the relative influence of various factors on fog occurrence in the absence of terrain effects. This indicates that fog is being collected rather than rainwater.The Netherlands is characterized by highly variable land use within a small area, and a strong influence of the North Sea on national climate.

Minutes later, the first tips are recorded on the “fog gauge,” while the rain gauge records no precipitation.

As the relative humidity reaches 100%, the solar irradiance drops from 1,000 W/m² to less than 100 W/m².

As the wind accelerates, the temperature on Table Mountain drops significantly, and the relative humidity drastically increases.

It moves from the south and toward the southeast.

In summer, the dry season, the wind typically picks up in the afternoon.

Reviewing the data from the Campbell Scientific weather stations, it is interesting to note the sequence of events that create the potential for fog harvesting: The mountain’s famous “tablecloth”-scientifically referred to as an orographic cloud formation-is responsible for much of the high-altitude moisture and optimism surrounding the fog harvesting program. Studies conducted since then have measured yearly fog precipitation at approximately 3,294 mm (129.7 in.), which is triple the average yearly rainfall recorded in Cape Town. The first official studies concerning moisture density on Table Mountain were conducted over a century ago by German-born botanist Rudolf Marloth. “The more we research and understand, the stronger and better prepared we become,” said Councillor Xanthea Limberg (Mayoral Committee Member for Water and Waste). The program creators hope this weather phenomenon will generate plenty of fog for harvesting. In winter, the Northwester brings the rain from the cold Atlantic Ocean in summer, the Southeaster blows off the Indian Ocean, typically forming a cloud that appears to hang on Table Mountain. There are two predominant wind directions in Cape Town. Each drop is equivalent to 0.649 mL (0.022 oz) of water. The droplets are fed through a tipping bucket rain gauge. As fog condensates on the surface of the screen, moisture accumulates on the surface and gathers in the gutter below. One screen is made from 40% shade cloth, while the other uses 316 stainless steel. The City of Cape Town is testing various available material options for the screens.

Both weather stations are equipped with 1.5 m² (16.2 ft²) screens specifically designed to capture or “harvest” the water from fog. The feasibility study and research phase are set to be completed by December 2022.Īs of this case study's publish date, two Campbell Scientific weather stations have been installed on Table Mountain to measure basic weather parameters, as well as the fog collected. While still in its infancy, the program’s creators hope to determine the feasibility of constructing multiple fog catchers on the mountain. Necessitated by the dry winters, the City of Cape Town instituted a project on Table Mountain to measure the potential of supplementing the area’s primary water supply via fog harvesting. More information about the aversion of this crisis can be found in this World Economic Forum article. Water-use restrictions had been relaxed, and “Day Zero”-the point at which Cape Town’s municipal water supply would be shut off-never came to pass. At this point, the city was just 90 days away from turning off the taps.Ī year later, the South African city’s parched dams were more than 80% full. Even restaurants and businesses encouraged patrons and employees to reduce wastewater. Cape Town’s water crisis worsened to the point that there were competitions to see who could wash their shirts the least. Southwestern South Africa had three consecutive dry winters-from 2015 through 2017-resulting in the Cape Town “Day Zero” drought of early 2018.

Fog weather