Dry-season soiling
Tap a region on the map Or pick one from the list below. Each shows the rate our calculator starts from, whether it was measured there, and what we'd check first.
Measured here
Northern Cape 0.04% a day Range: 0.02–0.04% a day, measured in the dry season
Arid Karoo and Kalahari: little rain and long dry spells.
Measured at Kalkbult, near De Aar, in the 2016 dry season (du Plessis, Stellenbosch University, 2017).
Borrowed from a similar climate
Western Cape 0.05% a day Range: 0.28–0.36% a day in dusty or farmland summers
Rain mostly in winter; dry summers.
No local measurement. Based on Mediterranean-climate sites in Spain and California (Micheli 2021; Caron 2013).
Measured here
Highveld and north 0.2% a day Range: 0.17–0.26% a day, measured in dry winters
Summer rain; dry winters with dust and smoke.
Measured on the CSIR campus in Pretoria in the 2017 and 2019 dry winters (IEA PVPS 2022); borrowed for the other four provinces.
Borrowed from a similar climate
KwaZulu-Natal and Eastern Cape 0.05% a day Range: 0.2% a day in dry inland winters
Humid, subtropical coast with summer rain; drier winters inland.
No local measurement. Based on NREL’s typical rate and humid-climate sites in Brazil (NREL 2018; Costa 2021).
Borrowed from a similar climate
Namibia 0.04% a day Range: 0.13–0.32% a day on the coast
Arid, with dust from pans and dry riverbeds; what rain there is falls mostly December to February.
No local measurement. Borrowed from Kalkbult, Northern Cape; coastal value from Chile’s coastal desert (Cordero 2018).
Borrowed from a similar climate
Botswana 0.04% a day Range: up to 0.2% a day near towns, mines and pans
Semi-arid Kalahari: rain October to April; dry, dusty winters.
No local measurement. Borrowed from Kalkbult, Northern Cape.
Borrowed from a similar climate
Zimbabwe 0.2% a day Range: 0.17–0.32% a day
Rain November to March; a long dry season from May to November.
No accessible local rate. Borrowed from Pretoria’s dry winter (IEA PVPS 2022).
Borrowed from a similar climate
Mozambique 0.2% a day Range: 0.17–0.32% a day
Rain November to April; driest June to August; humid coast.
No local measurement. Borrowed from Pretoria’s dry winter (IEA PVPS 2022).
Borrowed from a similar climate
Zambia 0.2% a day Range: 0.17–0.32% a day
Rain November to April; dry from May to mid-October.
No local measurement. Borrowed from Pretoria’s dry winter (IEA PVPS 2022).
Borrowed from a similar climate
Malawi 0.2% a day Range: 0.17–0.32% a day
Rain November to April; dry from May to October.
No local measurement. Borrowed from Pretoria’s dry winter (IEA PVPS 2022).
Borrowed from a similar climate
Lesotho 0.2% a day
Highlands: rain October to April; cold, dry winters.
No local measurement. Borrowed from the Highveld (IEA PVPS 2022).
Borrowed from a similar climate
Eswatini 0.2% a day
Rain October to April; dry from May to August.
No local measurement. Borrowed from the Highveld (IEA PVPS 2022).
All 12 regions Northern CapeMeasured 0.04% Western Cape 0.05% Highveld and northMeasured 0.2% KwaZulu-Natal and Eastern Cape 0.05% Namibia 0.04% Botswana 0.04% Zimbabwe 0.2% Mozambique 0.2% Zambia 0.2% Malawi 0.2% Lesotho 0.2% Eswatini 0.2%