On behalf of the Swedish Environmental Protection Agency, we have developed a nationwide soil moisture index. The index indicates whether a place is usually dry or moist and it can be used to compare the soil moisture of different places with each other.
The Soil Moisture Index is a 10-meter resolution raster map showing soil moisture in a continuous spectrum from wet to dry. It is available as open data in the Environmental Data Portal.
Soil moisture varies over time depending on what the weather is and has been like. Even if the weather has been similar in two places, their soil moisture can be very different. The relationship between them is usually the same whether it is unusually dry or unusually wet at the time. The top of the sandy hill will usually be drier than the wet clay loam area down in the valley, regardless of whether the area as a whole is currently experiencing drought or snowmelt and heavy rainfall.
Soil moisture is highly dependent on topography. The most important input to the soil moisture index is therefore Lantmäteriet's elevation model. Since the movement of water through the landscape depends not only on differences in altitude but also on the permeability of the soil layers, information on soil type and soil depth from the Geological Survey of Sweden (SGU) has also been used.
National comparability has been a guiding principle in the development of the soil moisture index. The method is therefore the same throughout the country, with the exception of those parts of the country that lack sufficiently detailed soil mapping. If you are curious to know more, read the article "Nationwide information on soil moisture " in Kartografiskas magazine Kart & Bildteknik.
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