Maps for each month use a 15 year average (1985-1999) to show what average soil moisture levels are like.
Soil moisture can also be interpreted and the percentage of saturation, where a dry soil has a low saturation level and a fully wet soil is 100% saturated. Soil moisture is difficult to describe because it is a 3D process, with water entering the top layer and slowly penetrating to deeper depths.
Soil moisture decreases by water leaving the soil by evaporation or penetrating to depth and recharging ground water stores. The 2 key sources of water in the soil are rainfall or snowmelt. On a global scale changes in Soil Moisture depend on the season and climate zone.
Dry areas such as deserts are clearly visible with little change over a year. But the edge of the Sahara desert shows change where the rainy season contributes to the soil moisture, as July to September is the rainy season for western Africa and maps for August to October show higher soil moisture content.
On the continent of Africa it is interesting to observe the Ethiopian Highlands and East African Highlands have consistently wetter soils than surrounding areas because these more elevated regions experience wetter conditions.
Northern latitudes close to the Arctic Circle have high soil moisture year round. The highest soil moisture occurs April to June when snow melt and thawing of permafrost occurs. Greenland soils are not modelled because of the permanent ice cover, and is set to zero for this display.
The rainy season for the northern part of South America is November to March and this is reflected in the estimated soil moisture for December to April. The lag in timing between rainfall and estimated soil moisture is due to the time it takes for soil to become wet.
- Average land for Jan
- Average land for Feb
- Average land for Mar
- Average land for Apr
- Average land for May
- Average land for Jun
- Average land for Jul
- Average land for Aug
- Average land for Sep
- Average land for Oct
- Average land for Nov
- Average land for Dec
Soil moisture legend as percentages