Soil Moisture in Average Year

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.

Africa

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.

North

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.

South America

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.