This dataset shows the global distribution of histosols that cover the tropics and subtropics (38° N to 56° S; 161° E to 117° W), excluding small islands. It was mapped in 236 meters spatial resolution by combining a hydrological model and annual time series of satellite-derived estimates of soil moisture to represent water flow and surface wetness, which were then combined with geomorphological data.
Process information: Compared to previous mapping efforts (e.g. remotely sensed through inundation patterns or vegetation cover, or analytically derived through a hydrological model), our method incorporates a higher level of complexity by developing three biophysical indices that capture three key properties of wetlands:
|1.||The need for sufficient water supply for a long-enough time period;|
|2.||the need for water logged soils; and|
|3.||the need for a geomorphological position where water can be supplied and retained.|
Methodologically, histosols are identified using the same method as wetlands but with an important alteration: the surface has to be continuously wet (e.g. minimum wet conditions forced to be positive (pTWImin > 0) and the wettest annual conditions are forced to be above a certain threshold (pTWImax > 500) (Gumbricht 2015). Our model identifies areas with hydrological potential for histosol formation, without considerations of activities in the land that might remove this organic matter (e.g. drainage, fires, etc.).
For the classification of histosols, the model was optimized using Indonesian peat data (peat domes and peat swamps) but ground validation would be needed to measure carbon contents and soil depths to validate that these areas of potential histosol formation are peats, as defined in Page et al. (2011) – 65% of organic carbon content and at least 20 cm of organic matter thickness.