Harmonized soil property values for broad-scale modelling (WISE30sec) with estimates of global soil carbon stocks

Abstract

Soils play a key role in providing a range of ecosystem services. Quality-assessed soil information, with quantified uncertainty levels, is needed to address a range of global issues. Traditional mapping methods, which recognize that soil classes are “important carriers of soil information”, were used to prepare an updated harmonized dataset of derived soil properties for the world at a nominal resolution of 30 by 30arc sec (WISE30sec). The map unit composition was determined using an overlay of the Harmonized World Soil Database, with minor corrections, and the Köppen–Geiger climate zones map as categorical co-variate. Property estimates for the respective component soil units were derived using taxonomy-based transfer rules that draw on a statistical analysis of some 21,000 soil profiles. Best estimates (mean±standard deviation) for twenty soil properties were calculated for seven depth intervals (up to 2m depth or less when thinner): organic carbon content, total nitrogen, C/N ratio, pH(H2O), CECsoil, CECclay, effective CEC, total exchangeable bases (TEB), base saturation, aluminium saturation, calcium carbonate content, gypsum content, exchangeable sodium percentage (ESP), electrical conductivity, particle size distribution (content of sand, silt and clay), proportion of coarse fragments (>2mm), bulk density, and available water capacity (−33 to −1500kPa); also the dominant soil drainage class. Coefficients of variation tend to be large. WISE30sec may be used for applications at a broad scale (<1:1M) upon consideration of the underlying data lineage, generalizations, and the associated uncertainties. As an example, the database was used to calculate the global soil organic carbon (SOC) stock to 2m depth. Some 30% (607±87PgC) of this stock (2060±215PgC) is held in the Northern Circumpolar Region, which is considered most sensitive to climate change.