hwsd

Land Usev02.00 credits/per_km2

Responsible:Niccolò Calandri

Soils — Harmonized World Soil Database v2.0

Overview

The HWSD (Harmonized World Soil Database) layer provides comprehensive soil characterization based on HWSD version 2.0, the most authoritative global soil database jointly developed by FAO, IIASA, ISRIC, and JRC.

The database maps 34 WRB (World Reference Base) soil groups at approximately 1 km resolution globally, with detailed soil attributes for 7 depth layers spanning 0–200 cm. These attributes include texture (sand, silt, clay percentages), organic carbon content, pH, cation exchange capacity, bulk density, and available water capacity.

From these raw soil properties, five aggregated quality indices are computed:

Index	Description	Components
Composition Index	Soil texture balance	Sand/silt/clay ratios, stoniness
Fertility Index	Nutrient availability	Organic carbon, CEC, pH, base saturation
Hydraulic Index	Water retention/drainage	Available water capacity, drainage class
Productive Limitations	Constraints on agriculture	Depth to bedrock, salinity, sodicity
Master Suitability Index	Overall soil quality	Weighted combination of all indices

Calculation Methodology

Soil data extraction and index computation:

Spatial query — The HWSD raster is clipped to the analysis area, extracting soil mapping units (SMUs)
Attribute retrieval — For each SMU, soil properties are retrieved for up to 7 depth layers:
- Layer 1: 0–20 cm (topsoil)
- Layer 2: 20–40 cm
- Layer 3: 40–60 cm
- Layer 4: 60–80 cm
- Layer 5: 80–100 cm
- Layer 6: 100–150 cm
- Layer 7: 150–200 cm
Index computation — Each index is calculated as a normalized score (0–1):
- Composition Index: penalizes extreme texture (>85% sand or >60% clay)
- Fertility Index: rewards high OC (>2%), neutral pH (5.5–7.5), high CEC (>25 cmol/kg)
- Hydraulic Index: rewards moderate drainage and high available water capacity
- Productive Limitations: penalizes shallow depth, high salinity (>4 dS/m), high sodicity (ESP >15%)
- Master Suitability Index: weighted average with configurable weights

Data Sources

Code	Name	Provider	Type	Coverage	Resolution	Version
HWSD v2.0	Harmonized World Soil Database	FAO/IIASA/ISRIC/JRC	Raster + database	Global	~1 km (30 arc-sec)	2.0 (2023)

Documentation: FAO HWSD

Technical Notes

HWSD resolution (~1 km) is suitable for regional assessments but cannot capture field-scale soil variability
The database is compiled from heterogeneous national soil surveys, leading to quality differences across countries
Soil properties represent modal (most common) values for each mapping unit, not pixel-specific measurements
The quality indices are designed for comparative assessment across sites, not for absolute soil fertility determination
Depth layer data may be incomplete in some regions, particularly for deeper layers

References

FAO & IIASA (2023). "Harmonized World Soil Database version 2.0". FAO, Rome, Italy and IIASA, Laxenburg, Austria.
Nachtergaele, F., van Velthuizen, H., Verelst, L., Wiberg, D. (2023). "Harmonized World Soil Database v2.0: Documentation". FAO/IIASA.
IUSS Working Group WRB (2022). "World Reference Base for Soil Resources 2022". International Union of Soil Sciences.

Data Sources & References

Sources

WRD_HWSDB_23

Methodology

La mappa HWSD (Harmonized World Soil Database) utilizza la versione 2.0 del database globale dei suoli prodotto congiuntamente da FAO, IIASA, ISRIC, ISS-CAS e JRC, con risoluzione di circa 1 km (30 arc-seconds). Il database combina dati da diverse fonti regionali (FAO Digital Soil Map of the World, SOTER, European Soil Database). Il dato raster contiene per ogni pixel un SMU_ID (Soil Mapping Unit ID) che identifica l'unità di suolo. Da un database CSV associato si ottengono per ogni SMU_ID gli attributi dettagliati: - Classe di suolo secondo WRB 2022 (World Reference Base), con 34 gruppi principali (Acrisols, Andosols, Arenosols, Calcisols, Cambisols, Chernozems, Ferralsols, Fluvisols, Gleysols, Histosols, Leptosols, Luvisols, Podzols, Vertisols, ecc.); - Attributi per 7 strati di profondità (D1-D7: 0-5, 5-15, 15-30, 30-60, 60-100, 100-150, 150-200 cm); - Proprietà fisiche: tessitura (sabbia, limo, argilla), densità apparente, pietrosità; - Proprietà chimiche: pH, CEC (capacità di scambio cationico), carbonio organico, azoto totale. Vengono calcolati indici di qualità del suolo: Composition Index (qualità della composizione), Fertility Index (fertilità), Hydraulic Index (proprietà idrauliche), Productive Limitations Index (limitazioni produttive), Master Suitability Index (idoneità complessiva).