Indicator: Water Holding Capacity

Indicator	Water Holding Capacity
Description	Maximum amount of water that soil can retain, measured in m³/Plot and m³/ha, with an estimate of uncertainty provided as the average standard deviation of WHC estimates.
Unit	m³ (total and per hectare)
Temporal Resolution	Annual Assessment
Spatial Resolution	100m
Data	Satellite data (SMAP, SMOS, Landsat, MODIS, Sentinel 2); ISRIC SoilGrids v2.
Method	Water holding capacity is estimated based on soil moisture dynamics over time, analyzing the ability of soil to retain water against gravity (also known as field capacity). It is derived from a time-series of soil moisture data and constrained by soil texture information from SoilGrids.
Confidence interval	Confidence intervals for water-holding capacity (WHC) are derived by averaging values within the 10th–15th percentiles for wilting point and the 92nd–95th percentiles for field capacity. This method reduces noise and improves reliability by smoothing out variability and minimizing outlier effects. Additionally, the standard deviation within these ranges serves as a confidence flag—lower values indicate more consistent, reliable estimates, while higher values highlight greater variability. This approach enhances the precision and robustness of soil hydraulic property estimates.
Benchmarking	Benchmarks for water-holding capacity (WHC) are based on predicted soil texture (sand and clay fractions) from the SoilGrids v2 dataset. Using a pedotransfer function (Saxton & Rawls, 2006), WHC is estimated across a range of possible soil organic carbon concentrations. From the resulting distribution, the low benchmark is set at the minimum WHC value, the high benchmark at the maximum, and the middle benchmark at the median WHC value for the soil type predicted on the plot.