Rationale

Justification for indicator selection

Soil water retention is a major soil hydraulic property that governs soil functioning in ecosystems and greatly affects soil management. Soil moisture forms a major buffer against flooding, and water capacity in subsoil is a major steering factor for plant growth. The effects of changes in soil water retention depend on the proportions of the textural components and the amount of organic carbon present in the soil. At low carbon contents, an increase in carbon content leads to an increase in water retention in coarse soils and a decrease in fine-textured soils. At high carbon contents, an increase in carbon content results in an increase in water retention for all soil textures (Rawls et al., 2003). Soil organic matter can absorb up to twenty times its weight in water. Changes in temperature result in changes in evapotranspiration, soil moisture, and infiltration. These will also influence groundwater recharge by changing the ratio of surface run-off to infiltration. Projections for climate change indicate greater droughts in some areas, which might lead to substantial reductions in summertime soil moisture, and more rainfall -- even too much -- in others, and also increases in the off-site impacts of soil erosion. Maintaining or even enhancing the water retention capacity of soils can therefore play a positive role in mitigating the impacts of more extreme rainfall intensity and more frequent and severe droughts. Harmonised time-series on relevant soil properties are not available but should be developed. The development of projections for the soil characteristics presented here (subsoil available water capacity and topsoil moisture), which depend entirely on soil properties, is difficult due to lack of data to validate the models. Further research is needed using satellite information and linking this to representative observed data.

Scientific references

• References Calanca, P.; Roesch, A.; Jasper, K.; Wild, M., 2006. Global warming and the summertime evpotranspiration regime of the Alpine region. Climatic Change 79: 65-78. Rawls, W. J.; Pachepsky, Y. A.; Ritchie, J. C.; Sobecki, T. M.; Bloodworth, H., 2003. Effect of soil organic carbon on soil water retention, Geoderma, 2003. Elsevier.