Thematic Issue on Soil Water Infiltration

Interpretive Summary: When water is applied to the land surface through irrigation or rainfall, it infiltrates into the soil surface and percolates deeper through the soil profile under the influence of gravity and capillary forces. Soil infiltration is one of the most complex processes within the terrestrial hydrologic cycle, yet the process is only partially understood. Infiltration is affected by the physical, chemical and biological properties of the soil, vegetation cover, rainfall, irrigation properties, and management practices. Measurement of infiltration rate is essential in studies concerning water budget, hydrology, runoff, erosion, irrigation, drainage and water conservation. However, the complex process of infiltration presents considerable difficulty in its measurements. Therefore, various types of infiltrometers, methods and techniques have been developed and used to measure infiltration In general; these measurement methods involve either flooding the soil or sprinkling water to simulate rain. Soils and their physical, chemical and biological properties significantly influence the terrestrial hydrologic cycle through infiltration processes. To understand the terrestrial hydrologic cycle, we must first understand one of its critical components, “infiltration”. To enhance our knowledge of the infiltration process, this thematic issue describes in some details the physics of infiltration, profile water distribution and wetting fronts during infiltration, infiltration models and parameters’ estimation, factors affecting infiltration, and new measurement techniques. Technical Abstract: Infiltration is the term applied to the process of water entry into the soil, generally by downward flow through all or part of the soil surface. Understanding of infiltration concept and processes has greatly improved, over the past 30 years, and new insights have been given into modeling of non-uniform and anisotropic flow. Over the past couple of decades, we have seen the development of many new measurement techniques of soil infiltrability under controlled conditions (water pressure head and initial water content) and the creation of innovative devices (ponded or tension infiltrometers). This thematic issue collected 11 original contributions presented during the session “Infiltration: measurements, assessment and modelling” organized by the authors at the General Assembly of European Geosciences Union (EGU), held in Vienna, Austria from 17–22 April, 2016. In summary, the combined use of water infiltration experiments and numerical/ analytical models presented in the papers of this thematic issue on “Soil Water Infiltration” provided an insight into some of the most challenging problems in water infiltration research and prediction of water and solute movement in the vadose zone at different scales.