Research

Partitioning of subsurface evaporation into unsaturated and saturated zone components

In semi-arid or arid areas, during dry seasons, evapotranspiration (ET) is the main component of the hydrological water balance. In the areas with sparse vegetation and large percentage of bare land, transpiration is negligible so the soil evaporation represents dominant contribution in the total ET. An accurate quantification of this component is essential for water management but also for agricultural practices to prevent soil salinization (http://www.agric.wa.gov.au/PC_92418.html?s=1001). A good understanding of the mechanism of evaporation process and the quantification of groundwater evaporation (Eg) and evaporation from unsaturated zone (Eu) is critically important since the Eg directly affects the sustainability of groundwater resources and the Eu leads to salinization of soils.

In the last decades, the interest in a better understanding of the vadose zone has grown, due to availability of new powerful instruments; for instance, computer codes able to solve numerically complex partial differential equations for the water and heat flow in unsaturated multi-phase porous media, but also new sophisticated sensors for field and laboratory studies, able to work automatically and store long datasets without much maintenance. These new techniques permit a deeper study focused on the movement of water in the unsaturated zone, and its balance with respect to groundwater and soil surface.

The core of my research project is to estimate accurately the evaporation from bare soils and to identify clearly the sources of water moving (in vapour or liquid state) through the unsaturated zone profiles. The main challenge will be to quantify how much of the water vapour leaving the soil at the surface originates from groundwater and how much from the vadose zone. This problem is not trivial, but rather has heavy relevance for groundwater management and agricultural purposes, especially in areas with long and hot dry seasons (e.g. arid or semi-arid areas).

My research is divided into the following different stages:

• Development of a conceptual model for evaporation partitioning, based on literature studies and field observation;
• Development of a numerical model, accounting for coupled heat and water vapour and liquid flows, in order to partition evaporation process;
• Testing of the model validity, internal (numerical stability, sensitivity analysis) first, and then with laboratory and field experiments;
• Upscaling of the developed local scale partitioning into the catchment scale;
• Application and validation of the developed procedure in specific, saline soil conditions of the dry lake Fuente de Piedra (south of Spain) – tentative task.