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Sourcing subsurface evaporation (E ss ) into groundwater (E g ) and unsaturated zone (E u ) components has received little scientific attention so far, despite its importance in water management and agriculture. We propose a novel sourcing framework, with its implementation in dedicated post-processing software called SOURCE (used along with the HYDRUS1D model), to study evaporation sourcing dynamics, define quantitatively "shallow" and "deep" water table conditions and test the applicability of water table fluctuation (WTF) and "bucket" methods for estimation of E g and E u separately.For the "shallow" and "deep" water table we propose E g > 0.95E ss and E g = 0 criteria, respectively. Assessment of the WTF method allowed sourcing of very small fluxes otherwise neglected by standard hydrological methods. Sourcing with SOURCE software was more accurate than the standard "bucket" method mainly because of greater flexibility in spatio-temporal discretization. This study emphasized the dry condition relevance of groundwater evaporation which should be analysed by applying coupled flow of heat, vapour and liquid water. ARTICLE HISTORY

Evaporation is one of the main components of the hydrologic cycle in semi-arid and arid areas, where topsoil (the first few decimeters of soil material) is often very dry, especially during dry season (Wang, 2015). Such areas, often referred to as water limited environments (Parsons & Abrahams, 1994) are characterized by low precipitation and high potential evaporation rates; the precipitation events are mostly concentrated in few months (wet season) but rare during the rest of a year, when long periods of droughts are common (dry season).When a dry spell is long enough for evaporation to deplete the soil moisture in a topsoil, a dry soil layer (DSL) forms, that is, a layer where water moves only in vapor form (Brutsaert, 2014;. Semi-arid and arid regions are generally characterized by sandy soils (Bestelmeyer et al., 2015); hence, most of the time, a thick (5-50 cm) DSL is present in the topsoil (Koonce, 2016;Wang, 2015). During the dry season, due to the high potential evaporation, the top soil becomes increasingly dry and the short precipitation events typically infiltrate only the first few centimeters of soil and quickly evaporate (Sun et al., 2016).The evaporation process from an initially saturated soil material is thought to occur in two stages : during the first stage the depth of the upper boundary of the saturated zone (the drying front, equivalent to the upper boundary of the capillary rise from the saturate zone, Figure 1) increases because of the loss of water through upward transport in the liquid phase to the ground surface, where evaporation takes place. When the drying front reaches a certain depth, liquid water continuity with the surface is disrupted and a DSL is formed between the ground surface and the vaporization plane, that is, the plane from which all the water moves by vapor to the surface, with depth determined by soil material properties and soil temperature (Figure 1, Lehmann et al., 2008; Neriah et al., 2014). This is the beginning of the second stage of evaporation, when there is a zone through which liquid water moves upward from the drying front to the vaporization plane (Figure 1) where it evaporates and is transported as water vapor through the DSL to the surface (Shokri et al., 2009).

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High-resolution electrical resistivity tomography (ERT) with electrode spacing of 1 m proved to be an effective methodology to characterize ephemeral, sparse, and discontinuous freshwater lenses within the almost completely salinized shallow aquifer of the low coastal zone near Ravenna. ERT profiles with a vertical resolution of 0.25–0.5 m, once calibrated with groundwater data (water table depth and electrical conductivity) collected in multi-level sampler systems at the same spatial resolution, are reliable and provide repeatable measurements in time. The ERT methodology allows for fast data acquisition over large areas and it also permits the study of the evolution in time of freshwater availability in coastal zones, which is important for local ecosystems and soil resources. This makes high-resolution ERT a valid tool to aid local stakeholders and decision makers to effectively manage freshwater lenses, and guarantee their preservation or augmentation by means of managed aquifer recharge.