Integration of various data sources for transient groundwater modeling with spatio-temporally variable fluxes—Sardon study case, Spain

Spatio-temporal variability of recharge (R) and groundwater evapotranspiration (ETg) fluxes in a granite Sardon catchment in Spain (∼80 km2) have been assessed based on integration of various data sources and methods within the numerical groundwater MODFLOW model. The data sources and methods included: remote sensing solution of surface energy balance using satellite data, sap flow measurements, chloride mass balance, automated monitoring of climate, depth to groundwater table and river discharges, 1D reservoir modeling, GIS modeling, field cartography and aerial photo interpretation, slug and pumping tests, resistivity, electromagnetic and magnetic resonance soundings. The presented study case provides not only detailed evaluation of the complexity of spatio-temporal variable fluxes, but also a complete and generic methodology of modern data acquisition and data integration in transient groundwater modeling for spatio-temporal groundwater balancing. The calibrated numerical model showed spatially variable patterns of R and ETg fluxes despite a uniform rainfall pattern. The seasonal variability of fluxes indicated: (1) R in the range of 0.3–0.5 mm/d within ∼8 months of the wet season with exceptional peaks as high as 0.9 mm/d in January and February and no recharge in July and August; (2) a year round stable lateral groundwater outflow (Qg) in the range of 0.08–0.24 mm/d; (3) ETg=0.64, 0.80, 0.55 mm/d in the dry seasons of 1997, 1998, 1999, respectively, and <0.05 mm/d in wet seasons; (4) temporally variable aquifer storage, which gains water in wet seasons shortly after rain showers and looses water in dry seasons mainly due to groundwater evapotranspiration. The dry season sap flow measurements of tree transpiration performed in the homogenous stands of Quercus ilex and Quercus pyrenaica indicated flux rates of 0.40 and 0.15 mm/d, respectively. The dry season tree transpiration for the entire catchment was ∼0.16 mm/d. The availability of dry season transpiration measurements considered as root groundwater uptake (Tg), allowed estimation of dry season catchment groundwater evaporation (Eg) as 0.48, 0.64, 0.39 mm/d for 1997, 1998 and 1999, respectively.