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Vegetation plays a key role in riparian area functioning by controlling water and nitrate (NNO3-) transfers to streams. We investigated how spatial heterogeneity modifies the influence of vegetation transpiration on soil water and NNO3- balances in the vadose soil of a Mediterranean riparian forest. On the basis of field data, we simulated water flow and NNO3- transport in three riparian zones (i.e., near-stream, intermediate, and hillslope) using HYDRUS-1D model. We investigated spatiotemporal patterns across the riparian area over a 3-year period and future years using an IPCC/CMIP5 climate projection for the Mediterranean region. Potential evapotranspiration was partitioned between evaporation and transpiration to estimate transpiration rates at the area. Denitrification in the forest was negligible, thus NNO3- removal was only considered through plant uptake. For the three riparian zones, the model successfully predicted field soil moisture (theta). The near-stream zone exchanged larger volumes of water and supported higher theta and transpiration rates (666 +/- 75 mm) than the other two riparian zones. Total water fluxes, theta, and transpiration rates decreased near the intermediate (536 +/- 46 mm transpired) and hillslope zones (406 +/- 26 mm transpired), suggesting that water availability was restricted due to deeper groundwater. Transpiration strongly decreased theta and soil NNO3- in the hillslope and intermediate zones. Our climate projections highlight the importance of groundwater availability and indicate that soil NNO3- would be expected to increase due to changes in plant-root uptake. Lower water availability in the hillslope zone may reduce the effectiveness of NNO3- removal in the riparian area, increasing the risk of excess NNO3- leaching into the stream.