Modeling the impact of the spatial structure of a hedge network on the hydrology of a small catchment in a temperate climate

Hedges are widely encountered throughout the world. In Brittany (Western France), as well as more generally in Western and Central Europe, they are mainly represented as “bocage”, a rural landscape with cultivated fields enclosed by hedges. In temperate climates, the impact of evapotranspiration from hedges on soil water content and dynamics is seldom addressed as a management issue at the catchment scale, in spite of some evidence that hedges may modify catchment hydrology. The present study uses a modeling approach to estimate the impact of different hedge networks on the hydrology of a small temperate catchment. This study uses a spatialized hydrological model (TNT2) in which the hedge effect takes into account an additional and deeper soil water uptake through evapotranspiration. The modeling is based on the actual hedge networks in 1948 and 2000 on an experimental catchment, as well as different scenarios of landscape management and a large set of rainfall conditions. At the local scale, the impact of hedges depends on their location on the hillslope and hence on the depth of the groundwater level below the soil surface. At the catchment scale, the additional annual actual evapotranspiration (AET) due to hedges represents between 5 and 30% of the annual AET. This effect depends on the hedge network density and spatial structure. It depends also on the climate, with an increasing impact for the driest years. This study is a preliminary simple approach to the impact of hedges on the hydrology of a small rural catchment. The advantage of this approach is that it takes into account the spatial interactions in the catchment and facilitates the comparison of different scenarios of hedge spatial structure. Despite the lack of precise information on hedge evapotranspiration in the region and the simple description of AET in the model, we are able to give orders of magnitude for the hedge effect based on choices of model parameterization as well as different modalities of hedge density and location.