Analysis and simulation of the water and energy balance of intense agriculture in the Upper Rhine valley, south-west Germany

The Upper Rhine valley (SW Germany) belongs to one of the agriculturally most intense used regions in Germany. Climatic favourable conditions with mild winters, early springs and warm autumns lead to long vegetation periods and high agricultural productivity. One limiting factor is the water supply because of a negative annual climatic water balance, which has been increasing by −10 mm per decade in the last 50 years to −150 mm at present. Thus irrigation measures become more and more important for agricultural production in this region. Aim of this study was to measure and simulate water and energy fluxes on farm level in respect to the effects of irrigation measures in a region where farm sizes are small and diversity of land use high. In future these results will be used to conduct studies of energy and water fluxes on spatial scale (e.g. water catchments). The dynamics of the water and energy balance was observed with micrometeorological measurements using the eddy covariance methodology. Our investigation area had a size of about 6.5 ha and was cultivated with spring barley ( Hordeum vulgare L.). Continuous measurements of all components of the water and energy balance as well as the vegetation specific-parameters, such as LAI, crop height and phenological macrostages, were conducted during the growing season which lasted from the beginning of April to 16 July 2014 (95 days). Additional irrigation was applied three times in this period by using a mobile sprinkler irrigation system. The observed dynamics were simulated with the physically based hydrological model TRAIN, which uses the Penman–Monteith approach for evapotranspiration simulation. Model efficiency was evaluated with Nash–Sutcliffe coefficient (NS). The TRAIN model was performing the simulations well with an r 2 = 0.72 with an slope of 1 and a NS = 0.77.