Estimating the agricultural irrigation demand for planning of non-potable water reuse projects

Water reclamation and reuse represent a promising approach to mitigate water related use conflicts especially in the agricultural sector where challenges with regard to water management are increasingly exacerbated by the effects of climate change. However, for the conceptualization and implementation of non-potable water reuse projects for agricultural purposes a comprehensive understanding of the irrigation requirements is required. But this information is frequently not readily available. Within the scope of this study modelling based on the approach implemented within the CROPWAT 8.0 software was applied in order to determine the irrigation requirements for an agricultural area in Gochsheim, Lower Franconia (Germany) since locally recorded data were missing, inconsistent or incomplete. The model was validated not only by available locally recorded groundwater extraction rates for agricultural irrigation purposes but also by comparison with findings from the literature. Based thereon, the annual and daily crop specific net irrigation requirements of ten commonly cultivated crops were computed - those comprised celery, lettuce, onions, potatoes, cabbage and others. The crops showed crop specific typical annual as well as daily net irrigation requirements, e.g. celery with an annual and daily demand of 228-602 mm and 5-20 mm, respectively. Particularly important for the planning of a water reuse project was the determination of the overall daily peak gross irrigation requirement. The modelling approach revealed a value of 14.3 mm/day for this area, which represents the technically as well as economically most feasible benchmark, and a good approximation to the historical recorded overall daily peak gross irrigation demand.