Numerical exploration of the impact of hydrological connectivity on rainfed annual crops in Mediterranean hilly landscapes

Within hilly agricultural landscapes, topography induces lateral transfers of runoff water, so-called interplot hydrological connectivity. Runoff water from upstream plots can infiltrate downstream plots, thus influencing the water content in the root zone that drives crop functioning. The impact of runoff on crop functioning can be crucial for optimizing agricultural landscape management strategies. However, to our knowledge, no study has specifically focused on the impact on crop yield. The current study aims to comprehensively investigate the impact of runoff on crop functioning in the context of Mediterranean rainfed annual crops. To quantify this impact, we conduct a numerical experiment using the AquaCrop model and consider two hydrologically connected plots. The experiment explores a range of upstream and downstream agro-pedo-climatic conditions: crop type, soil texture and depth, climate forcing, and the area of the upstream plot. The experiment relies on data collected over the last 25 years in OMERE, an environment research observatory in northeastern Tunisia, and data from literature. A key finding in the results is that water supply through hydrological connectivity can enhance annual crop production under semiarid and subhumid climate conditions. Specifically, the results show that the downstream infiltration of upstream runoff has a positive impact on crop functioning in a moderate number of situations, ranging from 16% (wheat) to 33% (faba bean) as the average across above ground biomass and yield. Positive impact is mostly found for higher soil available water capacity and under semiarid and dry subhumid climate conditions, with a significant impact of rainfall intra-annual distribution in relation to crop phenology. These research needs to be expanded by considering both a wider range of crops and future climate conditions.