The impacts of local and sectoral adaptations (mainly from the irrigated agriculture sector constituting the main water use), on the global behavior oh the hydrosystem, under constraints of management strategies specified at the scale of the sub-catchment (incentives, regulations.). We will iteratively measure the impact of the implemented local feedback loops on the outputs computed at the scale of the sub-catchment. The scope of the PhD thesis is limited to the main sectors of activity of the two chosen sub-catchments of the Durance river. This link will enable to specify local feedback loops related to human activities and furthermore to get spatial simulation outputs matching stakeholders' variables of interest. Hence, the exercice of coupling the agent model and the hydrological model will consist mainly in defining agents's variables of interest and to relate them to state variables or outputs of the hydrological model. this implies to put the focus on the variables of interest of the agent (perceived variables and control variables, including hydrological variables) that are most of the time local variables. In this context, the decision making process of one or several agents is based on the set of actions that he can possibly realize at each moment. We propose to use the theory of situed action (providing a framework to describe individual actions and decisions) and the concept of stigmergy (providing a framework to describe indirect interactions amongst actors) to build the agent based model. The objectives of the thesis is to couple an existing distributed hydrological model to an agent based model representing social dynamics and driving the local feedback loops related to human activities. Distributed hydrological modeling enables the simulation of hydrological dynamics considering spatial heterogeneity of the catchments and consequently gives the opportunity to imagine local feedback loops related to human activites. However, before they can produce relevant prospective scenarios, several improvments are required, in particular accounting for feedbacks loops between social and physical dynamics. Hydrological processes are rather well know and modeling and simulation platforms are available for their simulation. Modeling and simulation tools, dedicated to prospective analysis, are being developed at Irstea, in partnership with stakehoders of water management. In a context of global change, management of water resources between actors with sometimes conflicting objectives should be revisited. We investigated the hydro-logic effect of three irrigation scenarios (non-regulated: NREG, regulated: REG, and regulated with groundwater pumping: REG+GW) aimed at reducing crop water stress derived by one-way coupling of MODFLOW with the crop model Decision Support System for Agrotechnology Transfer (DSSAT). The model was specifically used to simulate the vadose zone water availability due to irrigation, and water-food security aspects associated with extremely dry years.
Normalized root mean squared error (NRMSE) values of 0.047, 0.05, and 0.06 were obtained through calibration for H, θ, and ET, respectively. The groundwater model was calibrated with in situ data collected via a Citizen Science Initiative (CSI) for hydraulic head (H) and soil moisture(θ) and against a distributed hydrological model (CREST) simulated evapotranspiration (ET). The coupling of groundwater modelling with crop water modelling in data scarce environments is a key contribution of this work. The framework was implemented in an irrigated site namely, the Koga irrigation scheme, located within in the UBN Basin, Ethiopia.
To explore this issue, we developed a numerical framework, based on a groundwater model using MODFLOW-NWT, coupled with the outputs of the crop model DSSAT. This is more sensitive in the Upper Blue Nile (UBN) basin, where precipitation uncertainty and hydrological droughts often overshadow the effectiveness of these irrigation schemes, challenging the water-food security efforts in general. Agriculture in Ethiopia has a historical dependency on rainfed (wet season) and surface water-based (dry season) irrigation projects, the performances of which rely heavily on JJAS precipitation.