D4.4: Assessment of NSWRM effectiveness under current and future climate at the catchment scale. Deliverable D4.4 of the EU Horizon 2020 project OPTAIN

The objective of this deliverable D4.4 is to provide an integrated, model-based assessment of the effectiveness of Natural/Small Water Retention Measures (NSWRMs) in 14 small agricultural catchments in Europe under current and projected climate conditions. The objective of a harmonised application of the hydrological and water quality model SWAT+ (Soil & Water Assessment Tool) was successfully achieved. The modelling work in each case study closely follows OPTAIN's deliverable D4.2, 'SWAT+ modelling protocol for the assessment of water and nutrient retention measures in small agricultural catchments' (Schürz et al., 2022), as outlined in this deliverable. The report presents the new Contiguous Object COnnectivity Approach (COCOA) as the most significant and novel contribution to process-based modelling. COCOA can represent landscape features at the field scale and account for connectivity between land phase objects. The report provides a detailed description of the modelling workflow, including input data preparation, model setup, verification, calibration, and application in climate and NSWRM scenario runs. This report presents a synthesis of modelling results, focusing on model evaluation, simulated water and nutrient balance, crop yield outputs, and the impacts of climate change from eight case studies located in Belgium, Germany, Hungary, Italy, Norway, Poland, and Switzerland. The report includes 14 annexes providing in-depth reports dedicated to specific catchments from all OPTAIN CS modelling teams. Seven annexes contain results on the simulated effectiveness of selected NSWRMs quantified by a set of environmental performance indicators. The effectiveness of NSWRMs under future climate scenarios was quantified for illustrative purposes for one catchment located in Germany (CS1). Additionally, this deliverable includes a suite of scripted workflows in R that cover different steps of the SWAT+ modelling process. The calibrated SWAT+ model setups generated within this task will serve to identify optimal implementation schemes for NSWRMs, including their combination and allocation within the catchment (OPTAIN WP5). The synthesis of modelling results will continue under WP6.