Remote Sensing-based Agricultural Water Accounting Projections for irrigated maize under different climate change scenarios in 5 European locations

The latest update on planetary boundaries states both the blue and green freshwater change are beyond the safe operating space for the first time since the initial findings in 2009. Moreover, agricultural water use, which nowadays accounts for about two-thirds of global freshwater resources, is projected to increase by 2080. Under this scenario, river basin management plans include short-term crop water requirements projections. The presented abstract therefore proposes a remote sensing-based approach combined with climate change scenarios to provide short-, medium- and long-term green and blue crop water use (CWU) projections at 5 different European locations for irrigated maize.

The methodological framework for the Remote Sensing-based Agricultural Water Accounting  Projections (RS-AWA^↑) here presented is based on: a) using current and locally adapted crop behaviour monitored through remote sensing Sentinel 2 satellite images time series to derive NDVI crop pattern profile; b) using daily future climate projections (temperature and precipitation) based on an ensemble of 4 different Regional Climate Models that are driven by 3 different Global Climate Models, under the Representative Concentration Pathways (RCP) 4.5 and RCP 8.5; c) combining actual crop behaviour and daily climate projections in a Remote Sensing-based Soil Water Balance based on FAO56 to obtain both the green and blue CWU along short-, medium- and long-term periods; and d) obtaining changes in CWU regarding the baseline period. It was applied for irrigated maize within the Júcar River Basin (Spain), the Isonzo River Basin (Italy), the Soča River Basin (Slovenia), the Pinios River Basin (Greece) and the Dolj municipality (Lower Danube River Basin, Romania).

The 5 locations' results showed a common decline in the green CWU and a rise in the blue CWU, indicating lower CWU from precipitation events with the consequent increase in blue CWU from groundwater or superficial reservoirs, hence more irrigation requirements. By location, Pinios and Júcar present the lower increasements in irrigation requirements ranging from 6 to 10 % (RCP 4.5) and 10 to 17 % (RCP 8.5), followed by the Dolj location that ranges from 15 to 20 % (RCP 4.5) and 10 to 17 % (RCP 8.5), then the Isonzo location where ranges from 26 % (RCP 4.5) and 14 to 59 % (RCP 8.5), and finally the highest increasements corresponds to the Soča location that ranges from 45 to 73 % (RCP 4.5) and 50 to 147 % (RCP 8.5).

The presented results incorporate to the climate change family results and indicators, a locally adapted crop pattern derived from actual NDVI time series that will support better knowledge to water managers, as it could be adapted to the crops that are most interested in their managing areas, as we did in the project that support these research, the EU Horizon 2020 project REXUS (Managing Resilient Nexus Systems Through Participatory Systems Dynamics Modelling), in which stakeholders from water user associations to river basin water managers are evaluating the information. Finally, the authors acknowledge the contribution of land use map providers for irrigated maize in each of the locations considered.