Impact of climate change on freshwater macronutrients and agricultural yields across Britain

Climate models project higher temperatures and altered rainfall patterns in the future. This will significantly affect terrestrial and hydrological systems, with implications for agricultural yields, freshwater quality, and ecosystem health. To understand and quantify these changes, we used the Long-Term Large-Scale Integrated Model (LTLS-IM), a national-scale terrestrial and freshwater model, to simulate the effect of projected climate change on both agricultural yield and freshwater macronutrient (carbon, nitrogen, and phosphorus) fluxes and concentrations in Great Britain. To generate macronutrient inputs to rivers, the LTLS-IM combines predictions of nutrient losses to water from the semi-natural landscape model N14CP and the agricultural Rothamsted Landscape Model (RLM), with inputs from groundwater, urban runoff, sewage, and septic tanks. These inputs are routed through a freshwater model that simulates water flow and in-stream processes responsive to changes in temperature. Using 12 realisations of the UK Climate Projections 2018 (UKCP18) under the high-emission Representative Concentration Pathway (RCP) 8.5 scenario, we compared recent past (1980-2010) with near-future (2020-2050) conditions. Our projections indicate that for most crops, yields drop by 5-20% due to climate change alone and that despite relatively stable annual nutrient loads, freshwater macronutrient concentrations could increase by 20-30% because of reduced river flows.