Impacts of extreme weather events on water quality and nutrient losses in agricultural catchments: Past, Present, and Future

The global aquatic threat imposed by agriculturally-sourced pollution is further exacerbated due to the shifts in the weather patterns, resulting in changes in catchment hydrology, water cycle, and soil processes. Understanding the timing, extent, and impact of the extreme-weather-events on nutrient losses is hence essential to develop efficient climate-smart adaptation measures to avoid further increases in nutrient pollution in receiving water bodies.

Our research has applied an empirical modelling (EM) approach on +14 years of very high-temporal resolution weather and water quality data from six hydrologically-diverse agriculturally-dominated catchments in Ireland in order to i-detect climate-induced increases in Nitrogen (N) and Phosphorous (P) losses during 2010-2024, and ii- estimate likelihood occurrence of similar loss events until turn of the 21^st century using climate change projections. We considered the following criteria to model the historical prevalence of loss-events, and to project the possibility of occurrence in the future under two representative concertation pathways of RCP 4.5 (moderate) and 8.5 (extreme) for three different time periods of 30-years each: effective rainfall (ER)>five mm in one day and/or the day before, ER>10mm over one day, and average air temperature>15℃ over 5 consecutive days.

Although the sensitivity of each catchment to prolonged warm period and intensive short-term precipitation depended highly on the catchment-characteristics, the monthly trend analysis of projected temperature and precipitation indicated very significant increase in the extent of warm and dry periods, as well as the intensity of wet/very wet days, toward the end of the century. The EM captured over 60% of events triggering N losses and up to 80% of P-loss triggering events.

Considering the potential underestimation of projected temperature and precipitation probability, and assuming no changes in N and P inputs in the future scenarios, the average annual number of temperature-related and precipitation-related N-triggering events would reach 120 and 79, respectively, in the far-future RCP 8.5. EM also projected >60% increase in the number of P loss events under both representative pathways while the projections indicated average discharge of over 8 mm per a single event which would directly contribute to increases in mass loads leaving the catchments.

As the water quality is threatened further by the changing weather patterns, it is critical to incorporate the influence of climate change on nutrient losses and develop climate-resilient measures that are tailored to different catchment typologies.