An empirical modelling approach to investigate nutrient losses in view of more frequent extreme hydrological events using future climate-scenarios

Changing weather patterns and extreme hydrological events, i.e. heavy rainfall and prolonged droughts, have resulted in further degradation of water quality within the agricultural landscapes by exacerbating nutrient transfer processes to surface water bodies. More frequently occurring extreme weather events require development of robust adaptation/mitigation strategies, which further requires an improved understanding of both the timing and conditions of the intensified hydro-meteorological drivers.

In order to evaluate the impact of extreme events on nutrient losses, an empirical modelling approach was taken in six intensively-monitored hydrologically-diverse agricultural catchments (ca 3-30 km²) across Ireland. The objective was to link the occurrence of pulses of N and P, driven by hydrology, with sub-hourly water quality monitoring and weather data over a 14-year period. Then using the downscaled future climate change scenarios for moderate (RCP 4.5) and severe (RCP 8.5) emission pathways, the occurrence probability and timing of such triggering events were investigated for three different time periods until end of the century.

The investigation of high-temporal resolution data confirmed capturing all subtle changes in the nutrient concentrations and extreme weather events while the empirical modelling of associated nutrient losses events due to extreme hydrological events revealed various criteria contributing to nutrient-losses. These criteria were in terms of air temperature and effective rainfall and explained more than 50% of any nutrient loss events across all the catchments at different temporal scales. Temporal aspects of data analysis showed that certain months would require specific attention in terms of adaptation, management, and re-evaluating nutrients’ pathways.

 Comparison between RCP 4.5 and 8.5 across three time periods of near future (2010-2039), mid-future (2040-2069), and far-future (2070-2100), suggested that the upward trends in number of events continue to increase stepwise in each time period whereas the percentage increase of nutrient-concentrations’ increasing events would almost double in RCP8.5. There would be over 60% and 40%  increase in the number of P-loss and N-loss triggering events, respectively, from near-future to far-future considering the sum of different empirically-driven criteria. Meanwhile, the catchment characteristics played a major role in defining the response of each landscapes to various drivers. Such catchment-specific response was explained by hydrological connectivity, soil chemistry and texture, drainage status, and agricultural practices.

Prolonged drought and warm periods and increased hydrological connectivity would result in increasing number of nutrient losses events as we move toward end of the century. The detected differences in catchments’ characteristics and in the frequency of triggering events across climate scenarios were indicative of consequence for future mitigation strategies and policy decisions which have to be climate smart, resilient, catchment-specific, and tailored to different environments

This research has been conducted as part of the WaterFutures project (Irish-EPA-funded).