# Modelling the impacts of climate change on agrochemical fate and transport by water on a catchment scale

## TL;DR

This study models how climate change affects the movement and breakdown of agrochemicals in water, focusing on extreme weather scenarios.

## Contribution

The paper introduces a novel integrated modeling framework coupling climate data with agrochemical transport to assess climate impacts on chemical fate.

## Key findings

- Very wet and high-temperature scenarios increase river concentrations of agrochemicals and transformation products.
- High-temperature scenarios enhance degradation of S-Metolachlor, reducing soil retention.
- Intense hourly rainfall leads to higher peak concentrations of agrochemicals in rivers.

## Abstract

The export of agrochemicals and their transformation products (TPs) following their application in the agricultural fields poses a threat to water quality. Future changes in climatic conditions (e.g. extreme weather events such as heavy rainfall or extended dry periods) could alter the degradation and mobility of agrochemicals. In this research, we use an integrated modelling framework to understand the impact of extreme climate events on the fate and transport of the agrochemical S-Metolachlor and two of its TPs (M-OXA, Metolachlor Oxanilic Acid and M-ESA, Metolachlor Ethyl Sulfonic Acid). This is done by coupling climate model outputs to the Zin-AgriTra agrochemical reactive transport model in four simulation scenarios. 1) Reference (2015–2018), 2) Very dry (2038–2041), 3) Very wet (2054–2057) and 4) High temperature (2096–2099) conditions of a selected RCP8.5 based regional climate scenario. The modelling framework is tested on an agricultural catchment, Wulka, in Burgenland, Austria. The model results indicate that 13–14 % of applied S-Metolachlor is retained in the soil, and around 85 % is degraded into TPs in the different scenarios. In very dry and high-temperature scenarios, degradation is higher, and hence, there is less S-Metolachlor in the soil. However, a large share of formed M-OXA and M-ESA are retained in the soil, which is transported via overland and groundwater flow, leading to a build-up effect in M-OXA and M-ESA river concentrations over the years. Though a small share of S-Metolachlor and TPs are transported to rivers, their river export is affected by the intensity and amount of rainfall. The very wet and high-temperature scenarios show higher S-Metolachlor and TP concentrations at the catchment outlet due to higher river discharge. The reference scenario shows higher river peak concentrations associated with higher overland flow caused by measured hourly rainfall compared to disaggregated daily precipitation data in the other scenarios.

•Fate and transport of agrochemicals and TPs under extreme climate events is studied.•Climate model outputs are coupled to Zin-AgriTra model in four simulation scenarios.•Very wet scenario shows higher S-metolachlor river concentrations.•High-temperature scenarios show higher agrochemical degradation.•Intense hourly rainfall causes peaks in agrochemical river concentrations.

Fate and transport of agrochemicals and TPs under extreme climate events is studied.

Climate model outputs are coupled to Zin-AgriTra model in four simulation scenarios.

Very wet scenario shows higher S-metolachlor river concentrations.

High-temperature scenarios show higher agrochemical degradation.

Intense hourly rainfall causes peaks in agrochemical river concentrations.