Context

Precipitation and temperature are the most important variables to determine the agricultural production. Combined effects of less precipitation amounts and more extreme events, higher temperatures and atmospheric CO₂ concentrations, highly influences crop yield European Environment Agency., 2019. Climate scenarios show that agricultural conditions will improve in some regions of northern Europe, but crop productivity will half in southern Europe by 2050, especially in non-irrigated crops like wheat, corn and sugar beet De Ridder et al., 2020. Unique climatic anomalies in 2018 caused severe crop yield reductions up to 50% due to dry conditions in northern Europe while excess rainfall in southern Europe produced up to 34 % yield increase, compared with the previous 5-year average Toreti et al., 2019. According to Statbels’ Land- En Tuinbouwbedrijven in Belgium, the drought in spring/summer 2018 led to high yield reductions in important crops compared to the previous year: -31 % in potatoes, -34 % in grain maize, and -13 % in sugar beet. In contrast, yield decreases in 2021 in winter wheat (-12.5 %), spelt (-10.8 %) and triticale (-20.7 %) were caused by wet conditions. Since climate change scenarios point towards an increase of precipitation and temperature extremes, there is a call for urgent adaptation strategies in agricultural practices and water resources management at landscape scale Toreti et al., 2019.

The European Agricultural Policy 2021-2027 European Environment Agency., 2019 proposes different adaptation measures at national, regional and farm levels to cope with the effects of Climate Change. Flood and drought management measures are not isolated and thus need to be integrated (Bressers et al., 2016). Several of these result in temporary or permanent increases of the water table, in and near land which is currently used by agriculture. Strategies include the restoration of floodplains near agricultural fields or land use change of those fields to natural retention areas against flooding. Other strategies involve restoration and sustainable management of former peatlands by stopping agricultural activities, peat extraction and drainage De La Haye et al., 2021. Drainage of wetlands for cities and intensive agriculture have led to an important increase in agricultural land, but also to new environmental problems. For example, oxidation and subsidence of peat soil converting drained peatlands in big carbon dioxide emitters and flood-prone areas Verhoeven & Setter, 2010. Since the decade of 1970, conservation policies for the wise use of wetlands were included in the 1971 Ramsar Convention European Commission, 2007, and currently large wetland recovery programs exists in The Netherlands, The U.K., Denmark, Germany, Belgium and other European countries Verhoeven, 2014. The Care-Peat, Carbon Connects, and the Life Peat Restore programs are some European examples De La Haye et al., 2021.

Rewetting and restoring wetlands provide many services such as drinking water supply, groundwater recycle, CO2 fixation and storage, and biodiversity and aquatic life Verhoeven, 2014Commission, 2007. Benefits to agriculture include water supply for irrigation, water table stability and nutrient retention (floodplains), increasing the buffer capacity against flooding and drought, crucial problems nowadays due to climate change. Some disadvantages for agriculture could also arise and reduce crop yield due to excess soil moisture or waterlogging (direct effects), cause cultivation problems and increase disease pressure (indirect effects).

The Flemish coalition agreement 2019-2024 focuses on preventive and adaptative measures, and places a strong emphasis on increasing our resilience to drought, including the active use of a resilient space with (extra) nature to mitigate the effects of climate change. The Blue Deal plan aims to create additional wet nature or restore/remediate drained wetlands to promote infiltration and water storage, in about 38 locations in Flanders. This means that farmers and policy-makers do not only need to adapt to an increased occurrence of droughts, but probably also to the impacts of excessive soil water. However, little information is available to estimate the impact of shallow groundwater levels on agriculture due to the implementation of these adaptation measures.

Objectives¶

The main objective of this research is to determine the impact of groundwater levels on the yield of common crops in Flanders. Specific objectives include:

1. Perform a systematic literature review on impact estimation of rewetting in agriculture and soil electrochemical processes as well as new crops adapted to wet conditions.
2. Develop a modelling framework using the model SWAP-WOFOST, adapted to Flemish conditions, to evaluate quantitatively the impact of groundwater levels on most common crops in Flanders.
3. Apply the model framework in the case study “De Zegge”.
4. Perfom a plausibility check of the model to evaluate whether it can give acceptable results in the Flemish context.
5. Make the model freely available and documented for interested parties.