Expertise
More water for crop production? – Challenges and approaches
Nataliya Stupak, Thomas de Witte | 04.05.2023
Water demand in German plant production is likely to increase as a consequence of climate change. Thünen Institute investigates how water demand will develop in the future, and which approaches can be used to secure future water supply for plant production.
Sufficient water supply is the basis for successful plant production. Plant production – in particular crop production – in Germany is rainfed except for several historically evolved irrigation regions. Advancing climate change influences precipitation patterns.
Seasonal and interannual precipitation changes can be already observed. Future development of precipitations, especially within the growing season, is highly uncertain. Current climate projections by the German Meteorological Service (DWD) suggest that annual rainfall in the country won’t change up to 2050. At the same time the alteration of seasonal precipitations is to be expected. Specifically, the rainfall in autumn and winter months is likely to increase by 2-8%, and in spring – up to 7%. No significant changes in the amount of summer precipitations within the same time horizon have been so far determined. However, the projected development of spring rainfall is subject to uncertainties with regard to the trend of increasing spring droughts observed within the last years. Additionally, water supply in summer months is likely to become more limiting factor for arable farming in some regions due to spatial change in precipitations and increasing frequency of extreme weather events.
Water supply of cultivated plants depends not only on the amount of precipitations, but also on their form and the evaporation, the latter being determined by temperature. According to the DWD, precipitations in form of heavy rain will increase by 5-15% in Germany. Such events lead to high run-off and to lower water infiltration and retention in soils causing negative effects on water availability for plants.
Drought stress driven by increasing summer temperatures
The following maps demonstrate that increasing summer temperatures can lead to negative development of climatic water balance in the growing season in spite of consistent rainfall. If climate mitigation does not succeed, many German regions will experience the decrease of climatic water balance in summer by 50-75 mm/m2. Even in case of the more optimistic climate scenario the decline of climatic water balance by 25mm/m2 in some important crop production areas is to be expected. As a consequence, water demand for plant production and the risk of summer droughts will increase.
Already within the last years agricultural producers in some German regions experienced significant yield losses due to extreme weather events. In particular extreme heat and extreme drought have been responsible for the major economic losses in the production of wheat, barley, rapeseed, corn, potatoes and sugar beets on average for the last 25 years. Wheat production was affected by heat and drought in Saxony-Anhalt, Brandenburg and northwest Bavaria/Franconia. In the northern farming regions considerable losses in rapeseed were caused by extreme heat. Further details on the previous damages in crop production due to extreme weather events are to be found in Söder et al. 2022 and Schmitt et al. 2022.
In this context the Thünen Institute focuses on the development of water management concepts which would allow sufficient water supply for future plant production. For this purpose, it is essential to provide an overview of water availability from different sources as well as of the current and future water demands. The Thünen Institute contributes to this task with its nationwide analysis of irrigation demand within the LAWAMAD subproject C. On the regional scale irrigation requirements for Bavaria have been already determined. The results of this study suggest that medium irrigation requirement for all considered crops is expected to increase by 19% till 2050 compared to the time period 1991-2020. Currently, irrigation requirements of agriculture in Hesse is being analysed.
Though irrigation is one of the most effective measures to counter drought stress, it can lead to conflicts of interests about limited water resources with other water users, in particular if irrigation affects the levels of groundwater and surface waters. Further information on potential conflict of interests between agricultural production and water management is provided in the report of the LAWA working group (in German).
Water retention reservoirs
Water retention reservoirs, which are the focus of the joint project LAWAMAD, have the potential to reduce such conflicts of interests. The reservoirs can be filled in with rainwater or with extractions from surface waters in the autumn and winter months in order to use the retained water for irrigation in the growing season.
Within the LAWAMAD project long-term water retention needs for selected landscape areas are being modelled, relevant water reservoirs of various volumes and designs are being developed, and their costs and benefits are being analysed. So far the construction of water retention reservoirs is profitable for irrigation in horticulture and of special crops. In case of arable farming, a water retention reservoir for irrigation of potatoes can be economically viable. In cooperation with Fraunhofer Institute for Solar Energy Systems the option of the floating photovoltaic systems on water reservoirs and its effects on water savings through reduced evaporation and profitability of reservoirs are being analysed.
