Quantifying heat vs. drought-induced yield decline of German cropping systems and the mitigating potential of irrigation

Accurately modelling crop yield reductions from heat and drought stress is essential for predicting how a changing climate will impact future crop production. Here we demonstrate the capability of the biogeochemical model LandscapeDNDC to simulate recent crop yields across Germany, including the extreme drought year 2018, when crop yields fell 25 % below the long-term average. 
This is achieved via a two-step calibration process, in which key model parameters governing the growth of wheat and maize (the two major crops in Germany) are optimised to simulate crop yields in both stressed and unstressed conditions. We show that recent yield losses in Germany were predominantly caused by drought stress. Consequently, yield losses could have been largely eliminated through irrigation, with an average of 156 ± 60 mm of water in 2018 across Germany necessary. We show that irrigation demand increases exponentially with decreasing plant available water, indicating that the importance of this mitigation measure will grow under future climate conditions.
The biogeochemical models’ ability to accurately capture the consequences of recent extreme climatic events on crop yields makes it a suitable candidate for evaluating the implications of climate change on both crop production and, more generally, on the carbon, nitrogen and water cycles of cropping systems in Central Europe.