Earth observation reveals reduced winter wheat growth and the importance of plant available water during drought

Drought poses increasing challenges to global food production. Knowledge about the influence of drought on crop development and the role of soil properties for crop drought severity is important in drought risk analysis and for mitigating drought impacts at the landscape level. Here, we tested if satellite images from Sentinel-2 could be used to assess the impacts of drought on crop development and the influence of soil properties on crop drought responses at the landscape scale and what the responses were. As a case study, we assessed winter wheat growth on 13 fields belonging to commercial farmers in southern Sweden in a dry year (2018) and in a year with normal weather conditions (2021). To track crop growth, the green leaf area index (GLAI) was estimated from satellite imagery using a radiative transfer model. Proxies for winter wheat growth rate, peak GLAI, and the timing of peak GLAI were derived from the GLAI development at the single-field level. We then compared the crop growth proxies between the 2 years and related the year-to-year differences between fields to measured soil properties. We found lower estimated growth rates, lower peak GLAI, and earlier peak GLAI in the dry year compared to the year with normal weather conditions. A higher peak GLAI in the dry year was related to a higher growth rate, and this was not shown in the year with normal precipitation. Differences in crop development between years were large for some fields but small for other fields, suggesting that soil properties play a role in crop response to drought. We found that fields with a higher plant available water capacity had a higher growth rate in the dry year and smaller relative differences in growth rate between the 2 years. This shows the importance of soils in mitigating drought conditions, which will likely become more relevant in an increasingly drier climate. Our case study demonstrates that satellite-derived crop growth proxies can identify crop responses to drought events and that satellite imagery can be used to discover impacts of soil properties on crop development at scales relevant to commercial farming.