Earth observation reveals reduced winter wheat growth and the importance of soil water storing capacity during drought

Abstract. Drought poses increasing challenges to global food production. Knowledge about the influence of drought on crop development and about the role of soil properties in drought risk analysis and mitigating drought impacts at the landscape level is important to guide climate change adaptation. Satellite earth observations can provide area-wide insights into crop growth processes that may help identify risk factors and quantify vulnerability to drought. Here, we evaluate the potential of Sentinel-2 to reveal interactions of plant-growth and soil parameters during variable weather conditions. As a case study, we assess winter wheat growth on 13 fields belonging to commercial farmers in southern Sweden in a dry year and a year with normal weather conditions. To track crop growth, 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 two years and across the fields and related them to measured soil properties. We found a lower growth rate, lower peak GLAI and earlier peak GLAI in the dry year compared to the year with normal weather conditions. An increase in peak GLAI in the dry year was also shown to be 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 amount of plant available water capacity had better crop performance in the dry year and smaller relative differences in growth rate between the two years. The observed lower growth rate, lower peak GLAI, and earlier peak in the dry year compared to the year with normal weather conditions, demonstrate that satellite imagery can be used to quantify plant-soil-weather interactions at scales relevant to commercial farming. Our investigation serves as a first step towards supporting drought risk management, drought adaptation and communication activities on this important topic.