Ambiguous agricultural drought: characterising soil moisture and vegetation droughts in Europe from earth observation

Abstract. Climate change will likely lead to more regular and more severe drought events in the near future, with large impacts on agriculture, especially during long-lasting precipitation deficits or heat waves. This study focuses on agricultural droughts, which are generally defined as soil moisture deficits so severe, that vegetation is negatively impacted. However, during short soil moisture drought events, vegetation is not always negatively affected, and sometimes even thrives under these conditions. Because of this duality in agricultural drought impacts, the use of the term agricultural droughts is ambiguous. Here we show that, in major European droughts over the past two decades, clear asynchronies and discrepancies occur between soil moisture and vegetation anomalies. A clear delay is visible between the onset of soil moisture drought and vegetation drought, and correlation between the two types of drought generally peaks at the end of the growing season. This behaviour seems to be different in droughts at lower latitudes, where correlations peak earlier in the season, likely due to water limited conditions occurring much earlier there. Moreover, results indicate that in some cases, vegetation can show a positive anomaly, even when soil moisture anomalies are negative. As a result, the use of the term agricultural drought could lead to misclassification of drought events and false drought alarms depending on whether vegetation or soil moisture is used to quantify the drought. We argue that it is necessary to make a distinction between soil moisture drought and anomalies in vegetation.