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

Abstract

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.

Hydrological System Complexity Induces a Drought Frequency Paradox

“…Similar findings of increased evapotranspiration and vegetation productivity during drought in (pre-)Alpine regions were reported by Jolly et al (2005), Buitink et al (2018), andMastrotheodoros et al (2020). The complex and climate-dependent relation between soil moisture and vegetation provides an argument to consider vegetation and soil moisture separately in analyses of agricultural drought (van Hateren et al, 2020). Hydrological drought dynamics also differ from meteorological drought.…”

“…The region is small enough for the meteorological drought conditions to be fairly homogeneous (so spatial variability in other drought types is not induced by spatial variability in precipitation), yet large enough to have considerable variation in soil, vegetation, and drainage properties. The extensive groundwater system under the Veluwe Massif, where the depth to the groundwater table can reach tens of meters (Kumar et al, 2016) is an important resource for drinking water and irrigation (van Engelenburg et al, 2018), while its location downstream of three river basins (the Rhine, Meuse, and Berkel) makes it an important hub for shipping and surface water management. The three river systems vary considerably in size: 900 km 2 for the Berkel, 34,500 km 2 for the Meuse, and 185,000 km 2 for the Rhine.…”

Impact of the North Sea–Caspian pattern on meteorological drought and vegetation response over diverging environmental systems in western Eurasia

“…Previous studies examined the relationship between droughts and vegetation growth in water‐ and energy‐limited environments over Europe (Denissen et al, 2020; Peled et al, 2010; van Hateren et al, 2021). Peled et al (2010) and van Hateren et al (2021) found strong correlations between NDVI and drought indices in water‐limited environments.…”

“…Droughts are traditionally quantified by water availability indices, such as Standardized Precipitation Index (SPI) (Cancelliere et al, 2007; Livada & Assimakopoulos, 2007; McKee et al, 1993). Given the direct effects of droughts on vegetation, vegetation indices (van Hateren et al, 2021) have also been used as drought indicators (Buitink & Swank, 2020; Hu et al, 2019; Sepulcre‐Canto et al, 2012; Di Wu et al, 2015). However, there are various factors, such as warming temperatures (Peng et al, 2011; X. Wang et al, 2017; G. Xu et al, 2014), increasing solar irradiation (Teuling, 2013), and increasing CO 2 fertilization (Lian et al, 2021), which may lead the vegetation to be less affected by the declining water availability.…”

Machine Learning With GA Optimization to Model the Agricultural Soil-Landscape of Germany: An Approach Involving Soil Functional Types With Their Multivariate Parameter Distributions Along the Depth Profile

“…In today's agricultural landscapes in Central Europe and other parts of the world, we face multiple challenges for soil functionality impacting ecosystem services. In the last decades, drought events that empty the soils' water stores causing yield losses are becoming more frequent in Europe (van Hateren et al, 2020;Markonis et al, 2021). Inadequate agricultural management may lead to losses in soil organic carbon to the atmosphere, whereas the opposite can enhance carbon sequestration and, thereby, help to mitigate climate change (Liu et al, 2006;Wiesmeier et al, 2019).…”