Abstract
Abstract. The soil moisture status near the land surface is a key determinant of vegetation productivity. The critical soil moisture content determines the transition from an energy-limited to a water-limited evapotranspiration regime. This study quantifies the critical soil moisture content by comparison of in situ soil moisture profile measurements of the Raam and Twente networks in the Netherlands, with two satellite-derived vegetation indices (near-infrared reflectance of terrestrial vegetation, NIRv, and vegetation optical depth, VOD) during the 2018 summer drought. The critical soil moisture content is obtained through a piece-wise linear correlation of the NIRv and VOD anomalies with soil moisture on different depths of the profile. This non-linear relation reflects the observation that negative soil moisture anomalies develop weeks before the first reduction in vegetation indices: 2–3 weeks in this case. Furthermore, the inferred critical soil moisture content was found to increase with observation depth, and this relationship is shown to be linear and distinctive per area, reflecting the tendency of roots to take up water from deeper layers when drought progresses. The relations of non-stressed towards water-stressed vegetation conditions on distinct depths are derived using remote sensing, enabling the parameterization of reduced evapotranspiration and its effect on gross primary productivity in models to study the impact of a drought on the carbon cycle.
Highlights
Droughts can have wide environmental and socio-economic impacts, ranging from their effects on climate, the carbon cycle, and food security to water availability
vegetation optical depth (VOD) shows a similar response to near-infrared reflectance of terrestrial vegetation (NIRv); yet the VOD anomalies exceed the climatological values during the start of the summer
The decrease in soil moisture proceeded into deeper layers with time as a consequence of root water uptake shifting predominantly to those layers
Summary
Droughts can have wide environmental and socio-economic impacts, ranging from their effects on climate, the carbon cycle, and food security to water availability. Droughts are typically induced by a lack of precipitation and/or an aboveaverage atmospheric demand for evapotranspiration (ET), which leads to an associated reduced availability of soil moisture in the root zone (Seneviratne et al, 2010; Teuling, 2018). The former is typically referred to as meteorological drought, whereas the latter is referred to as agricultural drought. Reduction in ET through the closing of plants’ stomata affects the carbon cycle by reducing gross primary productivity (GPP) (van der Molen et al, 2011; Reichstein et al, 2013).
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