Land‐Atmosphere Interactions Exacerbated the Drought and Heatwave Over Northern Europe During Summer 2018

Abstract

The summer of 2018 saw a combination of drought and heat concentrated over northern Europe. The conditions had far-reaching economic and ecological impacts, with spring and summer dryness affecting crops and natural vegetation, leading to increased tree and forest mortality, and unprecedented wildfires in Sweden (Albergel et al., 2019;Rösner et al., 2019). The summer of 2018 was among the warmest, sunniest, and driest on record in the UK (Kendon et al., 2019). Figure 1 quantifies the drought and heatwave, showing the fraction of the 122 days spanning May through August 2018 that lie within the indicated tails of maximum 2 m air temperature anomalies and surface (top 7 cm) volumetric soil water content (VWC), based on the European Centre for Medium-range Weather Forecasts (ECMWF) fifth reanalysis (ERA5) from 1979 to 2018 (Hersbach et al., 2020). One would expect by chance a value of 0.05 at any location in the maximum temperature plot, and 0.25 for VWC. There is strong spatial correspondence between the two panels, but the core

COSMOS-UK: national soil moisture and hydrometeorology data for environmental science research

“…COSMOS-UK data could also provide insight into alternative scientific research, such as the relationship between soil moisture and pest behaviour (Hertl et al, 2001), the impact of soil moisture on local infrastructure (Pritchard et al, 2013), investigation of ground-level cosmic ray events (Flückiger et al, 2005), and meteorological data with respect to bacterial infection seasonality (Djennad et al, 2019).…”

When the Land Surface Shifts Gears

“…The results of Dirmeyer et al (2021) illustrate that hot spot regions of land-atmosphere coupling can occur in comparatively wet and cold climate in the case of extreme events. The strong coupling, which is well known to occur in semiarid regions (Koster et al, 2004), thereby shifts and extends to humid regions (Seneviratne et al, 2006).…”

“…However, the 2018 summer drought introduced water-limited conditions to Great Britain and large parts of Northern Europe (Dirmeyer et al, 2021). Thereby, this region became a hot spot of land-atmosphere interactions; in addition to the prevailing impact of the meteorological conditions on soils and vegetation (atmosphere → land), soil moisture availability affected vegetation functioning and therefore evapotranspiration and the (near-surface) atmospheric moisture and energy budgets (land → atmosphere).…”

“…Soil moisture is a key variable controlling the land-atmosphere coupling regime and its strength (Seneviratne et al, 2010). Dirmeyer et al (2021) determine soil moisture thresholds across Europe, below which evaporative cooling becomes water-limited, enhancing peak temperatures. These thresholds vary in space, highlighting the role of vegetation and soil types in modulating land-atmosphere interactions (Denissen et al, 2020).…”

“…The benefits of jointly analyzing measurements and model simulations in this context are demonstrated by Dirmeyer et al (2021); in situ measurements are limited in temporal and spatial coverage but represent ground truth and can be used to test how well models can represent the analyzed relationship and that their simulations can accordingly be employed to extend the analyses in time and space. Satellite and ground-based Earth observations of multiple variables are assimilated by models to yield high-quality reanalyses, as for example the ERA5 (Hersbach et al, 2020) used by Dirmeyer et al (2021). Furthermore, machine learning is an emerging tool in Earth system science (Reichstein et al, 2019) to derive large-scale data sets of, for example, soil moisture (O. S. & Orth, 2021) or evapotranspiration (Jung et al, 2019) by establishing relationships between respective in situ observations and meteorological data which are then used for spatiotemporal extrapolation.…”