Altered energy partitioning across terrestrial ecosystems in the European drought year 2018

Abstract

Drought and heat events, such as the 2018 European drought, interact with the exchange of energy between the land surface and the atmosphere, potentially affecting albedo, sensible and latent heat fluxes, as well as CO 2 exchange. Each of these quantities may aggravate or mitigate the drought, heat, their side effects on productivity, water scarcity and global warming. We used measurements of 56 eddy covariance sites across Europe to examine the response of fluxes to extreme drought prevailing most of the year 2018 and how the response differed across various ecosystem types (forests, grasslands, croplands and peatlands). Each component of the surface radiation and energy balance observed in 2018 was compared to available data per site during a reference period 2004–2017. Based on anomalies in precipitation and reference evapotranspiration, we classified 46 sites as drought affected. These received on average 9% more solar radiation and released 32% more sensible heat to the atmosphere compared to the mean of the reference period. In general, drought decreased net CO 2 uptake by 17.8%, but did not significantly change net evapotranspiration. The response of these fluxes differed characteristically between ecosystems; in particular, the general increase in the evaporative index was strongest in peatlands and weakest in croplands. This article is part of the theme issue ‘Impacts of the 2018 severe drought and heatwave in Europe: from site to continental scale’.

Spring enhancement and summer reduction in carbon uptake during the 2018 drought in northwestern Europe

“…This positive spring anomaly was also detected independently in eddy-covariance data, remote sensing products, biosphere model results, and in the CarbonTracker data assimilation system as constrained by CO 2 observations from an extensive tower network. As warm conditions persisted, and possibly fed by a positive land-atmosphere feedback discussed in various publications [59][60][61][62][63], soil moisture levels continually decreased to a point where photosynthesis, latent heat release, and to a lesser degree ecosystem respiration, fell well below normal summer values [47,64]. The eventual cancellation of this early spring and late summer anomalous carbon uptake during warmer and dryer years agrees with the analyses of Bastos et al and Kowalska et al [27,65], as well as that of Angert et al [66], who have suggested such a possible tradeoff in response to slow climate warming.…”

Improving the representation of cropland sites in the Community Land Model (CLM) version 5.0

“…The use of cover crops is a common agricultural management practice to reduce soil erosion, soil compaction, and nitrogen leaching and to increase agricultural productivity by nitrogen fixation (Sainju et al, 2003;Lobell4 et al, 2006;Basche et al, 2014;Plaza-Bonilla et al, 2015;Tiemann et al, 2015;Kaye and Quemada, 2017). The biogeochemical effects and benefits of cover crops, as well as their potential to mitigate climate change, are the focus of many studies (e.g., Sainju et al, 2003;Lobell et al, 2006;Groff, 2015;Plaza-Bonilla et al, 2015;Basche et al, 2016;Carrer et al, 2018;Lombardozzi et al, 2018;Hunter et al, 2019). Despite recent development efforts, the representation of these management practices has not yet been included in CLM5.…”

Soil Nitrogen Dynamics in a Managed Temperate Grassland Under Changed Climatic Conditions

“…Indeed, as found by Rahmati et al [37], there has been, since 2015, a decrease in the minimum soil water content of both sites. The year 2018 was also an especially warm, sunny, and rain-deficient year [37,38]. Moreover, we could observe that both sites suffer from a net loss of N. This shows that the current status corresponds to a transitory period.…”

“…We also compare observations from 2018, an especially dry year in Germany [38], with observations from wetter years.…”