The Nordic region was subjected to severe drought in 2018 with a particularly long-lasting and large soil water deficit in Denmark, Southern Sweden and Estonia. Here, we analyse the impact of the drought on carbon and water fluxes in 11 forest ecosystems of different composition: spruce, pine, mixed and deciduous. We assess the impact of drought on fluxes by estimating the difference (anomaly) between year 2018 and a reference year without drought. Unexpectedly, the evaporation was only slightly reduced during 2018 compared to the reference year at two sites while it increased or was nearly unchanged at all other sites. This occurred under a 40 to 60% reduction in mean surface conductance and the concurrent increase in evaporative demand due to the warm and dry weather. The anomaly in the net ecosystem productivity (NEP) was 93% explained by a multilinear regression with the anomaly in heterotrophic respiration and the relative precipitation deficit as independent variables. Most of the variation (77%) was explained by the heterotrophic component. Six out of 11 forests reduced their annual NEP with more than 50 g C m⁻² yr⁻¹ during 2018 as compared to the reference year. The NEP anomaly ranged between −389 and +74 g C m⁻² yr⁻¹ with a median value of −59 g C m⁻² yr⁻¹.

This article is part of the theme issue ‘Impacts of the 2018 severe drought and heatwave in Europe: from site to continental scale’.

2018年北欧地区遭遇严重干旱，其中丹麦、瑞典南部和爱沙尼亚土壤缺水持续时间较长且严重。在这里，我们分析了干旱对 11 个不同组成的森林生态系统（云杉、松树、混合林和落叶林）碳和水通量的影响。我们通过估计 2018 年与无干旱参考年之间的差异（异常）来评估干旱对通量的影响。出乎意料的是，与参考年相比，2018 年两个地点的蒸发量仅略有减少，而所有其他地点的蒸发量均有所增加或几乎没有变化。这是在平均表面电导率下降 40% 至 60% 且由于天气温暖干燥而蒸发需求同时增加的情况下发生的。净生态系统生产力（NEP）的异常有 93% 可以通过以异养呼吸异常和相对降水赤字作为自变量的多元线性回归来解释。大部分变异（77%）是由异养成分解释的。与参考年相比，2018 年期间，11 个森林中有 6 个的年度 NEP 减少了超过 50 g C m ^-2 yr ^{-1 。}NEP异常范围在-389和+74 g C m ^-2 yr ^-1之间，中值为-59 g C m ^-2 yr ^-1。

本文是“2018 年欧洲严重干旱和热浪的影响：从地点到大陆规模”主题的一部分。