Understanding drought risks for European ecosystems through conceptual risk models

Ecosystems in Europe are increasingly faced with more frequent and more intense drought events. The impacts of droughts do not only undermine ecosystem health and the provision of ecosystem services, but can lead to the deterioration of the system’s long-term resilience to droughts. In order to effectively assess, reduce, and manage the risks posed by droughts on ecosystems, it is first necessary to gain a thorough understanding of how droughts affect a particular ecosystem, what the underlying risk drivers and root causes are, and how these interact to produce that risk. 

Addressing this need, we have developed conceptual models of drought risks for two highly-relevant European ecosystem types, forest and freshwater ecosystems. The conceptual models were developed and visualized using the impact chain methodology, building on extensive literature review and expert consultations, and validated in a series of expert workshops. Following this process, the risks of decreased primary production, forest die-off, and soil degradation and desertification were identified for forest ecosystems, and the risk of disruption of environmental flow for freshwater ecosystems.

The resulting impact chains provide insights into how different climatic, ecological, and societal risk drivers interact to produce drought risks for ecosystems, with some drivers being specific to a certain risk (e.g. forest composition), and others shared across them (e.g. societal water demand and abstractions). While some of these drivers relate to purely ecological features (e.g. plant physiology or soil conditions), many relate to how ecosystems are managed, and to the influence of other sectors/systems upon them (e.g. hydropower, river transportation or intensive agriculture and their adverse effects on freshwater ecosystems). Moreover, the impact chains also highlight some of the root causes (e.g. increased demand for energy, farmers' lack of awareness about agriculture's impacts on freshwater ecosystems, or incentives to enhance navigability) behind these drivers, indicating potential entry points for risk reduction and adaptation. 

The visualization in impact chains is useful to enhance the understanding and at the same time break down the complexity of the risks for these systems, which can support data-driven risk assessment, as well as the identification of entry points for risk management and adaptation. 

While in this work the risks posed by droughts for forests and freshwater ecosystems were assessed on European level, the impact chain approach presented here can be used at different scales and transferred to different ecosystems at risk from droughts. Moreover, it can be used to identify common risk drivers between ecosystems that could be addressed jointly, contributing to a more systemic drought risk management.