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Abstract. Forests serve as a natural means of protection against small rockfalls. Due to their barrier effect, they reduce the intensity and the propagation probability of falling rocks and thus reduce the occurrence frequency of a rockfall event for a given element at risk. However, despite established knowledge on the protective effect of forests, they are generally neglected in quantitative rockfall risk analyses. Their inclusion in quantitative rockfall risk assessment would, however, be necessary to express their efficiency in monetary terms and to allow comparison of forests with other protective measures, such as nets and dams. The goal of this study is to quantify the effect of forests on the occurrence frequency and intensity of rockfalls. We therefore defined an onset frequency of blocks based on a power-law magnitude–frequency distribution and determined their propagation probabilities on a virtual slope based on rockfall simulations. Simulations were run for different forest and non-forest scenarios under varying forest stand and terrain conditions. We analysed rockfall frequencies and intensities at five different distances from the release area. Based on two multivariate statistical prediction models, we investigated which of the terrain and forest characteristics predominantly drive the role of forest in reducing rockfall occurrence frequency and intensity and whether they are able to predict the effect of forest on rockfall risk. The rockfall occurrence frequency below forested slopes is reduced between approximately 10 and 90 % compared to non-forested slope conditions; whereas rockfall intensity is reduced by 10 to 70 %. This reduction increases with increasing slope length and decreases with decreasing tree density, tree diameter and increasing rock volume, as well as in cases of clustered or gappy forest structures. The statistical prediction models reveal that the cumulative basal area of trees, block volume and horizontal forest structure represent key variables for the prediction of the protective effect of forests. In order to validate these results, models have to be tested on real slopes with a wide variation of terrain and forest conditions.

The initial employment of tree rings in natural hazard studies was simply as a dating tool and rarely exploited other environmental information and records of damage contained within the tree. However, these unique, annually resolved, tree-ring records preserve valuable archives of past earth-surface processes on timescales of decades to centuries. As many of these processes are significant natural hazards, understanding their distribution, timing and controls provides valuable information that can assist in the prediction, mitigation and defence against these hazards and their effects on society. Tree Rings and Natural Hazards provides many illustrations of these themes, demonstrating the application of tree rings to studies of snow avalanches, rockfalls, landslides, floods, earthquakes, wildfires and several other processes. Several of the chapters are "classic studies", others represent recent applications using previously unpublished material. They illustrate the breadth and diverse applications of contemporary dendrogeomorphology and underline the growing potential to expand such studies, possibly leading to the establishment of a range of techniques and approaches that may become standard practice in the analysis of natural hazards in the future.

This paper reports on the conclusions of a workshop dedicated to science and data gaps in EU-funded projects relevant to water resources and water management, where over 25 EU projects were represented. Institutional and financial obstacles to data access for use in modeling exercises were identified, and gaps in scientific knowledge that contribute to uncertainty were highlighted. The paper identifies a number of sectors where these gaps often represent crucial barriers to successful research outcomes, and suggests ways and means of alleviating some of these difficulties. One approach could be through the implementation of policies aimed at ensuring free and unrestricted access to data, especially those generated by the numerous research projects that focus on issues of water availability, quality and management. Another complementary initiative could be the setting up of a centralized ''clearinghouse'' for data exchange between scientists, end-users and policymakers. It is hoped that, if implemented, some of the recommendations formulated in the present paper may help pave the way for a more rapid and efficient production of research results that are of importance for policy guidance at the local, national and supra-national (EU) levels.