Palaeoclimate reconstructions extend our knowledge of how climate varied in times before expansive networks of measuring instruments became available. These reconstructions are founded on an understanding of theoretical and statistically-derived associations acquired by comparing the parallel behaviour of palaeoclimate proxies and measurements of varying climate. Inferences about variations in past climate, based on this understanding, necessarily assume that the associations we observe now hold true throughout the period for which reconstructions are made. This is the essence of the uniformitarian principle. In some northern areas of the world, recent observations of tree growth and measured temperature trends appear to have diverged in recent decades, the so called 'divergence' phenomenon. There has been much speculation, and numerous theories proposed, to explain why the previous temperature sensitivity of tree growth in these areas is apparently breaking down. The existence of divergence casts doubt on the uniformitarian assumption that underpins a number of important tree-ring based (dendroclimatic) reconstructions. It suggests that the degree of warmth in certain periods in the past, particularly in medieval times, may be underestimated or at least subject to greater uncertainty than is currently accepted. The lack of a clear overview of this phenomenon and the lack of a generally accepted cause had led some to challenge the current scientific consensus, represented in the 2007 report of the IPCC on the likely unprecedented nature of late 20th century average hemispheric warmth when viewed in the context of proxy evidence (mostly from trees) for the last 1300 years. This project will seek to systematically reassess and quantify the evidence for divergence in many tree-ring data sets around the Northern Hemisphere. It will establish a much clearer understanding of the nature of the divergence phenomenon, characterising the spatial patterns and temporal evolution. Based on recent published and unpublished work by the proposers, it has become apparent that foremost amongst the possible explanations is the need to account for systematic bias potentially inherent in the methods used to build many tree-ring chronologies including many that are believed to exhibit this phenomenon. This proposal is designed to build on recent innovations in tree-ring chronology production techniques, also developed by the proposers. These new methods will produce tree-ring chronologies whose variability is unbiased, either by temporal changes in the age structure of the constituent sample series, or by any distortion in the data that can arise when using the previously applied techniques. The extensive reprocessed and improved data sets will then form the basis for many detailed, site-by-site comparisons of local climate and various tree-growth parameters in order to re-characterise the nature, strength and temporal stability of the climate/growth associations. This will represent a systematic and objective re-assessment of the evidence for divergence in different forest contexts. The project will then explore all of the current theories for the cause(s) of divergence employing both statistical and process-modelling techniques. The project will go on to use the reprocessed tree-ring data sets to re-calibrate many important climate reconstructions, with varying levels of spatial detail, and carefully assess the implications of the divergence effect, as newly characterised, on reconstruction uncertainty. This project will provide results that will inform the international scientific debate and widespread public perception of the reliability of tree-ring-based climate reconstructions in particular, but also our current understanding of the reliability of current evidence for high-resolution temperature changes during the late Holocene.

Floods and landslides affect the UK every year, both inland and along the coast, causing disruption, occasional fatalities and severe economic loss. An increase in storminess under climate change and population pressure are resulting in an increase in landslide and flood hazards in the UK and globally and threatening the defences put in place to manage these hazards. Monitoring of unstable hillslopes and flood-prone rivers as well as defences designed to manage these is increasingly vital. Landslides and floods are both triggered by heavy rainfall, often occur at the same time, and may interact to generate a chain reaction of knock-on hazardous effects. SENSUM proposes a new integrated way to tackle these 'hydrogeological' hazards, taking advantage of advances in Wireless Sensor Network (WSN) and Internet of Things (IoT) technologies, microelectronics and machine learning. Those exciting new tools will be used to monitor the stability of defences, provide warnings of hazard events, and improve mathematical models and visualisation of hazardous phenomena. Landslides and floods have traditionally been monitored using a combination of satellite-based remote-sensing techniques and wired ground-based instruments to measure factors that control the related hazard, such as river flow level, displacement and soil moisture. Wireless sensor networks (WSNs) show great potential for monitoring and early warning of these hazards. Their main advantage is their use of easily deployable, low-power sensors enabling continuous, long-term, low-cost monitoring of the environment. For landslides and floods, which occur infrequently and unpredictably, this is an important technological advance. SENSUM proposes to develop innovative smart tracking devices, embedded in boulders and woody debris on hillslopes and in rivers to give real-time warning of movement related to landslide and flood processes. Collaborating closely with external partners, the team of experts in the SENSUM project will develop and test the tracking devices both in dedicated laboratory experiments and in the field, with the deployment of trial networks of smart boulders and woody debris in different localities in the UK and abroad. The large set of data obtained from sites and experiments will be used to improve mathematical models, to develop innovative early warning systems and in 3D digital visualisations. This integrated approach will enable us to establish a comprehensive understanding of landslide and flood processes which will significantly reduce risk to society. The SENSUM team is a diverse, interdisciplinary and multinational team made up of a range of environmental scientists and engineers, computer scientists and science communication specialists from three leading UK universities: University of Exeter, University of East Anglia and University of Plymouth and will involve several project partners including the Environment Agency, Forest England, Natural England and AECOM. It will work closely with these project partners to design an effective digital environment for monitoring and managing landslide and flood hazards in the UK, and to target applied risk management challenges. For example, in the UK, the Environment Agency is tasked with giving a 2-hour warning to the population affected by floods. However, these warnings are lacking in the upland areas of the UK's landscape due to a lack of instruments to monitor river flow. The smart tracking devices embedded within boulder and woody debris in landslides and river channels proposed by SENSUM will help address that limitation, and therefore will significantly improve early warning of movement and consequently the assessment of potential high-risk natural events. The team will also engage stakeholders and the general public through the creation of compelling visualizations of landslide and flood hazards and through project workshops and outreach activities.

Most plants do not produce regular annual seed crops, but switch between years of bumper seed crops (known as "mast years") and years with low seed production. Intriguingly, these bumper crops occur simultaneously in plants living alongside each other, and synchronisation can extend across hundreds of kilometres. For example, we have previously shown that in 1976, 1992, 1995 and most recently in 2011, beech trees across Western Europe (including the UK, Germany, France and Poland) all produced heavy seed crops in the same year. Interestingly, 1992 and 1995 were also bumper years for pine-cone production in spruce forests in the same region. This highly variable production of seeds is an important process in ecosystems. Producing seeds is a key step towards successfully establishing the next generation of plants. Masting is beneficial for plants because in years of bumper seed crops, seed predators cannot consume all the available seeds, which ensures that some survive to germinate the next spring. In ecosystems that are influenced by disturbance such as wildfires, windstorms and logging by humans, the timing of the next bumper seed year is also crucial to the ability of plants to regenerate. However, the importance of masting extends beyond plants. Bumper seed crops in forest trees represent a pulse of food resources, and cause population booms in small mammals (e.g. voles and mice) and seed-eating birds (e.g. woodpeckers and great tits). Low seed crops in sequential following years can eventually result in population crashes. These boom-and-bust cycles of small animals have further impacts on ecosystems. One of the most important for humans is the effect on tick numbers, which fluctuate in response to the number of host animals. Ticks act as a host for the Lyme disease pathogen, and research has shown that Lyme infection rates in humans peak two years after bumper seed crops in forest trees, including beech and oak. Masting is not just important in natural ecosystems, however. Many fruit and nut crops come from "masting" species. In agriculture, this phenomenon is usually known as "alternate cropping". Fruits grown in the UK, including apples and cherries, show this characteristic year-to-year variation in crop size, which causes variation in annual crop yield for farmers. It is also important in many other commercially valuable species, including olives, almonds and pistachios. For these reasons, we need to be able to predict seed crops in "masting" species accurately. This information is necessary for the management of natural ecosystems and agricultural systems that rely on masting species. Furthermore, predicting bumper seed crops will allow us to forecast years of high risk from infectious diseases carried by animal feeding vectors, such as Lyme. An important question is how seed production in masting species will change in the future with changes in climate. This project is designed as the first crucial step to achieving these objectives. It will establish an international network of researchers to build the datasets necessary to understand the causes of bumper seed crops, and to predict seed production in masting species. We will draw together data from the tropics with data from boreal forests to understand how masting varies between species, and will use long-term monitoring conducted by members of the network to understand how seed production varies over time, and what triggers bumper seed years. We will also search archives and scientific literature for useful data: in a previous project we found useful data on seed crops collected by 18th century foresters, demonstrating that in some species, there is potential to develop very long records of seed production. The datasets that we will build in this project will then act as a spring-board for future research, including projects linked to public health, habitat management, and agriculture, taking advantage of the wide range of network expertise.

Debris flows are natural hazards that threaten people and infrastructure in mountainous terrain. They are becoming more frequent due to the increasing number of high rainfall intensity events (Petely et al., 2012, Global patterns of loss of life from landslides. Geology 40, 927-930). The destructive potential of debris flows is strongly enhanced by the development of surge waves (Fig 3 + video), which concentrate the flow into large amplitude waves that often carry large rocks and boulders. Despite nearly forty years of research there is still a lack of understanding about why these waves form, as well as a dearth of good field data sets (in-situ measurements of active flow thickness and velocity) that can be used to test models. This severely limits the accuracy of debris-flow risk analysis, because current debris-flow models are not able to capture quantitatively these waves or the particle-size segregation that concentrates the largest particles in the deepest and fastest-flowing part of the flow. This proposal aims to make a major breakthrough in our ability to predict debris-flow surge wave formation by coupling (a) new innovations (hybrid LiDAR/HD video) in environmental sensing at the Illgraben debris-flow observation station in Switzerland with (b) recent theoretical advances in modelling nonlinear wave formation and particle-size segregation made in Manchester (Gray & Edwards 2014, Gray 2018, Rocha et al. 2019). The assembled research team is uniquely suited to address this question, as it combines a diverse range of experts who have a strong theoretical background as well as expertise in laboratory and field data collection. This will enable the team to integrate state-of-the-art in-situ data currently being collected at Illgraben (and improved on as part of this proposal) into cutting-edge theoretical and numerical models in order to generate a step change in our understanding of surge waves as well as new computational tools for use by the debris-flow community in hazard risk assessment.

During the recent two decades, drought has increased in intensity and frequency in some parts of the world and, in particular, in much of the Mediterranean. While many of the drought-adapted species of the Mediterranean have been reported to show reduced growth rates, the worry lies mostly with species, such as Scots pine, which are present across many of the mountain ranges of the Mediterranean (Pyrenees, Alps, Balcans, Anatolia), but are not really drought-adapted species. As a consequence, species such as Scots pine are currently the focus of much attention, as it has been shown to suffer from extensive mortality across the whole of the Mediterranean, with reported episodes of mortality spanning from Spain, Italy, Switezerland, Austria, Hungary up to Greece and Turkey. Many of these forests are now turning into scrublands consisting of small oaks and juniper, which possess a much higher resistance to drought, but with unknown consequences on the carbon and water cycles of these new ecosystems. In addition, the mortality of these forests is expected to accelerate in future decades, because increased drought is forecast as a result of climate change. Forests carry out a very important role in these countries, by regulating the water supply to the crowded cities of the coast. Forests in countries around the Mediterranean Sea are estimated to provide fundamental ecosystem services to ~0.4 billion people. Water supply in particular is dependent on the health, structure and functioning of forests, with the number of water-poor Mediterranean people now reaching ~180 million inhabitants. We aim to study the physiological causes underlining the observed processes of mortality for Scots pine across three sites spanning the whole of the Mediterranean, i.e., Spain, Switzerland and Turkey. This is of interest because 1) we need to understand exactly why trees die, and 2) we need to learn how to represent these mortality processes in global models, which are currently only very crudely include these processes. We also aim to study the degree by which the adaptations to heat and drought of this species vary across its various populations. For example, we want to know whether some of the populations from southern Scots pine (e.g., in Spain) are more adapted to heat and drought than more Nordic populations of Poland and of Finland. Because the range of this species is forecast to spread further north, it is of interest to understand whether the existing populations at any location in Europe will be well suited to the changed climatic conditions, or whether more Sourtherly populations will have to migrate Northward as the climate also shifts Northward. The findings of this project have direct interest to the strategies of conservation for other European countries, including the UK, because almost all plant species are forecast to move their ranges poleward and upward on the mountains as a result of climate change. In many of these cases, the movement is a direct result of the increased drought and heat conditions prevailing at the so-called trailing edge of the species distribution.