Compared to research on eutrophication in lakes, there has been significantly less work carried out on rivers despite the importance of the topic. However, over the last decade, there has been a surge of interest in the response of aquatic plants to eutrophication in rivers. This is an area of applied research and the work has been driven by the widespread nature of the impacts and the significant opportunities for system remediation. A conceptual model has been put forward to describe how aquatic plants respond to eutrophication. Since the model was created, there have been substantial increases in our understanding of a number of the underlying processes. For example, we now know the threshold nutrient concentrations at which nutrients no longer limit algal growth. We also now know that the physical habitat template of rivers is a primary selector of aquatic plant communities. As such, nutrient enrichment impacts on aquatic plant communities are strongly influenced, both directly and indirectly, by physical habitat. A new conceptual model is proposed that incorporates these findings. The application of the model to management, system remediation, target setting, and our understanding of multi-stressor systems is discussed. We also look to the future and the potential for new numerical models to guide management.
The effect of climate change on agriculture in the UK is here assessed using a comprehensive series of policy-relevant agro-climate indicators characterising changes to climate resources and hazards affecting productivity and operations. This paper presents projections of these indicators across the UK with gridded observed data and UKCP18 climate projections representing a range of greenhouse gas emissions scenarios. The projections can be used to inform climate change mitigation and adaptation policy. There will be substantial changes in the climate resource and hazard across the UK during the twenty-first century if emissions continue to follow a high trajectory, and there will still be some changes if emissions reduce to achieve international climate policy targets. Growing seasons for certain crops will lengthen, crop growth will be accelerated, and both drought and heat risks (for some types of production) will increase. Soils will become drier in autumn, although there will be less change in winter and spring. The longer growing seasons and warmer temperatures provide opportunities for new crops, subject to the effects of increasing challenges to production. Most of the changes are relatively consistent across the UK, although drought risk and heat stress risk increase most rapidly in the south and east. The climate change trend is superimposed onto considerable year to year variability. Although there is strong consensus across climate projections on the direction of change, there is considerable uncertainty in the rate and magnitude of change for a given emissions scenario. For the temperature-based indicators, this reflects uncertainty in climate sensitivity, whilst for the precipitation-based indicators largely reflects uncertainty in projected changes in the weather systems affecting the UK.
Assessments of the impacts of climate change are typically made using climate scenarios based on assumptions about future emissions of greenhouse gases, but policymakers and climate risk communicators are increasingly asking for information on impacts at different levels of warming. This paper provides this information for a set of indicators of climate risks in the UK for levels of warming up to 4 °C above pre-industrial levels. The results show substantial increases in climate risks at 2 °C, which is often inferred in the media to be a ‘safe’ level of climate change. In a 2 °C world, the chance of a heatwave is doubled, and the frequency of heat stress affecting people, crops and animals can be increased by a factor of five. Cooling degree days more than double, wildfire danger can increase by 40%–70%, the frequency of agricultural and water resources droughts doubles in England, and flood frequency in Wales increases by 50%. At 4 °C the increases in risk are considerably greater: heatwaves occur in virtually every year. The frequency of cold weather extremes reduces, but is not eliminated, with increasing warming. The rate of change in an indicator with warming varies across the UK. For temperature-based indicators this reflects variability in current climate, but for rainfall-based indicators reflects variations in the change in climate. Most indicators show a generally linear increase in risk with level of warming (although the change in risk from now is around 2.4 times higher in a 4 °C world than a 2 °C world because of warming experienced so far). However, some indicators—particularly relating to heat extremes—show a highly non-linear increase with level of warming. The range in change in indicator at a given level of warming is primarily caused by uncertainty in the estimated regional response of to increasing forcing.
The UK is vulnerable to wildfire, and vulnerability is likely to increase due to climate change. Whilst the risk is small compared with many other countries, recent fires have raised awareness and highlighted the potential for environmental damage and loss of property and key infrastructure. Most UK wildfires are a result of inadvertent or deliberate human action, but the environmental conditions depend on antecedent and current weather. This paper presents projections of the effects of climate change on UK wildfire danger, using a version of an operational fire danger model, UKCP18 climate projections representing low and high emissions, and several indicators of fire danger. Fire danger will increase across the whole of the UK, but the extent and variability in change varies with indicator. The absolute danger now and into the future is greatest in the south and east (the average number of danger days increases 3–4 times by the 2080s), but danger increases further north from a lower base. The variation in change across the UK for indicators based on absolute thresholds is determined by how often those thresholds are exceeded now, whilst the (lesser) variability in percentile-based indicators reflects variability in the projected change in climate. Half of the increase in danger is due to increased temperature, and most of the rest is due to projected reductions in relative humidity. Uncertainty in the magnitude of the change is due to uncertainty in changes in temperature, relative humidity, and rainfall, and there is a large difference between two of the UKCP18 climate model ensembles. Reducing emissions to levels consistent with achieving international climate policy targets significantly reduces, but does not eliminate, the increase in fire danger. The results imply that greater attention needs to be given to wildfire danger in both emergency and spatial planning, and in the development of guidelines for activities that may trigger fires. They suggest the need for the development of a fire danger system more tailored to UK conditions, and the combination of fire danger modelling with projections of sources of ignition to better estimate the change in wildfire risk.
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