Role of low intensity environmental disturbance in structuring the earliest (Ediacaran) macrobenthic tiered communities

Rangeomorphs were important components of Ediacaran macrobenthic ecosystems, yet their biology and ecology remain poorly constrained. They formed high-density, tiered communities that were subjected to intermittent burial events, the largest of which killed entire communities. Abundant thin event beds in the Ediacaran succession of Charnwood Forest indicate the additional, frequent impact of minor obrution events. The type surface of Charnia masoni is immediately underlain by one such lamina (a tuff) and preserves a distinctly bimodal population. It is dominated by Charnia fronds that are of smaller or comparable length to the holotype (19.4 cm), but also includes notably larger specimens (> 45 cm) that would traditionally have been assigned to Charnia grandis. Multiple morphological- and morphometric parameters (length, width, spacing of primary branches) demonstrate that these are indistinguishable from the holotype of C. masoni, affirming the synonymy of the two taxa. Nevertheless, these outsized individuals are distinguished by their proportionally fewer primary branches per unit length. Taphonomic evidence indicates that they were survivors of an incumbent population, the rest of which was culled by a minor ashfall. We suggest that this temporary reduction in competition from neighbours allowed the survivors to grow larger and thereby gain access to a greater proportion of the water column. As the community recovered, their large size would have continued to provide them with an advantage, divorcing them from the density-dependent competition seen in the new understory. The interlude between cohorts implies that new recruits were substrate-sensitive, presumably awaiting re-establishment of the biomat. Sub-lethal disturbance events thus played a significant role in structuring Ediacaran communities, and help explain the observed bed-by-bed variability. Taken as a whole, the growth trajectory of C. masoni resembles that of extant organisms with indeterminate growth programmes and no genetically-controlled upper size limit

Regionalisation of climate impacts on flood flows to support the development of climate change guidance for Flood Management

Current Defra / Environment Agency guidance (FCDPAG3 supplementary note: http://www.defra.gov.uk/environ/fcd/pubs/pagn/climatechangeupdate.pdf) requires all flood management plans to allow for climate change by incorporating, within a sensitivity analysis, an increase in river flows of up 20% over the next 50 years, and beyond. This guidance is the same for all of England and Wales, making no allowance for regional variation in climate change or catchment type. This reflects the lack of scientific evidence to resolve the spatial distribution of potential impacts on flood flows with enough confidence to set such policy regionally. The 20% allowance was first raised in 1999 for MAFF and subsequently reviewed following the release of the UKCIP02 scenarios. Although the 20% figure is a memorable precautionary target, there is the risk that it leads to a significant under- or over-estimation of future flood risk in individual catchments. Defra and the Environment Agency procured project FD2020 (Regionalisation of climate change impacts on flood flows) to provide a more rigorous science base for refreshing the FCDPAG3: supplementary note guidance. The FD2020 approach is exploring the relationships between catchment characteristics and climate change impacts on peak flows in a “scenario neutral” way. This is done by defining a regular set of changes in climate that encompass all the current knowledge from the new scenarios available from the IPCC Fourth Assessment Report. For each of the 155 catchments included in the research, this broad approach will provide multiple scenarios to produce a “vulnerability surface” for change in the metrics of peak flows (e.g. the 20-year flood flow). Some of the UKCP09 products have also been used to understand what these projections may mean for changes to peak flow. The catchment-based analysis will be used to generalise to other gauged sites across Britain, using relationships with catchment characteristics, providing the scientific evidence for the development of regional guidance on climate change allowances. Specifically the project is: Investigating the impact of climate change on peak river flows in over 150 catchments across Britain to assess the suitability of the FCDPAG3 20% climate change allowance. Investigating catchment response to climate change to identify potential similarities such that the FCDPAG3 nationwide allowance could be regionalised. Investigating the uncertainty in changes to future peak river flows from climate change. Developing an approach that has longevity beyond the project timeframe and the lifetime of the latest generation of climate model results

Persistence of hydrometeorological droughts in the United Kingdom: a regional analysis of multi-season rainfall and river flow anomalies

This paper investigates the spatial and temporal properties of persistent meteorological and hydrological droughts in the UK at national to sub-regional scales. Using 1961–1990 as the reference period, it is shown that the longest observed run of below average rainfall since the 1870s persisted for four years in northern England and parts of Scotland during 1892–1896. The longest observed run of below average discharge since the 1950s/1960s was found for some groundwater fed rivers in the English lowlands and lasted up to 5.5 years during 1988–1993. Distributions of dry-spell lengths were represented by a Markov model fit to each rainfall and discharge record. This model provides a good fit to observed geometric distributions of spell lengths and provides credible runs of below average river flows lasting up to a decade in some vulnerable catchments in southern England. Droughts of this persistence may not yet have occurred within the instrumented record but could have profound water management implications for the region. Predicted 100-year drought durations for catchments in northern England may not be as long but could have serious ramifications for surface water supplies. These findings point to a risk of irreversible drought impacts on aquatic communities that are simultaneously stressed by unsustainable abstractions, poor water quality and/or habitat modifications

Nocturnal river water temperatures: spatial and temporal variations

NOTICE: this is the author’s version of a work that was accepted for publication in Science of the Total Environment. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Science of the Total Environment, vol 482-483, June 2014, DOI: 10.1016/j.scitotenv.2014.02.123Nocturnal water temperature (Tw) affects the behaviour of aquatic biota and metabolism of whole rivers. However, night-time water temperature (nTw) is poorly understood because spot samples are typically taken during daylight hours, or Tw series are aggregated in ways that mask sub-daily properties. This paper examines 15-minute measurements of Tw and air temperature (Ta) collected at 36 sites in the Rivers Dove and Manifold, English Peak District. Data were stratified by day and night then analysed using hysteresis, auto-correlation and logistic regression techniques. Daily hysteresis loops show lagged responses between nTw and previous daylight air temperatures (dTa), plus the influence of groundwater and discharge variations. Logistic regression models were modified using a seasonal factor and explained between 80 and 94% of the variance in daily maximum nTw; minimum nTw were predicted with less skill, particularly for headwater sites in summer. Downstream variations in model parameters also reflect the influence of groundwater and/or riparian shade, and prevailing weather conditions. A case is presented where an intense summer storm resulted in the propagation of a thermal wave that produced maximum Tw at some sites during hours of darkness. Hence, our findings show that Tw management by riparian shade has to be seen in a catchment wide context, with anticipated benefits normalised for weather variability, extreme rainfall events, local influence of groundwater, and channel structures

Embodied water imports to the UK under climate change

Commodities such as food and manufactured goods, particularly those that rely on land and water, are increasingly recognised as being potentially sensitive to climate change on a global scale, suggesting that the international dimension is critical when considering future supply susceptibilities of import-dependent countries, such as the UK. We estimated embodied water imported to the UK for 25 economically significant and climate-sensitive sub-sectors, then explored the current and future susceptibilities of these sub-sectors under climate change. In 2010, these products represented 31% of total UK imports by value (US$) and 12.8 billion m of embodied water. Of this total, rice, bovine and pig meat production, plastics and paper account for ~60% of the volume of water embodied in the import categories considered. By combining product-based water volume estimates with economic and climate model information, we show how the UK could be increasingly susceptible to loss of these water supplements in the future. In doing so, we provide an indication of how countries that depend upon climate-sensitive imported resources can account for these dependencies in a systematic way. For example, international adaptation and development funding may be targeted to the securing of supplies from existing exporting countries, or trade relations may be encouraged with potential new suppliers who are likely to be less resource-constrained. © Inter-Research 2014

Navigating cascades of uncertainty — as easy as ABC? Not quite…

The uncertainties in scientific studies for climate risk management can be investigated at three levels of complexity: “ABC”. The most sophisticated involves “Analyzing” the full range of uncertainty with large multi-model ensemble experiments. The simplest is about “Bounding” the uncertainty by defining only the upper and lower limits of the likely outcomes. The intermediate approach, “Crystallizing” the uncertainty, distills the full range to improve the computational efficiency of the “Analyze” approach. Modelers typically dictate the study design, with decision-makers then facing difficulties when interpreting the results of ensemble experiments. We assert that to make science more relevant to decision-making, we must begin by considering the applications of scientific outputs in facilitating decision-making pathways, particularly when managing extreme events. This requires working with practitioners from outset, thereby adding “D” for “Decision-centric” to the ABC framework

Spatial and temporal scaling of sub-daily extreme rainfall for data sparse places

Global efforts to upgrade water, drainage, and sanitation services are hampered by hydrometeorological data-scarcity plus uncertainty about climate change. Intensity–duration–frequency (IDF) tables are used routinely to design water infrastructure so offer an entry point for adapting engineering standards. This paper begins with a novel procedure for guiding downscaling predictor variable selection for heavy rainfall simulation using media reports of pluvial flooding. We then present a three-step workflow to: (1) spatially downscale daily rainfall from grid-to-point resolutions; (2) temporally scale from daily series to sub-daily extreme rainfalls and; (3) test methods of temporal scaling of extreme rainfalls within Regional Climate Model (RCM) simulations under changed climate conditions. Critically, we compare the methods of moments and of parameters for temporal scaling annual maximum series of daily rainfall into sub-daily extreme rainfalls, whilst accounting for rainfall intermittency. The methods are applied to Kampala, Uganda and Kisumu, Kenya using the Statistical Downscaling Model (SDSM), two RCM simulations covering East Africa (CP4 and P25), and in hybrid form (RCM-SDSM). We demonstrate that Gumbel parameters (and IDF tables) can be reliably scaled to durations of 3 h within observations and RCMs. Our hybrid RCM-SDSM scaling reduces errors in IDF estimates for the present climate when compared with direct RCM output. Credible parameter scaling relationships are also found within RCM simulations under changed climate conditions. We then discuss the practical aspects of applying such workflows to other city-regions