Regional rainfall response to the North Atlantic Oscillation (NAO) across Great Britain

© IWA Publishing 2019. The North Atlantic Oscillation (NAO) has been long studied as the primary teleconnection affecting the British and European climate. However, previous studies have focused on extremes or have been spatially and temporally limited. In recent years, our ability to predict the NAO has improved. Also, new research is emerging, suggesting that the NAO is a key driver of hydrological extremes. These factors mean that there is a renewed value in enhancing our understanding of how the NAO influences general rainfall patterns. In this study, we spatially analyse correlations between NAO indices and monthly rainfall data and the Standardised Precipitation Index. We also map mean monthly rainfall differences under NAO-positive and -negative conditions. Based on our results, we identify three main observations: (I) there is sensitivity in the rainfall patterns to the chosen NAO index; (II) there is a clear winter north/west and south/east divide in rainfall patterns; and (III) the NAO does have an effect on summer rainfall patterns, although the spatiality of these patterns is less distinctive than in winter. As far as we are aware, this is the first national scale, monthly NAO-rainfall analysis undertaken for a long period

Toward an analytical framework for understanding complex socialecological systems when conducting environmental impact assessments in South Africa

© 2015 by the author(s). Consideration of biophysical impacts has historically dominated environmental impact assessment (EIA) practice. Despite the emergence of social impact assessment, the consideration of socioeconomic impacts in EIA is variable, as is the extent of their integration in EIA findings. There is growing recognition for the need to move EIA practice toward sustainability assessment, characterized by comprehensiveness, i.e., scope of impacts, integration, i.e., of biophysical and socioeconomic impacts, and a greater strategic focus. This is particularly the case in developing regions and in countries like South Africa, which have statutory requirements for the full consideration of socioeconomic impacts in EIA. We suggest that EIA practice could benefit from incorporating evolving theory around social-ecological systems (SES) as an effective way of moving toward sustainability assessment. As far as we are aware, our study constitutes the first attempt to apply and formalize SES constructs to EIA practice within a regulated procedure. Our framework goes beyond conventional scoping approaches reliant on checklists and matrices by requiring the EIA practitioner to cocreate a conceptual model of the current and future social-ecological system with the implicated communities. This means social and biophysical impacts are assessed integratively, and that communities participate meaningfully in the EIA process, thereby helping address two of the most common shortfalls of EIA practice. The framework was applied in two case studies, establishment of communitybased accommodation linked to existing tourism infrastructure (Eastern Cape, South Africa), and a proposed wine estate (KwaZulu- Natal, South Africa). The framework revealed impacts, which would not be considered in a biophysically-oriented EIA, and helped identify development synergies and institutional and governance needs that are equally likely to have been overlooked. We suggest the framework has value as a counterpoint to established approaches and could contribute to improving the quality of EIAs with respect to the complex SESs that characterize the developing world

An integrated modelling approach to the management of freshwater inflow to South African estuaries.

Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1998.Estuaries are recognised for their biological diversity and productivity, as well as the vital role they play in providing habitat for organisms which utilise them as nurseries and feeding grounds. In many parts of the world concern has been expressed that the important functions and values of estuaries are being increasingly impacted upon by human activity. In South Africa diminishing freshwater inflow is a particular concern as this has led to an increase in the frequency and duration of mouth closure, which together with other factors has resulted in a marked deterioration in the condition of many estuaries. Global environmental imperatives require an approach to ecosystem management that is defensible and sustainable in the long term. Current approaches to estuary management in South Africa do not meet these criteria, and consequently, this study set out to develop methodologies to address these shortcomings. Three modelling approaches are presented, which can be used independently, or conjunctively, in defining the freshwater requirements of estuaries. The models assess the consequences of change in freshwater inflow for (i) juvenile fish which utilise estuaries as nurseries, (ii) the availability of intertidal and species specific habitats, and (iii) the population structure and production of a common estuarine invertebrate (Upogebia africana), endemic to the region. These techniques are applied in a case study of the Great Brak estuary (Western Cape, South Africa). The results indicate the utility of the approach and are supported, in part, by the findings of a long-term monitoring programme. The study also recognises the need for resource management to occur in the context of an integrated framework, which includes the explicit definition of ecological goals. Such a framework is presented, and is consistent with the Ecological Society of America's guidelines on sustainable ecosystem management. As this approach has been devised to be applicable to South African estuaries, characterised by poor data availability, it is anticipated that methodologies will be equally applicable to estuaries in other developing countries with a similar lack of data. The methodologies also extend current international approaches to the management of estuary freshwater inflow, and would therefore be of value to estuaries in the United States of America, Australia and other regions where diminishing freshwater inflow has been raised as a concern

‘Learning for resilience’: Developing community capital through flood action groups in urban flood risk settings with lower social capital

© 2017 Elsevier Ltd The role of civil agency in preparing and adapting to changing risk is an increasingly critical element within devolved local flood risk management. However, effective civil agency for flood resilience needs to draw on, and if necessary develop, community capital. Community Action Groups form one model for local resilience building for flood risk, and one actively supported by some governments. This research evaluates the participatory model of flood group development involving horizontal support rather than top-down or bottom-up generation. The process involved nascent groups working with an NGO facilitator in the implementation of a set of processes framed in the context of ‘learning for resilience’ that supported flood group development in a situation of challenged social capital (lower socio-economic status; health issues, lack of previous flood experience) in the UK. The methodology involved repeat semi-structured interviews with flood group members and flood risk management (FRM) agencies who worked with them through the process, as well as observation of flood group meetings. Results outline how groups emerge from transient and disconnected communities, the value of local knowledge, evolving communication skills and agency, normalisation of group members within participatory processes, frustrations within these processes, group sustainability and FRM agency perspectives. Discussion then critiques the co-working/partnership model and assesses its implications for social ‘learning for resilience’ within challenged flood groups with variable social capital. The authors propose a framework (’The 6Ss’) for anticipating concerns or barriers within such participatory processes as a guide to future local urban DRR practice

Spatio-temporal variability in North Atlantic oscillation monthly rainfall signatures in Great Britain

The North Atlantic Oscillation (NAO) is the primary atmospheric-oceanic circulation/teleconnection influencing regional climate in Great Britain. As our ability to predict the NAO several months in advance increases, it is important that we improve our spatio-temporal understanding of the rainfall signatures that the circulation produces. We undertake a high resolution spatio-temporal analysis quantifying variability in rainfall response to the NAO across Great Britain. We analyse and map monthly NAO-rainfall response variability, revealing the spatial influence of the NAO on rainfall distributions, and particularly the probability of wet and dry conditions/extremes. During the winter months, we identify spatial differences in the rainfall response to the NAO between the NW and SE areas of Britain. The NW area shows a strong and more consistent NAO-rainfall response, with greater probability of more extreme wet/dry conditions. However, greater NAO-rainfall variability during winter was found in the SE. The summer months are marked by a more spatially consistent rainfall response; however, we find that there is variability in both wet/dry magnitude and directionality. We note the implications of these spatially and temporally variable NAO-rainfall responses for regional hydrometeorological predictions and highlight the potential explanatory role of other atmospheric-oceanic circulations

Monthly rainfall signatures of the North Atlantic oscillation and East Atlantic pattern in Great Britain

Atmospheric-oceanic circulations (teleconnections) have an important influence on regional climate. In Great Britain, the North Atlantic Oscillation (NAO) has long been understood as the leading mode of climate variability, and its phase and magnitude have been found to influence regional rainfall in previous research. The East Atlantic Pattern (EA) is also increasingly recognised as being a secondary influence on European climate. In this study we use high resolution gridded rainfall and Standardised Precipitation Index (SPI) time series data for Great Britain to map the monthly rainfall signatures of the NAO and EA over the period January 1950–December 2015. Our analyses show that the influence of the two teleconnections varies in space and time with distinctive monthly signatures observed in both average rainfall/SPI-1 values and incidences of wet/dry extremes. In the winter months the NAO has a strong influence on rainfall and extremes in the north-western regions. Meanwhile, in the southern and central regions stronger EA-rainfall relationships are present. In the summer months opposing positive/negative phases of the NAO and EA result in stronger wet/dry signatures which are more spatially consistent. Our findings suggest that both the NAO and EA have a prominent influence on regional rainfall distribution and volume in Great Britain, which in turn has implications for the use of teleconnection forecasts in water management decision making. We conclude that accounting for both NAO and EA influences will lead to an enhanced understanding of both historic and future spatial distribution of monthly precipitation

The spatio-temporal influence of atmospheric circulations on monthly precipitation in Great Britain

It has long been understood that the North Atlantic Oscillation (NAO) is a key driver of regional climate in Great Britain and across Europe. However, studies have also noted that there is spatio-temporal variability in NAO-rainfall signatures which arguably limits its practical inclusion in water management. In this study we quantify, at high spatio-temporal resolution, the influence of a broader set of atmospheric circulations on monthly precipitation. Using Standardised Precipitation Indices for the Integrated Hydrological Unit (IHU) Groups of Great Britain we apply univariate and multivariate regression models to understand the potential of five atmospheric circulation indices to explain precipitation variability. As far as we are aware this represents the first high spatial and temporal resolution analysis quantifying the influence of a broad set of atmospheric circulations, both individually and in combination. We highlight the influence of each circulation and establish that the NAO only partially explains precipitation variability, especially in the southern regions and during the summer months, where circulations, such as the East Atlantic Pattern, also have an important influence. In summary, we suggest that there is significant explanatory value in looking beyond the NAO when seeking to understand hydroclimatological variability in Great Britain, and there is potential for future work to explore how this understanding can translate into the practical application of atmospheric circulation indices in water management

Extreme multi-basin flooding linked with extra-tropical cyclones [Poster]

Fluvial floods are typically investigated as ‘events’ at the single basin-scale, hence flood management authorities may underestimate the threat of flooding across multiple basins driven by large-scale and nearly concurrent atmospheric event(s). We pilot a national-scale statistical analysis of the spatio-temporal characteristics of extreme multi-basin flooding (MBF) episodes, using peak river flow data for 260 basins in Great Britain (1975-2014), a sentinel region for storms impacting northwest and central Europe. During the most widespread MBF episode, 108 basins (~46% of the study area) recorded Annual Maximum (AMAX) discharge within a 16-day window. Such episodes are associated with persistent cyclonic and westerly atmospheric circulations, atmospheric rivers, and precipitation falling onto previously saturated ground, leading to hydrological response times <40h and documented flood impacts. Furthermore, peak flows tend to occur after 0-13 days of very severe gales causing combined and spatially-distributed, yet differentially time-lagged, wind and flood damages. These findings have implications for emergency responders, insurers and contingency planners worldwide

Geospatial cluster analysis of the state, duration and severity of drought over Paraíba State, northeastern Brazil

Droughts threaten water resources, agriculture, socio-economic activities and the population at the global and regional level, so identifying areas with homogeneous drought behaviors is an important consideration in improving the management of water resources. The objective of this study is to identify homogenous zones over Paraíba State in relation to the state, duration and severity of droughts that have occurred over the last 20 years (1998–2017) using hierarchical cluster analysis based on both gauge-measured and Tropical Rainfall Measuring Mission (TRMM) estimated rainfall data (TMPA 3B42). The drought series were calculated using the Standardized Precipitation Index (SPI) based on eight time scales and were grouped according to drought state, duration and severity time series. The integrated results of state, duration and severity of droughts indicate that there is a basis for dividing Paraíba State into two major regions (a) Zone I, formed by Mata Paraibana and Agreste Paraibano, and (b) Zone II, composed by Borborema and Sertão Paraibano. This division is evident when assessing short-term droughts, but in the case of long-term droughts, Paraíba State has a high similarity in terms of drought state, duration, and severity. Factors such as proximity to the ocean, active climatic systems, and the local relief configuration were identified as influencing the drought regime. Finally, it is concluded that TMPA rainfall estimates represent a valuable source of data to regionalize and identify drought patterns over this part of Brazil and that other studies of this type should be carried out to monitor these phenomena based on other satellite-based rainfall data, including the Global Precipitation Mission (GPM)

Exploring the sensitivity of coastal inundation modelling to DEM vertical error

© 2018 Informa UK Limited, trading as Taylor & Francis Group. As sea level is projected to rise throughout the twenty-first century due to climate change, there is a need to ensure that sea level rise (SLR) models accurately and defensibly represent future flood inundation levels to allow for effective coastal zone management. Digital elevation models (DEMs) are integral to SLR modelling, but are subject to error, including in their vertical resolution. Error in DEMs leads to uncertainty in the output of SLR inundation models, which if not considered, may result in poor coastal management decisions. However, DEM error is not usually described in detail by DEM suppliers; commonly only the RMSE is reported. This research explores the impact of stated vertical error in delineating zones of inundation in two locations along the Devon, United Kingdom, coastline (Exe and Otter Estuaries). We explore the consequences of needing to make assumptions about the distribution of error in the absence of detailed error data using a 1 m, publically available composite DEM with a maximum RMSE of 0.15 m, typical of recent LiDAR-derived DEMs. We compare uncertainty using two methods (i) the NOAA inundation uncertainty mapping method which assumes a normal distribution of error and (ii) a hydrologically correct bathtub method where the DEM is uniformly perturbed between the upper and lower bounds of a 95% linear error in 500 Monte Carlo Simulations (HBM+MCS). The NOAA method produced a broader zone of uncertainty (an increase of 134.9% on the HBM+MCS method), which is particularly evident in the flatter topography of the upper estuaries. The HBM+MCS method generates a narrower band of uncertainty for these flatter areas, but very similar extents where shorelines are steeper. The differences in inundation extents produced by the methods relate to a number of underpinning assumptions, and particularly, how the stated RMSE is interpreted and used to represent error in a practical sense. Unlike the NOAA method, the HBM+MCS model is computationally intensive, depending on the areas under consideration and the number of iterations. We therefore used the HBM+ MCS method to derive a regression relationship between elevation and inundation probability for the Exe Estuary. We then apply this to the adjacent Otter Estuary and show that it can defensibly reproduce zones of inundation uncertainty, avoiding the computationally intensive step of the HBM+MCS. The equation-derived zone of uncertainty was 112.1% larger than the HBM+MCS method, compared to the NOAA method which produced an uncertain area 423.9% larger. Each approach has advantages and disadvantages and requires value judgements to be made. Their use underscores the need for transparency in assumptions and communications of outputs. We urge DEM publishers to move beyond provision of a generalised RMSE and provide more detailed estimates of spatial error and complete metadata, including locations of ground control points and associated land cover