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Periodic Report Summary 1 - PREFACE (Enhancing prediction of tropical Atlantic climate and its impacts)

Project Context and Objectives:
The tropical Atlantic climate recently experienced shifts of great socio-economic importance. The oceanic changes were largest in the eastern boundary upwelling systems, globally important regions for marine productivity and climate. African countries bordering the Atlantic depend upon their ocean for societal development, fisheries, and tourism. They were strongly affected by these changes and will face important adaptation challenges associated with global warming. Compounding this, the tropical Atlantic is a region of key uncertainty in the earth-climate system: state-of-the-art climate models exhibit large systematic errors, climate change projections are highly uncertain, and how climate change will impact marine ecosystems is largely unknown, as are the possible global socio-economic impacts.
To redress this situation, PREFACE joins European and African expertise to provide the first comprehensive assessment of the tropical Atlantic. In four research foci, sophisticated observation systems, extensive field experiments, regional and global scale modelling capabilities, and socio-economic marine ecosystem models are combined to improve the prediction of tropical Atlantic climate and its impacts.
The first research focus – Role of ocean processes in climate variability – aims to better understand the oceanic processes affecting sea surface temperature (SST) in eastern tropical Atlantic upwelling regions on seasonal to decadal time scales, by using historical and new data as well as medium to very-high-resolution forced ocean models. We focus on the mixed layer heat and freshwater budgets, the tropical Atlantic circulation, and the equatorial and coastal wave response. By evaluating the ocean models, we will suggest improvements to reduce biases (systematic errors) in ocean and coupled climate models.
Evaluation of current climate models and reduction of model bias is the second focus, aiming to better understand and subsequently reduce systematic errors in climate models in the tropical Atlantic. Our strategy is to analyse the development of model systematic error in climate predictions and then perform coordinated, multi-model sensitivity experiments to identify the key processes that require improved model representation to mitigate these systematic error. Additionally, we aim to understand the relation among errors in variability, feedbacks, and atmospheric-links to other regions of the globe.
Our third focus – Climate prediction in the tropical Atlantic – aims to clarify the mechanisms for climate variability and predictability on seasonal to decadal time scales, by analysing observations and numerical experimentation. We also investigate interactions between the Atlantic and other regions, and both natural and anthropogenic factors. The goal is to improve the prediction of tropical Atlantic climate, and to assess the impact of model systematic error on prediction skill. We are developing a unified statistical prediction framework, and will also use state-of-the-art climate prediction models.
PREFACE’s last research focus – Impacts of climate change on pelagic functional diversity in the tropical Atlantic with effects on western African fisheries economies – aims to disentangle environmental and anthropogenic pressures on pelagic fish stocks in the tropical Atlantic, through exploratory analysis of historical and newly collected data. We also aim to better understand climate change effects on small-scale fisheries and coastal communities, and to assess uncertainties and implications for management. Our approach is to develop socio-economic models, built on knowledge of the marine ecosystem and fishing communities, and to drive them with climate change projections.
Besides the scientific goals a closer cooperation between European and West African partner institutions is envisioned leading to enhancement of research capacities in the fields of ocean physics, ecosystem and fisheries as well as climate research in West Africa.

Project Results:
A year and a half since it began, PREFACE has made significant advances towards its overarching goal of enhanced prediction of tropical Atlantic climate and its impacts.
PREFACE is improving understanding of key oceanic processes in the tropical Atlantic. The observing system was enhanced along the equatorial and coastal waveguides, by installing surface buoys and subsurface moorings, and by shipboard observations of hydrography and currents. These, together with historical and remote sensing data, were used to better understand (1) the climatological heat and freshwater budgets in the upwelling regions, especially during seasonal cooling, (2) intraseasonal wave propagation along the coastal waveguide southward from the equator, and (3) the seasonal to interannual variability of circulation and hydrography at the equator and southward down the coast. Different ocean model simulations, validated with these observations, show that parameterizing short wave absorption due to chlorophyll concentration and using high-resolution satellite derived wind products can improve simulations. Close cooperation between different European and African partner institutions were established or improved resulting in common experiments at sea, data sharing and analysis, as well as application of ocean modelling on regional scale.
PREFACE investigated the causes of systematic error in the tropical Atlantic in climate models. Wind stress biases were highlighted as drivers of SST errors in retrospective seasonal predictions, as well as errors in the position of the Angola-Benguela oceanic front. It is likely that the benefits of improved ocean representation will not be seen before atmospheric model errors are reduced. Surface winds improve with better atmospheric horizontal and vertical resolution. Despite poorly simulating the climatology, models do capture elements of the mechanisms generating tropical Atlantic variability and in certain cases, also represent observed inter-basin connections. Errors in simulated variability and climatology are not easily linked, perhaps because oceanic dynamics are poorly represented and thermodynamic processes appear to dominate.
PREFACE is advancing understanding of the mechanisms for tropical Atlantic variability and predictability. Intraseasonal equatorial oceanic waves were shown to generate, through non-linear interactions, a resonant interannual oscillation, while Atlantic multi-decadal variability was shown to modulate the link between Atlantic and Pacific interannual variability. Droughts over Central Africa and the Sahel were related to tropical Atlantic, Indian, and Pacific Oceans SST. Furthermore, models indicate that internal climate dynamics likely drove the observed, long-term South Atlantic warming, as well as Atlantic multi-decadal variability. Beyond mechanisms, advanced statistical methods were developed to improve SST and rainfall predictions, and to account for model bias; while initiating dynamical predictions from contemporary observations was shown to enhance decadal predictions of Sahel rainfall.
PREFACE is increasing understanding of the interrelation among marine ecosystems, climate variability and change, and fisheries; and of the possible socio-economic implications of future climate change. Several shipboard surveys, with participation of regional partners, provided new data, while the EAF Nansen project archives provided data from over the last three decades. These were used to investigate the correspondence between climate variations and trends in the south- and north-eastern Atlantic, and the abundance and distribution of small pelagic fish distribution. Ecological-economic models applicable to African fisheries were compiled; and 300 Senegalese skippers and boat owners completed a baseline questionnaire for deriving information for these models, of the economic and social situation of local fishing communities, and their vulnerability to climate driven changes in the ecosystem.

Potential Impact:
PREFACE is a bold and ambitious project that targets one of the marine regions that will be more affected by climate change and its consequences. The project will provide the first comprehensive assessment of the tropical Atlantic climate, from multidisciplinary observations to predicting its socio-economic impacts.
PREFACE activities will contribute to an improved observing system, allowing a continuous monitoring of tropical Atlantic variability and climate change due to anthropogenic forcing. PREFACE has installed key moorings in the southern and northern coastal wave-guides, extended the PIRATA (Prediction and Research Moored Array in the Atlantic, network toward the eastern tropical South Atlantic. Exemplary is the deployment, in association with several laboratories across West Africa, of an oceanographic and meteorological measuring buoy in the heart of the Senegal-Mauritania upwelling. PREFACE is not only generating knowledge for the optimal design of the future network, but is helping to ensure the long-term sustainability of the network, by increasing awareness and developing required competence among regional players.
PREFACE will lead to an improved understanding of variability in both eastern boundary upwelling African regions and the Gulf of Guinea. The comparison of observational and modelling results will provide a detailed process-based understanding that should lead to improved ocean and climate modelling capabilities.
PREFACE shall contribute to a better understanding of the mechanisms and predictability of tropical Atlantic climate, and of its global impacts. This includes the mechanisms for seasonal to decadal variability, and assessing also the contribution of external forced climate change.
PREFACE will lead to enhanced climate modelling and prediction capabilities, on seasonal to centennial time scales. It will provide a detailed understanding of the causes of model systematic errors, develop strategies to reduce them, and quantify their impact on climate prediction. PREFACE shall assess the potential of advanced statistical methods and bias correction techniques to improve climate predictions. We have already shown that climate predictions can skilfully predict Sahel rainfall on decadal time scales. Such improved predictions of climate can have major socio-economic benefits.
PREFACE activities will result in a deeper understanding of the function of marine ecosystem so that climate driven shifts can be better predicted. For example, we have shown that the warming of the South Atlantic during the last three decades was associated with threefold increase and southward shift in Sardinella biomass. By coupling such knowledge to improved climate predictions, PREFACE will provide framework to predict such changes in small pelagic fish distributions.
PREFACE will provide policy relevant guidance on sustainable development of West African fisheries in the context of climate change. Knowledge gained of local fishing communities, better understanding of climatic and anthropogenic influences on marine ecosystems, and improved predictions will together lead to improved ecological-economic models and predictions for the region.
PREFACE shall lead to enhanced cooperation between European and African researchers working on Tropical Atlantic climate and its impacts, by fostering existing collaborations and improving project synergy.
PREFACE is helping to train a new generation of researchers, including those from the region. Its summer schools, targeted workshops, and interdisciplinary meetings are providing the required education to continue important research on the tropical Atlantic climate and its impacts.

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