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Patterns and mechanisms of climate extremes in East Africa (PAMEXEA)

The catastrophic droughts which affected Kenya, Ethiopia and Somalia in recent years once more highlighted the heavy impact of a variable climate on the vulnerable populations and socio-economic systems of (semi-)arid East Africa, and the enormous challenge to develop a sustainable agricultural economy in a future of climate change, growing demographic pressure and naturally scarce land and water resources. Increasingly frequent events of extreme weather now regularly disrupt the traditionally predictable succession of dry and rainy seasons, and appear to be super-imposed on a longer-term drying trend that has been linked to anthropogenic global warming. Severe, recurrent drought is hence the principal weather-related hazard in the region, and the quality of long-term weather and climate predictions a major bottleneck hampering successful drought mitigation and adaptation. Most worrying is the uncertain impact of 21st-century climate change on regional freshwater resources, due to at best fragmentary understanding of the hydroclimatic effects of a warming atmosphere at the regional scale. Current climate change scenarios for East Africa (e.g. those used by the IPCC), which are based on global climate model (GCM) simulations, have insufficient spatial downscaling to meaningfully guide the region-specific water-resource planning which developing economies need to prepare for the future.
Applying state-of-the-art methods of the powerful ‘the past is the key to the (present and) future’ approach, PAMEXEA aims to improve understanding of these climate trends and extremes, as a basis for appropriate management of East Africa’s land and water resources. Specifically, we aim to find out how processes of natural climate variability at seasonal, inter-annual and decadal time scales will interact with anthropogenic climate forcing to create future trends in rainfall and drought. The results of this project will contribute to improved long-term rainfall prognoses for East Africa at the sub-regional scale, and the capability of climate models to predict the future occurrence of extreme drought. In other words, this project will produce basic knowledge and know-how that is crucial to develop sound risk-management, adaptation and sustainable-development policies for specific areas within East Africa, including short-term catastrophe prediction and management.
PAMEXEA consists of four inter-connected work packages. First, next-generation regional climate models that are currently being developed must be tested against long time series of past climate trends and weather extremes which adequately represent the frequency (recurrence interval) and intensity or amplitude of such events. In East Africa only a small handful of such datasets currently exist, hampering meaningful analysis of spatial patterns. In work package 1 (WP1) we will apply diverse geological, geochemical and biological methods of lake-based palaeohydrological reconstruction to the sediment records from three lakes in Kenya to optimize the documentation of past climate variability in equatorial East Africa during the last 2000 years. In WP2 we will integrate these new climate records with a quality-screened compilation of all existing climate-proxy data from East Africa and surrounding areas over the past 2000 years, to produce a spatially-resolved history of past East African climate change. Our effort is framed within the ‘Africa-2k’ working-group contribution to the International Geosphere-Biosphere Programme (IGBP) initiative to produce syntheses of climate-proxy data for each of the world’s continents, supporting the development of improved climate-model simulations that can inform future IPCC climate-change assessment reports. Our effort differs from previous East African paleodata syntheses in two important aspects. First, we will integrate all palaeohydrological time series, also those which are fragmentary or have low time resolution, into the regional climate-proxy meta-database, as long as these ‘time windows’ on past climate events at particular locations are reliably dated. Second, since all continuous climate-proxy datasets available for East Africa involve moisture-balance indicators extracted from lake sediments, we will use (inverse) hydrological modeling of those datasets for three important sites to assess the relationship between reconstructed moisture-balance variation (e.g., a record of past lake-level change) and the timing and amplitude of the rainfall variability which caused this variation. Since this exercise translates the proxy data into real time series of past rainfall, the results will allow, for the first time, a direct comparison of climate-model simulations with documented African climate history.
Improvements in the prediction of weather extremes and long-term climate change in East Africa clearly depend on the availability of climate models which capture the principal large-scale climate- dynamical processes (in particular, the tropical hydrological cycle), the principal mechanisms of tropical climate forcing at short and medium time scales, and all region-specific feedbacks and land-ocean-atmosphere interactions. In WP3 we will test the hind-casting performance of existing climate models, i.e. their ability to replicate the temporal and spatial patterns of past climate variability over East Africa as reconstructed in WP2, as a guide to their relative ability to simulate future climate trends and variability under prescribed combinations of natural and anthropogenic climate forcing. The results of this exercise will serve as reference framework for the development of next-generation regional climate models.
The ultimate goal of the PAMEXEA project is to contribute to the better forecasting of seasonal and longer-term climate variability that is urgently required for adequate preparation, mitigation, and management of extreme weather in largely semi-arid East Africa. As regards direct policy guidance on climate extremes and water-resource availability, the challenge is to make climate-change and weather-hazard projections sufficiently robust to allow delineating specific areas in East Africa where policies should promote either the cultivation of drought-tolerant varieties of commercial and food crops, livestock ownership by subsistence farmers, or pure and mobile livestock herding; and for each of these economic activities develop measures to prevent soil loss and land degradation. In WP4 we focus on communicating to local governments, dryland communities and other stakeholders which improvements in climate forecasting have been made and what its future prospects are, but also the reality of its limitations.
Date:1 Oct 2013 →  31 Dec 2017