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Tea is a major contributor to exports and the economy, as well as an important source of incomes for rural livelihoods in Kenya, Malawi and Rwanda. While the tea sectors of these countries are expanding, they are extremely vulnerable to the impacts of climate change. Tea plants are particularly sensitive to the climate, needing very specific climate conditions for high production and quality, and for that reason are grown in particular agro-climatic zones. Tea plants are also affected by climate extremes such as heat waves, droughts or floods. Climate change is altering the average climate and the pattern of extremes, and this will have implications for tea production in the future.

This infographic outlines some of the potential impacts of tea production in three different possible future climates for the growing regions

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The impacts of climate change on the yields and quality of tea in Africa, significantly impact the economies and livelihoods dependent on the tea sector. As a crop which is already very sensitive to the climate, future climate change poses an increasing risk for tea production. Implementing climate smart agricultural practices is becoming more and more important to ensure African countries can continue to grow their tea industries in the future. Understanding what the future climate might look like and the types of hazards facing tea growing regions are important in identifying adaptation options that are relevant in the local context.

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Roy Bouwer, Julio Araujo, Neha Mittal, Paul Watkiss

Climate change poses a significant risk to tea growing regions, not only because of changes in average climate conditions but also due to the changing intensity and frequency of climate extremes such as heat waves, dry spells and heavy rainfall. Research from FCFA has provided new understanding for how the climate might change and how this may impact tea growing regions of Kenya, Malawi and Rwanda. Work has demonstrated the value of locally-relevant and context specific climate information to help tea farmers plan for climate change. The potential impacts of climate change for tea growing regions, requires urgent adaptation to safeguard tea production.  This report outlines the climate sensitivity of tea plants, the likely impacts on tea crops and markets and potential adaptation options. The report provides on overview of risks and adaptation within Kenya, Malawi and Rwanda. 

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Christopher Taylor, Conni Klein, Victoria Barlow, James Miller, David Rowell, Benjamin Sultan, Babacar Faye, Theo Vischel, Youssouph Sane, Françoise Guichard, Fowe Tazen

THE CLIMATE OF THE PLANET IS CHANGING, as is evident from steady increases in global temperatures and sea levels over the last 100 years. Scientists are clear that these changes are due to man-made emissions of greenhouse gases, notably carbon dioxide from fossil fuel burning. In spite of efforts by the United Nations Intergovernmental Panel on Climate Change (IPCC), emissions have continued to rise. How much the world will warm in the future is strongly related to how rapidly the global economy can decarbonise.

In this policy brief, we set out how the climate of the Sahel has changed in recent decades, what future changes are expected, and some implications of these changes for agriculture and flooding. There are many uncertainties when considering future impacts of global warming within a specific region. Here we present the range of plausible futures so that this uncertainty can be taken into account by decision-makers.

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Fall, C.M.N., Lavaysse, C., Kerdiles, H., Dramé, M.S., Roudier, P. and Gaye, A.T.

Studying the relationship between potential high-impact precipitation and crop yields can help us understand the impact of the intensification of the hydrological cycle on agricultural production. The objective of this study is to analyse the contribution of intra seasonal rainfall indicators, namely dry and wet spells, for predicting millet yields at regional scale in Senegal using multiple linear regression. Using dry and wet spells with traditional indicators i.e. proxies of crop biomass and cumulated rainfall, hereafter called remote sensing indicators (NDVI, SPI3, WSI and RG), we analysed the ability of dry and wet spells alone or combined with these remote sensing indicators to provide intraseasonal forecasts covering the period 1991–2010. We analysed all 12 regions producing millet and found that results vary strongly between regions and also during the season, as a function of the dekad of prediction. At the spatial scale, the strongest performing combinations include the dry spell indicators DSC20 and DSxl in the peanut basin. While in the south of the country, the combination of wet period indicators WS1 or WSC5 with the RG is fairly reliable. Focussing on Thies, our best region in the groundnut basin, we showed that dry and wet spells indicators can explain up to 80% of yield variations, alone or in combination with remote sensing indicators. Regarding the timing of prediction, millet yield can be forecast as early as July with an accuracy of 40% of the mean yield but the best forecast is obtained in early September, at the peak of crop development (accuracy of 100 kg/ha i.e. 20% of the mean yield). Although, the estimated yields show biases over some years identified as extremely deficient or in oversupply in terms of agricultural yields.

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Woodhams, B.J., Barrett, P.A., Marsham, J.H., Birch, C.E., Bain, C.L., Fletcher, J.K., Hartley, A.J., Webster, S. and Mangeni, S.

The lake–land breeze circulation over Lake Victoria was observed in unprecedented detail with a research aircraft during the HyVic pilot flight campaign in January 2019. An evening and morning flight observed the lake and land breezes respectively under mostly dry conditions. The circulation was observed at various heights along a transect across the lake and onshore in Tanzania. Profiles of the lower troposphere were recorded by dropsondes over the lake and land. Convection-permitting MetUM simulations with different horizontal grid-spacings (including sub-km) were run for the flight periods. During the evening flight, the aircraft crossed the lake breeze front over land at 1627 LT, approximately 50 km to the east of the lake shore, recording a 6 g kg–1 decrease in specific humidity and reversal in wind direction over ~5 km. During the morning flight, a shallow land breeze was observed across the eastern shore at 0545 LT. At least one region of increased and deeper moisture (previously seen in simulations but never observed) was sampled over the lake surface between 0527–0855 LT. This bulge of moisture was likely formed from the lifting of near-surface moist air above the lake by low-level convergence. The observations and model simulations suggest that low-level convergence occurred at the leading edge of the land breeze, which had detached from the main land breeze and independently propagated westward across the lake with wave-like characteristics. The MetUM simulations were able to reasonably reproduce the lake breeze front, bulge feature, and its propagation, which is a major achievement given the sparse observational data for model initialisation in this region. However, some timing, resolution and boundary layer depth biases require further investigation. Overall, this pilot campaign provided an unprecedented snapshot of the Lake Victoria lake–land breeze circulation and motivates a more comprehensive field campaign in the future.

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Mahony, J., Dyer, E. and Washington, R.

The unique precipitation patterns over the Serengeti National Park in East Africa form the foundation of an internationally important ecosystem. Quantifying these precipitation patterns, and identifying the causal atmospheric processes, can improve understanding of past and future changes to regional rainfall. Precipitation and reanalysis datasets (CHIRPS v2.0, TRMM 3B42, ERA5) were used to quantify the regional climatic conditions on annual, monthly and hourly timescales. Hierarchical cluster analysis identified regions with distinct annual cycles of precipitation. Annual and monthly precipitation over the wider Serengeti domain (1°–4°S, 33°–37°E) was spatially heterogeneous. Cluster analysis identified five sub-regions with distinct annual cycles, with differing rainfall totals during January–February and June–September, wet season peak rainfall months, and rainfall peak symmetry. Seasonality was broadly controlled by the biannual passage of the tropical rainfall belt. Low-level wind, humidity and convergence patterns were impacted by the topography and Lake Victoria. An afternoon convergence zone between tropical easterlies and lake breeze winds always ran through the park and was associated with ascending motion and convection. The spatial progression of diurnal rainfall over the Serengeti followed the direction of 750 hPa tropical easterlies. The majority of the park received a late-afternoon rainfall peak, but from October to March an early afternoon peak was present between the wind convergence line over the central Serengeti and the rift topography. We propose that interactions between tropical easterlies, lake breeze westerlies and the topography control the spatial distribution of Serengeti precipitation, and that the seasonally changing rainfall gradient over the Serengeti may be generated by storms forming at the lake front and propagating in the direction of tropospheric easterlies. We suggest the early precipitation peak in the eastern Serengeti may be due to variability in the position of the lake front, or small storms generated by localized solar heating.

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Spavins‐Hicks, Z.D., Washington, R. and Munday, C.

Low-level jets (LLJs) are well established as critical features of regional climates globally. However, across sub-Saharan Africa, LLJs have received relatively little attention, in part due to a lack of data. Utilizing high-resolution reanalysis data, this paper develops the first climatology of a neglected feature of the southern African circulation – the Limpopo LLJ – and investigates its role in delivering water vapor to the continental interior. We demonstrate that the LLJ has a clear diurnal cycle and is a regular feature of the circulation throughout the year, forming on 80.9% of days. The pressure gradient between southern Mozambique and the continental interior acts as a first-order control on the annual cycle of jet strength, which peaks in October, achieving average maximum windspeeds of 15.8 m.s−1 at the core. Water vapor transport follows the same clear diurnal cycle, with at least 72% occurring over 18:00–08:00, and is closely related to jet strength: On average the strongest jet events advect 1.04 × 1012 kg (1.02 × 1012 kg) more moisture each night than the weakest in October-December (January-March). Strong jet events are typically linked to ridging anticyclones along the east coast of South Africa and are associated with increased rainfall in central and southern Botswana and northern South Africa the following day.

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Mittal, N., Rowell, D.P., Dougill, A.J., Becker, B., Marsham, J.H., Bore, J., Tallontire, A., Vincent, K., Mkwambisi, D. and Sang, J.

Tailored climate change information is essential to understand future climate risks and identify relevant adaptation strategies. However, distilling and effectively communicating decision-relevant information from climate science remains challenging. In this paper, we develop and apply an iterative stakeholder engagement approach and a Site Specific Synthesis of Projected Range (SPR), to co-produce future climate information for Africa’s largest tea producing nations – Kenya and Malawi – for the mid-and late-21st century. SPR provides a novel analysis approach, which combines long-term station observations with projections from 29 global climate models and the first convection-permitting high-resolution climate projection for Africa (CP4A). This addresses the mismatch between spatial scales of projections, large-scale modelling uncertainties and stakeholder need for site-specific information. Iterative stakeholder engagement and communication helped to build trust, allowed use of new observation data and improved visualisations of climate information for stakeholders. SPR demonstrates site-specificity in changes in all metrics, showing risks of large changes in tea crop sensitive metrics. All nine locations analysed show substantial (up to four times) increases in heatwave days and large decreases in cold nights by 2050s compared to the current climate. While tea producers are already witnessing changing climatic conditions, potential future changes will greatly affect the resilience of tea production, thereby affecting the sustainability and quality of tea production in the region. Site specific climate information iteratively co-produced with stakeholders helps them to identify location-specific adaptation strategies and investment priorities, potentially safeguarding supply-chains and millions of livelihoods.

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Klein, C., Jackson, L.S., Parker, D.J., Marsham, J.H., Taylor, C.M., Rowell, D.P., Guichard, F., Vischel, T., Famien, A.M.L. and Diedhiou, A.

Due to associated hydrological risks, there is an urgent need to provide plausible quantified changes in future extreme rainfall rates. Convection-permitting (CP) climate simulations represent a major advance in capturing extreme rainfall and its sensitivities to atmospheric changes under global warming. However, they are computationally costly, limiting uncertainty evaluation in ensembles and covered time periods. This is in contrast to the Climate Model Intercomparison Project (CMIP) 5 and 6 ensembles, which cannot capture relevant convective processes, but provide a range of plausible projections for atmospheric drivers of rainfall change. Here, we quantify the sensitivity of extreme rainfall within West African storms to changes in atmospheric rainfall drivers, using both observations and a CP projection representing a decade under the Representative Concentration Pathway 8.5 around 2100. We illustrate how these physical relationships can then be used to reconstruct better-informed extreme rainfall changes from CMIP, including for time periods not covered by the CP model. We find reconstructed hourly extreme rainfall over the Sahel increases across all CMIP models, with a plausible range of 37%–75% for 2070–2100 (mean 55%, and 18%–30% for 2030–2060). This is considerably higher than the +0–60% (mean +30%) we obtain from a traditional extreme rainfall metric based on raw daily CMIP rainfall, suggesting such analyses can underestimate extreme rainfall intensification. We conclude that process-based rainfall scaling is a useful approach for creating time-evolving rainfall projections in line with CP model behaviour, reconstructing important information for medium-term decision making. This approach also better enables the communication of uncertainties in extreme rainfall projections that reflect our current state of knowledge on its response to global warming, away from the limitations of coarse-scale climate models alone.

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