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Abstract:In the Sahel region, moderate to coarse spatial resolution remote sensing time series are used in early warning monitoring systems with the aim of detecting unfavorable crop and pasture conditions and informing stakeholders about impending food security risks. Despite growing evidence that vegetation productivity is directly related to phenology, most approaches to estimate such risks do not explicitly take into account the actual timing of vegetation growth and development. The date of the start of the season (SOS) or of the peak canopy density can be assessed by remote sensing techniques in a timely manner during the growing season. However, there is limited knowledge about the relationship between vegetation biomass production and these variables at the regional scale. This study describes the first attempt to increase our understanding of such a relationship through the analysis of phenological variables retrieved from SPOT-VEGETATION time series of the Fraction of Absorbed Photosynthetically Active Radiation (FAPAR). Two key phenological variables (growing season length (GSL); timing of SOS) and the OPEN ACCESSRemote Sens. 2014, 6 5869 maximum value of FAPAR attained during the growing season (Peak) are analyzed as potentially related to a proxy of biomass production (CFAPAR, the cumulative value of FAPAR during the growing season). GSL, SOS and Peak all show different spatial patterns of correlation with CFAPAR. In particular, GSL shows a high and positive correlation with CFAPAR over the whole Sahel (mean r = 0.78). The negative correlation between delays in SOS and CFAPAR is stronger (mean r = −0.71) in the southern agricultural band of the Sahel, while the positive correlation between Peak FAPAR and CFAPAR is higher in the northern and more arid grassland region (mean r = 0.75). The consistency of the results and the actual link between remote sensing-derived phenological parameters and biomass production were evaluated using field measurements of aboveground herbaceous biomass of rangelands in Senegal. This study demonstrates the potential of phenological variables as indicators of biomass production. Nevertheless, the strength of the relation between phenological variables and biomass production is not universal and indeed quite variable geographically, with large scattered areas not showing a statistically significant relationship.

Taking advantage of multiple new remote sensing data sources, especially from Chinese satellites, the CropWatch system has expanded the scope of its international analyses through the development of new indicators and an upgraded operational methodology. The approach adopts a hierarchical system covering four spatial levels of detail: global, regional, national (thirty-one key countries including China) and "sub-countries" (for the nine largest countries). The thirty-one countries encompass more that 80% of both production and exports of maize, rice, soybean and wheat. The methodology resorts to climatic and remote sensing indicators at different scales. The global patterns of crop environmental growing conditions are first analyzed with indicators for rainfall, temperature, photosynthetically active radiation (PAR) as well as potential biomass. At the regional scale, the indicators pay more attention to crops and include Vegetation Health Index (VHI), Vegetation Condition Index (VCI), Cropped Arable Land Fraction (CALF) as well as Cropping Intensity (CI). Together, they characterize crop situation, farming intensity and stress. CropWatch carries out detailed crop condition analyses at the national scale with a comprehensive array of variables and indicators. The Normalized Difference Vegetation Index (NDVI), cropped areas and crop conditions are integrated to derive food production estimates. For the nine OPEN ACCESSRemote Sens. 2015, 7 3908 largest countries, CropWatch zooms into the sub-national units to acquire detailed information on crop condition and production by including new indicators (e.g., Crop type proportion). Based on trend analysis, CropWatch also issues crop production supply outlooks, covering both long-term variations and short-term dynamic changes in key food exporters and importers. The hierarchical approach adopted by CropWatch is the basis of the analyses of climatic and crop conditions assessments published in the quarterly "CropWatch bulletin" which provides accurate and timely information essential to food producers, traders and consumers.

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Questions related to the distribution and spatio‐temporal dynamics of the terrestrial carbon fluxes are at the core of current scientific and policy debates. In recent years, the primary concern has been the increasing CO2 content in the atmosphere, its effect on climate, and the associated role of terrestrial ecosystems in mitigating the increase and impact of climate change. However, terrestrial carbon dynamics is also closely related to biodiversity land degradation, and other pressing policy and assessment questions. Yet at the global level, no system in place now can provide quantitative information about carbon sources and sinks systematically, reliably, and accurately.

Agriculture is deeply interconnected with weather and climate, the main drivers of agriculture production, but also the dominant factors in the overall variability of food production. Agriculture constitutes the principal livelihood of 70% of the world's poor; many of them are hungry and living in vulnerable, climate-sensitive areas. Since the undernourished population reached 1 billion persons in 2009, raising food production by some 70% to meet the needs of a projected world population of 9.1 billion people in 2050 may be one of the greatest challenges of the century. In addition, changes in climatic conditions are already having impacts on agriculture and the use of natural resources for food production. Climate science has much to offer in addressing these challenges, especially with respect to the characterisation of agroclimatic resources and development of climateresponsive food and agriculture policies, programmes and practices. However, as food systems expand into marginal and vulnerable areas, the need for a renewed, holistic focus is becoming evident, taking into account ecological, economic and social perspectives. Climate and agriculture services must therefore consider climate as a resource, understand current and future vulnerabilities and risks, and develop synergies that embrace innovation in climate science in order to facilitate sustainable agriculture and food security. The emerging ability of climate science to provide timely and accurate climate information, together with innovative tools and methods for analysis, presents opportunities for managing current climate risks and for initiating strategic climate-resilient adaptation in agriculture. However, to make effective use of these advancements, action-oriented climate advice should integrate information on different time scales (intra-seasonal, seasonal and long-term) for risk/ opportunity management and strategies for optimal and sustainable use of land, water and genetic resources. Strong partnerships and collaboration among international institutions, national hydrometeorological services, agricultural extension agencies, national research institutions, communitybased organisations and social networks are a prerequisite for the advancement of action-oriented advice. All of these efforts present key challenges, but offer immense opportunities, for both climate science and agriculture services, with respect to supporting sustainable agriculture and food security.