Suchergebnisse

La phytomasse des plantes herbacées et ligneuses est la principale source d'alimentation du bétail pastoral dans les savanes sahéliennes. L'évaluation de la matière première disponible joue un rôle clé dans les politiques nationales d'élevage et nécessite généralement de nombreux relevés de mesures de terrain des plantes herbacées et ligneuses. Dans cette étude, nous avons testé la possibilité d'utiliser un drone à bandes spectrales rouge-vert-bleu (RGB) pour évaluer la phytomasse des espèces ligneuses et herbacées. Avec un drone Dji Spark nous avons ainsi cartographié 38 parcelles d'un hectare dans le nord du Sénégal. La phytomasse herbacée a été mesurée au sol. Pour les communautés ligneuses, nous avons évalué la phytomasse foliaire en utilisant des paramètres dendrométriques associés à des équations allométriques. Nous avons effectué des régressions des moindres carrés partiels entre les indices (en trois dimensions et couleurs) obtenus par drone et la phytomasse. Les résultats ont montré un Q² (résultats de validation croisée pour chaque variable de réponse) de 0,57 pour la phytomasse des ligneux, 0,68 pour la masse sèche des herbacées, et 0,76 pour leur masse fraîche. Cette étude a confirmé la pertinence de l'utilisation d'un drone RGB à faible coût pour l'évaluation de la phytomasse des savanes.

Abstract. Urbanization resulting from sharply increasing demographic pressure and
infrastructure development has made the populations of many tropical areas
more vulnerable to extreme rainfall hazards. Characterizing extreme rainfall
distribution in a coherent way in space and time is thus becoming an
overarching need that requires using appropriate models of
intensity–duration–frequency (IDF) curves. Using a 14 series of 5 min
rainfall records collected in Senegal, a comparison of two generalized
extreme value (GEV) and scaling models is carried out, resulting in the
selection of the more parsimonious one (four parameters), as the recommended model for
use. A bootstrap approach is proposed to compute the uncertainty associated
with the estimation of these four parameters and of the related rainfall
return levels for durations ranging from 1 to 24 h. This study
confirms previous works showing that simple scaling holds for characterizing
the temporal scaling of extreme rainfall in tropical regions such as
sub-Saharan Africa. It further provides confidence intervals for the
parameter estimates and shows that the uncertainty linked to the estimation
of the GEV parameters is 3 to 4 times larger than the uncertainty linked to
the inference of the scaling parameter. From this model, maps of IDF
parameters over Senegal are produced, providing a spatial vision of their
organization over the country, with a north to south gradient for the
location and scale parameters of the GEV. An influence of the distance from
the ocean was found for the scaling parameter. It is acknowledged in
conclusion that climate change renders the inference of IDF curves sensitive
to increasing non-stationarity effects, which requires warning end-users that
such tools should be used with care and discernment.

There is growing awareness among governments, businesses, and the general public of risks arising from changes to our climate on time scales from months through to decades. Some climatic changes could be unprecedented in their harmful socioeconomic impacts, while others with adequate forewarning and planning could offer benefits. There is therefore a pressing need for decision-makers, including policy-makers, to have access to and to use high-quality, accessible, relevant, and credible climate information about the past, present, and future to help make better-informed decisions and policies. We refer to the provision and use of such information as climate services. Established programs of research and operational activities are improving observations and climate monitoring, our understanding of climate processes, climate variability and change, and predictions and projections of the future climate. Delivering climate information (including data and knowledge) in a way that is usable and useful for decision-makers has had less attention, and society has yet to optimally benefit from the available information. While weather services routinely help weather-sensitive decision-making, similar services for decisions on longer time scales are less well established. Many organizations are now actively developing climate services, and a growing number of decision-makers are keen to benefit from such services. This article describes progress made over the past decade developing, delivering, and using climate services, in particular from the worldwide effort galvanizing around the Global Framework for Climate Services under the coordination of UN agencies. The article highlights challenges in making further progress and proposes potential new directions to address such challenges.

Adaptation to anthropogenic climate change is the biggest challenge that humankind faces. The Intergovernmental Panel on Climate Change (IPCC) provides a synthesis of the state of the science, impacts, and policy, with a focus on long-term climate trends. However, the worst impacts of climate change are likely to come from its exacerbation of weather and climate variability. For example, higher temperatures in a particular region could lead to harsher droughts and more deadly heat waves. These are also the kinds of hazards that are regularly monitored and forecast by governments and institutions at the national, regional, and international scale. This paper argues that climate services are a critical component of adaptation. Communities that benefit from climate services will be better adapted to long-term climate change as well as the weather events and the year to-year variability it could make worse. Climate services involve the production, translation, transfer, and use of climate knowledge and information in relevant decision-making, policy and planninga. They involve far more than climate data, encompassing an understanding of the needs of decision makers and delivering useful information in ways it can be applied for better results. A well-functioning climate service can help decision-makers understand, anticipate, and manage climate-related risks across the range of relevant time scales, from days to decades, much in the way a national meteorological service (NMS) does for weather. Yet, in most of the world, climate services are not sufficiently developed, nor are they properly aligned with the needs of decision-makers in the sectors and systems that are most at risk. The urgency of the climate challenge calls for a critical examination of the current state of climate services relative to the needs of decision-makers; it also requires aggressive action to address long-standing obstacles to meeting those needs. While several decades of research, investment, and implementation provide a strong foundation for climate services, more deliberate action is needed to position climate services as essential to adaptation.