Morocco, located at the southern margin of the Mediterranean climate-change hotspot, is exposed to a rapidly evolving precipitation regime whose national-scale characterization remains incomplete. This study delivers an integrated assessment of the spatio-temporal variability and trends of precipitation and its extremes over the country during the most recent World Meteorological Organization (WMO) climate-normal period (1991–2020), based on daily observations from 31 synoptic stations operated by the Direction Générale de la Météorologie (DGM). Trends in annual, seasonal and monthly precipitation were quantified using the non-parametric Mann–Kendall test combined with Sen’s slope estimator, while the structural transformation of the rainfall regime was characterized through three indices recommended by the Expert Team on Climate Change Detection and Indices (ETCCDI): the Consecutive Dry Days (CDDs), the Simple Daily Intensity Index (SDII) and the amount of precipitation from very wet days (R95pTOT). The results reveal an apparent tendency toward a negative trend, with a predominance of negative precipitation trends in winter and early spring, most pronounced in February, that reach statistical significance at only a limited number of stations, partly offset by a spatially coherent wetting in November over central and eastern Morocco. The joint analysis of the three ETCCDI indices indicates a north–south contrasted reorganization: northern stations exhibit longer dry spells coexisting with intensified extreme rainfall, whereas southern stations show a generalized weakening of both intensity and extremes. These findings point to a structural shift toward more episodic and contrasted precipitation regimes, with the wet season starting later, ending earlier and concentrating rainfall into fewer but more intense events. The analysis provides an updated observational baseline for the validation of CMIP6 based regional projections and for the design of climate-resilient water and agricultural strategies in Morocco.

Air pollution episodes involving fine particulate matter (PM₂.₅) are tightly linked to synoptic meteorology, which regulates accumulation and dispersion. This study evaluates the ability of Copernicus Atmosphere Monitoring Service (CAMS) reanalyses (2015–2023) to support a daily-scale classification of circulation regimes relevant for air quality in eastern France. CAMS near-surface parameters (temperature, relative humidity, wind) were compared with the high-resolution SAFRAN reanalyses, and CAMS sea-level pressure fields were used to derive a reproducible classification benchmarked against Großwetterlagen.The present study highlights three main regimes. Anticyclonic situations promote strong PM₂.₅ accumulation under stable, poorly ventilated conditions. Low-pressure regimes enhance dispersion through stronger winds and mixing, limiting concentrations. An intermediate regime, less documented in previous classifications, combines moderate pressure gradients and variable transport pathways, producing heterogeneous pollution levels and occasional long-range particle transport.Results show good climatological agreement between CAMS and SAFRAN, with CAMS reproduces the main meteorological and synoptic patterns, while smoothing finer-scale contrasts. The classification explains both seasonal patterns and interannual variability, while underlining the persistent contribution of local emissions (traffic, heating, industry).Overall, CAMS provides a robust synoptic-scale framework for meteorological typologies relevant to air quality. Although its coarse resolution constrains intra-urban representation, coupling with high-resolution urban models could substantially enhance the diagnosis, forecasting, and management of particulate pollution episodes. This approach would not only improve the characterization of wintertime events but also capture the broader annual particle season, thereby providing more robust support for the development of effective mitigation strategies.

Le changement climatique remet en question les stratégies de gestion des milieux naturels. Dans la Réserve Naturelle Régionale et Forêts d’Exception du Val Suzon (RNR-FE), la richesse de la biodiversité tient en partie au climat spécifique de la vallée et aux microclimats variés de ses multiples vallons nommés combes en Bourgogne. On y trouve aussi bien des conditions subméditerranéennes chaudes et sèches que des ambiances montagnardes fraîches et humides. Le changement climatique peut considérablement bouleverser ces conditions. Conscient de ce nouvel enjeu, l’Office National des Forêts (ONF), gestionnaire de la RNR-FE, a intégré dans sa gestion plusieurs actions pour y faire face, dont certaines avec le monde universitaire. En 2022, un partenariat entre l’ONF et le Centre de Recherches de Climatologie (CRC) a donné lieu à l’installation de 4 stations météorologiques pour mieux caractériser le climat de la RNR-FE. En 2023, dans le cadre d’un projet pédagogique du master Changement Climatique Adaptation Territoire (CClimAT), les microclimats sous couvert forestier, au sein des fonds de combes et des versants, sont l’objet d’un travail ayant nécessité l’installation de 41 capteurs thermiques. Le dispositif permet à la fois d’esquisser une caractérisation de la RNR-FE du Val Suzon comme un espace de fraîcheur à proximité de l’agglomération dijonnaise et de caractériser la variabilité de la température au sein des combes. Ce dispositif et cette analyse amorcent un suivi pérenne du climat et des microclimats de la RNF-FE afin de mieux caractériser les effets du changement climatique sur les milieux et les espèces présentes.

The physical mechanisms associated with heat waves (HWs) are well known in the midlatitudes but still under-documented in the Sahel. Specifically, the role of anthropogenic and natural changes in tropospheric aerosols regarding HWs remains an issue to address. Our study focuses on the characterisation of the dusty HWs in the Sahel, which generally occur from March to June. The goal is to reinforce or invalidate the assumption proposed in previous studies recently carried out in southern Europe and according to which mineral dust may locally change irradiance at the surface, thus atmospheric temperatures at 2 m, intensifying the HW. The work is carried out in three steps: (i) detect and describe the HW over the 2003–2014 period based on maximum daily 2-m temperatures (Tmax) from ERA-Interim reanalyses; (ii) characterise the dust optical properties during the HW using the Deep Blue aerosols products from MODIS (Moderate Resolution Imaging Spectroradiometre): the Aerosol Optical Depth at 550 nm (AOD550), the Angstrom Exponent (AE440−870) and the Single Scattering Albedo at 412 nm (SSA412) as a proxy of quantity over atmospheric column, size and absorption of aerosols, respectively; (iii) relate HW intensity to the aerosol conditions during the HW. Over the 12-year study period, 14 HWs are detected when Tmax exceeds the 90th percentile (P90). The HWs are dusty with AOD550 ranging between 0.46 and 1.17 and all the dust types are absorbent with a SSA412 value of 0.93 (round to hundredths). The HW classification according to aerosol conditions gave three HWs: Type 1 corresponds to Pure Dust Situation (PDS with AE440−870 = 0.1), Type 2 and Type 3 are associated with Mixed Situation (MS) with dominance of Coarse Particles (CP with AE440−870 = 0.35) and Fine Particles (FP with AE440−870 = 0.65), respectively. The main result obtained is that the intensity of the dusty HW, computed as the difference between daily Tmax and its P90 (Tmax−P90)), is higher for Type 1 HW (+1.1 °C) in the case of the most absorbent aerosol situation (SSA412 = 0.931). A non-significant difference between Type 2 and Type 3 especially for temperature (+0.5 °C and +0.4 °C, respectively) and SSA (0.938 and 0.935, respectively) is observed and, during these mixing situations, the HWs are less intense than those during the PDS. Finally, the analysis of two huge Type 1 HWs in 2007 and 2010 shows that dust mass concentrations at the surface were particularly high, up to 214 μg/m3 on average. These findings enable us to assess that highly absorbent and concentrated pure dust situations observed in spring in the Sahel may have a potential warming effect at the surface.

This study analyses the long‐term (1950–2100) observed and projected changes in springtime (March–May) heat waves (HWs) in West Africa under climate change. To that end, 28 climate models participating to the fifth Coupled Model Intercomparison Project (CMIP5) are considered, after a statistical post‐correction of their biases. A multi‐scale approach is proposed, covering the Sahel, Senegal, and three thermally‐coherent zones within Senegal. HWs are defined as a sequence of at least three consecutive days above a moving 95th percentile of current temperature distributions. Climate change over Senegal translates into a general shift of the whole statistical distribution towards higher temperature values, with a general stability in the shape of the distribution. Ongoing mean warming could reach +5°C in 2100 under RCP8.5 scenario, implying that coastal Senegal could experience then a mean climate comparable to the hinterland parts today. HWs have increased in intensity, frequency and duration across Sahel and Senegal over the past years, such intensification being higher on recent decades. Future HWs over all regions present intrinsic properties that radically differ from those observed so far. The severity and length of HWs displayed stationary conditions until the late 1990s, but started increasing since then. Projected changes show marked and rapid increase in these variables, the amplitude of which is primarily RCP‐dependent, and secondarily region‐dependent. For both metrics, the largest changes occur over hinterland Senegal and Sahel. There, under RCP8.5 and after the 2070s, the whole spring season could be considered as a permanent HW lasting 3 months. Along the coast, by contrast, average temperatures are both weaker and more variable, causing more frequent threshold crossings and limiting the duration of HWs. The multi‐scale approach used here highlights contrast within Senegal, which constitutes important information for public policy decision‐makers and its inhabitants in terms of adaptation to climate change.

Cet article présente les caractéristiques spatio-temporelles de l’humidité des sols à l’échelle de la France entre deux sous-périodes (1959-1987 et 1988-2019). Les principaux résultats montrent un assèchement généralisé des sols, surtout au printemps et en été, notamment pour trois secteurs : le sud-ouest, le nord-est et le pourtour méditerranéen. L’assèchement des sols peut s’expliquer par un important réchauffement des températures, généralisé et significatif à l’échelle de l’ensemble du territoire, mais bien plus marqué dans le sud-ouest et le nord-est, au printemps et en été. Cette élévation importante des températures entre les deux sous-périodes semble expliquer une très forte hausse de la demande évaporatoire de l’atmosphère, extrêmement marquée du printemps à la fin de l’été. Cette augmentation de l’évapotranspiration potentielle est ici présentée comme un des facteurs déterminant de l’assèchement des sols et de l’aggravation du risque de sécheresses agricoles liés au réchauffement climatique.

Following the high temperatures recorded in the Sahel during 2010 and most recently in May 2013 in the northern part of Senegal where the temperature oscillated between 45 and 50 degrees, significant human deaths were recorded. A good understanding of the dynamics of these heat waves thus become necessary not only to improve the prediction of these events, but also to better assess the impact of future climate change on the occurrence and intensification of these heat waves. To address this issue, simulated CMIP5 daily bias-corrected temperature data interpolated on a 0.5° grid over 1950-2099 have been used by focusing on 3 RCP (Representative Concentration Pathways) scenarios, RCP8.5, RCP4.5 and RCP2.6 . The heat waves in Senegal are defined by relying on exceeding of a moving percentile relative to maximum, minimum and mean temperature during 3 consecutive days over the MAM (March-April-May), the hottest season of the year. Senegal is characterized by a steep zonal temperature gradient from the coast to hinterland. In RCP8.5, the general temperature increase present for the last 60 years (+1.5°C) will continue and reach ~ +5°C in 2100. In this context, at the end of the century the mean temperatures of the western coastal zone will be similar to the present ones of the eastern continental zone, and the warmest spring seasons recorded over the last 15 years will be the norm around 2040. Then exceptional and yet unknown intense heat waves are planned and policy and decision makers will have to anticipate reliable adaptation strategies.

Daily rainfall in southern West Africa (4–8° N, 7° W–3° E) is analyzed with the aim of documenting the intense rainfall events which occur in coastal Ivory Coast, Ghana, Togo, and Benin. The daily 99th percentile (P99) shows that the coastline experiences higher intensity rainfall than inland areas. Using Tropical Rainfall Measuring Mission (TRMM) rainfall data for 1998–2014, a novel way of classifying the intense events is proposed. We consider their space-time structure over a window of 8° latitude-longitude and five days centered on the event. A total 39,680 events (62 at each location) are classified into three major types, mainly found over the oceanic regions south of 5° N, the Bight of Benin, and the inland regions respectively. These types display quite distinct rainfall patterns, propagation features, and seasonal occurrence. Three inland subtypes are also defined. The atmospheric circulation anomalies associated with each type are examined from ERA-interim reanalysis data. Intense rainfall events over the continent are mainly a result of westward propagating disturbances. Over the Gulf of Guinea, many intense events occur as a combination of atmospheric disturbances propagating westward (mid-tropospheric easterly waves or cyclonic vortices) and eastward (lower tropospheric zonal wind and moisture anomalies hypothesized to reflect Kelvin waves). Along the coast, there is a mixture of different types of rainfall events, often associated with interacting eastward- and westward-moving disturbances, which complicates the monitoring of heavy precipitation.

The southern coastal belt of West Africa (SCWA) with its high population density and many major cities, combined to the low elevation and poor urban planning, is very vulnerable to floods resulting from extreme rainfall events. The aim of this paper is to analyze the characteristics of extreme rainfall in the SCWA during the 1981–2015 period, in terms of frequency, intensity, seasonality, and trends. Therefore, daily rainfall of 31 stations located in the southern part of Côte d’Ivoire, Ghana, Togo, and Benin and rainfall estimation products combining in situ observations and satellites rainfall estimation data have been used. For each station and pixel, the local 95th percentile (P95) computed on all rain days of at least 1 mm was used to define extreme rainfall events. Rainfall on the coastal belt is heavier than further inland, with P95 values reaching 82 and 52 mm/day for coastal and continental stations, respectively. Extreme rainfall along the coast occurs predominantly between May and July. Interannual variations of different indicators of extreme rainfall show a broad agreement between rain gauge data and rainfall estimates from CHIRPS (Climate Hazards Group InfraRed Precipitation with Station) data. In the southern part of Côte d’Ivoire and Togo/Benin, increase of number of extreme rainfall event (NP95) and stability number of days with rainfall less than P95 (NL95) are recorded, which induces an increase of total rainfall. But, in the southern part of Ghana, there is a stable total rainfall due to an increase in NP95 compensated by a decrease in NL95.

The potential to use sub-seasonal to seasonal (S2S) prediction systems for outcomes in health is presented, using four case studies of malaria, dengue, heat waves, and meningococcal meningitis. While promising, many such applications are currently in the demonstration phase, and examples of operationalizing S2S-based early warning systems, fully integrated with decision support, have yet to emerge. Potential reasons for this operationalization bottleneck are discussed, which include restrictions on open access to health and climate data, the unfulfilled requirement for training in the use of such systems, and the mismatch between the prediction paradigm and the decision entry points in health-planning systems. The S2S project sponsored by the World Meteorological Organization may help to demonstrate the potential application of climate information, but the lack of real-time access inhibits the operationalization of evaluated systems. It is recommended that partnership platforms, established through the Global Framework for Climate Services and related mechanisms, enable the climate and health academic and operational communities to work together on real-time provision and assessment of health early warning systems. This is particularly important in developing countries where climate-driven health outcomes can be severe.

The relationships between precipitation and temperature in the central Sudano-Sahelian belt are investigated by analyzing 50 years (1959–2008) of observed temperature (Tx and Tn) and rainfall variations. At daily time-scale, both Tx and Tn show a marked decrease as a response to rainfall occurrence, with a strongest departure from normal 1 day after the rainfall event (−0.5 to −2.5 °C depending on the month). The cooling is slightly larger when heavy rainfall events (>5 mm) are considered. The temperature anomalies weaken after the rainfall event, but are still significant several days later. The physical mechanisms accounting for the temperature response to precipitation are analysed. The Tx drop is accounted for by reduced incoming solar radiation associated with increased cloud cover and increased surface evaporation following surface moistening. The effect of evaporation becomes dominant a few days after the rainfall event. The reduced daytime heat storage and the subsequent sensible heat flux result in a later negative Tn anomaly. The effect of rainfall variations on temperature is significant for long-term warming trends. The rainfall decrease experienced between 1959 and 2008 accounts for a rainy season Tx increase of 0.15 to 0.3 °C, out of a total Tx increase of 1.3 to 1.5 °C. These results have strong implications on the assessment of future temperature changes. The dampening or amplifying effects of precipitation are determined by the sign of future precipitation trends. Confidence on temperature changes under global warming partly depend on the robustness of precipitation projections.

Thirteen CMIP5 models are used to analyse changes in climate over the West African monsoon region between the near future (2031–2070 under the RCP4.5 emission scenario), and a control period (1960–1999 under the historical emission scenario), with a focus on the late rainy season. The monsoon circulation is projected to strengthen and to shift northward leading to more rainfall during the Sahelian season. The results show an increase of the Rainfall amounts in September–October and a delay in the monsoon withdrawal. The increased moisture that fuels the rainfall anomalies is associated with an increase in moisture flux convergence and with local moisture recycling. The moisture transport dominates the water budget change in September while the local recycling is prominent in October. The delay in monsoon withdrawal, although expected from the increase in rainfall in September–October, is not strongly correlated with the size of the monthly anomalies.

BACKGROUND:Dengue fever epidemic dynamics are driven by complex interactions between hosts, vectors and viruses. Associations between climate and dengue have been studied around the world, but the results have shown that the impact of the climate can vary widely from one study site to another. In French Guiana, climate-based models are not available to assist in developing an early warning system. This study aims to evaluate the potential of using oceanic and atmospheric conditions to help predict dengue fever outbreaks in French Guiana. METHODOLOGY/PRINCIPAL FINDINGS:Lagged correlations and composite analyses were performed to identify the climatic conditions that characterized a typical epidemic year and to define the best indices for predicting dengue fever outbreaks during the period 1991-2013. A logistic regression was then performed to build a forecast model. We demonstrate that a model based on summer Equatorial Pacific Ocean sea surface temperatures and Azores High sea-level pressure had predictive value and was able to predict 80% of the outbreaks while incorrectly predicting only 15% of the non-epidemic years. Predictions for 2014-2015 were consistent with the observed non-epidemic conditions, and an outbreak in early 2016 was predicted. CONCLUSIONS/SIGNIFICANCE:These findings indicate that outbreak resurgence can be modeled using a simple combination of climate indicators. This might be useful for anticipating public health actions to mitigate the effects of major outbreaks, particularly in areas where resources are limited and medical infrastructures are generally insufficient.

An exercise has been carried out to assess to what extent the Euro-Atlantic Weather Regimes (WR), described from the ERA-interim Reanalysis in the summer season, projects onto a pool of AGCMAMIP simulations in which sea surface temperatures (SST) are prescribed from observations. Although the model simulations present some biases in the spatial structure and seasonality of WRs, exhibiting also less variability, they are able to capture main WR over the region in summer season: +Middle East –Middle East, +NAO, -NAO. WR paradigm is used to quantify changes in the atmosphere under warmer/colder than normal conditions over the Mediterranean Sea. To address this problem, firstly, changes in the frequency and spatial pattern are evaluated versus the spread of the ensemble. A change in the spatial pattern of –NAO is found with higher (lower) pressures centred over France when conditions over the Mediterranean are warmer (colder) than normal. Changes in frequency in the ensemble mean along the season are also evaluated and compared with the signal to noise ratio over the whole season. When temperatures over Mediterranean Sea are warmer (colder) than normal significant changes of WR frequency are: i) more (less) frequency for the -Middle East in June/July ii) shift of the frequency of occurrence for the WR associated with +NAO and iii) less (more) occurrence of –NAO in September-October. Despite the limitation, the analysis suggests that extreme conditions over the Mediterranean basin could modulate WR frequencies, which could have an impact on European weather conditions. Further analysis need to be performed in order to isolate the atmosphere variability forced by the Mediterranean Sea.

An exercise has been carried out to assess to what extent the Euro-Atlantic Weather Regimes (WR), described from the ERA-interim Reanalysis in the summer season, projects onto a pool of AGCM-AMIP simulations in which sea surface temperatures (SST) are prescribed from observations. Although the model simulations present some biases in the spatial structure and seasonality of WRs, exhibiting also less variability, they are able to capture main WR over the region in summer season: +Middle East -Middle East, +NAO, -NAO. WR paradigm is used to quantify changes in the atmosphere under warmer/colder than normal conditions over the Mediterranean Sea. To address this problem, firstly, changes in the frequency and spatial pattern are evaluated versus the spread of the ensemble. A change in the spatial pattern of -NAO is found with higher (lower) pressures centred over France when conditions over the Mediterranean are warmer (colder) than normal. Changes in frequency in the ensemble mean along the season are also evaluated and compared with the signal to noise ratio over the whole season. When temperatures over Mediterranean Sea are warmer (colder) than normal significant changes of WR frequency are: i) more (less) frequency for the -Middle East in June/July ii) shift of the frequency of occurrence for the WR associated with +NAO and iii) less (more) occurrence of -NAO in September-October. Despite the limitation, the analysis suggests that extreme conditions over the Mediterranean basin could modulate WR frequencies, which could have an impact on European weather conditions. Further analysis need to be performed in order to isolate the atmosphere variability forced by the Mediterranean Sea.

L'utilisation de Modeles de Climat Regionaux (MCR) se developpe, ces derniers offrant des potentialites et des limites que nous analysons. Les travaux realises au CRC montrent neanmoins que selon la duree des simulations (de l'evenement meteorologique a l'etude du changement climatique), la fenetre geographique (des tropiques aux regions temperees), la resolution spatiale (de quelques dizaines de km a quelques centaines de m) et les variables etudiees (temperature, precipitation, convection atmospherique, ...), les conditions d'utilisation varient beaucoup. L'utilisation des MCR requiert ainsi une expertise relativement lourde a acquerir, necessitant a la fois recherches collaboratives et continuite.

The accuracy of African Monsoon (AM) simulations together with expected future changes are presented using eight available CMIP5/AR5 AOGCMs under the RCP4.5 emission scenario and eight CMIP3/AR4 AOGCMs under the A1b scenario, with a multimodel approach and the “one model one vote” concept. The results refer to the ‘present’ period (1960–1999) and to a ‘future horizon’ (2031–2070), and are discussed in terms of monsoon dynamics and climate change. Overall the new simulations seem more realistic. They exhibit more accurate rainfall patterns, although some biases reported in CMIP3 models remain. The future changes show an inverse tendency regarding rainfall amounts with less (more) rainfall expected over the western (central‐eastern) Sahel. The deficits are associated with increasing air subsidence and the surplus with a more intense monsoon circulation. An African Rainfall Pattern Index (ARPI), based on standardized rainfall differences between these regions, is defined for capturing the rainfall contrast over the period from 1900 to 2100. This index increases suggesting that the contrasted rainfall anomaly pattern at Sahelian latitudes is expected to occur more frequently in the future.

Future climate changes in African regions are model‐dependent and there is no consensus regarding Sahelian rainfall by the end of this century. Using 12 atmosphere‐ocean global climate models of the third Coupled Model Intercomparison Project (CMIP3) we propose a multi‐model (MM) analysis contrasting the 1960–1999 period (20c3m integration) and the 2031–2070 period (A1B emission scenario). The analyses are based on MM response but also on the ‘one model‐one vote’ concept to give the same weight to each model. The results show robust signals in the rainfall response, i.e., increasing (decreasing) amounts in central (western) Sahel associated with specific changes in atmospheric dynamics. The rainfall excesses expected in central Sahel are mainly linked to an enhancement of the northern Hadley‐type cell and probably to its northward shift. At low‐levels increasing temperature and evaporation strengthen the monsoon flux. Rainfall deficits predicted westward are due to a reinforcement of the African Easterly Jet and to anomalies in the zonal circulation between the Indian and the Atlantic Oceans, favouring air subsidence and moisture export outside the region. The weakening of the meridional circulation is also able to prevent rainfall amounts in the western part of the Sahel. More generally, these analyses show that in future works the Sahel region must not be considered as one consistent region but as two separate areas, both sides of the Greenwich meridian. The authors propose to consider this feature in the next Fifth Assessment cycle (AR5) in order to better understand the impacts of the climate change on West Africa. Copyright © 2012 Royal Meteorological Society