Early Warning of Drought in Europe

The performances of the first month of the ECMWF probabilistic extended forecast and the seasonal forecast to predict droughts over Europe are compared. The Standardized Precipitation Index is used to quantify droughts. It can be shown that on average the extended forecast has higher skill than the seasonal forecast whilst both outperform climatology. No significant spatial or temporal patterns can be observed but the scores are improved when we focus on large scale droughts. This report further analyses several different methods to convert the probabilistic forecasts of SPI into a Boolean drought warning. It can be demonstrated that methodologies which convert low percentiles of the forecasted cumulative distribution function of SPI into warnings are superior in comparison to alternatives such as the mean or the median of the ensemble. This work demonstrates that around 40% of droughts in Europe are correctly forecasted one month in advance. Nevertheless, due to the lack of the significant difference between the distributions of the ensemble members for false alarms or misses on one hand side and correct forecasts on the other hand side, it is not yet possible to quantify the uncertainty of the drought forecasts.JRC.H.7-Climate Risk Managemen

Recent climatological trend of the Saharan heat low and its impact on the West African climate

The Saharan heat low (SHL) plays a pivotal role in the West African monsoon system in spring and summer. The recent trend in SHL activity has been analysed using two sets of numerical weather prediction (NWP) model reanalyses and Atmospheric Models Intercomparison Project simulations from 15 climate models performed in the framework of the 5th Coupled Models Intercomparison Project (CMIP5) exercise. A local increase of temperature in the Sahara during the 90s is found in the two sets of NWP models temperature. This increase is stronger within the SHL region than over the surrounding areas. Using different temporal filters (under 25 days, 25–100 days and above 300 days), we show that this is accompanied by a slight but widespread increase of temperature, and a change in the filtered signal under 25 days during the transition period of the 90s. We also show that SHL pulsations occurring at different time scales impact the West Africa climate on a variety of spatial scales, from the regional scale (for the high band pass) to the synoptic scale (for the low band pass signal). Despite a large variability in the temporal trends for 15 climate models from the CMIP5 project, the warming trend in the 90s is observed in the models ensemble mean. Nevertheless, large discrepancies are found between the NWP models reanalyses and the climate model simulations regarding the spatial and temporal evolutions of the SHL as well as its impact on West African climate at the different time scales. These comparisons also reveal that climate models represent the West African monsoon interactions with SHL pulsations quite differently. We provide recommendations to use some of them depending on the time scales of the processes at play (synoptic, seasonal, interannual) and based on key SHL metrics (location, mean intensity, global trend, interaction with the West African monsoon dynamics).JRC.H.7-Climate Risk Managemen

Fennec dust forecast intercomparison over the Sahara in June 2011

International audienceIn the framework of the Fennec international programme , a field campaign was conducted in June 2011 over the western Sahara. It led to the first observational data set ever obtained that documents the dynamics, thermodynam-ics and composition of the Saharan atmospheric boundary layer (SABL) under the influence of the heat low. In support to the aircraft operation, four dust forecasts were run daily at low and high resolutions with convection-parameterizing and convection-permitting models, respectively. The unique airborne and ground-based data sets allowed the first ever intercomparison of dust forecasts over the western Sahara. At monthly scale, large aerosol optical depths (AODs) were forecast over the Sahara, a feature observed by satellite retrievals but with different magnitudes. The AOD intensity was correctly predicted by the high-resolution models, while it was underestimated by the low-resolution models. This was partly because of the generation of strong near-surface wind associated with thunderstorm-related density currents that could only be reproduced by models representing con-vection explicitly. Such models yield emissions mainly in the afternoon that dominate the total emission over the western fringes of the Adrar des Iforas and the Aïr Mountains in the high-resolution forecasts. Over the western Sahara, where the harmattan contributes up to 80 % of dust emission, all the models were successful in forecasting the deep well-mixed SABL. Some of them, however, missed the large near-surface dust concentration generated by density currents and low-level winds. This feature, observed repeatedly by the airborne lidar, was partly forecast by one high-resolution model only

ClimSA Station: Fitness For Purpose

This technical report describes a case study where the Fitness for Purpose (F4P), i.e., a series of benchmarking and analysis tools available in the ClimSA Station, were applied to four rainfall estimation (RFE) space-born products. The F4P toolbox aims at providing methods and frameworks for observational datasets and mutual comparison of regional-scale models to give clear indication on which datasets are best fitting for user purposes. The analysis took in consideration 21 years of data (2001, 2021) obtained from CHIRPS, FEWSNET, TAMSAT and ARC2 products. The document describes the main results derived from the application of the different F4P metrics: longitudinal average diagram, scatter density diagrams, histograms, cumulated distribution functions, gamma-index analysis and trend analysis. The general conclusion reported a good agreement between the four RFE products, as an example, the scatter density analysis highlighted that some product pairs are in better agreement with each other. The longitudinal average diagram showed that all products are able to describe the same precipitation behaviour, over the considered time period, on the African continent. The Mann-Kendall seasonal test results in good agreement of the four trend distributions. The F4P toolbox proven its ability in assessing products reliability and complements the ClimSA station as a key tool for the implementation of the Integrated African Meteorology Strategy, strengthening political decision-making at all levels.JRC.D.6 - Nature Conservation and Observation

The effect of African Easterly Wave suppression by periodicity on Atlantic tropical cyclones

Research has shown that suppressing African Easterly Waves (AEWs) does not reduce basin-wide North Atlantic tropical cyclone (TC) frequency but can enhance TC environmental favorability. We investigated the AEW-TC relationship further by examining the effects of suppressing the two AEW periodicities individually on TC activity. Using regional model simulations, AEWs were prescribed or suppressed in the 2-6 d or 6-10 d ranges through the lateral boundary conditions. Seasonal TC frequency increased significantly when either AEW periodicity was suppressed, with a larger increase when the 2-6 d waves were suppressed. We also found that suppressing the 2-6 d waves increased mid-tropospheric moisture by up to 8%, as well as overall atmospheric instability, near the western coast of northern Africa. Furthermore, the convective disturbances that developed into TCs exhibited stronger rotation, increased ascending motion, and higher rainfall. Our results suggest that reduced 2-6 d AEW activity may trigger a more active TC season

Characterization of dust emission from alluvial sources using aircraft observations and high-resolution modeling

International audienceWe investigate mineral dust emission from alluvial sediments within the upland region in northern Mauritania in the vicinity of a decaying nocturnal low-level jet (LLJ). For the first time, the impact of valleys that are embedded in a rather homogeneous surrounding is investigated with regard to their role as dust source. Measures for local atmospheric dust burden were retrieved from airborne observations, satellite observations, and model simulations and analyzed in order to provide complementary information at different horizontal scales. Observations by the LEANDRE Nouvelle Generation backscatter lidar system flying aboard the French Falcon 20 aircraft were taken along five parallel flight legs perpendicular to the orientation of the main valley system dominating the topography of the study area. Results from a comparison of lidar-derived extinction coefficients with topography and aerial photographs confirm the relevance of (1) alluvial sediments at the valley bottoms as a dust source, and (2) the break-down of the nocturnal LLJ as a trigger for dust emission in this region. An evaluation of the AROME regional model, forecasting dust at high resolution (5 km grid), points toward an under-representation of alluvial dust sources in this region. This is also evident from simulations by the MesoNH research model. Although MesoNH simulations show higher dust loadings than AROME, which are more comparable to the observations, both models underestimate the dust concentrations within the boundary layer compared to lidar observations. A sensitivity study on the impact of horizontal grid spacing (5 km versus 1 km) highlights the importance of spatial resolution on simulated dust loadings

Artificial Intelligence at the JRC

This document presents the contributions presented at the first internal workshop on Artificial Intelligence (AI), organized by the Joint Research Centre (JRC) of the European Commission. This workshop was held on 23rd May at the premises of the JRC in Ispra (Italy), with video-conference to all JRC's sites. The workshop aimed to gather JRC specialists on AI to share their experience, to identify opportunities for meeting the EC demands on AI, and explore synergies among different JRC's working groups on AI. The full-day session workshop was organized around three main topical strands entitled Policy support, New Initiatives and Technology Development. Contributions covered a wide range of areas, including applications of AI to Cybersecurity, Transport, Environment, Health and other specific issues. This report is structured according to those main topics of study. According to the JRC Director General Vladimír Šucha: "The workshop was very stimulating and interesting presenting a broad spectrum of activities and competencies across JRC. It gave a great opportunity to build a strong and hopefully useful position in the field of AI/ML". While the first part of the workshop was mainly informative, in the second part we collectively discussed about JRC priorities and the set-up of a Community of Practice (now available at https://webgate.ec.europa.eu/connected/groups/community-of-practice-ai-and-big-data) dealing with AI and Big Data. Finally, the preliminary results of the online survey were presented. All colleagues were excellent in communicating their scientific activity in a flash and efficient way.JRC.B.6 - Digital Econom

Etude des relations Onde - Convection - Pluie et influence de la variabilité du flux de mousson en Afrique de l'Ouest

In the West Africa area and especially over the sahel, climate changing possess a great impact on the populationn where agricultural and breeding economies are exposed to drought threat. Therefore, the understanding of climate behavior and its variability, particulary the knowledge of atmospheric perturbations and theirs consequences on the rainfall dynamical processes are very important to define accomodate strategies.This thesis poit out rainfall variability due to atmospheric perturbations. The aims of this study are to understand how the perturbations in the 700 hPa wind field, the Africa Easterly Waves (AEWs) can modulate convective activity and rainfall, and the effects of these AEWs in the intra seasonal and interannal tie scales.The first part of this thesis describes the state of art of the West African climate. In the second part, the AEWs detection methodology, as well as its main characteristics are presented. In the third part, the inter annual variability of the rainfall is analysed by signal treatment method. The fourth part shows the interaction between AEWs convective activity and rainfall. The impact of AEWs sector exibits a great spatial variability. This study is extended by the local and large scale effects of AEWs. The low level conditions appear important to generate both convection and rainfall. In the last part, the intra seasonal variability of the Monsoon flux is analysed. The impact of AEWs and convection on these pulsations are shown.Les variations climatiques en Afrique de l'Ouest ont un impact parfois catastrophique, particuliérement au Sahel ou les populations sont exposées aux aléas des ressources en eau. Cette thèse s'inscrit dans la recherche des différents modes de variabilités atmosphèrique et de leurs conséquences sur les processus qui générent les pluies, afin de mieux apprehender le climat et ses variabilités dans cette région. Ce travail porte sur la part de la variabilité des précipitations au Sahel qui peut être expliquée par la variabilité atmosphérique. L'objectif principal est de comprendre comment les perturbations du champ de vent à 700 hPa - les ondes d'est africaines (AEWs) - agissent sur la convectionqui est elle meme à l'origine des précipitations. Après avoir exposé les connaissances actuelles de la climatologie en Afrique de l'Ouest, et expliqué la méthodologie développée pour étudier les ondes d'est, la variabilité des précipitations est étudiée à différentes échelles. La modulation de la convection et des précipitations par les ondes est ensuite traitée et permet de distinguer des secteurs propices aux fortes précipitations, ou au contraire inhibiteurs. L'impact des ondes sur la dynamique et la thermodynamique atmosphérique est également abordé, en particulier dans les basses couches atmosphériques. Un autre aspect original de cette thèse est d'étudier comment les ondes d'est s'insèrent dans la variabilité interannuelle et intra saisonnière du flux de mousson. Après avoir mis en évidence des phases actives et inactives du flux de mousson, le comportement des ondes, de la convection et des précipitations est discriminé en fonction des phases de l'onde