The intensification of thermal extremes in west Africa

International audienceThis study aims in filling the gap in understanding the relationship between trend and extreme in diurnal and nocturnal temperatures (Tx and Tn) over the Gulf of Guinea area and the Sahel. Time-evolution and trend of Tx and Tn anomalies, extreme temperatures and heat waves are examined using regional and station-based indices over the 1900–2012 and 1950–2012 periods respectively. In investigating extreme temperature anomalies and heat waves, a percentile method is used. At the regional and local scales, rising trends in Tx and Tn anomalies, which appear more pronounced over the past 60 years, are identified over the two regions. The trends are characterized by an intensification of: i) nocturnal/Tn warming over the second half of the 20th century; and ii) diurnal/Tx warming over the post-1980s. This is the same scheme with extreme warm days and warm nights. Finally annual number of diurnal and nocturnal heat waves has increase over the Gulf of Guinea coastal regions over the second half of the 20th century, and even more substantially over the post-1980s period. Although this trend in extreme warm days and nights is always overestimated in the simulations, from the Coupled Model Intercomparison Project Phase 5 (CMIP5), those models display rising trends whatever the scenario, which are likely to be more and more pronounced over the two regions in the next 50 years

The EuroSTARRS-2001 aircraft campaign of the European Space Agency in support of the SMOS Mission

Ponencia presentada en: III Congreso de la Asociación Española de Climatología “El agua y el clima”, celebrado en Palma de Mallorca del 16 al 19 de junio de 2002.This work was carried out in the framework of the ESA-ESTEC contract no: 15949/02/NL/SF, and the Spanish National Space Research Programme Project no: PNE-009/2001-C-03

SMOS based high resolution soil moisture estimates for Desert locust preventive management

This paper presents the first attempt to include soil moisture information from remote sensing in the tools available to desert locust managers. The soil moisture requirements were first assessed with the users. The main objectives of this paper are: i) to describe and validate the algorithms used to produce a soil moisture dataset at 1 km resolution relevant to desert locust management based on DisPATCh methodology applied to SMOS and ii) the development of an innovative approach to derive high-resolution (100 m) soil moisture products from Sentinel-1 in synergy with SMOS data. For the purpose of soil moisture validation, 4 soil moisture stations where installed in desert areas (one in each user country). The soil moisture 1 km product was thoroughly validated and its accuracy is amongst the best available soil moisture products. Current comparison with in-situ soil moisture stations shows good values of correlation (R>0.7R>0.7) and low RMSE (below 0.04 m3 m−3). The low number of acquisitions on wet dates has limited the development of the soil moisture 100 m product over the Users Areas. The Soil Moisture product at 1 km will be integrated into the national and global Desert Locust early warning systems in national locust centres and at DLIS-FAO, respectively

The Precipitation Inferred from Soil Moisture (PrISM) Near Real-Time Rainfall Product: Evaluation and Comparison

Near real-time precipitation is essential to many applications. In Africa, the lack of dense rain-gauge networks and ground weather radars makes the use of satellite precipitation products unavoidable. Despite major progresses in estimating precipitation rate from remote sensing measurements over the past decades, satellite precipitation products still suffer from quantitative uncertainties and biases compared to ground data. Consequently, almost all precipitation products are provided in two modes: a real-time mode (also called early-run or raw product) and a corrected mode (also called final-run, adjusted or post-processed product) in which ground precipitation measurements are integrated in algorithms to correct for bias, generally at a monthly timescale. This paper describes a new methodology to provide a near-real-time precipitation product based on satellite precipitation and soil moisture measurements. Recent studies have shown that soil moisture intrinsically contains information on past precipitation and can be used to correct precipitation uncertainties. The PrISM (Precipitation inferred from Soil Moisture) methodology is presented and its performance is assessed for five in situ rainfall measurement networks located in Africa in semi-arid to wet areas: Niger, Benin, Burkina Faso, Central Africa, and East Africa. Results show that the use of SMOS (Soil Moisture and Ocean Salinity) satellite soil moisture measurements in the PrISM algorithm most often improves the real-time satellite precipitation products, and provides results comparable to existing adjusted products, such as TRMM (Tropical Rainfall Measuring Mission), GPCC (Global Precipitation Climatology Centre) and IMERG (Integrated Multi-satellitE Retrievals for GPM), which are available a few weeks or months after their detection

Evolution of Surface Hydrology in the Sahelo-Sudanian Strip: An Updated Review

In the West African Sahel, two paradoxical hydrological behaviors have occurred during the last five decades. The first paradox was observed during the 1968–1990s ‘Great Drought’ period, during which runoff significantly increased. The second paradox appeared during the subsequent period of rainfall recovery (i.e., since the 1990s), during which the runoff coefficient continued to increase despite the general re-greening of the Sahel. This paper reviews and synthesizes the literature on the drivers of these paradoxical behaviors, focusing on recent works in the West African Sahelo/Sudanian strip, and upscaling the hydrological processes through an analysis of recent data from two representative areas of this region. This paper helps better determine the respective roles played by Land Use/Land Cover Changes (LULCC), the evolution of rainfall intensity and the occurrence of extreme rainfall events in these hydrological paradoxes. Both the literature review and recent data converge in indicating that the first Sahelian hydrological paradox was mostly driven by LULCC, while the second paradox has been caused by both LULCC and climate evolution, mainly the recent increase in rainfall intensity

Visibilité hydrologique de radars météorologiques opérant en régions montagneuses (application au bassin versant de l'Ardèche)

L'utilisation du radar météorologique pour des applications hydrologiques est encore assez peu répandue. Si l'aspect qualitatif de la mesure radar représente un atout pour l'hydrologie, la mesure quantitative des précipitations bute en revanche sur l'existence de nombreuses sources d'erreurs inhérente à la physique de la mesure radar. En régions montagneuses, le relief constitue une limitation évidente de l'utilisation de cet appareil et le site d'implantation ainsi que le choix du protocole d'exploration apparaissent déterminants dans la qualité des mesures radar. Un objectif de ce travail consiste à prédéterminer la qualité de couverture d'un radar météorologique sur une région donnée. L'influence de trois sources d'erreurs prépondérantes de la mesure radar est modélisée permettant de quantifier et de visualiser la distribution spatiale des erreurs commises sur les intensités pluvieuses. L'intégration de ces cartes d'erreurs simulées dans un modèle hydrologique permet d'observer la répercussion sur la reconstitution des débits à l'exutoire d'un bassin versant de l'Ardèche (Vogué, 640kms2). Une évaluation de la qualité de mesure de deux radars du réseau ARAMIS de Météo France est proposée ainsi qu'une analyse des besoins en terme de corrections.Une partie de ce travail consiste par ailleurs à tirer parti de la présence d'échos de sol pour tester la stabilité temporelle de l'étalonnage électronique d'un radar en analysant le signal rétrodiffusé par un relief.GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF

Surface soil moisture retrieval from L-band radiometry: a global regression study

International audienceUsing a global simulation of L-band (1.4 GHz) brightness temperature (T(B)) for two years (1987 and 1988), the relationship between L-band brightness temperatures and surface soil moisture was analyzed using simple regression models. The global T(B) dataset describes continental pixels at a half-degree spatial resolution and accounts for within-pixel heterogeneity, based on 1-km resolution land cover maps. Two different statistical methods were investigated. First, a single regression model was obtained using a linear combination of T(B) indexes. This method consisted in retrieving surface soil moisture using the same global regression model for all the pixels. Second, a regression model was calibrated over each pixel using similar linear combinations of the T(B) indexes. In both cases, the influence of the radiometric noise on T(B) was investigated. Applying these two methods, the capability of L-band T(B) observations to monitor surface soil moisture was evaluated at the global scale and during a two-year time period. Global maps of the estimated accuracy of the soil moisture retrievals were produced. These results contribute to better define the potential of the observations from future spaceborne missions such as the Soil Moisture and Ocean Salinity (SMOS) mission

Global Simulation of Brightness Temperatures at 6.6 and 10.7 GHz Over Land Based on SMMR Data Set Analysis

International audiencen the framework of the Soil Moisture and Ocean Salinity mission, a two-year (1987-1988) global simulation of brightness temperatures (TB) at L-band was performed using a simple model [L-band microwave emission of the biosphere, (L-MEB)] based on radiative transfer equations. However, the lack of alternative L-band spaceborne measurements corresponding to real-world data prevented from assessing the realism of the simulated global-scale TB fields. In this study, using a similar modeling approach, TB simulations were performed at C-band and X-band. These simulations required the development of C-MEB and X-MEB models, corresponding to the equivalent of L-MEB at C-band and X-band, respectively. These simulations were compared with Scanning Multichannel Microwave Radiometer (SMMR) measurements during the period January to August 1987 (corresponding to the end of life of the SMMR mission). A sensitivity study was also carried out to assess, at a global scale, the relative contributions of the main MEB parameters (particularly the roughness and vegetation model parameters). Regional differences between simulated and measured TBs were analyzed, discriminating possible issues either linked to the radiative transfer model (C-MEB and X-MEB) or due to land surface simulations. A global agreement between observations and simulations was discussed and allowed to evaluate regions where soil moisture retrievals would give best results

Hydraulic response of a tropical urban estuary to a typhoon event: case study of Ho Chi Minh City and typhoon Usagi

Abstract. We investigate the most severe rainfall event ever experienced in Ho Chi Minh City (HCMC), Vietnam. It occurred on November 25th, 2018 when typhoon (TY) Usagi directly hit HCMC. During this event, there was more than 300 mm in rainfall over 24 h which led to flooding and considerable material damages. We propose an in-depth study of the hydrological response of this urban estuary region at a short time scale by focusing on the days before and after typhoon Usagi. We use a set of data analysis and signal processing tools to characterize and quantify both coastal and continental effects on the hydrosystem. We found that TY Usagi made landfall without forming a significant storm surge. The extreme rainfall does not translate in immediate river discharge but presents a 10 hour time lag between peak precipitation and peak residual discharge. Nevertheless, increased water levels can be seen at both urban and upstream river stations with a similar time lag. At the upstream station, residual discharge represents 1.5 % of available rain water and evidence of upstream wide spread flooding was found. At the urban station, we assess the potential surface run off during the event to be 8.9 % of the upstream residual discharge. Hence, the Saigon river would be capable of evacuating the urban flood water after the event. However, a time lag in peak water level and peak rainfall was found and attributed to the combination of high tide and impervious streets which prevented the evacuation of rain water and resulted in street flooding of up to 0.8 m. Overall, it was found that despite not having a significant storm surge, the coastal tidal forcing is predominant in the hydrodynamics of the river even during severe heavy rainfall with tidal fluctuations of water level and respective discharge much larger than the residuals