The Megha-Tropiques satellite, dedicated to water and energy budget in the Tropical atmosphere ... more The Megha-Tropiques satellite, dedicated to water and energy budget in the Tropical atmosphere was successfully launched in October 2011. This Tropical member of GPM will provide an enhanced sampling of the convective systems in the inter-tropical band and will contribute to better estimations of the precipitation in this zone. Applications of the MT rainfall products are expected in a range of fields, ranging from climate studies to hydrology, or even health (vector based disease monitoring). We will review the Megha-Tropiques Ground Validation Activities in the inter-tropical zone. Both direct evaluation of the rainfall products by comparison with ground reference, and integrated (or hydrological) validation are planned. The ground reference will be provided by weather radar or rain gage networks, from operational or research projects. A validation super site based on a polarimetric radar has been set up in West Africa. We will discuss the various methods that will be applied to...
Cette communication presente les principales caracteristiques d’un modele d’inondations urbaines ... more Cette communication presente les principales caracteristiques d’un modele d’inondations urbaines operant a l’echelle de l’agglomeration complete a une tres fine resolution spatiale (~10m), dans une optique de prevision en temps reel. Alors que les inondations sont caracterisees par des ecoulements multi-directionnels, il n’est pas possible d’utiliser des modeles d’ecoulement 2D a l’echelle de l’agglomeration entiere, en raison de temps de calcul tres longs et de difficultes d’acces a une information topographique detaillee. Nous proposons donc une alternative de modelisation simplifiee, offrant des performances raisonnables, une mise en place rapide et des temps de calcul de quelques minutes, compatibles avec la prevision en temps reel. Le modele opere sur la base d’un Modele Numerique de Terrain au pas de 10m, modifie pour prendre en compte les conditions urbaines : drainage artificiel, obstacles lies au bâti. Les conditions de production (ex : occupation des sols) ou de transfert ...
Urban floods due to intense precipitation are a major problem in many tropical regions as in Afri... more Urban floods due to intense precipitation are a major problem in many tropical regions as in Africa. Rainfall measurement using microwave links from cellular communication networks has been proposed as a cost effective solution to monitor rainfall in these areas where the gauge network is scarce. The method consists in retrieving rainfall from the attenuation estimated along the commercial microwave links (CMLs) thanks to the power levels provided by an operator. In urban areas where the network is dense, rainfall can be estimated and mapped for hydrological prediction. Rainfall estimation from CMLs is subject to uncertainties. This paper analyzes the advantages and limitations of this rainfall data for a distributed hydrological model applied to an urban area. The case study is in West Africa in Ouagadougou where a hydrological model has been set up. The analysis is based on numerical simulations, using high resolution rain maps from a weather radar to emulate synthetic microwave l...
A method that formulates the retrieval of drop size distribution (DSD) parameters from polarimetr... more A method that formulates the retrieval of drop size distribution (DSD) parameters from polarimetric radar variables at attenuating frequency as the solution of an inverse problem is presented. The DSD in each radar bin is represented by a normalized Gamma distribution defined by three parameters (Dm,N0*,μ). The direct problem that describes polarimetric radar observables—scattering and propagation terms—and their dependency on DSD parameters is analyzed based on T-matrix scattering simulations. The inverse algorithm and its application to the DSD retrieval are then presented. The inverse method is applied to an African Monsoon Multidisciplinary Analysis (AMMA) field campaign that deployed an X-band dual-polarization Doppler radar and optical disdrometers in Benin, West Africa, in 2006 and 2007. The dataset is composed of X-band polarimetric radar PPIs and disdrometer data for 15 organized convective systems observed in 2006. A priori information on DSD parameters (benchmark method) ...
Quarterly Journal of the Royal Meteorological Society, Jun 25, 2018
Funding information French Spatial Agency CNES. A series of multi-platform rainfall estimates is ... more Funding information French Spatial Agency CNES. A series of multi-platform rainfall estimates is evaluated at the daily 1 • resolution over three dense rain-gauge networks in West Africa, in Niger, Burkina Faso and Benin, for the period 2012-2016. The quality of the ground reference, its dependence on the number of gauges and the consequences on the validation are discussed. The primary objective of this work is the evaluation of the newly released Tropical Analysis of Precipitation with an Estimation of Errors (TAPEER) daily one-degree rainfall accumulation from the Megha-Tropiques mission. Several other multi-platform products, GSMAP, CMORPH, PERSIANN, TMPA and IMERG, are also evaluated over the same area to put TAPEER performance into perspective. For each product only the version that uses solely satellite information (no gauge adjustment) is used. The analysis concentrates on the heart of the rainy season in West Africa, from June to September. TAPEER exhibits good skill over the region, with a high correlation and a good reproduction of the frequency distribution of the rain rates, especially in the Sahelian region-Niger and Burkina Faso-where the biases are close to zero. The bias is stronger (and negative) in Benin. This overall good performance is stable from year to year. The other products exhibit less bias in Benin and more in the Sahel. CMORPH stands out with relatively good correlations, GSMAP slightly less and PERSIANN has a very strong bias in the Sahel. IMERG, analysed over a shorter period, is also promising.
AbstractSpatiotemporal rainfall variability is a key parameter controlling the dynamics of mosqui... more AbstractSpatiotemporal rainfall variability is a key parameter controlling the dynamics of mosquitoes/vector-borne diseases such as malaria, Rift Valley fever (RVF), or dengue. Impacts from rainfall heterogeneity at small scales (i.e., 1–10 km) on the risk of epidemics (i.e., host bite rate or number of bites per host and per night) must be thoroughly evaluated. A model with hydrological and entomological components for risk prediction of the RVF zoonosis is proposed. The model predicts the production of two mosquito species within a 45 km × 45 km area in the Ferlo region, Senegal. The three necessary steps include 1) best rainfall estimation on a small scale, 2) adequate forcing of a simple hydrological model leading to pond dynamics (ponds are the primary larvae breeding grounds), and 3) best estimate of mosquito life cycles obtained from the coupled entomological model. The sensitivity of the model to the spatiotemporal heterogeneity of rainfall is first tested using high-resolut...
Urban floods due to intense precipitation are a major problem in many tropical regions as in Afri... more Urban floods due to intense precipitation are a major problem in many tropical regions as in Africa. Rainfall measurement using microwave links from cellular communication networks has been proposed as a cost effective solution to monitor rainfall in these areas where the gauge network is scarce. The method consists in retrieving rainfall from the attenuation estimated along the commercial microwave links (CMLs) thanks to the power levels provided by an operator. In urban areas where the network is dense, rainfall can be estimated and mapped for hydrological prediction. Rainfall estimation from CMLs is subject to uncertainties. This paper analyzes the advantages and limitations of this rainfall data for a distributed hydrological model applied to an urban area. The case study is in West Africa in Ouagadougou where a hydrological model has been set up. The analysis is based on numerical simulations, using high resolution rain maps from a weather radar to emulate synthetic microwave l...
Proceedings of the International Association of Hydrological Sciences
Urban floods due to intense precipitation is a major problem in many developing countries, especi... more Urban floods due to intense precipitation is a major problem in many developing countries, especially in Africa. There are few available solutions for effective and yet affordable flood early warning systems for these regions. Weather radar is common in industrialized countries but too costly for most tropical cities. Satellite provides interesting information in real time but not yet quantitative enough at the space and time scales needed for urban flood monitoring. Rainfall measurement using commercial microwave links (CML) from cellular communication networks is a cost effective alternative to conventional methods. The method is based on measuring rain induced fluctuations between telecommunication antennas; if the operator provides this information rain maps can be produced and used for hydrological prediction. Many CML studies have been carried out in Europe and Israel. Recently IRD implemented pilot sites in Africa in order to test this rainfall estimation technique and quantify the uncertainties. After reviewing the method principles and providing an overview of the current research on CML, we present a simulation framework to analyse the propagation of CML rainfall uncertainties in an urban hydrological model.
Journal of Applied Meteorology and Climatology, Feb 1, 2016
The particle identification scheme developed by Dolan and Rutledge for X-band polarimetric radar ... more The particle identification scheme developed by Dolan and Rutledge for X-band polarimetric radar is tested for the first time in Africa and compared with in situ measurements. The data were acquired during the Megha-Tropiques mission algorithm-validation campaign that occurred in Niger in 2010. The radar classification is compared with the in situ observations gathered by an instrumented aircraft for the 13 August 2010 squall-line case. An original approach has been developed for the radar–in situ comparison: it consists of simulating synthetic radar variables from the microphysical-probe information and comparing the two datasets in a common “radar space.” The consistency between the two types of observation is good considering the differences in sampling illustrated in the paper. The time evolution of the hydrometeor types and their relative proportion in the convective and stratiform regions are analyzed. The farther away from the convection one looks, the more aggregation dominates, riming diminishes, and hydrometeors are less dense. Particle identification based on the polarimetric radar will be applied to a 5-yr African dataset in the future.
African cities are prone to recurrent flooding due to unfavourable rainfall conditions, often ins... more African cities are prone to recurrent flooding due to unfavourable rainfall conditions, often insufficient drainage infrastructure and fast and poorly controlled urban development. It is thus important to put forward efficient tools to characterize flooding and its consequences over large urban areas, e.g. the entire agglomeration. However, scarce data and long computation time limit the use of classic hydraulic models in such cases and require to propose alternative models. Therefore, a GIS-based urban flood model is proposed as a case study in the city of Ouagadougou (Burkina Faso), in order to produce flood mapping at small spatial resolution over the entire conglomeration. Spatial discretization is done using a Digital Elevation Model (DEM) forced by various obstacles (urban blocks) or drainage axis (roads or water collectors). The mesh size is set to 10 m to get a good representation of the urban objects and drainage directions. Runoff at the cell scale is calculated using an S...
The Megha-Tropiques satellite, dedicated to water and energy budget in the Tropical atmosphere ... more The Megha-Tropiques satellite, dedicated to water and energy budget in the Tropical atmosphere was successfully launched in October 2011. This Tropical member of GPM will provide an enhanced sampling of the convective systems in the inter-tropical band and will contribute to better estimations of the precipitation in this zone. Applications of the MT rainfall products are expected in a range of fields, ranging from climate studies to hydrology, or even health (vector based disease monitoring). We will review the Megha-Tropiques Ground Validation Activities in the inter-tropical zone. Both direct evaluation of the rainfall products by comparison with ground reference, and integrated (or hydrological) validation are planned. The ground reference will be provided by weather radar or rain gage networks, from operational or research projects. A validation super site based on a polarimetric radar has been set up in West Africa. We will discuss the various methods that will be applied to...
Cette communication presente les principales caracteristiques d’un modele d’inondations urbaines ... more Cette communication presente les principales caracteristiques d’un modele d’inondations urbaines operant a l’echelle de l’agglomeration complete a une tres fine resolution spatiale (~10m), dans une optique de prevision en temps reel. Alors que les inondations sont caracterisees par des ecoulements multi-directionnels, il n’est pas possible d’utiliser des modeles d’ecoulement 2D a l’echelle de l’agglomeration entiere, en raison de temps de calcul tres longs et de difficultes d’acces a une information topographique detaillee. Nous proposons donc une alternative de modelisation simplifiee, offrant des performances raisonnables, une mise en place rapide et des temps de calcul de quelques minutes, compatibles avec la prevision en temps reel. Le modele opere sur la base d’un Modele Numerique de Terrain au pas de 10m, modifie pour prendre en compte les conditions urbaines : drainage artificiel, obstacles lies au bâti. Les conditions de production (ex : occupation des sols) ou de transfert ...
Urban floods due to intense precipitation are a major problem in many tropical regions as in Afri... more Urban floods due to intense precipitation are a major problem in many tropical regions as in Africa. Rainfall measurement using microwave links from cellular communication networks has been proposed as a cost effective solution to monitor rainfall in these areas where the gauge network is scarce. The method consists in retrieving rainfall from the attenuation estimated along the commercial microwave links (CMLs) thanks to the power levels provided by an operator. In urban areas where the network is dense, rainfall can be estimated and mapped for hydrological prediction. Rainfall estimation from CMLs is subject to uncertainties. This paper analyzes the advantages and limitations of this rainfall data for a distributed hydrological model applied to an urban area. The case study is in West Africa in Ouagadougou where a hydrological model has been set up. The analysis is based on numerical simulations, using high resolution rain maps from a weather radar to emulate synthetic microwave l...
A method that formulates the retrieval of drop size distribution (DSD) parameters from polarimetr... more A method that formulates the retrieval of drop size distribution (DSD) parameters from polarimetric radar variables at attenuating frequency as the solution of an inverse problem is presented. The DSD in each radar bin is represented by a normalized Gamma distribution defined by three parameters (Dm,N0*,μ). The direct problem that describes polarimetric radar observables—scattering and propagation terms—and their dependency on DSD parameters is analyzed based on T-matrix scattering simulations. The inverse algorithm and its application to the DSD retrieval are then presented. The inverse method is applied to an African Monsoon Multidisciplinary Analysis (AMMA) field campaign that deployed an X-band dual-polarization Doppler radar and optical disdrometers in Benin, West Africa, in 2006 and 2007. The dataset is composed of X-band polarimetric radar PPIs and disdrometer data for 15 organized convective systems observed in 2006. A priori information on DSD parameters (benchmark method) ...
Quarterly Journal of the Royal Meteorological Society, Jun 25, 2018
Funding information French Spatial Agency CNES. A series of multi-platform rainfall estimates is ... more Funding information French Spatial Agency CNES. A series of multi-platform rainfall estimates is evaluated at the daily 1 • resolution over three dense rain-gauge networks in West Africa, in Niger, Burkina Faso and Benin, for the period 2012-2016. The quality of the ground reference, its dependence on the number of gauges and the consequences on the validation are discussed. The primary objective of this work is the evaluation of the newly released Tropical Analysis of Precipitation with an Estimation of Errors (TAPEER) daily one-degree rainfall accumulation from the Megha-Tropiques mission. Several other multi-platform products, GSMAP, CMORPH, PERSIANN, TMPA and IMERG, are also evaluated over the same area to put TAPEER performance into perspective. For each product only the version that uses solely satellite information (no gauge adjustment) is used. The analysis concentrates on the heart of the rainy season in West Africa, from June to September. TAPEER exhibits good skill over the region, with a high correlation and a good reproduction of the frequency distribution of the rain rates, especially in the Sahelian region-Niger and Burkina Faso-where the biases are close to zero. The bias is stronger (and negative) in Benin. This overall good performance is stable from year to year. The other products exhibit less bias in Benin and more in the Sahel. CMORPH stands out with relatively good correlations, GSMAP slightly less and PERSIANN has a very strong bias in the Sahel. IMERG, analysed over a shorter period, is also promising.
AbstractSpatiotemporal rainfall variability is a key parameter controlling the dynamics of mosqui... more AbstractSpatiotemporal rainfall variability is a key parameter controlling the dynamics of mosquitoes/vector-borne diseases such as malaria, Rift Valley fever (RVF), or dengue. Impacts from rainfall heterogeneity at small scales (i.e., 1–10 km) on the risk of epidemics (i.e., host bite rate or number of bites per host and per night) must be thoroughly evaluated. A model with hydrological and entomological components for risk prediction of the RVF zoonosis is proposed. The model predicts the production of two mosquito species within a 45 km × 45 km area in the Ferlo region, Senegal. The three necessary steps include 1) best rainfall estimation on a small scale, 2) adequate forcing of a simple hydrological model leading to pond dynamics (ponds are the primary larvae breeding grounds), and 3) best estimate of mosquito life cycles obtained from the coupled entomological model. The sensitivity of the model to the spatiotemporal heterogeneity of rainfall is first tested using high-resolut...
Urban floods due to intense precipitation are a major problem in many tropical regions as in Afri... more Urban floods due to intense precipitation are a major problem in many tropical regions as in Africa. Rainfall measurement using microwave links from cellular communication networks has been proposed as a cost effective solution to monitor rainfall in these areas where the gauge network is scarce. The method consists in retrieving rainfall from the attenuation estimated along the commercial microwave links (CMLs) thanks to the power levels provided by an operator. In urban areas where the network is dense, rainfall can be estimated and mapped for hydrological prediction. Rainfall estimation from CMLs is subject to uncertainties. This paper analyzes the advantages and limitations of this rainfall data for a distributed hydrological model applied to an urban area. The case study is in West Africa in Ouagadougou where a hydrological model has been set up. The analysis is based on numerical simulations, using high resolution rain maps from a weather radar to emulate synthetic microwave l...
Proceedings of the International Association of Hydrological Sciences
Urban floods due to intense precipitation is a major problem in many developing countries, especi... more Urban floods due to intense precipitation is a major problem in many developing countries, especially in Africa. There are few available solutions for effective and yet affordable flood early warning systems for these regions. Weather radar is common in industrialized countries but too costly for most tropical cities. Satellite provides interesting information in real time but not yet quantitative enough at the space and time scales needed for urban flood monitoring. Rainfall measurement using commercial microwave links (CML) from cellular communication networks is a cost effective alternative to conventional methods. The method is based on measuring rain induced fluctuations between telecommunication antennas; if the operator provides this information rain maps can be produced and used for hydrological prediction. Many CML studies have been carried out in Europe and Israel. Recently IRD implemented pilot sites in Africa in order to test this rainfall estimation technique and quantify the uncertainties. After reviewing the method principles and providing an overview of the current research on CML, we present a simulation framework to analyse the propagation of CML rainfall uncertainties in an urban hydrological model.
Journal of Applied Meteorology and Climatology, Feb 1, 2016
The particle identification scheme developed by Dolan and Rutledge for X-band polarimetric radar ... more The particle identification scheme developed by Dolan and Rutledge for X-band polarimetric radar is tested for the first time in Africa and compared with in situ measurements. The data were acquired during the Megha-Tropiques mission algorithm-validation campaign that occurred in Niger in 2010. The radar classification is compared with the in situ observations gathered by an instrumented aircraft for the 13 August 2010 squall-line case. An original approach has been developed for the radar–in situ comparison: it consists of simulating synthetic radar variables from the microphysical-probe information and comparing the two datasets in a common “radar space.” The consistency between the two types of observation is good considering the differences in sampling illustrated in the paper. The time evolution of the hydrometeor types and their relative proportion in the convective and stratiform regions are analyzed. The farther away from the convection one looks, the more aggregation dominates, riming diminishes, and hydrometeors are less dense. Particle identification based on the polarimetric radar will be applied to a 5-yr African dataset in the future.
African cities are prone to recurrent flooding due to unfavourable rainfall conditions, often ins... more African cities are prone to recurrent flooding due to unfavourable rainfall conditions, often insufficient drainage infrastructure and fast and poorly controlled urban development. It is thus important to put forward efficient tools to characterize flooding and its consequences over large urban areas, e.g. the entire agglomeration. However, scarce data and long computation time limit the use of classic hydraulic models in such cases and require to propose alternative models. Therefore, a GIS-based urban flood model is proposed as a case study in the city of Ouagadougou (Burkina Faso), in order to produce flood mapping at small spatial resolution over the entire conglomeration. Spatial discretization is done using a Digital Elevation Model (DEM) forced by various obstacles (urban blocks) or drainage axis (roads or water collectors). The mesh size is set to 10 m to get a good representation of the urban objects and drainage directions. Runoff at the cell scale is calculated using an S...
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Papers by Matias Alcoba