Browsing by Autor "F. Timouk"

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Absolute and relative height-pixel accuracy of SRTM-GL1 over the South American Andean Plateau
(Elsevier BV, 2016) Frédéric Satgé; Matheus Denezine; Ramiro Pillco Zolá; F. Timouk; Sébastien Pinel; Jorge Molina‐Carpio; Jérémie Garnier; F. Seyler; Marie‐Paule Bonnet
Accuracy assessment of SRTM v4 and ASTER GDEM v2 over the Altiplano watershed using ICESat/GLAS data
(Taylor & Francis, 2015) Frédéric Satgé; Marie‐Paule Bonnet; F. Timouk; Stéphane Calmant; Ramiro Pillco Zolá; Jorge Molina‐Carpio; Waldo Lavado‐Casimiro; A. Arsen; Jean‐François Crétaux; Jérémie Garnier
The new Global Digital Elevation Model (GDEM v2) has been available since 17 October 2011. With a resolution of approximately 30 m, this model should provide more accurate information than the latest version of Shuttle Radar Topographic Mission (SRTM v4) with a resolution of 90 m outside of the USA. The accuracies of these two recently released digital elevation models (DEMs) were assessed over the Altiplano watershed in South America using ICESat/GLAS data (Ice, Cloud and Land Elevation Satellite/Geoscience Laser Altimeter System). On the global scale, GDEM v2 is more accurate than SRTM v4, which presents a negative bias of approximately 8.8 m. Strong correlations between the DEMs’ accuracies and mean slope values occurred. Regarding land cover, SRTM v4 could be more accurate or easier to correct on a smaller scale than GDEM v2. Finally, a merged and corrected DEM that considers all of these observations was built to provide more accurate information for this region. The new model featured lower absolute mean errors, standard deviations, and root mean square errors relative to SRTM v4 or GDEM v2.
Assessment of satellite rainfall products over the Andean plateau
(Elsevier BV, 2015) Frédéric Satgé; Marie‐Paule Bonnet; Marielle Gosset; Jorge Molina‐Carpio; Wilson Hernan Yuque Lima; Ramiro Pillco Zolá; F. Timouk; Jérémie Garnier
Comparative Assessments of the Latest GPM Mission’s Spatially Enhanced Satellite Rainfall Products over the Main Bolivian Watersheds
(Multidisciplinary Digital Publishing Institute, 2017) Frédéric Satgé; Alvaro Xavier; Ramiro Pillco Zolá; Yawar Hussain; F. Timouk; Jérémie Garnier; Marie‐Paule Bonnet
The new IMERG and GSMaP-v6 satellite rainfall estimation (SRE) products from the Global Precipitation Monitoring (GPM) mission have been available since January 2015. With a finer grid box of 0.1°, these products should provide more detailed information than their latest widely-adapted (relatively coarser spatial scale, 0.25°) counterpart. Integrated Multi-satellitE Retrievals for GPM (IMERG) and Global Satellite Mapping of Precipitation version 6 (GSMaP-v6) assessment is done by comparing their rainfall estimations with 247 rainfall gauges from 2014 to 2016 in Bolivia. The comparisons were done on annual, monthly and daily temporal scales over the three main national watersheds (Amazon, La Plata and TDPS), for both wet and dry seasons to assess the seasonal variability and according to different slope classes to assess the topographic influence on SREs. To observe the potential enhancement in rainfall estimates brought by these two recently released products, the widely-used TRMM Multi-satellite Precipitation Analysis (TMPA) product is also considered in the analysis. The performances of all the products increase during the wet season. Slightly less accurate than TMPA, IMERG can almost achieve its main objective, which is to ensure TMPA rainfall measurements, while enhancing the discretization of rainy and non-rainy days. It also provides the most accurate estimates among all products over the Altiplano arid region. GSMaP-v6 is the least accurate product over the region and tends to underestimate rainfall over the Amazon and La Plata regions. Over the Amazon and La Plata region, SRE potentiality is related to topographic features with the highest bias observed over high slope regions. Over the TDPS watershed, the high rainfall spatial variability with marked wet and arid regions is the main factor influencing SREs.
Modeling Lake Titicaca Daily and Monthly Evaporation
(2018) Ramiro Pillco Zolá; Lars Bengtsson; Ronny Berndtsson; Belén Martí-Cardona; Frédéric Satgé; F. Timouk; Marie‐Paule Bonnet; Luis Mollericon; Cesar Gamarra; José Pasapera
Abstract. Lake Titicaca is an important water ecosystem of South America. Due to uncertainties in estimating the evaporation losses from the lake, surface water storage calculations are uncertain. In this paper, we try to improve evaporation loss estimations by comparing different methods to calculate daily and monthly evaporation from Lake Titicaca. These were: water balance, heat balance, mass transfer method, and the Penman equation. The evaporation was computed at daily time step and compared with estimated evaporation using mean monthly meteorological observations. We found that the most reliable method of determining the annual lake evaporation is using the heat balance approach. To estimate the monthly lake evaporation using heat balance, the heat storage changes must be known in advance. Since convection from the surface layer is intense during nights resulting in a well-mixed top layer every morning, it is possible to determine the change of heat storage from the measured morning surface temperature. The mean annual lake evaporation was found to be 1700 mm. Monthly evaporation computed using daily data and monthly means resulted in minor differences.
Modelling Lake Titicaca's daily and monthly evaporation
(Copernicus Publications, 2019) Ramiro Pillco Zolá; Lars Bengtsson; Ronny Berndtsson; Belén Martí-Cardona; Frédéric Satgé; F. Timouk; Marie‐Paule Bonnet; Luis Mollericon; Cesar Gamarra; José Pasapera
Abstract. Lake Titicaca is a crucial water resource in the central part of the Andean mountain range, and it is one of the lakes most affected by climate warming. Since surface evaporation explains most of the lake's water losses, reliable estimates are paramount to the prediction of global warming impacts on Lake Titicaca and to the region's water resource planning and adaptation to climate change. Evaporation estimates were done in the past at monthly time steps and using the four methods as follows: water balance, heat balance, and the mass transfer and Penman's equations. The obtained annual evaporation values showed significant dispersion. This study used new, daily frequency hydro-meteorological measurements. Evaporation losses were calculated following the mentioned methods using both daily records and their monthly averages to assess the impact of higher temporal resolution data in the evaporation estimates. Changes in the lake heat storage needed for the heat balance method were estimated based on the morning water surface temperature, because convection during nights results in a well-mixed top layer every morning over a constant temperature depth. We found that the most reliable method for determining the annual lake evaporation was the heat balance approach, although the Penman equation allows for an easier implementation based on generally available meteorological parameters. The mean annual lake evaporation was found to be 1700 mm year−1. This value is considered an upper limit of the annual evaporation, since the main study period was abnormally warm. The obtained upper limit lowers by 200 mm year−1, the highest evaporation estimation obtained previously, thus reducing the uncertainty in the actual value. Regarding the evaporation estimates using daily and monthly averages, these resulted in minor differences for all methodologies.
Role of Climate Variability and Human Activity on Poopó Lake Droughts between 1990 and 2015 Assessed Using Remote Sensing Data
(Multidisciplinary Digital Publishing Institute, 2017) Frédéric Satgé; Raúl Espinoza-Villar; Ramiro Pillco Zolá; Henrique Llacer Roig; F. Timouk; Jorge Molina‐Carpio; Jérémie Garnier; Stéphane Calmant; F. Seyler; Marie‐Paule Bonnet
In 2015, an emergency state was declared in Bolivia when Poopó Lake dried up. Climate variability and the increasing need for water are potential factors responsible for this situation. Because field data are missing over the region, no statements are possible about the influence of mentioned factors. This study is a preliminary step toward the understanding of Poopó Lake drought using remote sensing data. First, atmospheric corrections for Landsat (FLAASH and L8SR), seven satellite derived indexes for extracting water bodies, MOD16 evapotranspiration, PERSIANN-CDR and MSWEP rainfall products potentiality were assessed. Then, the fluctuations of Poopó Lake extent over the last 26 years are presented for the first time jointly, with the mean regional annual rainfall. Three main droughts are highlighted between 1990 and 2015: two are associated with negative annual rainfall anomalies in 1994 and 1995 and one associated with positive annual rainfall anomaly in 2015. This suggests that other factors than rainfall influenced the recent disappearance of the lake. The regional evapotranspiration increased by 12.8% between 2000 and 2014. Evapotranspiration increase is not homogeneous over the watershed but limited over the main agriculture regions. Agriculture activity is one of the major factors contributing to the regional desertification and recent disappearance of Poopó Lake.
Unraveling the impacts of droughts and agricultural intensification on the Altiplano water resources
(Elsevier BV, 2019) Frédéric Satgé; Yawar Hussain; Alvaro Xavier; Ramiro Pillco Zolá; Leandro de Almeida Salles; F. Timouk; F. Seyler; Jérémie Garnier; Frédéric Frappart; Marie‐Paule Bonnet