Use of a Distributed Sensor Network to Parameterize a Model of Flows between the Soil, Vegetation, and Atmosphere in a Mixed Savanna-Agricultural Catchment in South Eastern Burkina Faso.

Natalie Claire Ceperley
2012
Discussion par affiche

Résumé

The hydrologic processes underlying a natural savanna in a semi-arid environment is altered when savanna is converted to agriculture. Inﬁltration is often observed to decrease while rapid runoff increases to the detriment of crop productivity, downstream populations and local water sources. Planting a mix of vegetation in cultivated fields, mimicking the dispersal of trees in a savanna has been proposed as a solution to help buffer these consequences. However the hydrologic behavior of savanna, agricultural, and agroforestry land cover is not fully understood for the Sudanian vegetation zone of West Africa and the consequences of land use changes are debatable. We use a distributed sensor network of seventeen wireless meteorological stations including soil moisture sensors in addition to two eddy covariance stations and sap ﬂow probes dispersed across cultivated rice and millet ﬁelds, natural savanna, fallow ﬁelds, and around agroforestry trees, specifically Sclerocarya birrea, to understand land cover controls on variations in evapotranspiration and infiltration over a semi arid watershed in Southeastern Burkina Faso. N ormalized difference vegetation indexes taken from weekly MODIS images as well as personal field observations were used to inform seasonal and spatial variations in albedo, rate of transfer to ground heat flux, and roughness length. Measurements are used parameterize a distributed model of energy and hydrologic fluxes between the soil and atmosphere controlled by the vegetated surface and presence of agroforestry trees. We use this model to further understanding of the effect of Sudanian land cover on the water and energy balances by exploring the effects of modifications in the arrangement and dispersion of vegetation types. Outreach work in the community is on-going and our hope is that the results of our modeling will inform local farming practices.

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https://infoscience.epfl.ch/record/196167?ln=fr

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Natalie Claire Ceperley
2012
Discussion par affiche

Résumé

Official source

https://infoscience.epfl.ch/record/196167?ln=fr

À propos de ce résultat

Concepts associés (23)

thumb|Culture intensive de pomme de terre en plein champ, Maine (États-Unis), 2002|alt= vignette|Production de blé à Oman L’agriculture (du latin agricultura, composé à partir de ager, « champ », et

L'eau est une substance chimique constituée de molécules . Ce composé, très stable, mais aussi très réactif, est un excellent solvant à l'état liquide. Dans de nombreux contextes, le terme eau est e

Le Burkina Faso (prononciation : ou ), littéralement « patrie des (personnes) intègres » ou « patrie de l'intégrité », anciennement République de Haute-Volta et couramment appelé Burkina, est un pa

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Water use by Sclerocarya birrea Agroforestry Trees in Sudanian Savanna: Application of Wireless Sensor Networks

Natalie Claire Ceperley

Small scale rain fed agriculture is the primary livelihood for a large part of the population of Burkina Faso. Regional climate change means that this population is becoming increasingly vulnerable. Additionally, as natural savanna is converted for agriculture, hydrological systems are observed to become less stable as inﬁltration is decreased and rapid runoff is increased to the detriment of crop productivity, downstream populations and local water sources. The majority of the Singou River Basin, located in South East Burkina Faso is managed by hunting reserves, geared to maintaining high populations of wild game; however, residents surrounding the protected areas have been forced to intensify agriculture that has resulted in soil degradation as well as increases in the frequency and severity of ﬂooding and droughts. Agroforestry, or planting trees in cultivated ﬁelds, has been proposed as a solution to help buffer these negative consequences, however the speciﬁc hydrologic behavior of the watershed land cover is unknown. Sclerocarya birrea, or Marula, is a dominant agroforestry tree in the region valued for its medicinal, ritual, and hydrologic services. We explore the effect of Sclerocarya birrea trees on the soil moisture response to precipitation in millet-dominated agricultural ﬁelds in the village of Tambarga, Burkina Faso. We compare the water budget constructed surrounding a single Sclerocarya birrea tree with that in an open ﬁeld using measured values of soil water content, canopy inﬁltration, precipitation, evaporation. Data are collected through a distributed sensor network of 17 Sensorscope wireless meteorological stations in addition to 2 eddy covariance stations and sap ﬂow probes. These stations are dispersed across cultivated rice and millet ﬁelds, natural savanna, fallow ﬁelds, and around agroforestry ﬁelds. Three of the stations are uniquely conﬁgured around Sclerocarya birrea trees. Sensorscope routes data through the network of stations to be delivered by a GPRS connection to a main server. Data are available in real time via a website that can be accessed by a mobile phone. The stations are powered autonomously by small photovoltaic panels. This deployment is the ﬁrst time that these meteorological stations have been used on the African continent. Results from this research are being coupled with outreach activities in the community in order to best integrate them into local practices. Our hope is that the results of our modeling will inform local farmers and thus help improve their adaption to changing weather patterns and land cover.

2011

Chargement

Small scale rain fed agriculture is the primary livelihood for a large part of the population of Burkina Faso. Regional climate change means that this population is becoming increasingly vulnerable. Additionally, as natural savanna is converted for agriculture, hydrological systems are observed to become less stable as infiltration is decreased and rapid runoff is increased to the detriment of crop productivity, downstream populations and local water sources. The majority of the Singou River Basin, located in South East Burkina Faso is managed by hunting reserves, geared to maintaining high populations of wild game; however, residents surrounding the protected areas have been forced to intensify agriculture that has resulted in soil degradation as well as increases in the frequency and severity of flooding and droughts. Agroforestry, or planting trees in cultivated fields, has been proposed as a solution to help buffer these negative consequences, however the specific hydrologic behavior of the watershed land cover is unknown. We have installed a distributed sensor network of 17 Sensorscope wireless meteorological stations. These stations are dispersed across cultivated rice and millet fields, natural savanna, fallow fields, and around agroforestry fields. Sensorscope routes data through the network of stations to be delivered by a GPRS connection to a main server. This multi hop network allows data to be gathered over a large area and quickly adapts to changes in station performance. Data are available in real time via a website that can be accessed by a mobile phone. The stations are powered autonomously by small photovoltaic panels. This deployment is the first time that these meteorological stations have been used on the African continent. Initial calibration with measures from 2 eddy covariance stations allows us to calculate the energy balance at each of the Sensorscope stations. Thus, we can observe variation in evaporation over the various land cover in the watershed. This research will both contribute to scientific understanding of West African vegetation and inform local reforestation and agricultural management. Concurrent to this scientific research, the community is improving natural resource management efforts including reforestation, a botanical garden and environmental education. Our hope is that the results of our evaporation modeling will inform local farmers and thus help improve their adaption to changing weather patterns and land cover.

2010

Chargement

Hydrology of the Sudanian Savannah in West Africa, Burkina Faso

Theophile Mande

As in all semi-arid regions, Tambarga, a small village surrounded by national parks in the landlocked country of Burkina Faso, is affected by the seasonality of the local hydrology. Seasonal and spatial variability of rainfall shapes the livelihoods of rural farmers who depend mainly on rain-fed agriculture. We instrumented the Tambarga catchment (area=~4 km2) to investigate the rainfall patterns, the resulting hydrologic processes (surface runoff, base flow) and the evaporation effects on the local water balance. Thus, we have measured hydrological, meteorological and soil parameters at high spatial and temporal resolution over the catchment since 2009. Data for this research were acquired from the 2010 to 2012 rainy seasons using a network of automatic wireless weather stations (SensorScope stations), two weirs, eight piezometric wells, and two surface energy balance stations. Rain at Tambarga is triggered by the convective mechanism, which is mainly controlled by the sensible heat flux. The daytime rain events at Tambarga are convective and are characterized by their high intensities and short durations. An overall increase in rainfall of 10-30% is observed in the savannah forest when compared to the agricultural field from 2010 to 2012. Biotic (leaf area index) and abiotic (well drained soil) factors, causing enhanced sensible heat flux at the savannah site, lead to an increased predisposition toward convective rainfall. The hydrologic processes concomitant to the rain events were identified over the basin and intermittent responses of streamflow were isolated. The rise of the perched water tables located in the upstream and downstream regions of the basin generated two separate flows in the riverbed after the first rain. The intermediate zone operates like a deep storage tank, and by filling, it creates a connection between the two perched water tables. This connection induces a continuous flow throughout the 2.8 km of the stream. The hydrologic response at the basin outlet is observed to alternate between two different states over the course of the season. At the start of the rainy season, when the soils are very dry and the groundwater level is deep, a typical single-peak hydrograph is observed. This evolves into a double-peak hydrograph when the rainy season is completely established. The single-peak hydrograph is correlated with rainfall intensity, while the double-peak hydrograph is also correlated with the antecedent soil moisture condition. The baseflow, meanwhile, occurs when the groundwater level is higher than the riverbed at certain locations in the basin. In contrast, during dry days (no rain) the baseflow exhibits a diurnal flow pattern. This diurnal pattern consists of decreased flow rate from sunrise (6:00 A.M.) to 1:00 P.M. and flow rate recovery to its previous level from 1:00 P.M. to sunset (6:00 P.M.). The diurnal pattern of the streamflow was found to be derived both from infiltration in the riverbed and evaporation over the river edges. The infiltration process dominates during the beginning of the season. While late in the season, when the groundwater network is interconnected and its overall level is higher than the riverbed elevation, evaporation controls the diurnal pattern. An evaporation contributing area is defined when the diurnal pattern is controlled by the evaporation. This area is about 0.6% of the basin area and could be rationally represented by the riparian area and the outlet wetland. Given the importance of rainfall-runoff processes over this catchment, a water balance was completed based on a simple lumped model. This model allowed for testing some water management strategies to improve agricultural production. Its implementation suggests that storing water underground for irrigation purpose with deeper wells is a way to achieve better agricultural productivity and therefore, reduce the vulnerability of the local people.

EPFL2013

Chargement

Water use by Sclerocarya birrea Agroforestry Trees in Sudanian Savanna: Application of Wireless Sensor Networks

Natalie Claire Ceperley

2011

Small scale rain fed agriculture is the primary livelihood for a large part of the population of Burkina Faso. Regional climate change means that this population is becoming increasingly vulnerable. Additionally, as natural savanna is converted for agriculture, hydrological systems are observed to become less stable as infiltration is decreased and rapid runoff is increased to the detriment of crop productivity, downstream populations and local water sources. The majority of the Singou River Basin, located in South East Burkina Faso is managed by hunting reserves, geared to maintaining high populations of wild game; however, residents surrounding the protected areas have been forced to intensify agriculture that has resulted in soil degradation as well as increases in the frequency and severity of flooding and droughts. Agroforestry, or planting trees in cultivated fields, has been proposed as a solution to help buffer these negative consequences, however the specific hydrologic behavior of the watershed land cover is unknown. We have installed a distributed sensor network of 17 Sensorscope wireless meteorological stations. These stations are dispersed across cultivated rice and millet fields, natural savanna, fallow fields, and around agroforestry fields. Sensorscope routes data through the network of stations to be delivered by a GPRS connection to a main server. This multi hop network allows data to be gathered over a large area and quickly adapts to changes in station performance. Data are available in real time via a website that can be accessed by a mobile phone. The stations are powered autonomously by small photovoltaic panels. This deployment is the first time that these meteorological stations have been used on the African continent. Initial calibration with measures from 2 eddy covariance stations allows us to calculate the energy balance at each of the Sensorscope stations. Thus, we can observe variation in evaporation over the various land cover in the watershed. This research will both contribute to scientific understanding of West African vegetation and inform local reforestation and agricultural management. Concurrent to this scientific research, the community is improving natural resource management efforts including reforestation, a botanical garden and environmental education. Our hope is that the results of our evaporation modeling will inform local farmers and thus help improve their adaption to changing weather patterns and land cover.

2010

Hydrology of the Sudanian Savannah in West Africa, Burkina Faso

Theophile Mande

EPFL2013