Estimating crop-specific evapotranspiration using remote-sensing imagery at various spatial resolutions for improving crop growth modelling

in International Journal of Remote Sensing (2013)

By governing water transfer between vegetation and atmosphere, evapotranspiration (ET) can have a strong influence on crop yields. An estimation of ET from remote sensing is proposed by the EUMETSAT ... [more ▼]

By governing water transfer between vegetation and atmosphere, evapotranspiration (ET) can have a strong influence on crop yields. An estimation of ET from remote sensing is proposed by the EUMETSAT ‘Satellite Application Facility’ (SAF) on Land Surface Analysis (LSA). This ET product is obtained operationally every 30 min using a simplified SVAT scheme that uses, as input, a combination of remotely sensed data and atmospheric model outputs. The standard operational mode uses other LSA-SAF products coming from SEVIRI imagery (the albedo, the downwelling surface shortwave flux, and the downwelling surface longwave flux), meteorological data, and the ECOCLIMAP database to identify and characterize the land cover. With the overall objective of adapting this ET product to crop growth monitoring necessities, this study focused first on improving the ET product by integrating crop-specific information from high and medium spatial resolution remote-sensing data. A Landsat (30 m)-based crop type classification is used to identify areas where the target crop, winter wheat, is located and where crop-specific Moderate Resolution Imaging Spectroradiometer (MODIS) (250 m) time series of green area index (GAI) can be extracted. The SVAT model was run for 1 year (2007) over a study area covering Belgium and part of France using this supplementary information. Results were compared to those obtained using the standard operational mode. ET results were also compared with ground truth data measured in an eddy covariance station. Furthermore, transpiration and potential transpiration maps were retrieved and compared with those produced using the Crop Growth Monitoring System (CGMS), which is run operationally by the European Commission’s Joint Research Centre to produce in-season forecast of major European crops. The potential of using ET obtained from remote sensing to improve crop growth modelling in such a framework is studied and discussed. Finally, the use of the ET product is also explored by integrating it in a simpler modelling approach based on light-use efficiency. The Carnegie–Ames–Stanford Approach (CASA) agroecosystem model was therefore applied to obtain net primary production, dry matter productivity, and crop yield using only LSA-SAF products. The values of yield were compared with those obtained using CGMS, and the dry matter productivity values with those produced at the Flemish Institute for Technological Research (VITO). Results showed the potential of using this simplified remote-sensing method for crop monitoring. [less ▲]

Estimating regional wheat yield from the shape of decreasing curves of green area index temporal profiles retrieved from MODIS data

in International Journal of Applied Earth Observation and Geoinformation (2012), 18

Earth observation data, owing to their synoptic, timely and repetitive coverage, have been recognized as a valuable tool for crop monitoring at different levels. At the field level, the close correlation ... [more ▼]

Earth observation data, owing to their synoptic, timely and repetitive coverage, have been recognized as a valuable tool for crop monitoring at different levels. At the field level, the close correlation between green leaf area (GLA) during maturation and grain yield in wheat revealed that the onset and rate of senescence appeared to be important factors for determining wheat grain yield. Our study sought to explore a simple approach for wheat yield forecasting at the regional level, based on metrics derived from the senescence phase of the green area index (GAI) retrieved from remote sensing data. This study took advantage of recent methodological improvements in which imagery with high revisit frequency but coarse spatial resolution can be exploited to derive crop-specific GAI time series by selecting pixels whose ground-projected instantaneous field of view is dominated by the target crop: winter wheat. A logistic function was used to characterize the GAI senescence phase and derive the metrics of this phase. Four regression-based models involving these metrics (i.e., the maximum GAI value, the senescence date and the thermal time taken to reach 50% of the green surface in the senescent phase) were related to official wheat yield data. The performances of such models at this regional scale showed that final yield could be estimated with an RMSE of 0.57 ton ha−1, representing about 7% as relative RMSE. Such an approach may be considered as a first yield estimate that could be performed in order to provide better integrated yield assessments in operational systems. [less ▲]

Les systèmes agropastoraux :viabilité et adaptation aux risques climatiques

Scientific conference (2010, November 04)

A SIMPLIFIED APPROACH FOR WHEAT YIELD ESTIMATES BASED ON METRICS DERIVED FROM GREEN AREA INDEX DECREASING CURVES.

Poster (2010, September)

Modélisation spatiale des flux organiques et minéraux assurant la productivité durable des agroécosystèmes culture-élevage dans le sahel nigérien

Doctoral thesis (2010)

Agriculture (including crop and livestock) employs more than 80% of the work force in semi-arid regions of West Africa and provide most of the food requirements and incomes. In most developing countries ... [more ▼]

Agriculture (including crop and livestock) employs more than 80% of the work force in semi-arid regions of West Africa and provide most of the food requirements and incomes. In most developing countries, soil nutrient depletion is a major issue for soil degradation. Crop-livestock integration is an effective means by which nutrients can be rapidly recycled within and between farms. In West Niger, where mixed farming systems dominate, livestock's role in recycling organic matter and mineral nutrients (nitrogen, phosphorus and potassium) must be better assessed to increase production and ensure sustainable food security. Nutrient flows through forage uptake and excretion deposit by grazing livestock must be assessed at a wider scale than the farm. Organic matter and nutrients balance and fluxes were used as measurable criteria for sustainable agriculture production. This research focuses on these indicators assessments at farm, land use unit and village level. This study was conducted in three agropastoral territories in the Fakara region of western Niger (Dantiandou District) that lies between the Niger River to the west and the Dallol Boboye (Bosso), a fossil valley tributary of the Niger, to the east. The area has homogeneous geological characteristics and rainfall conditions, but land use history, human and animal population density and cropping intensity vary within the region. 461 farms were concerned. In the mixed crop-livestock systems, the duality of the spatial organization, crop management at field level and livestock management with communal rangeland is a major issue for nutrients balance and fertility management modeling. Two models were then used to assess flows and nutrients balances. The NUTMON Toolbox developed by Dutch researchers is used to assess agricultural fluxes at farm parcels level. Spatial modeling was done with NUTPAST, a GIS tool developed in this thesis framework to assess livestock intake and excretion fluxes at land use scale. This tool takes into account the spatiotemporal patterns of vegetation as well as livestock seasonal variation. Quantile regression analysis and multinomial polytomous logistic regression modeling was used to assess soil fertility depletion risk indicator based on farm agriculture viability variables and nutrients partial balance. The results obtained show a less negative partial nutrients balance than in previous studies when the livestock spatio-temporal effect is taken into account. The results bring functional improvement and analytical evaluation of flows and partial nutrients balance calculation, while taking into account the functions of livestock in the organic matter recycling. The overall partial balance of N, P, K are 0.3 ± 0.6, 1.2 ± 0.2, 0.9 ± 0.5 kg/ha. The review highlighted a wide disparity between farms which show a strongly positive balance among livestock owners and negative balance among Fakara small farmers with few land and livestock endowments. Owning animals allows some households to maintain soil fertility by capturing and mobilizing soil nutrients. Risk indicators, based on land pressure indicator at 3x3 km geographic grid level, livestock endowments and land per capita reveal that despite a slow intensification, the trend for a risk of relative depletion of soil fertility is very high. This trend may compromise the sahelian agriculture sustainability. The problems of unequal benefit from communal resources remain a big issue of the sahelian agriculture. With increasing pressure on land, it is necessary to look beyond the traditional free range communal grazing systems to more intensive alternatives and stronger land tenure policies. [less ▲]

Bulletin agrométéorologique - Situation au 30 avril 2010

in Bulletin Agrométéorologique (2010), 8(1), 1-4

La période hivernale fut caractérisée par des températures inférieures aux moyennes des 20 dernières années. L’hiver fut également marqué par d’abondantes chutes de neige. Les sommes de températures ... [more ▼]

La période hivernale fut caractérisée par des températures inférieures aux moyennes des 20 dernières années. L’hiver fut également marqué par d’abondantes chutes de neige. Les sommes de températures calculées depuis le début du mois de janvier sont inférieures d’environ 170 degrés.jours par rapport à la situation moyenne, ce qui signifie un retard moyen des cultures d’une bonne semaine, voire davantage. Les images satellites montrent cependant que ce retard calculé à partir du cumul de températures serait en grande partie rattrapé fin avril. En dehors du retard phénologique calculé par une de nos deux méthodes, aucun autre élément agrométéorologique important n’est à signaler. Aucune prévision de rendement n’est faite à ce stade. [less ▲]

Managing climatic risks for enhanced food security : key information capabilities

in Procedia Environmental Sciences (2010), 1

Food security is expected to face increasing challenges from climatic risks that are more and more exacerbated by climate change, especially in the developing world. This document lists some of the main ... [more ▼]

Food security is expected to face increasing challenges from climatic risks that are more and more exacerbated by climate change, especially in the developing world. This document lists some of the main capabilities that have been recently developed, especially in the area of operational agroclimatology, for an efficient use of natural resources and a better management of climatic risks. Many countries, including the developing world, now benefit from well-trained staff in the use of climate data, physical and biological information and knowledge to reduce negative climate impacts. A significant volume of data and knowledge about climate–agriculture relationships is now available and used by students, scientists, technicians, agronomists, decision-makers and farmers alike, particularly in the areas of climate characterization, land suitability and agroecological zoning, seasonal climate forecasts, drought early warning systems and operational crop forecasting systems. Climate variability has been extensively modelled, capturing important features of the climate through applied statistical procedures, agroclimatic indices derived from raw climatic data and from remote sensing. Predictions of climate at seasonal to interannual timescales are helping decision-makers in the agricultural sector to deal more effectively with the effects of climate variability. Land suitability and agroclimatic zoning have been used in many countries for agricultural planning, thanks to the availability of new and comprehensive methodologies; developments in climate, soil and remote sensing data collection and analysis; and improved applications in geographic information systems (GIS). Drought early warning systems are available worldwide at both national and international levels. These systems are helping decisionmakers and farmers to take appropriate decisions to adapt to short-term climatic risks. Also, operational crop forecasting systems are now becoming available at the regional and national levels. In some developed countries, several efficient and well tested tools are now available for optimizing on-farm decisions based on the combination of crop simulation models and seasonal forecasts. However, in developing countries few tools have been developed to efficiently manage crops at the farm level to cope with climate variability and climate risks. Climate change impacts on agriculture and food security have been assessed in international studies using specific and efficient methodologies and tools. Adaptation to climate change and variability can also be facilitated through effective planning and implementation of strategies at the political level. The role of technological progress, risk transfer mechanisms and financial instruments and their easy accessibility to rural people are critical elements of climate risk management. [less ▲]

Bulletin agrométéorologique - Situation au 30 avril 2009

in Bulletin Agrométéorologique (2009), 7(1), 1-3

Alors que l’on pouvait craindre les conséquences de l’hiver froid que nous avons connu cette année, il apparaît, au niveau de nos indicateurs météorologiques et de nos indicateurs spatiaux dérivés de la ... [more ▼]

Alors que l’on pouvait craindre les conséquences de l’hiver froid que nous avons connu cette année, il apparaît, au niveau de nos indicateurs météorologiques et de nos indicateurs spatiaux dérivés de la télédétection, que les grandes cultures ont dans l’ensemble bien passé l’hiver et elles ont largement rattrapé le retard accumulé au cours des mois d’hiver et du tout début de printemps. Ceci se vérifie également sur le terrain où les stades phénologiques sont très proches de la situation normale. Aucune prévision de rendement n’est faite à ce stade. [less ▲]

Trends in productivity of crops, fallow and rangelands in Southwest Niger: Impact of land use, management and variable rainfall

in Journal of Hydrology (2009), 375 (1-2)

To document trends in land use and herbaceous production, 71 field sites sampled among cropped fields, fallow fields and rangelands in the Fakara region (Niger) were monitored from 1994 to 2006. The ... [more ▼]

To document trends in land use and herbaceous production, 71 field sites sampled among cropped fields, fallow fields and rangelands in the Fakara region (Niger) were monitored from 1994 to 2006. The overall trend in land use confirmed the historical increase of the cropped areas since mid 20th century, at an annual rate of 2% from 1994 to 2006. This trend is the result of changes in the relative extent of fields permanently cropped and fields under shifting cultivation, and for the latter, the relative proportion of short (3 years) and long (10 years) duration fallows. Type of land use together with topography and soil type determine the herbaceous production and the resulting yield measured towards the end of the wet season. The variation in site yields between years is of the same order of magnitude as the variation in yields between sites within a year. There is an overall decreasing trend in site yields by 5% annually from 1994 to 2006 that is not explained by variations in rainfall. The decreasing trend is observed on fields under shifting cultivation, fallowed fields and rangelands, although not all sites are equally affected. Causes are likely to be multiple which might include changes in land use, decline of soil fertility and increased grazing pressure. Indeed, the remaining rangelands on marginal land and the fallows still accessible to livestock are subject to such a heavy grazing during the rainy season that the herbaceous standing mass measured at the end of the season reflects poorly the actual production. After the two first years of cropping, the herbaceous yield in fields under shifting cultivation with no fertilisation is negatively affected by the number of successive years of cropping. Moreover, clearing fallow after a decreasing number of years affects the mean herbaceous yield of fallowed fields by reducing the contribution of more productive old fallows. Changes in land use, grazing pressure and soil fertility also triggered changes in species composition with a strong reduction in diversity from rangelands to fallows, and again from fallows to cropland weeds. No correlations was found however between productivity and species composition. Cumulative rainfall does not explain between site or between year deviations in herbaceous yield even when sites are sorted by land use type or by soil type in the case of fallow and rangelands. Simulated production calculated with the STEP model does not explain herbaceous yields much better even when sites are grouped by land use and soil type. However, relative changes of herbaceous yields are reasonably predicted on sites that remained fallowed and were not heavily grazed for at least four consecutive years. [less ▲]

Les Zones à risque environnementales et socio-économiques - ZARESE

Report (2006)