The Penman-Monteith (PM) equation is a state-of-the-art modelling approach to simulate evapotranspiration (ET) at site and local scale. However, its practical application is often restricted by the availability and quality of required parameters. One of these parameters is the canopy conductance. Long term measurements of evapotranspiration by the eddy-covariance method provide an improved data basis to determine this parameter by inverse modelling. Because this approach may also include evaporation from the soil, not only the ‘actual’ canopy conductance but the whole surface conductance (gc) is addressed. Two full cycles of crop rotation with five different crop types (winter barley, winter rape seed, winter wheat, silage maize, and spring barley) have been continuously monitored for 10 years. These data form the basis for this study. As estimates of gc are obtained on basis of measurements, we investigated the impact of measurements uncertainties on obtained values of gc. Here, two different foci were inspected more in detail. Firstly, the effect of the energy balance closure gap (EBCG) on obtained values of gc was analysed. Secondly, the common hydrological practice to use vegetation height (hc) to determine the period of highest plant activity (i.e., times with maximum gc concerning CO2-exchange and transpiration) was critically reviewed. The results showed that hc and gc do only agree at the beginning of the growing season but increasingly differ during the rest of the growing season. Thus, the utilisation of hc as a proxy to assess maximum gc (gc,max) can lead to inaccurate estimates of gc,max which in turn can cause serious shortcomings in simulated ET. The light use efficiency (LUE) is superior to hc as a proxy to determine periods with maximum gc. Based on this proxy, crop specific estimates of gc,maxcould be determined for the first (and the second) cycle of crop rotation: winter barley, 19.2 mm s−1 (16.0 mm s−1); winter rape seed, 12.3 mm s−1 (13.1 mm s−1); winter wheat, 16.5 mm s−1 (11.2 mm s−1); silage maize, 7.4 mm s−1 (8.5 mm s−1); and spring barley, 7.0 mm s−1 (6.2 mm s−1).

Policy makers adopt irrigated agriculture for food security, since irrigation doubles crop production. Therefore, the development of large irrigation systems has a long history in many places worldwide. Although large-scale irrigation schemes play an important role in improving food security, many schemes, especially in Africa, do not yield the expected outcomes. This is related to poor water management, which is generally due to a lack of effective evaluation and monitoring. The objective of this study, therefore, is to propose a new methodology to assess, evaluate and monitor large-scale irrigation systems. Information on irrigation indicators is needed to enable the evaluation of irrigation performance. The evaluation is the first and the most significant step in providing information about how it is performing. After reviewing extensive literature, a list of indicators related to the performance of irrigation, rainwater supply and productivity is suggested. The irrigation efficiency indicators Relative Irrigation Supply (RIS) and Relative Water Supply (RWS) are selected. Potential rainwater supply to crops can be tested based on the Moisture Availability Index (MAI) and the Ratio of Moisture Availability (RMA). Water productivity can be assessed by Crop Yield (Y) and Water Use Efficiency (WUE). However, the central problem facing large-scale irrigation schemes is always the lack of data, which calls for the development of a new method of data acquisition that allows evaluation and monitoring. Remote Sensing (RS) technology makes it possible to retrieve data across large areas. Two different approaches via RS, the Normalized Difference Vegetation Index (NDVI) and Actual Evapotranspiration (ETa), can be utilized for monitoring. The well-known Vegetation Condition Index (VCI), derived from the NDVI, is modified (MVCI) to allow a qualitative spatio-temporal assessment of irrigation efficiency. MVCI takes into account crop response to water availability, while ETa indicates whether water is used as intended. Furthermore, the assessment of the possible hydrological impact of the irrigation system should be considered in the evaluation and monitoring process. The Sudanese Gezira Scheme of 8,000 square kilometers in the Nile Basin, where performance evaluation and monitoring are absent or poorly conducted, is no exception. This research takes the large-scale irrigation of the Gezira Scheme as a case study, as it is the largest scheme, not only in the Nile Basin but also in the world, under single management. The first long-term historical evaluation of the scheme is conducted for the period 1961–2012 rather than only on a short-time scale as is the common practice. An increase in RIS and RWS values from 1.40 and 1.70 to 2.23 and 2.60, respectively, since the 1993/94 season shows decreasing irrigation efficiency. MAI and RMA for summer crops indicate a promising rainfall contribution to irrigation in July and August. The Gezira Scheme achieves low yield and WUE in comparison to many irrigation schemes of the globe. Low productivity is mainly due to poor distribution and irrigation mismanagement. This is indicated by the 15-year MVCI spatio-temporal analysis, which shows that the northern part of the scheme experiences characteristic drought during the summer crop season. Although MVCI can be considered a monitoring tool, the index does not deduct the soil water content, and water could be wasted and available in other ways (e.g. water depressions). Spatio-temporal information for ETa is required to better quantify water depletion and establish links between land use and water allocation. However, several RS models have been developed for estimating ETa. Thus, improving the understanding of performance of such models in arid climates, as well as large-scale irrigation schemes, is taken into account in this study. Four different models based on the energy balance method, the Surface Energy Balance Algorithm for Land (SEBAL), Mapping EvapoTranspiration at High Resolution with Internalized Calibration (METRIC™), Simplified Surface Energy Balance (SSEB) and MOD16 ET are applied in order to determine the optimal approach for obtaining ETa. Outputs from these models are compared to actual water balance (WB) estimates during the 2004/05 season at field scale. Several statistical measures are evaluated, and a score is given for each model in order to select the best-performing model. Based on ranking criteria, SSEB gives the best performance and is seen as a suitable operational ETa model for the scheme. SSEB subsequently is applied for summer and winter crop seasons for the period 2000–2014. Unfortunately, one of the limitations faced in the current research is the absence of validation data on a regional scale. Therefore, the assessment focuses on spatial distribution and trends rather than absolute values. As with the MVCI distribution, the seasonal ETa for the Gezira Scheme is higher in the southern and central parts than in the northern part. This confirms the robustness of the developed MVCI. To avoid using absolute values of ETa, the ratio of ETa from agricultural areas (ETagr) to the total evapotranspiration (ET) from the scheme (ETsum) is calculated. The ETagr/ETsum ratio shows a descending trend over recent years, indicating that the water is available but not being utilized for agricultural production. This study shows that SSEB is also useful for identifying the location of water losses on a daily basis. Around 80 channels are identified as having leakage problems for the 2013/14 crop season. Such information is very useful for reducing losses at the scheme. In addition, Rainwater Harvesting (WH) is addressed and found to be applicable as an alternative solution for accounting for rainfall in irrigation. It is seen that these management scenarios could save water and increase the overall efficiency of the scheme. It is possible to save 68 million cubic meters of water per year when the overall irrigation efficiency of the scheme is improved by only 1%. A level of efficiency of 75% is predicted from the proposed management scenarios, which could save about 2.6 billion cubic meters of water per year. In conclusion, the present study has developed an innovative method of identifying the problems of large-scale schemes as well as proposing management scenarios to enhance irrigation water management practice. Improved agricultural water management in terms of crop, water and land management can increase food production, thereby alleviating poverty and hunger in an environmentally sustainable manner.

The Penman-Monteith (PM) equation is a state-of-the-art modelling approach to simulate evapotranspiration (ET) at site and local scale. However, its practical application is often restricted by the availability and quality of required parameters. One of these parameters is the canopy conductance. Long term measurements of evapotranspiration by the eddy-covariance method provide an improved data basis to determine this parameter by inverse modelling. Because this approach may also include evaporation from the soil, not only the ‘actual’ canopy conductance but the whole surface conductance (gc) is addressed. Two full cycles of crop rotation with five different crop types (winter barley, winter rape seed, winter wheat, silage maize, and spring barley) have been continuously monitored for 10 years. These data form the basis for this study. As estimates of gc are obtained on basis of measurements, we investigated the impact of measurements uncertainties on obtained values of gc. Here, two different foci were inspected more in detail. Firstly, the effect of the energy balance closure gap (EBCG) on obtained values of gc was analysed. Secondly, the common hydrological practice to use vegetation height (hc) to determine the period of highest plant activity (i.e., times with maximum gc concerning CO2-exchange and transpiration) was critically reviewed. The results showed that hc and gc do only agree at the beginning of the growing season but increasingly differ during the rest of the growing season. Thus, the utilisation of hc as a proxy to assess maximum gc (gc,max) can lead to inaccurate estimates of gc,max which in turn can cause serious shortcomings in simulated ET. The light use efficiency (LUE) is superior to hc as a proxy to determine periods with maximum gc. Based on this proxy, crop specific estimates of gc,maxcould be determined for the first (and the second) cycle of crop rotation: winter barley, 19.2 mm s−1 (16.0 mm s−1); winter rape seed, 12.3 mm s−1 (13.1 mm s−1); winter wheat, 16.5 mm s−1 (11.2 mm s−1); silage maize, 7.4 mm s−1 (8.5 mm s−1); and spring barley, 7.0 mm s−1 (6.2 mm s−1).

Policy makers adopt irrigated agriculture for food security, since irrigation doubles crop production. Therefore, the development of large irrigation systems has a long history in many places worldwide. Although large-scale irrigation schemes play an important role in improving food security, many schemes, especially in Africa, do not yield the expected outcomes. This is related to poor water management, which is generally due to a lack of effective evaluation and monitoring. The objective of this study, therefore, is to propose a new methodology to assess, evaluate and monitor large-scale irrigation systems. Information on irrigation indicators is needed to enable the evaluation of irrigation performance. The evaluation is the first and the most significant step in providing information about how it is performing. After reviewing extensive literature, a list of indicators related to the performance of irrigation, rainwater supply and productivity is suggested. The irrigation efficiency indicators Relative Irrigation Supply (RIS) and Relative Water Supply (RWS) are selected. Potential rainwater supply to crops can be tested based on the Moisture Availability Index (MAI) and the Ratio of Moisture Availability (RMA). Water productivity can be assessed by Crop Yield (Y) and Water Use Efficiency (WUE). However, the central problem facing large-scale irrigation schemes is always the lack of data, which calls for the development of a new method of data acquisition that allows evaluation and monitoring. Remote Sensing (RS) technology makes it possible to retrieve data across large areas. Two different approaches via RS, the Normalized Difference Vegetation Index (NDVI) and Actual Evapotranspiration (ETa), can be utilized for monitoring. The well-known Vegetation Condition Index (VCI), derived from the NDVI, is modified (MVCI) to allow a qualitative spatio-temporal assessment of irrigation efficiency. MVCI takes into account crop response to water availability, while ETa indicates whether water is used as intended. Furthermore, the assessment of the possible hydrological impact of the irrigation system should be considered in the evaluation and monitoring process. The Sudanese Gezira Scheme of 8,000 square kilometers in the Nile Basin, where performance evaluation and monitoring are absent or poorly conducted, is no exception. This research takes the large-scale irrigation of the Gezira Scheme as a case study, as it is the largest scheme, not only in the Nile Basin but also in the world, under single management. The first long-term historical evaluation of the scheme is conducted for the period 1961–2012 rather than only on a short-time scale as is the common practice. An increase in RIS and RWS values from 1.40 and 1.70 to 2.23 and 2.60, respectively, since the 1993/94 season shows decreasing irrigation efficiency. MAI and RMA for summer crops indicate a promising rainfall contribution to irrigation in July and August. The Gezira Scheme achieves low yield and WUE in comparison to many irrigation schemes of the globe. Low productivity is mainly due to poor distribution and irrigation mismanagement. This is indicated by the 15-year MVCI spatio-temporal analysis, which shows that the northern part of the scheme experiences characteristic drought during the summer crop season. Although MVCI can be considered a monitoring tool, the index does not deduct the soil water content, and water could be wasted and available in other ways (e.g. water depressions). Spatio-temporal information for ETa is required to better quantify water depletion and establish links between land use and water allocation. However, several RS models have been developed for estimating ETa. Thus, improving the understanding of performance of such models in arid climates, as well as large-scale irrigation schemes, is taken into account in this study. Four different models based on the energy balance method, the Surface Energy Balance Algorithm for Land (SEBAL), Mapping EvapoTranspiration at High Resolution with Internalized Calibration (METRIC™), Simplified Surface Energy Balance (SSEB) and MOD16 ET are applied in order to determine the optimal approach for obtaining ETa. Outputs from these models are compared to actual water balance (WB) estimates during the 2004/05 season at field scale. Several statistical measures are evaluated, and a score is given for each model in order to select the best-performing model. Based on ranking criteria, SSEB gives the best performance and is seen as a suitable operational ETa model for the scheme. SSEB subsequently is applied for summer and winter crop seasons for the period 2000–2014. Unfortunately, one of the limitations faced in the current research is the absence of validation data on a regional scale. Therefore, the assessment focuses on spatial distribution and trends rather than absolute values. As with the MVCI distribution, the seasonal ETa for the Gezira Scheme is higher in the southern and central parts than in the northern part. This confirms the robustness of the developed MVCI. To avoid using absolute values of ETa, the ratio of ETa from agricultural areas (ETagr) to the total evapotranspiration (ET) from the scheme (ETsum) is calculated. The ETagr/ETsum ratio shows a descending trend over recent years, indicating that the water is available but not being utilized for agricultural production. This study shows that SSEB is also useful for identifying the location of water losses on a daily basis. Around 80 channels are identified as having leakage problems for the 2013/14 crop season. Such information is very useful for reducing losses at the scheme. In addition, Rainwater Harvesting (WH) is addressed and found to be applicable as an alternative solution for accounting for rainfall in irrigation. It is seen that these management scenarios could save water and increase the overall efficiency of the scheme. It is possible to save 68 million cubic meters of water per year when the overall irrigation efficiency of the scheme is improved by only 1%. A level of efficiency of 75% is predicted from the proposed management scenarios, which could save about 2.6 billion cubic meters of water per year. In conclusion, the present study has developed an innovative method of identifying the problems of large-scale schemes as well as proposing management scenarios to enhance irrigation water management practice. Improved agricultural water management in terms of crop, water and land management can increase food production, thereby alleviating poverty and hunger in an environmentally sustainable manner.

With a changing climate and an increased competition over water resources for agricultural irrigation, the need to improve crop water productivity using time and cost-efficient methodologies have become critically important. The Malwathu Oya river basin in Sri Lanka is struggling with water scarcity, which threatens food security and the income of farmers. In this study, freely available remote sensed land- and water productivity data from FAO’s WaPOR database was evaluated. The evaluation consisted of a comparison of the WaPOR data and primary collected field data using the crop water model, AquaCrop, for three irrigation schemes in the Malwathu Oya river basin. Additionally, the spatio-temporal variability in crop water use within and across these three irrigation schemes was assessed using indicators derived from the WaPOR portal. The evaluation was conducted for the main cultivation season, called Maha, between 2010 and 2021.  The WaPOR and AquaCrop actual evapotranspiration (ETa) values were found to be in relatively good agreement (312–537 and 400–465 mm respectively). WaPOR yield values (2.5–2.9 ton/ha) were however lower compared to the AquaCrop simulated yield values and historical yield data (4.6–5.7 and 4.4–5.6 ton/ha respectively). Difference in calculation methodology, possible sources of error in WaPOR conversion calculations and limitations in accuracy caused by cloud coverage when collecting satellite data could be explanations for this. Prior knowledge and accurate allocation of the crop type and parameters used in conversion calculations in WaPOR is therefore of significant influence. From the spatio-temporal variation assessment with WaPOR indicators, a fair uniformity of the water distribution within the irrigation schemes was shown (CV 11–19 %). The beneficial water use (BWU) in the irrigation schemes showed lower values (50–90 % allocated to T) for years when the available water amount was higher, which could be explained by the higher rate of water lost through soil evaporation. Crop water productivity (CWP) values showed higher values (about 0.70 kgDM/m3) when the available water amount was higher, indicating that yield production is sensitive to water-scarce environments. Applying a yield boundary function, representing the best attainable yield in relation to water resource, showed that there is potential to achieve the same yield with less amount of water. There are thus possibilities for improved water productivity in the three irrigation schemes investigated. For future research it is recommended to perform a sensitivity analysis for WaPOR and ground truth with yield data to obtain a better understanding of potential limitations. To obtain more precise site descriptions it is also recommended to ground truth AquaCrop with yield and soil data.

Les toitures végétalisées ont des répercussions très positives sur la performance énergétique des bâtiments. L’objectif est d’évaluer l’incidence des toitures végétalisées sur la performance énergétique des bâtiments à travers des moyens numériques et expérimentaux. La modélisation du comportement thermo-hydrique des toitures végétalisées permet de quantifier ces effets et contribue à promouvoir cette technique.Cette thématique requiert en premier lieu des compétences en énergétique du bâtiment et de modélisation thermique dynamique, si l’on souhaite établir un modèle représentatif du comportement thermo-hydrique d’un composant de toiture végétalisée. Afin de développer ces différents aspects, un travail préliminaire qui consiste en une étude bibliographique approfondie portant sur les modèles proposés dans la littérature a été entrepris. Sur la base de cette étude bibliographique, un modèle couplé de transfert de chaleur et d’humidité a été développé. Ce modèle est basé sur l’établissement des équations de bilan énergétique sur la surface du feuillage et la surface du sol. Afin d’affiner le modèle développé et d’obtenir de meilleurs résultats numériques, diverses caractérisations expérimentales des matériaux qui entrent dans la composition de la toiture végétalisée ont été effectuées. Une plateforme expérimentale (Climabat, échelle 1/10) a été conçue sur le site de l’Université de La Rochelle dans le but de mesurer l’incidence des toitures végétalisées sur les bâtiments et fournir des données permettant de calibrer et de vérifier le modèle développé. Des comparaisons ont été entreprises entre toiture végétalisée et toiture classique, une différence de température de surface extérieure de 30°C a été notée pendant la période d’été. Les résultats des simulations montrent aussi que la végétalisation des toitures de bâtiment améliore non seulement les conditions de son confort thermique mais aussi sa performance énergétique. Des campagnes de mesures ont été également effectuées sur des bâtiments réels équipés avec des toitures végétalisées. La validation expérimentale du modèle développé a été ensuite entreprise à deux échelles, l’une à échelle réduite (maquette échelle 1:10) sur des bancs d’essais sur le site de l’Université de La Rochelle et une à échelle réelle, sur des pavillons BBC existants où différentes typologies de toitures végétalisées ont été instrumentées. Une fois le modèle développé et sa pertinence vérifiée par comparaison à des mesures expérimentales, il a été couplé à un code de simulation thermique dynamique des bâtiments (TRNSYS). Cela a permis de prédire la performance énergétique et le calcul des besoins de chauffage et de climatisation des bâtiments équipés d'une toiture végétalisée. Les résultats de simulations ont montré que la présence d'une toiture végétalisée permet une réduction des besoins des bâtiments et protège la membrane d’étanchéité de la toiture des températures extrêmes et des grandes fluctuations de température. De plus, il a été constaté que l'effet des toitures végétalisées sur la réduction de la température de l'air intérieur est plus important en été. Aussi, il a été constaté que les besoins de climatisation et de chauffage dépendent fortement du niveau d'isolation de la toiture. Enfin, les simulations réalisées pour différents climats ont montré que la toiture végétalisée est bénéfique pour le climat des pays européens. / Green roofs have a positive effect on the energy performance of buildings, providing a cooling effect in summer, along with a more efficient harnessing of the solar radiation, due to the reflective properties of the foliage. To assess these effects, a thermodynamic model was developed as well as the thermo-physical properties of the green roof components were characterized.The proposed model is based on energy balance equations expressed for foliage and soil media. The influence of the mass transfer on the thermal properties, and evapotranspiration were taken into account. Then, the water balance equation was added into the developed model and numerical simulations were performed. In order to evaluate the temperatures evolution at foliage and soil ground levels.Three of the main physical properties of green roofs were experimentally investigated to determine some of the green roofs’ modeling key parameters. First, the thermo-physical properties of green roofs were characterized by correlating the thermal conductivity of the substrate with the water content for different substrates and maximum water capacities. Next, the moisture storage was characterized using the dynamic vapor sorption technique. Third, themicro-structural properties of green roof substrate were characterized using mercury intrusion porosimetry. In addition to these characterizations, the evapotranspiration term, which is very important in the water balance, was measured.The model was experimentally validated according to a green roof platform (scale 1:10) constructed on the site of the University of La Rochelle. Measurements have also been conducted in a full scale building equipped with green roofs. Once the proposed model validated, it has been coupled to a building thermal code (TRNSYS) to evaluate the impact of green roofs on the energy performance of buildings.The results show that the effect of mass transfer in the subtract was very effective in reducing the model errors. Comparisons were undertaken with a roof slab concrete model; a significant difference in temperature (up to 30 °C) between the outer surfaces of the two roofs was noticed in summer. The heat flux through the roof was also evaluated. The roof passive cooling effect was three times more efficient with the green roof. In the winter, the green roof reduced roof heat losses during cold days; however, it increased these losses during sunny days. With a green roof, the summer indoor air temperature was decreased by 2 °C, and the annual energy demand was reduced by 6% for an oceanic climate such as that of La Rochelle. Finally, the simulations performed for different climates suggest that green roofs are thermally beneficial for hot, temperate, and cold European climates.

Das erste Ziel dieser Arbeit ist eine umfassende Analyse der Wasserflüsse durchzuführen und Quellen und Senken des kontinentalen Niederschlags zu identifizieren. Als Analysemethode werden komplexe Netzwerke verwendet, ein Ansatz, mit dessen Hilfe das neuartige Konzept des “cascading moisture recycling'''' (CMR) eingeführt wird. CMR wird als vielfache Verdunstung von Niederschlag während des Feuchtigkeitstransports über bewaldeten Gebieten definiert. Dieses Verfahren ermöglicht es, den Anteil von CMR an der Menge des regionalen Niederschlags zu quantifizieren und Schlüsselregionen des CMR zu identifizieren. Die Analyse zeigt, dass der südliche Bereich des Amazonasbeckens nicht nur eine direkte Quelle für Niederschlag im La-Plata Becken ist, sondern auch als ``Brückenregion'''' dient, über die die verdunstete Feuchtigkeit des ganzen Amazonasbeckens auf dem Weg in die Subtropen transportiert wird. Die Ergebnisse zeigen, dass eine Neubewertung der Vulnerabilität des Amazonasregenwalds unter Umweltveränderungen unabdingbar ist. Dies ist das zweite Ziel der vorliegenden Arbeit. Durch diese Veränderungen könnten große Teile des Regenwaldes in eine Savanne umgewandelt werden. Dies würde wiederum den Niederschlag reduzieren, was sich negativ auf die Stabilität der verbleibenden Waldgebiete auswirken und ein Waldsterben verursachen kann. Für die Analyse dieser Zusammenhänge werden ebenfalls komplexe Netzwerke verwendet, um das Konzept der Ökosystem-Resilienz und CMR basierend auf Beobachtungsdaten zu kombinieren. Es werden die Schlüsselregionen, in denen Entwaldung zu einer Destabilisierung der verbleibenden Wald führt, identifiziert und die Möglichkeit eines großflächigen Absterben des Regenwaldes aufgrund von verlängerter Trockenzeit untersucht. Die Ergebnisse zeigen, dass die Diversität des Regenwaldes und die durch den Feuchtigkeitstransport gegebene Konnektivität der Waldgebiete eine wichtige Rolle für die Stabilität und ökologische Integrität dieses Ökosystems spielen. / The first aim of this thesis is to improve the understanding of vegetation-atmosphere interactions by means of complex network analysis of water fluxes from the sources to the sinks of rainfall in South America. This novel approach allows to introduce the concept of “cascading moisture recycling” defined as moisture recycling on the continent involving re-evaporation cycles along the way. A methodological framework is developed to quantify the importance of cascading moisture recycling and to identify key regions that sustain this process. It reveals, for instance, that the southern part of the Amazon basin is not only a direct source of rainfall for the La Plata basin as previously thought but also an intermediary region that re-distribute moisture evaporating from the entire Amazon basin towards the subtropics. This new concept lays the foundation for evaluating the vulnerability of the Amazon forest to environmental perturbations, which is the second aim of this thesis. Land-use and rainfall variability are expected to be intensified at the end of the twenty-first century and may push the south-eastern part of the Amazon forest towards a grass-dominated ecosystem. Such a forest loss would reduce local dry-season evapotranspiration and the resulting moisture supply for down-wind rainfall. In turn, this might erode the resilience of the remaining forest and lead to further forest losses. Using a complex network approach, the concepts of forest resilience and cascading moisture recycling are combined in a data-driven modeling framework. Key regions are identified where deforestation would greatly destabilize the remaining forest, as well as tipping points in dry-season intensification for large-scale self-amplified Amazon forest loss. The findings highlight the need to maintain the diversity and connectivity of forest patches in order to sustain the ecological integrity of the largest remaining tropical forest on Earth.

A cafeicultura possui grande destaque no cenário agrícola nacional e seu cultivo vem avançando para regiões não tradicionais, como o oeste do Estado da Bahia. Esta região apresenta relevo plano, facilmente mecanizável, proporcionando utilização de alta tecnologia, como a fertirrigação via pivô-central. Os cafeeiros desta região apresentam alta produtividade, alcançando a média de 55 sacas ha-1 ano-1. O cafeeiro necessita de água facilmente disponível no solo em sua fase vegetativa, promovendo o crescimento de ramos laterais e em sua fase reprodutiva (floração, granação e maturação dos frutos) para se desenvolver e produzir satisfatoriamente. O balanço hídrico - BH é um dos métodos utilizados para estimar essa demanda hídrica para os diferentes estádios de desenvolvimento das culturas. O BH consiste no somatório das quantidades de água que entram e saem de um elemento de volume de solo e, em dado intervalo de tempo, é a quantidade líquida de água que nele permanece. Através do componente drenagem profunda do BH é possível fazer a estimação da lixiviação de nitrato - NO3 -. Na região de Barreiras-BA não tem sido realizado, com frequência, pesquisa básica em relação ao cultivo do cafeeiro, de tal forma que pouco se sabe em relação à eficiência do uso de dose elevada de nitrogênio - N, que oscila na faixa de 600-800 kg ha-1, bem como sobre a sua possível perda por lixiviação. A uréia é o adubo mais utilizado em fertirrigação devido à sua alta solubilidade, o que facilita muito o preparo das soluções nutritivas, porém, possui o inconveniente de apresentar perdas por lixiviação em situações de altas doses aplicadas e altos volumes de irrigação. O parcelamento e a época de aplicação do adubo nitrogenado constituemse em alternativas para aumentar a eficiência dos adubos e da adubação nitrogenada pelas culturas e mitigar as perdas. As quantidades de NO3 - no perfil, susceptíveis à perda, são muito variáveis, dependendo da quantidade de N adicionado, do tipo de adubo, da taxa de mineralização do N nativo, da remoção pelas colheitas, do tipo de cultura e do volume de água drenada, fatores estes afetados significativamente pelas propriedades do solo (capacidade de troca iônica, pH, textura, estrutura, matéria orgânica, relação C:N, etc.) e pelo clima (principalmente precipitação). O uso de isótopos, na forma de fertilizante marcado com 15N, é uma ferramenta apropriada para avaliar o destino do fertilizante no sistema solo-cafeeiro-atmosfera, podendo-se inferir sobre a lixiviação. Assim sendo, este trabalho foi desenvolvido com o objetivo de avaliar a drenagem profunda, a estimação da lixiviação de NO3 - e de N (15N) do fertilizante através do BH sequencial com a utilização dos modelos de evapotranspiração de Thornthwaite - TH e Penman-Monteith - PM em uma cultura de café fertirrigada por pivô central no oeste baiano. Através dos modelos de evapotranspiração de TH e PM foi possível estimar a drenagem profunda, a lixiviação de NO3 - e de 15N. O modelo de evapotranspiração de TH é menos preciso, porém onde apenas há disponibilidade de dados de temperatura, pode ser usado na elaboração do BH. / The coffee crop is of great importance in the Brazilian scenario and its cultivation is expanding to non traditional growing areas as the west of the state Bahia. This region presents a very flat relief of easy mechanization, allowing for the implementation of high agricultural technology as it is the case of fertigation via central pivot irrigation. Crops of this region reach high productivities, with an average of 55 bags per hectare and per year. The coffee plant requires easily available water in the soil in its vegetative phase to promote the growth of lateral branches, and in its reproductive phase (flowering, fruit filling and maturation) to develop and produce satisfactorily. The water balance - WB is one of the methods used to estimate this water demand during the different growth stages of agricultural crops. It consists of the accounting of the water fluxes into and out of an elemental soil volume of a chosen time interval, resulting the net amount of water that is stored in the soil. Through the deep drainage component of the WB it is possible to estimate the nitrate leaching - NO3 -. In the region of Barreiras-BA very little research has been carried out in relation to the cultivation of coffee, so that not much is known in relation to the efficiency of the use of high N application rates, as those there applied in the range of 600-800 kg ha-1, as well as about the possible leaching losses. Urea is mostly used a N source during fertigation due to its high solubility in water, but that has the inconvenience of allowing leaching losses in case of high N and water applications. Splitting of doses and application times are alternatives to increase absorption efficiencies and minimize losses to the environment. The NO3 - quantities in the soil profile which are susceptible to leaching are very variable, depend on N application rates, type of fertilizer, mineralization rate in the soil, export by harvests, crop type and drainage volume. These factors are significantly affected by soil properties (cation exchange capacity, pH, texture, structure, organic matter, C:N ratio, etc.) and by climate (mainly rainfall). The use of isotopes in the form of 15N labeled fertilizer is an appropriate tool to evaluate the fate of fertilizer N in the soil-coffee plant-atmosphere system, including the estimation of N leaching. Therefore, this study was developed with the objective of evaluating the deep drainage and the leaching of NO3 - and fertilizer (15N) through the sequential water balance, using the evapotranspiration models of Thornthwaite - TH and Penman-Monteith PM, for a fertigated coffee crop under central pivot irrigation, in west Bahia. It was possible to estimate the internal drainage and the leaching of NO3 - and 15N. The TH model is less precise; however for regions where only air temperature data are available, it can be used with success.

La paramétrisation du transfert de chaleur par télédétection, basée sur le schéma SEBS, s'est déjà avérée très adaptée pour l'estimation de l'évapotranspiration (ET) sur des surfaces naturelles homogènes. Cependant, l'utilisation d'une telle méthode pour des paysages hétérogènes (e.g. régions semi-arides ou surfaces agricoles) est plus délicate, puisque le principe de la théorie de la similarité est compromis par la présence de différentes sources de chaleur et de hauteurs variées. Dans un premier temps, cette thèse a pour objectif de proposer et d'évaluer différents modèles basés sur la géométrie de la végétation qui permettent d'estimer la longueur de rugosité pour le transfert de quantité de mouvement à la surface (z0m), cette dernière étant un paramètre clé dans la caractérisation du transfert de chaleur. En revanche, une telle investigation ne peut être menée qu'à une petite échelle et à l'aide de données de télédétection très haute résolution permettant ainsi une description très détaillée de la surface. Ensuite, le second aspect de ce travail est de caractériser le transfert de chaleur dans le cas d'études régionales. Puis, la capacité de SEBS à estimer les flux de chaleur turbulents à de grandes échelles spatiales et temporelles sera évaluée. Pour ce faire, l’approche multi-échelle de SEBS (MSSEBS) a été implémentée afin de traiter une zone de 2,4 millions km2, incluant le Plateau du Tibet et l’amont des principaux fleuves d’Asie du sud-est. La combinaison de données horaires de température de surface FY-2 avec un rayonnement net journalier et des paramètres de surface avancés, permet de produire une série temporelle d’ET sur le Plateau du Tibet pour la période 2008-2010, et à une fréquence journalière. / The parameterization of heat transfer by remote sensing, and based on SEBS scheme for turbulent heat fluxes retrieval, already proved to be very convenient for estimating evapotranspiration (ET) over homogeneous land surfaces. However, the use of such a method over heterogeneous landscapes (e.g. semi-arid regions or agricultural land) becomes more difficult, since the principle of similarity theory is compromised by the presence of different heat sources with various heights. This thesis aims at first to propose and evaluate some models based on vegetation geometry for retrieving the surface roughness length for momentum transfer (z0m), which is a key parameter in the characterization of heat transfer. Such an investigation can only be led at a small scale with very-high resolution remote sensing data, for a precise description of the land surface. Therefore, the second aspect of this work is to determine how to address the characterization of heat transfer for regional studies. Then, the reliability of SEBS for estimating turbulent heat fluxes at large spatial and temporal scales has been evaluated. To do so, the Multi-Scale SEBS approach (MSSEBS) has been implemented for a 2.4 million km2 area including the Tibetan Plateau and the headwaters of the major rivers of East and South Asia. The addition of gap-filled hourly FY-2 LST data to advanced daily averaged net radiation and land surface parameters, allows to compute time-series of land surface ET over the Tibetan Plateau during the period 2008-2010, and on a daily basis.

A cafeicultura possui grande destaque no cenário agrícola nacional e seu cultivo vem avançando para regiões não tradicionais, como o oeste do Estado da Bahia. Esta região apresenta relevo plano, facilmente mecanizável, proporcionando utilização de alta tecnologia, como a fertirrigação via pivô-central. Os cafeeiros desta região apresentam alta produtividade, alcançando a média de 55 sacas ha-1 ano-1. O cafeeiro necessita de água facilmente disponível no solo em sua fase vegetativa, promovendo o crescimento de ramos laterais e em sua fase reprodutiva (floração, granação e maturação dos frutos) para se desenvolver e produzir satisfatoriamente. O balanço hídrico - BH é um dos métodos utilizados para estimar essa demanda hídrica para os diferentes estádios de desenvolvimento das culturas. O BH consiste no somatório das quantidades de água que entram e saem de um elemento de volume de solo e, em dado intervalo de tempo, é a quantidade líquida de água que nele permanece. Através do componente drenagem profunda do BH é possível fazer a estimação da lixiviação de nitrato - NO3 -. Na região de Barreiras-BA não tem sido realizado, com frequência, pesquisa básica em relação ao cultivo do cafeeiro, de tal forma que pouco se sabe em relação à eficiência do uso de dose elevada de nitrogênio - N, que oscila na faixa de 600-800 kg ha-1, bem como sobre a sua possível perda por lixiviação. A uréia é o adubo mais utilizado em fertirrigação devido à sua alta solubilidade, o que facilita muito o preparo das soluções nutritivas, porém, possui o inconveniente de apresentar perdas por lixiviação em situações de altas doses aplicadas e altos volumes de irrigação. O parcelamento e a época de aplicação do adubo nitrogenado constituemse em alternativas para aumentar a eficiência dos adubos e da adubação nitrogenada pelas culturas e mitigar as perdas. As quantidades de NO3 - no perfil, susceptíveis à perda, são muito variáveis, dependendo da quantidade de N adicionado, do tipo de adubo, da taxa de mineralização do N nativo, da remoção pelas colheitas, do tipo de cultura e do volume de água drenada, fatores estes afetados significativamente pelas propriedades do solo (capacidade de troca iônica, pH, textura, estrutura, matéria orgânica, relação C:N, etc.) e pelo clima (principalmente precipitação). O uso de isótopos, na forma de fertilizante marcado com 15N, é uma ferramenta apropriada para avaliar o destino do fertilizante no sistema solo-cafeeiro-atmosfera, podendo-se inferir sobre a lixiviação. Assim sendo, este trabalho foi desenvolvido com o objetivo de avaliar a drenagem profunda, a estimação da lixiviação de NO3 - e de N (15N) do fertilizante através do BH sequencial com a utilização dos modelos de evapotranspiração de Thornthwaite - TH e Penman-Monteith - PM em uma cultura de café fertirrigada por pivô central no oeste baiano. Através dos modelos de evapotranspiração de TH e PM foi possível estimar a drenagem profunda, a lixiviação de NO3 - e de 15N. O modelo de evapotranspiração de TH é menos preciso, porém onde apenas há disponibilidade de dados de temperatura, pode ser usado na elaboração do BH. / The coffee crop is of great importance in the Brazilian scenario and its cultivation is expanding to non traditional growing areas as the west of the state Bahia. This region presents a very flat relief of easy mechanization, allowing for the implementation of high agricultural technology as it is the case of fertigation via central pivot irrigation. Crops of this region reach high productivities, with an average of 55 bags per hectare and per year. The coffee plant requires easily available water in the soil in its vegetative phase to promote the growth of lateral branches, and in its reproductive phase (flowering, fruit filling and maturation) to develop and produce satisfactorily. The water balance - WB is one of the methods used to estimate this water demand during the different growth stages of agricultural crops. It consists of the accounting of the water fluxes into and out of an elemental soil volume of a chosen time interval, resulting the net amount of water that is stored in the soil. Through the deep drainage component of the WB it is possible to estimate the nitrate leaching - NO3 -. In the region of Barreiras-BA very little research has been carried out in relation to the cultivation of coffee, so that not much is known in relation to the efficiency of the use of high N application rates, as those there applied in the range of 600-800 kg ha-1, as well as about the possible leaching losses. Urea is mostly used a N source during fertigation due to its high solubility in water, but that has the inconvenience of allowing leaching losses in case of high N and water applications. Splitting of doses and application times are alternatives to increase absorption efficiencies and minimize losses to the environment. The NO3 - quantities in the soil profile which are susceptible to leaching are very variable, depend on N application rates, type of fertilizer, mineralization rate in the soil, export by harvests, crop type and drainage volume. These factors are significantly affected by soil properties (cation exchange capacity, pH, texture, structure, organic matter, C:N ratio, etc.) and by climate (mainly rainfall). The use of isotopes in the form of 15N labeled fertilizer is an appropriate tool to evaluate the fate of fertilizer N in the soil-coffee plant-atmosphere system, including the estimation of N leaching. Therefore, this study was developed with the objective of evaluating the deep drainage and the leaching of NO3 - and fertilizer (15N) through the sequential water balance, using the evapotranspiration models of Thornthwaite - TH and Penman-Monteith PM, for a fertigated coffee crop under central pivot irrigation, in west Bahia. It was possible to estimate the internal drainage and the leaching of NO3 - and 15N. The TH model is less precise; however for regions where only air temperature data are available, it can be used with success.