A evapotranspiração (ET) é um fenômeno natural que influencia diretamente mudanças no clima local e global, possuindo grande importância hidrológica e meteorológica. Este trabalho teve como objetivo estimar a ET através do método Penman-Monteith, e comparar com os resultados estimados pelo Método da Covariância de Vórtices Turbulentos. Os dados de IAF (Índice de Área Foliar) para descrição da vegetação foram obtidos a partir do sensor MODIS e de medições em campo da Rede SulFlux. A área de estudo desta pesquisa localizou-se no município de Cachoeira do Sul-RS, em uma propriedade de cultivo de arroz irrigado. O período de estudo referiu-se a safra que estendeu-se de outubro de 2010 a março de 2011. Os resultados mostraram que o IAF e as estimativas de ET apresentam um comportamento temporal semelhante. A comparação entre os resultados das estimativas de ET, utilizando dados obtidos em campo e estimados através de sensoriamento remoto, foram satisfatórios. No entanto, o resultado que apresentou os maiores valores para a ET foi proveniente do sensor MODIS. Sendo assim, pode-se concluir que a estimativa da ET, a partir de dados de vegetação, obtidos através de técnicas de sensoriamento remoto, constituem-se como uma alternativa para os métodos de ET que utilizam dados de vegetação medidos em campo. / The Evapotranspiration (ET) is a natural phenomenon that directly causes changes in the local and global climate, having a great hydrologic and meteorological importance. This work has as objective to estimate ET through the Penman-Monteith method and compare with the estimated results by the Eddy Covariance Method. The LAI (Leaf Area Index) data for the vegetation description were obtained from the MODIS sensor and from field measurements of the SulFlux network. The field of study of this research had place in the city of Cachoeira do Sul – Rio Grande do Sul state, in a irrigated rice crop property. The study period is referred to the crop that extended from October 2010 to March 2011. The results showed that the LAI and the ET estimates have a similar temporal behavior. The comparison between the results of ET estimates, using data obtained in field and estimated through remote sensing, were satisfactory. However, the result that showed the highest values for ET was from the MODIS sensor. This way, it can be concluded that the ET estimate, through vegetation data, obtained by remote sensing techniques, are an alternative for the ET methods that use vegetation field measured data.

Northeastern Brazil is hydrologically characterized by recurrent droughts leading to a highly vulnerable natural water resource system. The region contains the Caatinga biome, a sparsely studied ecosystem, covering an area of approximately 800,000 km2. Reduced wateravailability is projected to take place in large regions of the globe, including Northeastern Brazil. Given the strong interactions between climate and vegetation, research has addressed climate change effects on natural and agricultural ecosystems. In this context, soil hydraulic properties are essential to assess soil water flow, and thus the ability of soil to supply water to plants at potential rates under different ranges of pressure head. Based on that, the aims of this thesis are: to increase insight in water balance components for the Caatinga biome, under current and future climate scenarios; and to assess the ability of soils in supplying water to plants by the further development of an existing matric flux potential approach, followed by its application to a group of soils from two Brazilian climatic zones (semi-arid and subhumid). Both for current and future climate scenarios, hydrological simulations were performed with SWAP model parameterized for a preserved Caatinga basin of 12 km2. The validation of the simulations was performed using a dataset of daily soil-water content measurements taken at 0.2 m depth in the period from 2004 to 2012. The soil water supplying capacity was evaluated through a multilayer matric flux potential approach, coupling the soil hydraulic properties, root length density and plant transpiration. Regarding the current climate conditions, the Caatinga biome returns 75% of the annual precipitation to the atmosphere, whereas the partitioning of total evapotranspiration into its components (transpiration, evaporation and interception) on annual basis accounts for 41%, 40% and 19%, respectively. Evapotranspiration and air temperature are most sensitive to soil moisture during the periods June-September and December-January. Concerning the future climate, transpiration was enhanced by 36%, soil evaporation and interception losses reduced by 16% and 34%, respectively. The amount of precipitation returned to the atmosphere was on average 98%. For both climate scenarios, the soil-plant-atmosphere fluxes seem to be controlled by the surface soil layer (0-0.2 m) which provides, on average, 80% of the total transpiration, suggesting that the Caatinga biome may become completely soil-water pulse dominated under scenarios of reduced water availability. The matric flux potential analysis revealed that soils from the semiarid zone were able to deliver water to plants at potential rates under a wider range of bulk soil pressure head (-36 to -148 m), whereas the soils from the wetter zone showed more hydraulic restriction with limiting soil water potential above -1.5 m. For the analyzed soils, only a negligible increase in available water results from decreasing the root water potential below -150 m, therefore, in order to adapt to water-limited conditions, plant species may invest in other adaptive strategies, rather than spending energy in structures that allow a reduction of the lower suction limit in their tissues. / O Nordeste do Brasil é hidrologicamente caracterizado por secas recorrentes, tornando os recursos hídricos naturais altamente vulneráveis. Nesta região está o bioma Caatinga, ocupando uma área de aproximadamente 800.000 km2. Cenários de déficit hídrico são projetados para grandes regiões do globo, incluindo o Nordeste brasileiro. Devido às interações entre clima e vegetação, várias pesquisas têm abordado os efeitos das mudanças climáticas sobre os ecossistemas naturais e agrícolas. Neste contexto, as propriedades hidráulicas do solo são essenciais para avaliar o movimento de água, e assim a capacidade de fornecimento de água às plantas. Com base nesta contextualização, os objetivos desta tese são: simular os componentes do balanço hídrico do bioma Caatinga para cenários climáticos atuais e futuros; e avaliar a capacidade de alguns solos em fornecer água às plantas a partir de uma abordagem de potencial de fluxo matricial. Para os cenários climáticos atuais e futuros, simulações hidrológicas foram realizadas com o modelo SWAP, parametrizado para uma microbacia de 12 km2, inserida em área de Caatinga preservada. A validação das simulações foi processada a partir de medidas diárias do conteúdo de água do solo na profundidade de 0,2 m no período de 2004 a 2012. A capacidade do solo em fornecer água às plantas foi avaliada através da atualização de uma função de potencial de fluxo matricial, que acopla as propriedades hidráulicas do solo, densidade de comprimento radicular e transpiração das plantas, aplicada a um grupo de solos da zona climática semiárida e sub-úmida. Como resultados principais destacam-se: nas condições climáticas atuais, o bioma Caatinga retorna 75% da precipitação anual para a atmosfera como evapotranspiração, particionada entre seus componentes (transpiração, evaporação e intercepção) em 41%, 40% e 19%, respectivamente. Evapotranspiração e temperatura do ar foram sensíveis à umidade do solo durante os períodos de junho-setembro e dezembro-janeiro. Em relação ao cenário climático futuro, a taxa de transpiração foi acrescida em 36%. A evaporação do solo e a interceptação foram reduzidas em 16% e 34%, respectivamente. A quantidade de precipitação devolvida para a atmosfera foi em média 98%. Para ambos os cenários climáticos, é sugerido que os fluxos de água no sistema solo-planta-atmosfera são controlados pela camada superior do solo (0-0,2 m), fornecendo, em média, 80% do total transpirado, indicando que, caso os cenários de disponibilidade hídrica reduzida se confirmem, o bioma Caatinga pode se tornar completamente dependente dos pulsos de água no solo. A partir do potencial de fluxo matricial limitante revelou-se que os solos da região semiárida são capazes de manter o fluxo de água às plantas em taxas potenciais em condições de solo seco (potencial matricial limitante variando de -36 a -148 m), enquanto que, os solos da região mais úmida indicaram severa restrição hidráulica, com potencial matricial limitante maior do que -1,5 m. Ainda para os solos analisados, a atribuição de potencial na superfície da raiz inferior a -150 m não ocasionou aumento de disponibilidade hídrica, indicando que valores menores que -150 m não implicam em uma estratégia viável para suportar baixa disponibilidade hídrica.

O cafeeiro é uma planta que tem seu crescimento e desenvolvimento fortemente afetado pelo regime hídrico, ora prejudicando, ora favorecendo a produção final, dependendo do estádio fenológico em que este se encontra durante uma possível seca. Para ter um conhecimento mais aprofundado do consumo de água do cafeeiro, assim como para um manejo da irrigação mais eficiente, uma ferramenta muito útil é o balanço hídrico, que pode ser medido no campo ou estimado através de modelos. O balanço hídrico de campo é demasiado trabalhoso, por isso os modelos são mais usados em virtude de sua rapidez e facilidade. No entanto, os modelos são frequentemente aplicados em condições agronômicas e ambientais diferentes das em que foram concebidos, necessitando de testes regionais. Um dos principais elementos de entrada para o cálculo do balanço hídrico é a precipitação pluviométrica, e o rigor em sua medida pode determinar se este será ou não condizente com a realidade, devendo sua variabilidade espacial ser levada em conta, o que não ocorre na maioria dos casos. O presente trabalho traz um estudo entre balanço hídrico medido no campo com café e os balanços hídricos climatológicos baseados na estimativa da evapotranspiração pelos métodos de Thornthwaite e Penman-Monteith, confeccionados em um programa computacional. Uma segunda parte trata do número ideal de pluviômetros a serem utilizados em uma área pequena, além das comparações destas medidas com duas estações meteorológicas. Ambos os estudos foram feitos para o município de Piracicaba - SP, com dados meteorológicos do período de 2003 a 2005. / The coffee plant has its growth and development strongly influenced by the water regime, either in favor or depressing the final yield, all depending on phonological stage. In order to have a better knowledge of the water requirement of the coffee crop, and also to have a more efficient irrigation management, a very useful tool is the water balance, which can be obtained through direct field measurements or through model estimation. The first are laborious and costly, while the second are simple and fast to be obtained. However, models are frequently applied to agronomic or environmental conditions that differ from those in which they were developed. One of the most important components for the calculation of water balances is the rainfall, and the precision of its measurement determines the confidence of the balances, indicating the need of taking into account rainfall variability, which is neglected in most cases. This study makes a comparison between climatologic water balances, based on the estimation of the evapotranspiration through the methods of Thornthwaite and Penman-Monteith, obtained though a computational program, and field water balances of a coffee crop. A second part of this study deals with the ideal number of pluviometers to be used in small areas, and the comparison of these measurements with two automatic meteorological stations. Both studies were carried out in Piracicaba, SP, Brazil, with data collected during 2003 - 2005.

Spatially-distributed water consumption was modeled over a segment of the Lower Colorado River, which contains irrigated agricultural and Tamarisk-dominated riparian ecosystems. For the irrigation scheme, distributed evapotranspiration data were analyzed in conjunction with point measurements of precipitation and surface flow in order to close daily and annual water balance. The annual closure error was less than 1% of the total water diversion to the area. In addition, it was found that the soil water storage component of the water balance cannot be neglected if the analysis is performed over time frames shorter than annual (e.g. growing season). Water consumption was highly uniform within agricultural fields, and all the full-cover fields were transpiring close to their potential rates. Mapping several new and existing drainage performance indicators showed that neither soil salinization nor water-logging would be of concern in this irrigation scheme. However, the quality of high-volume return flow must be studied, especially since the degraded water quality of the western US rivers is believed to act in favor of the invasive riparian species in outcompeting native species. Over the Tamarisk forest, the remotely-sensed evapotranspiration estimates were higher than the results of an independent groundwater-based method during spring and winter months. This was chiefly due to the fixed satellite overpass time, which happened at low sun elevation angles in spring and winter and resulted in a significant presence of shadows in the satellite scene and consequently a lower surface temperature estimate, which resulted in a higher evapotranspiration estimate using the SEBAL model. A modification based on the same satellite imagery was proposed and found to be successful in correcting for this error. Both water use and crop coefficients of Tamarisk estimated by the two independent methods implemented in this study were significantly lower than the current approximations that are used by the US Bureau of Reclamation in managing the Lower Colorado River. Studying the poorlyunderstood stream-aquifer-phreatophyte relationship revealed that diurnal and seasonal groundwater fluctuations were strongly coupled with the changes in river stage at close distances to the river and with the Tamarisk water extraction at further distances from the river. The direction of the groundwater flow was always from the river toward the riparian forest. Thus the improved Tamarisk ET estimates along with a better understanding of the coupling between the river and the riparian aquifer will allow the Bureau of Reclamation to re-asses their reservoir release methodology and improve efficiency and water savings.

Irrigation systems are designed to deliver water to crops, but their efficacy varies widely due to operational decisions, weather variability, and water availability. The operation of an irrigation system is studied in this dissertation to determine irrigation performance and potential for improvement.Satellite remote-sensing was used to determine inter-annual variability in crop evapotranspiration and link it with weather patterns and operational decisions. A decade was studied to include several dry, wet and average years of snowfall. It was found that the irrigation district has the capacity to buffer a dry year, but crop evapotranspiration patterns indicated that the buffer capacity of the irrigation district is limited in a second dry year. Studying the current operations of an irrigation system also requires an analysis of the spatial variability within the system to identify potential areas for improvement. Achieving such information is challenging due to the spatial heterogeneity between farm fields. The Ador irrigation system simulation model is used in this study with satellite remote sensing data, which were combined in the calibration and validation process to ease the re-adjustment of management parameters. This approach provides a cost-effective and innovative method for model simulation when field observations are limited. Alternative water delivery scenarios were simulated with the Ador irrigation system simulation model to quantify changes in the water balance, irrigation performance, and water productivity. Results for implementing a minimal irrigation time indicated that irrigation events occurred with a higher frequency and reduced crop water stress. Water productivity for the irrigation district increased substantially in this scenario, whilst district water savings were achieved by diverting less irrigation water. Advantages are only achieved if farmers collectively make the decision to change. A water accounting analysis is required to examine if water savings are achieved at basin scale. There is a potential for the rebound effect to occur, which suggests that an increase of water efficiency causes the increase of water consumption. Simulation results indicated that if the efficiency is increased through improvements of the water delivery, the water consumption increased. Water savings achieved by reducing irrigation diversions did not compensate for the decrease in drainage that downstream users depend on.

The interaction between climate and land-surface hydrology is extremely important in relation to long term water resource planning. This is especially so in the presence of global warming and massive land use change, issues which seem likely to have a disproportionate impact on developing countries. This thesis develops tools aimed at the study and prediction of climate effects on land-surface hydrology (in particular streamflow), which require a minimum amount of site specific data. This minimum data requirement allows studies to be performed in areas that are data sparse, such as the developing world. ¶ A simple lumped dynamics-encapsulating conceptual rainfall-runoff model, which explicitly calculates the evaporative feedback to the atmosphere, was developed. It uses the linear streamflow routing module of the rainfall-runoff model IHACRES, with a new non-linear loss module based on the Catchment Moisture Deficit accounting scheme, and is referred to as CMD-IHACRES. In this model, evaporation can be calculated using a number of techniques depending on the data available, as a minimum, one to two years of precipitation, temperature and streamflow data are required. The model was tested on catchments covering a large range of hydroclimatologies and shown to estimate streamflow well. When tested against evaporation data the simplest technique was found to capture the medium to long term average well but had difficulty reproducing the short-term variations. ¶ A comparison of the performance of three limited area climate models (MM5/BATS, MM5/SHEELS and RegCM2) was conducted in order to quantify their ability to reproduce near surface variables. Components of the energy and water balance over the land surface display considerable variation among the models, with no model performing consistently better than the other two. However, several conclusions can be made. The MM5 longwave radiation scheme performed worse than the scheme implemented in RegCM2. Estimates of runoff displayed the largest variations and differed from observations by as much as 100%. The climate models exhibited greater variance than the observations for almost all the energy and water related fluxes investigated. ¶ An investigation into improving these streamflow predictions by utilizing CMD-IHACRES was conducted. Using CMD-IHACRES in an 'offline' mode greatly improved the streamflow estimates while the simplest evaporation technique reproduced the evaporative time series to an accuracy comparable to that obtained from the limited area models alone. The ability to conduct a climate change impact study using CMD-IHACRES and a stochastic weather generator is also demonstrated. These results warrant further investigation into incorporating the rainfall-runoff model CMD-IHACRES in a fully coupled 'online' approach.

La plaine semi-aride du Tensift au centre du Maroc est une région confrontée à des difficultés croissantes en terme de gestion de l'eau (pluviométrie faible et irrégulière, croissance des besoins sous l'effet de la démographie galopante et l'extension des zones irriguées). Dans ce contexte et dans le cadre du projet SudMed, l'objectif de la thèse est de décrire, dans l'espace (à la résolution kilométrique) et sur de longues périodes temporelles (la décennie), le fonctionnement hydrique des agro-systèmes irrigués de la plaine du Tensift (~3000 km²). La méthodologie développée repose sur le contrôle de modèles agro-météorologiques par des données satellites issues de capteurs optique à large champ (données MODIS de 2000 à 2006). Dans un premier temps, nous nous sommes intéressés à l'occupation du sol, connaissance préalable à la quantification des besoins en eau des cultures. Etant donné la résolution spatiale de MODIS (250 m), nous avons eu recours à des méthodes de désagrégation, qui ont permis d'identifier et de cartographier les trois principales classes d'occupation du sol: zones non irriguées, cultures annuelles, plantations arborées. Dans une deuxième partie, nous avons utilisé cette information pour spatialiser un modèle de bilan hydrique, en étudiant tout particulièrement les termes d'évapotranspiration et d'irrigation. L'évaluation du modèle est effectuée par comparaison: (1) aux données collectées sur les parcelles d'expérimentation du projet SudMed; (2) à des cartes établies à l'aide d'images à haute résolution spatiale et temporelleFORMOSAT-2 et (3) aux volumes d'eau des barrages distribués par l'office agricole régional. Cette étude ouvre des perspectives pour l'estimation des volumes d'eau d'irrigation transitant par les différents réseaux d'irrigation, et en particulier ceux prélevés dans la nappe phréatique du Tensift.

L'objectif de notre recherche est d'améliorer les performances des modèles pluie-débit par une meilleure prise en compte de l'ETP au sein de ces modèles. Pour cela, l'échantillon de bassins versants étudiés devait représenter diverses conditions climatiques et hydrologiques. L'assemblage des différentes données collectées (pluie, débit et paramètres climatiques) a permis l'élaboration d'un échantillon de 308 bassins versants dont 221 français, 79 nord-américains et 8 australiens. L'avantage de travailler sur un échantillon assez vaste est de tirer des conclusions relativement libres de toute dépendance vis à vis des caractéristiques particulières de tel ou tel bassin. De plus, quatre modèles pluie-débit ont été utilisés: le modèle GR4J et des versions globales des modèles HBV, IHACRES et TOPMODEL. Tout d'abord, une étude de sensibilité de ces modèles pluie-débit à l'entrée d'ETP a été entreprise. Deux aspects ont été traités en particulier. La première motivation était de tester l'impact d'une connaissance fine du climat par rapport à une connaissance des normales (moyennes interannuelles). Les résultats ont confirmé le manque d'utilisation judicieuse de l'information datée contenue dans les formules d'ETP par les modèles pluie-débit. Le deuxième aspect était de tester plusieurs formules pour représenter les variations de l'ETP au sein des modèles pluie-débit. Les résultats ont montré là aussi une faible sensibilité des modèles quant au choix fait pour la formule d'ETP. Nous avons porté en particulier notre attention sur la formule de Penman, couramment utilisée en modélisation, car elle est la plus satisfaisante d'un point de vue physique, à l'échelle de la parcelle. En modélisation pluie-débit, elle est dépassée par d'autres formules plus simples (utilisant moins de données climatiques). Ainsi, nous pouvons parler de la pertinence d'autres formules que Penman pour la modélisation: des formules simples faisant intervenir uniquement la température de l'air sont aussi performantes que la formule de Penman. D'un point de vue opérationnel, ces résultats sont extrêmement rassurants puisqu'ils suggèrent qu'une entrée d'ETP simple à obtenir peut être utilisée à la place de formules d'ETP plus demandeuses en données. Cependant, d'un point de vue scientifique, le constat d'apparente insensibilité des modèles pluie-débit à l'entrée d'ETP est préoccupant. En effet, le modèle semble se contenter d'une représentation extrêmement simplifiée de la demande évaporatoire. Pourtant, il est légitime de penser que le modèle serait plus performant s'il prenait mieux en compte cette information supplémentaire. Les hypothèses avancées pour expliquer la faible sensibilité des modèles à l'entrée d'ETP sont multiples : - S'agit-il d'un phénomène naturel que le modèle retranscrit assez fidèlement ? - Faut-il remettre en cause la structure du modèle, notamment la partie traitant l'évaporation ? - Les formules d'ETP traditionnelles sont-elles inadaptées à la modélisation pluie-débit ? Alors que la première interrogation nous semblait difficile à investiguer, les deux autres étaient plus à la portée d'un utilisateur de modèles pluie-débit conceptuels. Pour cela, nous avons utilisé une approche par données synthétiques d'ETP qui permet notamment de lever toute incertitude sur la pertinence des données d'ETP. Les résultats ont montré que les différences entre ETP datées et interannuelles étaient presque totalement absorbées par les réservoirs de production des modèles pluie-débit. Le modèle se comporte donc comme un filtre passe-bas pour les données atmosphériques, atténuant ainsi la variabilité temporelle des entrées climatiques.

Le processus d’évapotranspiration (ETR) reste actuellement difficile à évaluer. L’objectif poursuivi par cette recherche est de proposer une méthode suffisamment robuste pour pouvoir être appliquée à l’échelle pluriannuelle tout en permettant un suivi à pas de temps fin au cours de la journée. En s’appuyant sur l’état de l’art, l’étude s’intéresse successivement au cas idéalisé des surfaces homogènes puis à celui des surfaces hétérogènes. Depuis quelques années, l’IRM a entrepris d’automatiser son réseau de stations synoptiques. Un sous-ensemble de stations a été choisi afin d’être doté d’un équipement plus complet comprenant un mât météorologique destiné à effectuer des mesures de la température et de la vitesse du vent à plusieurs niveaux. Ces nouvelles données sont exploitées dans la méthode préconisée. Celle-ci combine la théorie de Monin-Obukhov et l’évaluation du bilan énergétique de surface pour calculer les flux turbulents de chaleur sensible et de chaleur latente ainsi que le flux d’ETR. La télédétection offre quant à elle la possibilité d’observer de vastes territoires. Un modèle diagnostique est proposé pour estimer les flux turbulents de surface et l’ETR sur l’ensemble de la Belgique. Il s’agit d’une variante simplifiée du schéma « Isba » de transfert sol-végétation-atmosphère. Des flux radiatifs déduits d’images du satellite Meteosat sont exploités en entrée. La résolution spatiale est celle du capteur infra-rouge utilisé jusque Meteosat-7 (5*9 km). L’application est réalisée sur la période 1994-2003 avec un pas de temps horaire ce qui représente une première dans le domaine. Des comparaisons sont effectuées avec les résultats obtenus aux stations automatiques de l’IRM et avec des données récentes des stations belges du réseau Fluxnet. Les résultats sont très satisfaisants. Le travail s’achève sur des perspectives de développements futurs, la recherche en la matière étant encore en pleine évolution.

Potato ground cover and spectral data were measured in the Columbia Basin during the 1990 growing season. Three spectral were correlated with ground cover; normalized difference, near infrared-red ratio, and the first derivative of the spectral curve at 750 nm. All models were statistically significant at the 99% level. Normalized was most correlated followed by the near infrared-red ratio, and the first derivative of the spectral curve at 750 nm. / Graduation date: 1992