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.

The need for efficient use of water resources has increased the importance of optimum soil water usage in agricultural systems. Soil temperature has been shown to be important in influencing the early development of many plant species. Many agricultural regions have suboptimal soil temperature regimes for plant growth, and some cultural practices have been shown to reduce near-surface soil temperatures. The seasonal influence of soil temperature on soil water extraction and aboveground and belowground plant growth under variable irrigation was investigated at the USU Greenville Farm in Logan, UT. Soil surface mulches and buried heat cables were used to modify soil temperature. A line-source sprinkler system provided a gradient of water application. During 1987 yields were mainly influenced by irrigation. During 1988 greater soil temperature differences resulted in significant plant growth and yield responses. Soil water depletion corresponded to soil temperature treatments during the early part of the growing seasons. Depth of maximum soil water depletion was about 20 cm deeper for warm treatments. Water uptake rates of earlier-maturing plants in warm treatments were reduced later in the season, so that cumulative seasonal soil water depletion was similar for all temperature treatments. Although depth of rooting was somewhat greater under high than low irrigation during 1988, low irrigation treatments depleted soil water to greater depth. There was no interactive response of plant growth and yield or of soil water depletion to soil temperature and irrigation treatments. Modifications were made to a computer simulation model of the soil-plant-atmosphere system in order to more mechanistically simulate plant water uptake and to include influences of soil temperature on seasonal rooting growth and soil water extraction. The model adequately simulated both the pattern and magnitude of soil temperature influences on soil water depletion, and conclusions drawn from model simulations agreed with field observations during 1987 and 1988.

The current study has been conducted in response to the growing problem of water scarcity and the need for more effective methods of irrigation water management. Remote sensing techniques have been used to match spatially and temporally distributed crop water demand to water application rates. Remote sensing approaches using Landsat imagery have been applied to estimate the components of a soil water balance model for an agricultural field by determining daily values of surface/root-zone soil moisture, evapotranspiration rates, and losses and by developing a forecasting model to generate optimal irrigation application information on a daily basis. Incompatibility of coarse resolution Landsat imagery (30m by 30m) with heterogeneities within the agricultural field and potential underestimation of field variations led the study to its main objective, which was to develop models capable of representing spatial and temporal variations within the agricultural field at a compatible resolution with farming management activities. These models support establishing real-time management of irrigation water scheduling and application. The AggieAirTM Minion autonomous aircraft is a remote sensing platform developed by the Utah Water Research Laboratory at Utah State University. It is a completely autonomous airborne platform that captures high-resolution multi-spectral images in the visual, near infrared, and thermal infrared bands at 15cm resolution. AggieAir flew over the study area on four dates in 2013 that were coincident with Landsat overflights and provided similar remotely sensed data at much finer resolution. These data, in concert with state-of-the-art supervised learning machine techniques and field measurements, have been used to model surface and root zone soil volumetric water content at 15cm resolution. The information provided by this study has the potential to give farmers greater precision in irrigation water allocation and scheduling.

Both empirical and process-simulation models are useful for evaluating the effects of management practices on environmental quality and crop yield. The use of these models is limited, however, because they need many soil property values as input. The first step towards modelling is the collection of input data. Soil properties can be highly variable spatially and temporally, and measuring them is time-consuming and expensive. Efficient methods, which consider the uncertainty and cost of measurements, for estimating soil hydraulic properties form the main thrust of this study. Hydraulic properties are affected by other soil physical, and chemical properties, therefore it is possible to develop empirical relations to predict them. This idea quantified is called a pedotransfer function. Such functions may be global or restricted to a country or region. The different classification of particle-size fractions used in Australia compared with other countries presents a problem for the immediate adoption of exotic pedotransfer functions. A database of Australian soil hydraulic properties has been compiled. Pedotransfer functions for estimating water-retention and saturated hydraulic conductivity from particle size and bulk density for Australian soil are presented. Different approaches for deriving hydraulic transfer functions have been presented and compared. Published pedotransfer functions were also evaluated, generally they provide a satisfactory estimation of water retention and saturated hydraulic conductivity depending on the spatial scale and accuracy of prediction. Several pedotransfer functions were developed in this study to predict water retention and hydraulic conductivity. The pedotransfer functions developed here may predict adequately in large areas but for site-specific applications local calibration is needed. There is much uncertainty in the input data, and consequently the transfer functions can produce varied outputs. Uncertainty analysis is therefore needed. A general approach to quantifying uncertainty is to use Monte Carlo methods. By sampling repeatedly from the assumed probability distributions of the input variables and evaluating the response of the model the statistical distribution of the outputs can be estimated. A modified Latin hypercube method is presented for sampling joint multivariate probability distributions. This method is applied to quantify the uncertainties in pedotransfer functions of soil hydraulic properties. Hydraulic properties predicted using pedotransfer functions developed in this study are also used in a field soil-water model to analyze the uncertainties in the prediction of dynamic soil-water regimes. The use of the disc permeameter in the field conventionally requires the placement of a layer of sand in order to provide good contact between the soil surface and disc supply membrane. The effect of sand on water infiltration into the soil and on the estimate of sorptivity was investigated. A numerical study and a field experiment on heavy clay were conducted. Placement of sand significantly increased the cumulative infiltration but showed small differences in the infiltration rate. Estimation of sorptivity based on the Philip's two term algebraic model using different methods was also examined. The field experiment revealed that the error in infiltration measurement was proportional to the cumulative infiltration curve. Infiltration without placement of sand was considerably smaller because of the poor contact between the disc and soil surface. An inverse method for predicting soil hydraulic parameters from disc permeameter data has been developed. A numerical study showed that the inverse method is quite robust in identifying the hydraulic parameters. However application to field data showed that the estimated water retention curve is generally smaller than the one obtained in laboratory measurements. Nevertheless the estimated near-saturated hydraulic conductivity matched the analytical solution quite well. Th author believes that the inverse method can give a reasonable estimate of soil hydraulic parameters. Some experimental and theoretical problems were identified and discussed. A formal analysis was carried out to evaluate the efficiency of the different methods in predicting water retention and hydraulic conductivity. The analysis identified the contribution of individual source of measurement errors to the overall uncertainty. For single measurements, the inverse disc-permeameter analysis is economically more efficient than using pedotransfer functions or measuring hydraulic properties in the laboratory. However, given the large amount of spatial variation of soil hydraulic properties it is perhaps not surprising that lots of cheap and imprecise measurements, e.g. by hand texturing, are more efficient than a few expensive precise ones.

Die verschiedenen Meßverfahren zur Bestimmung von Bodenwassergehalten und der Bodenfeuchte konnten während ihres Einsatzes im Uvs-Nuur-Becken über einen längeren Zeitraum hinweg erprobt werden. Dabei stellte sich heraus, daß die Thetasonde und die Stechzylinderproben sich zur Bestimmung des volumetrischen Bodenwassergehalts gut eignen. An den Standorten, an denen parallele Messungen mit beiden Verfahren möglich waren, zeigten Vergleiche der Meßreihen, daß sich die beiden Methoden gegenseitig bestätigen. Nur in Einzelfällen traten größere Abweichungen zwischen den Tageswerten auf. Einschränkend auf die Anwendbarkeit der Verfahren und die Genauigkeit der Meßergebnisse kann sich die Bodenbeschaffenheit auswirken. In stark verdichteten oder skelettreichen Böden ist das Einbringen der Sondenmeßstäbe schwierig und stellenweise nicht möglich. Derartige Böden sind auch für die Entnahme von Stechzylinderproben problematisch, da es schwierig ist Materialverluste bei der Entnahme gering zuhalten. Die Verfahren zur Bestimmung der Bodenfeuchte, Tensiometer und Gipsblocksensoren, hatten gegenüber den anderen Verfahren den Vorteil, daß sie automatisiert waren. Auf diese Weise konnte auch ohne intensive Betreuung eine hohe zeitliche Meßdichte erzielt werden. Über eine Eichkurve, die im Labor erstellt wurde, konnten den Wasserspannungen die entsprechenden Bodenwassergehalte zugeordnet werden. Für Station S 2 sind die Tensiometermeßwerte gut geeignet, um zusammen mit den Stechzylinderproben die Bodenwasserdynamik zu beschreiben. An den anderen Standorten liegen die Wassergehalte, die man über die Eichkurve erhält, verglichen mit Thetasonden- und Stechzylinderwerten sehr viel höher. Beim Einsatz von Tensiometern und Gipsblocksensoren in diesem Gebiet muß aufgrund des geringen Bodenwassergehalts vieler Standorte besonders darauf geachtet werden, daß die Sensoren bzw. die Kerzen eng vom Boden umschlossen sind, ansonsten kann es zu erheblichen Beeinträchtigungen der Meßgenauigkeit kommen. Bei den Tensiometern muß zusätzlich darauf geachtet werden, daß der Meßbereich nicht überschritten wird. Die Variabilität zwischen den Bodenwassergehalten der Standorte ergibt sich aus ihrer Lage im Untersuchungsgebiet und dem Witterungsgeschehen. Die deutlichsten Unterschiede zeigen sich beim Vergleich der Standorte der Ebenen und der Hangbereiche. An den Standorten in der Ebene ist die potentielle Evapotranspiration höher als an den Hangstandorten, dies wirkt sich auf die absolute Höhe der Bodenwassergehalte und auf ihre Variabilität aus. In der Ebene gehen die Bodenwassergehalte nach einer Erhöhung durch Niederschlagseinträge aufgrund der starken Evapotranspiration relativ schnell wieder zurück, so kommt es zu einer hohen Variabilität. An den Hangstandorten ist dieser Effekt abgeschwächt, besonders gering ist die potentielle Verdunstung im Wald am Standort S 7. Die Meßreihen dort weisen geringere Gegensätze zwischen den Extrema auf. Die signifikanten Unterschiede der Bodenwassergehalte verschiedener Meßtiefen eines Standortes werden anhand Variationskoeffizienten der Meßreihen deutlich. In 5 cm Bodentiefe spiegelt sich das aktuelle atmosphärische Geschehen wider. Niederschlagseinträge werden durch eine unmittelbare Erhöhung des Bodenwassergehalts sichtbar. Ist die potentielle Verdunstung nach einer Erhöhung der Bodenwassergehalte durch Niederschlagseinträge hoch, verringern sich die Bodenwassergehalte in dieser Meßtiefe auch schnell wieder. In den Bereichen ab 20 cm Bodentiefe sind kurzfristige Erhöhungen des Bodenwassergehalts nur nach sehr starken Niederschlägen zu beobachten. Veränderungen wie der allmähliche Rückgang des Bodenwassergehalts in den tieferen Bodenschichten an S 3 sind nur über einen längeren Zeitraum festzustellen. Die zeitliche Variabilität der Bodenwassergehalte wird vom Witterungsgeschehen, insbesondere den Niederschlägen und der potentiellen Verdunstung, bestimmt. Im Sommer 1998 ist das Verhältnis von Niederschlag und potentieller Verdunstung so, daß auch nach den Hauptniederschlägen des Jahres in den Sommermonaten keine Erhöhung der Bodenwassergehalte stattgefunden hat. An Station S 3 ist in den tieferen Bodenschichten eine Austrocknung zu verzeichnen. Dies ist der Hauptunterschied zwischen den Jahren 1997 und 1998. 1997 fällt sehr viel mehr Regen als 1998, es kommt zu einer nachhaltigen Durchfeuchtung des Bodens. Auch die Verdunstung ist 1997 geringer. Nach Niederschlägen findet daher kein so schneller Rückgang der Bodenwassergehalte wie 1998 statt, und die Variabilität der Meßwerte ist geringer. Es ist anzunehmen, daß die Bodenwassergehalte am Anfang der Meßperiode des Jahres 1998, die im Laufe des Meßzeitraums abnehmen, Vorräte aus den Einträgen des Jahres 1997 darstellen. Eine nachhaltige Durchfeuchtung des Bodens findet also nur bei sehr hohen Niederschlagseinträgen wie im Jahr 1997 statt. / Different methods to detect soil water contents were tested in the Uvs-Nuur basin, Mongolia, over a period of three months. Frequency domain probes and soil cores were suited to determine the volumetric soil water content. Accuracy depended on soil properties. Tensiometers and gypsum block methods were difficult to apply because of the loose soil structure. The variability of the soil water contents is caused by spatial variability and the weather situation. Clearest differences among soil water contents were found comparing sites in the plain and in mountainous areas due to higher evapotranspiration in the plain. Temporal variability is mostly depending on rainfall. Soil moisture is stored for longer time after rainfall in the mountainous areas due to less evapotranspiration.

Tracer methods are commonly used for estimation of soil water and groundwater recharge flux especially in arid and semiarid regions. These tracer methods are based on the solute profile shape (distribution of concentration with depth) and peak position. For soils of semi-arid to sub-humid climates, vertical water movement may seasonally vary in direction due to climate conditions and vegetative demands. The first objective of this thesis was to show that TDR (time domain reflectometry) can be a useful tool for estimation of soil water fluxes using tracer methods. The second objective was to study the effects of repeated cycles of directionally-varying flow upon solute profile shape and position used by tracer methods under controlled laboratory conditions. Three soil columns with a KCl tracer and Beaver Creek sand were used for this study. Rain and evaporative systems were used to cause the downward and upward soil water movements in the column, respectively. Soil moisture content and solute concentration were measured using TDR.<p> The result for the first objective was that the peak migration and the soil water balance methods gave similar average upward and downward soil water fluxes. This result indicates that the TDR method can be recommended for determination of soil water fluxes with tracer methods in fields or in laboratory studies for sufficient time and depth.<p> In the second objective, three different seasonal flow regimes were studied using the sand columns, and each flow regime simulated climatic seasons that might occur in the field. Several apparent and statistical parameters were used to evaluate the change of the solute profile shape and position under cycling conditions of the three different flow regimes. These parameters showed that the solute profile shape and position clearly changed under the three different repeated regimes of downward and upward seasonal flows. It was concluded that climate (seasonality) can have significant impacts on the estimation of soil water fluxes using tracer methods. The result from this investigation shows that the profile shape and position after a number of cycles (years of fluctuations) can provide a description of the previous climatic effects on the concentration profile. Therefore, the profile shape can be used as an indicator of the flow regime that has affected the solute profile shape. Moreover, if a reference of a solute profile is available (a solute profile before a period of time), it is easier to determine the flow regime affected the profile shape and position by determining the change of the profile shape and position using statistical parameters presented in this thesis.

The primary objective of this thesis is to develop a model for quantification of weather-related railway embankments hazards. The model for quantification of embankment hazards constitutes an essential component of a decision support system that is required for the management of railway embankment hazards. A model for the deterministic and probabilistic assessment of weather-related geo-hazards (W-GHA model) is proposed based on concepts of unsaturated soil mechanics and hydrology. The model combines a system of two-dimensional partial differential equations governing the thermo-hydro-mechanical behaviour of saturated/unsaturated soils and soil-atmosphere coupling equations. A Dynamic Programming algorithm for slope stability analysis (Safe-DP) was developed and incorporated into the W-GHA model. Finally, an efficient probabilistic and sensitivity analysis framework based on an alternative point estimate method was proposed. According to the W-GHA model framework, railway embankment hazards are assessed based on factors of safety and probabilities of failures computed using soil property variability and case scenarios. <p> A comprehensive study of unsaturated property variability is presented. A methodology for the characterization and assessment of unsaturated soil property variability is proposed. Appropriate fitting equations and parameter were selected. Probability density functions adequate for representing the unsaturated soil parameters studied were determined. Typical central tendency measures, variability measures, and correlation coefficients were established for the unsaturated soil parameters. The inherent variability of the unsaturated soil properties can be addressed using the probabilistic analysis framework proposed herein. <p> A large number of hypothetical railway embankments were analysed using the proposed model. The embankment analyses were undertaken in order to demonstrate the application of the proposed model and in order to determine the sensitivity of the factor of safety to the uncertainty in several input variables. The conclusions drawn from the sensitivity analysis study resulted in important simplifications of the W-GHA model. It was shown how unsaturated soil mechanics can be applied for the assessment of near ground surface stability hazards. The approach proposed in this thesis forms a protocol for application of unsaturated soil mechanics into geotechnical engineering practice. This protocol is based on predicted unsaturated soil properties and based on the use of case scenarios for addressing soil property uncertainty. Other classes of unsaturated soil problems will benefit from the protocol presented in this thesis.

The intensification of land-water management due to agriculture, forestry, and urbanization is a global phenomenon increasing the pressure on worlds water resources and threatening water security in North America. The Prairie Pothole Region of North America covers approximately 775,000 km2 and contains millions of wetlands that serve important hydrological and ecological functions. The unique hummocky topography and the variable effect of different processes contribute to high spatio-temporal variability in soil water, posing major challenges in hydrological studies. The objectives of this study were to a) examine the spatial pattern of soil water storage and its scale and location characteristics; and b) to identify its controls at multiple scales. Soil water content at 20 cm intervals down to 140 cm was measured along a transect extending over several knolldepression cycles in a hummocky landscape. High water storage in depressions and low water storage on the knolls created a spatial pattern that was inversely related to elevation. Spatial patterns were strongly similar within any given season (intra-season rank correlation coefficient as high as 0.99), moreso than between the same season over different years (inter-annual rank correlation coefficient as high as 0.97). Less similar spatial patterns were observed between different seasons (inter-season rank correlation coefficients as high as 0.90). While the intra-season and inter-annual spatial patterns were similar at scales >18 m, the inter-season spatial patterns were similar at much large scales (>72 m). This may be due to the variations in landform elements and micro-topography. The similarity at scales >72 m were present at any time and depth. However, small- and medium-scale spatial patterns changed with depth and with season due to a change in the hydrological processes. The relative dominance of a given set of processes operating both within a season and for the same season over different years yielded strong intra-season and inter-annual similarity at scales >18 m. Moreover, similarity was stronger with increasing depth, and was thought to be due to the dampening effect of overlying soil layers that are more dynamic. Similarity of spatial patterns over time helps to identify the location that best represents the field averaged soil water and improves sampling efficiency. Change in the similarity of scales of spatial pattern helps identify the change in sampling domain as controlled by hydrological processes. The scale information can be used to improve prediction for use in environmental management and modeling of different surface and subsurface hydrological processes. The similarity of spatial pattern between the surface and subsurface layers help make inferences on deep layer hydrological processes as well as groundwater dynamics from surface water measurements.

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The primary objective of this thesis is to develop a model for quantification of weather-related railway embankments hazards. The model for quantification of embankment hazards constitutes an essential component of a decision support system that is required for the management of railway embankment hazards. A model for the deterministic and probabilistic assessment of weather-related geo-hazards (W-GHA model) is proposed based on concepts of unsaturated soil mechanics and hydrology. The model combines a system of two-dimensional partial differential equations governing the thermo-hydro-mechanical behaviour of saturated/unsaturated soils and soil-atmosphere coupling equations. A Dynamic Programming algorithm for slope stability analysis (Safe-DP) was developed and incorporated into the W-GHA model. Finally, an efficient probabilistic and sensitivity analysis framework based on an alternative point estimate method was proposed. According to the W-GHA model framework, railway embankment hazards are assessed based on factors of safety and probabilities of failures computed using soil property variability and case scenarios. <p> A comprehensive study of unsaturated property variability is presented. A methodology for the characterization and assessment of unsaturated soil property variability is proposed. Appropriate fitting equations and parameter were selected. Probability density functions adequate for representing the unsaturated soil parameters studied were determined. Typical central tendency measures, variability measures, and correlation coefficients were established for the unsaturated soil parameters. The inherent variability of the unsaturated soil properties can be addressed using the probabilistic analysis framework proposed herein. <p> A large number of hypothetical railway embankments were analysed using the proposed model. The embankment analyses were undertaken in order to demonstrate the application of the proposed model and in order to determine the sensitivity of the factor of safety to the uncertainty in several input variables. The conclusions drawn from the sensitivity analysis study resulted in important simplifications of the W-GHA model. It was shown how unsaturated soil mechanics can be applied for the assessment of near ground surface stability hazards. The approach proposed in this thesis forms a protocol for application of unsaturated soil mechanics into geotechnical engineering practice. This protocol is based on predicted unsaturated soil properties and based on the use of case scenarios for addressing soil property uncertainty. Other classes of unsaturated soil problems will benefit from the protocol presented in this thesis.