The current design procedure for cantilever structures on spread footings in the Texas Department of Transportation (TxDOT) is based on horizontal pressure that is calculated by using Rankine's and Coulomb's theory. These are classical Geotechnical Engineering methods. Horizontal earth pressure due to moisture and volume change in high plasticity soil is not determined by these classical methods. However, horizontal pressure on most of the cantilever retaining structures in Texas is determined by following the classical methods. In recent years, a number of consultants have considered the horizontal pressure due to swelling on cantilever retaining structures in Texas. However, the proposed horizontal pressure by consultants is 10-20 times higher than the classical horizontal pressure. This method of cantilever retaining structure design without knowing the real pressure and stress pattern increases the thickness of the wall, and raises the cost of construction. This study focuses on providing adequate patterns of lateral earth pressure distribution on cantilever retaining structures in expansive soil. These retaining wall structures are subject to swelling pressures which cause horizontal pressures that are larger than the classical especially near the ground surface. Beside the prediction of lateral earth pressure distribution, the relations between water content, volume change and suction change are determined. Based on the laboratory testing program conducted, Soil Water Characteristic Curves (SWCC) are determined for a site located at the intersection of I-35 and Walters Street in San Antonio, Texas. Additionally, relations between volume change with confining pressure curve, water content change with the change of confining pressure curve, water content change with change of matric suction and volume change with change of matric suction curves are generated based on laboratory tests. There are a number of available mass volume measurement methods that use mostly mercury or paraffin to obtain volume measurements. Although these methods are reported in the literature, they are not used in practice due to application limitations like safety, time, and cost. In order to overcome these limitations, a new method was developed to measure the volume of soil mass by using sand displacement. This new method is an inexpensive, safe, and simple way to measure mass volume by Ottawa sand.

The experimental work reported in this thesis quantified the productivity of lucerne over a two-year period (2000-2001) for a Mediterranean climate at Roseworthy in South Australia (34°32′S, 138°45′E), and determined associated dynamics for water and nitrogen in duplex soil. Shoot growth of dryland lucerne was limited primarily by the pattern and amount of incident rainfall, but high temperature (30-35oC) also constrained summer production. These high summer temperatures induced greater production when irrigation was applied, but under the normally dry summer conditions high temperatures combined with soil water deficit (up to 200mm) caused growth to cease. Thus, shoot dry matter yield under rainfed conditions was 4.9 t ha⁻¹ in 2000 (from 7 harvests) and 1.8 t ha⁻¹ in 2001 (from 5 harvests) whereas summer irrigation increased yield to 14.9 t ha⁻¹ in 2000 (7 harvests) and 7.1 t ha⁻¹ in 2001 (5 harvests). Under rainfed conditions the RUE was 0.55 g DM MJ⁻¹ PARi compared with 1.08 g DM MJ⁻¹ PARi in the irrigated treatment in 2000, reducing to 0.4 g DM MJ⁻¹ for the rainfed and 0.7 g DM MJ⁻¹ under limited irrigation in 2001. Lucerne plant population declined from 69 to 20 (plants m⁻²) in the rainfed treatment and the plants partially compensated for this in 2000 by increasing stem density from 300 to 400 m⁻² in 2000 although this declined back to 300 m⁻² in 2001. In all treatments more than 70% of root biomass was in the top 40 cm soil, this was partially due to the vertical distribution of plant available water but also to subsoil constraints to root development below 0.6m. Nevertheless, lucerne was able to extract water and nitrate to 1800 mm soil depth. Large amounts of irrigation >400mm) over summer (Dec 1999-Mar 2000) increased total soil water content, approaching the drained upper limit; causing a 600% increase in shoot dry matter yield, similarly higher growth rate (71 kg DM d⁻¹) and higher RUE (~1.7 g DM MJ⁻¹ ), confirming that water availability was the main constraint to lucerne growth. Delayed benefits of summer irrigation, especially in the subsurface treatment, were also observed later (July to October) when lucerne was able to scavenge excess irrigation water and nitrate stored in the 600-1800 mm soil profile, which resulted in increased shoot growth. Drainage below the effective rooting depth was negligible, even under irrigation, confirming that lucerne can dry soil profiles and reduce deep drainage. Average annual water use efficiency was 9 kg DM ha⁻¹ mm⁻¹ under rainfed conditions compared to ~15 kg DM ha⁻¹ mm⁻¹ under irrigated conditions. Shoot dry mattter production was closely related to evapotranspiration in all treatments, however, under rainfed conditions losses from evaporation were proportionally higher compared to irrigated treatments. Sub-surface drip irrigation proved superior to surface irrigation using 22% less water compared to surface sprinkler irrigation treatment with comparable yields. Biological N₂fixation was strongly related to shoot production with 18 to 27 kg N fixed per tonne of shoot dry matter across all seasons and treatments. Dependence on N₂fixation appeared to be unrelated to soil mineral N concentration and amounts of nitrate in the profile (to 1m) were generally quite low <35 kg N ha⁻¹). Soil water dynamics under both rainfed and surface irrigated treatments were adequately simulated by the Agricultural Production System Simulator (APSIM) with RMSD < 10% of the observed means and R² > 0.80 for the total soil profile (0-2000 mm). Simulation of growth and development was less satisfactory. For example, the RMSD was ~50% of observed mean for shoot biomass (R² = 0.68) in the rainfed treatment, and 36% (R² = 0.77) in the irrigated treatment. Overall, simulation of shoot DM production was close to observed values during the growing season (Apr-Nov), however the model was unable to capture the observed shoot yield in response to summer irrigation, with simulated shoot DM 40% less than the observed value in 2000 and 35% less in 2001. N dynamics were poorly simulated under these soil and climate conditions. Amounts of soil mineral nitrogen (kg NO⁻₃-N ha⁻¹) were adequately simulated in rainfed conditions but consistently over-predicted under irrigated conditions. This evaluation of APSIM highlights both good and poor model performance and the analysis indicates the need for caution when applying the model in situations where observed data is scarce. Areas requiring improvements to the model are identified. Overall this research has improved understanding of the limitations to potential production of lucerne in a Mediterranean environment on duplex soils and shown that APSIM-Lucerne can be used confidently for many applications, particularly soil-water dynamics. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1352515 / Thesis (Ph.D.) - University of Adelaide, School of Earth and Environmental Sciences, 2009

The experimental work reported in this thesis quantified the productivity of lucerne over a two-year period (2000-2001) for a Mediterranean climate at Roseworthy in South Australia (34°32′S, 138°45′E), and determined associated dynamics for water and nitrogen in duplex soil. Shoot growth of dryland lucerne was limited primarily by the pattern and amount of incident rainfall, but high temperature (30-35oC) also constrained summer production. These high summer temperatures induced greater production when irrigation was applied, but under the normally dry summer conditions high temperatures combined with soil water deficit (up to 200mm) caused growth to cease. Thus, shoot dry matter yield under rainfed conditions was 4.9 t ha⁻¹ in 2000 (from 7 harvests) and 1.8 t ha⁻¹ in 2001 (from 5 harvests) whereas summer irrigation increased yield to 14.9 t ha⁻¹ in 2000 (7 harvests) and 7.1 t ha⁻¹ in 2001 (5 harvests). Under rainfed conditions the RUE was 0.55 g DM MJ⁻¹ PARi compared with 1.08 g DM MJ⁻¹ PARi in the irrigated treatment in 2000, reducing to 0.4 g DM MJ⁻¹ for the rainfed and 0.7 g DM MJ⁻¹ under limited irrigation in 2001. Lucerne plant population declined from 69 to 20 (plants m⁻²) in the rainfed treatment and the plants partially compensated for this in 2000 by increasing stem density from 300 to 400 m⁻² in 2000 although this declined back to 300 m⁻² in 2001. In all treatments more than 70% of root biomass was in the top 40 cm soil, this was partially due to the vertical distribution of plant available water but also to subsoil constraints to root development below 0.6m. Nevertheless, lucerne was able to extract water and nitrate to 1800 mm soil depth. Large amounts of irrigation >400mm) over summer (Dec 1999-Mar 2000) increased total soil water content, approaching the drained upper limit; causing a 600% increase in shoot dry matter yield, similarly higher growth rate (71 kg DM d⁻¹) and higher RUE (~1.7 g DM MJ⁻¹ ), confirming that water availability was the main constraint to lucerne growth. Delayed benefits of summer irrigation, especially in the subsurface treatment, were also observed later (July to October) when lucerne was able to scavenge excess irrigation water and nitrate stored in the 600-1800 mm soil profile, which resulted in increased shoot growth. Drainage below the effective rooting depth was negligible, even under irrigation, confirming that lucerne can dry soil profiles and reduce deep drainage. Average annual water use efficiency was 9 kg DM ha⁻¹ mm⁻¹ under rainfed conditions compared to ~15 kg DM ha⁻¹ mm⁻¹ under irrigated conditions. Shoot dry mattter production was closely related to evapotranspiration in all treatments, however, under rainfed conditions losses from evaporation were proportionally higher compared to irrigated treatments. Sub-surface drip irrigation proved superior to surface irrigation using 22% less water compared to surface sprinkler irrigation treatment with comparable yields. Biological N₂fixation was strongly related to shoot production with 18 to 27 kg N fixed per tonne of shoot dry matter across all seasons and treatments. Dependence on N₂fixation appeared to be unrelated to soil mineral N concentration and amounts of nitrate in the profile (to 1m) were generally quite low <35 kg N ha⁻¹). Soil water dynamics under both rainfed and surface irrigated treatments were adequately simulated by the Agricultural Production System Simulator (APSIM) with RMSD < 10% of the observed means and R² > 0.80 for the total soil profile (0-2000 mm). Simulation of growth and development was less satisfactory. For example, the RMSD was ~50% of observed mean for shoot biomass (R² = 0.68) in the rainfed treatment, and 36% (R² = 0.77) in the irrigated treatment. Overall, simulation of shoot DM production was close to observed values during the growing season (Apr-Nov), however the model was unable to capture the observed shoot yield in response to summer irrigation, with simulated shoot DM 40% less than the observed value in 2000 and 35% less in 2001. N dynamics were poorly simulated under these soil and climate conditions. Amounts of soil mineral nitrogen (kg NO⁻₃-N ha⁻¹) were adequately simulated in rainfed conditions but consistently over-predicted under irrigated conditions. This evaluation of APSIM highlights both good and poor model performance and the analysis indicates the need for caution when applying the model in situations where observed data is scarce. Areas requiring improvements to the model are identified. Overall this research has improved understanding of the limitations to potential production of lucerne in a Mediterranean environment on duplex soils and shown that APSIM-Lucerne can be used confidently for many applications, particularly soil-water dynamics. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1352515 / Thesis (Ph.D.) - University of Adelaide, School of Earth and Environmental Sciences, 2009

O presente trabalho foi realizado com o objetivo de quantificar e caracterizar a variabilidade espacial dos parâmetros equação K = Kq=0 exp(bq), determinada pelo método do perfil instantâneo. Nessa equação, Kq=0 é o coeficiente linear da reta lnK versus q ou a condutividade hidráulica (K) para o teor de água no solo (q) igual a zero e b o coeficiente angular. O experimento foi realizado no campus da "Escola Superior de Agricultura Luiz de Queiroz" - ESALQ/USP, localizado no município de Piracicaba (SP), em um Latossolo Vermelho Amarelo, álico, A moderado, textura média, (Typic Hapludox), moderadamente a bem drenado. A parcela experimental tinha um comprimento de 70 m e uma largura de 20 m; na sua linha central ao longo do comprimento foram considerados 50 pontos de observação, distanciados de 1 m entre si e, em cada um deles, instalados 5 tensiômetros eqüidistantes com suas cápsulas porosas localizadas às profundidades de 0,15; 0,30; 0,45; 0,60; 0,75 m. No ponto central de cada circunferência de 0,10 m de raio, na qual foram equidistantemente instalados 5 tensiômetros, foi instalada uma sonda de TDR para medida da umidade nas mesmas cinco profundidades em cada ponto de observação. As medições de umidade e potencial mátrico foram feitas durante 62 dias ou 1.370 horas, escolhendo se para este estudo o período compreendido entre os tempos de redistribuição 78 a 604 horas. Os resultados de umidade no solo (q), potencial mátrico (fm), lnKq=0 e b, foram submetidos à análise estatística exploratória e descritiva para verificação da distribuição e identificação de valores extremos. Também se calculou o número mínimo de subamostras necessárias para estimar o valor médio representativo dos parâmetros avaliados, para um nível de probabilidade de 95%, nos valores de 5, 10, 20 e 30% de coeficiente de variação em torno da média. Para os parâmetros lnKq=0 e b a análise do número de amostras foi também feita pela técnica "bootstrap". Análise da estabilidade temporal foi realizada com os dados de umidade no solo e potencial mátrico. Os resultados indicaram que o padrão de variabilidade dos parâmetros hídricos estudados (q, fm, b e lnKq=0 ) aumentou em profundidade, sendo os maiores coeficientes de variação aqueles apresentados pelo b. A variabilidade da umidade (q) foi baixa e aumentou com o tempo de redistribuição, enquanto que o potencial mátrico (fm), apresentou comportamento oposto, qual seja, variabilidade alta no início da redistribuição diminuindo para média no final da avaliação. Não houve relação entre os parâmetros quanto ao número de amostras necessárias para estimar a média, indicando que a utilização dos métodos para determinação de número de amostras pode gerar valores bem diferentes e que sua aplicação deve ser feita com prudência. Tanto a umidade do solo quanto o potencial mátrico apresentaram estabilidade temporal, o que permitiu identificar quais os locais mais indicados para a realização de amostragens com reduzido esforço e grande precisão. / This work was carried out with the objective of quantifying and characterizing the spatial variability of the K = Kq=0 exp(bq) equation parameters, determined by means of instantaneous profile method. In this equation, b is the slope and Kq=0 the intercept of the linear regression of lnK versus q. The experiment site is located at the Campus “Luiz de Queiroz”, University of São Paulo, county of Piracicaba (SP), Brasil (22 o 42’ 30” S e 47 o 38’ 00” W) in a Typic Hapludox. The experimental plot dimensions were: length = 70 m and width = 20 m. In the central line of the length, 50 observation points 1m among themselves were considered each one with i) 5 mercury manometer tensiometers equally spaced in a 0.10 m radius circumference with their porous cups installed at 0.15, 0.30, 0.45, 0.60 and 0.75 m soil depths and ii) one TDR probe in the central point of the above circumference to measure soil-water content at the same five soil depths. Measurements of soil-water content and matric potential were made during 62 days of soil water redistribution, but the study was carried out using the redistribution time range from 78 to 604 hours. Results of soil-water content (q), matric potential (fm), lnKq=0 and b were analyzed by the exploratory and descriptive statistics in order to verify the data distribution and to identify outliers values. The minimum number of samples necessary to estimate the mean value of the assessed parameters was also calculated at a probability level of 5%, for variation coefficient values of 5, 10, 20 and 30%. For the parameters lnKq=0 and b, the analysis of number of sa mples was also made by using the "bootstrap" technique. Time stability analysis was used for soil-water content and matric potential data. The results have indicated that the variability of the studied hydric parameters (q, fm, b and lnKq=0 ) increased with soil depth, being the higher variation coefficients those of the parameters b. The soil water-content (q) variability was low and increased with the soil water redistribution time, whereas the matric potential had an inverse behavior, that is, high variability at the beginning of the soil water redistribution, decreasing to a medium one at the end of evaluation. There was no relation among parameters in terms of number of samples needed to estimate the mean, indicating that the use of methods to determine the number of samples can led to values very differents; hence the appliance of these methods should be done with caution. Both soil-water content and matric potential presented time stability, which permitted to identify the best points for future samplings with less effort and high precision.

Orientador: José Anderson do Nascimento Batista / Dissertação (mestrado] - Universidade Estadual de Campinas, Faculdade de Engenharia Civil, Arquitetura e Urbanismo. / Made available in DSpace on 2018-08-20T02:23:11Z (GMT). No. of bitstreams: 1 Bossarino_Danilo_M.pdf: 1760894 bytes, checksum: ee8724892eb6c348cf45c3b4722dbdf8 (MD5) Previous issue date: 2012 / Resumo: Um dos mais importantes atributos físicos do solo é a curva de retenção. Diante das dificuldades de determinar este atributo em laboratório, devido ao comportamento histerético da curva em relação aos diferentes efeitos gerados pelo umedecimento e pelo secamento, recorre-se a modelos matemáticos. Assim, esta dissertação estudou a representatividade do modelo de van Genuchten de retenção de água no solo, modelo este amplamente difundido nas Ciências do Solo. Com o objetivo de estimar os parâmetros de ajuste deste modelo, efetuou-se a calibração do mesmo, utilizando seis métodos de otimização de funções não lineares, empregando os dados experimentais de curvas de retenção em solos com perfis profundos. Os resultados demonstraram que o método de Nelder-Mead obteve menores resíduos de ajuste do modelo nos dois tipos de solos estudados, com qualidade de ajuste superior aos de calibração manual. Em alguns casos, os melhores resultados entre menor erro, menos tempo computacional e menor número de chamadas, foram obtidos pelo método de Levenberg-Marquardt. A análise de sensibilidade demonstrou que os parâmetros de umidade de saturação e o expoente da carga mátrica são os decisivos para o sucesso da calibração / Abstract: One of the most important soil physical attributes is the retention curve. Due to the difficulties of determining this attribute in laboratories because of hysteretic behavior of the curve, one may recur to mathematical models. This dissertation studied the representation of van Genuchten model of soil water retention, which is being widely disseminated in Soil Science. With the objective to estimate the fitting parameters of this model, we performed the calibration, using six methods of optimization of nonlinear functions, using the experimental data retention curves in soils with deep profiles. The results showed that the method of Nelder-Mead found lower residues of model fit in both types of soils, with higher quality than those from manual calibration. In some cases, best results in terms of smallest error, less computational time and a smaller number of calls have been obtained using the method of Levenberg-Marquardt algorithm. The sensitivity analysis showed that the parameters of saturation moisture and the numerical exponent in the matric potential variable are decisive for the success of the calibration / Mestrado / Recursos Hidricos, Energeticos e Ambientais / Mestre em Engenharia Civil

>Magister Scientiae - MSc / Soil moisture forms an integral part of the hydrological cycle and exerts considerable influence on hydrological processes at or near the earth’s surface. Knowledge of soil moisture is important for planning and decision-making in the agricultural sector, land and water conservation and flood warning. Point measurements of soil moisture, although highly accurate, are time consuming, costly and do not provide an accurate indication of the soil moisture variation over time and space as soil moisture has a high degree of spatial and temporal variability. The spatial variability of soil moisture is due to the heterogeneity of soil water holding properties, the influence of plants, and land uses. The downscaling of satellite microwave soil moisture estimates and soil water balance modelling was investigated at six transects in the semi-arid, Western Cape Province of South Africa, as alternatives to in situ soil measurements. It was found that microwave soil moisture estimates compared well to in situ measurements at the six transects (study sites), with coefficient of determination (r2) values greater than 0.7 and root mean square error (RMSE) values less than 1.5%. Downscaling using the universal triangle method, performed well at 4 of the 6 transects, with r2 values great than 0.65 and low to moderate RMSE values (0.5-12%). Soil water balance modelling similarly performed well in comparison with in situ measurements at 4 of the transects with regards to r2 values (>0.6) but had moderate to high RMSE (4.5-19%). Poor downscaling results were attributed to fine scale (within 1 km) surface heterogeneity while poor model performance was attributed to soil hydrological and rainfall heterogeneity within the study areas.

Please read the abstract in the section 00front of this document / Thesis (PhD (Soil Science))--University of Pretoria, 2007. / Plant Production and Soil Science / unrestricted

Current irrigation scheduling technologies are limited to refilling the root zone based on measured or predicted amount of water stored within the root zone. This needs measurement of soil-water status and specifying soil field capacity that make this approach expensive and challenging. The FullStopTM wetting front detector (FS) was specifically developed to be a simple and affordable technology to help farmers manage water, nutrients and salts in the root zone. This device responds to a strong wetting front, but research has shown it is less sensitive to weak redistributing wetting fronts, and this may compromise its efficacy in certain situations. The objectives of this study were to recommend a modified version of the FS that responds to weak redistributing wetting fronts and to develop guidelines for the deployment of these detectors to schedule irrigation. The research described herein comprises of two phases: the first phase focused on literature review, field evaluation of wetting front detector of varying sensitivities (WFD) and laboratory measurements of hydraulic properties of soil and wick materials. The second phase validates the HYDRUS-2D/3D for the development of guidelines on how to use WFD to schedule irrigation. The first phase includes: i) a literature review on passive lysimetry that relates design features to the sensitivity of WFD and how prototypes of WFD operate; ii) hydraulic characterization of soil and wick materials to describe the functioning of the different WFD designs; iii) an empirical investigation to determine whether the wick characteristics limits the attainment of equilibrium between the opening of the outer tube and the water table in the inner tube; iv) field evaluations of five types of WFD under sprinkler and natural rainfall to examine the accuracy and sensitivity of the different WFD designs; and v) analysis of the equilibrium between the WFD and the surrounding soil, and recommendations for the best design options based on the sensitivity requirement for different situations. The second phase of the study used observed data sets to validate the Hydrus-2D/3D model. After validation, the model was used to simulate different irrigation scenarios to develop guidelines for the deployment of WFD to schedule irrigation. Field evaluations of various WFD designs showed that length has significant effect on the sensitivity of WFD (P ≤ 0.05). The 90-cm-long Tube wetting front detector (90TD) was significantly more sensitive than the original FS design. The hydraulic conductivity function of two wick materials (Diatomaceous Earth and Fine sand) were not limiting for the attainment of the equilibrium between the Tube Detector and the surrounding soil, and the opening of the Tube Detector and the water level in the inner tube. The Hydrus-2D/3D model performed well in simulating the measured responses of FS or 90TD and the experimental sensitivity thresholds of these detectors. This model was deployed to link WFD responses to different simulated irrigation scenarios to generate monitoring protocol such as detector placement depth, irrigation amount or interval. The model simulations showed that FS can be used to schedule irrigation objectively for sprinkler or drip irrigations, i.e. adjusting irrigation amount or interval based on the response of a detector. Though further study is warranted, model simulation has indicated that 90TD can be used to improving furrow irrigation management. It is envisaged that WFD technology can guide farmers to make informed irrigation decisions and alerting farmers to percolation losses below the root zone. / Thesis (PhD)--University of Pretoria, 2014 / gm2015 / Plant Production and Soil Science / PhD / Unrestricted

Previous studies of agricultural conditions in the Mekong Delta (MD) have identified soil compaction as an obstacle to sustainable production. A conceptual model for soil formation was presented to demonstrate the link between soil hydrology and plant response. Detailed studies of soil moisture dynamics in agricultural fields were conducted using a dynamic process-orientated model. Pressure head and water flow were simulated for three selected sites during a year for which empirical data were available. Daily meteorological data were used as dynamic input and measured pressure head was used to estimate parameter values that satisfied various acceptance criteria. The Generalised Likelihood Uncertainty Estimation (GLUE) approach was applied for calibration procedures with 10,000 runs, each run using random values within the chosen range of parameter values. To evaluate model performance and uncertainty estimation, re-sampling was carried out using coefficient of determination (R2) and mean error (ME) as the criteria. Correlations between parameters and R2 (and ME) and among parameters were also considered to analyse the relationship of the selected parameter set in response to increases/decreases in the acceptable simulations. The method was successful for two of the three sites, with many accepted simulations. For these sites, the uncertainty was reduced and it was possible to quantify the importance of the different parameters.

Increased frequency of severe drought events, coupled with rising air temperatures and vapor pressure deficits (VPD), pose a great threat to Mediterranean forests. Pinus halepensis Mill. is one of the most widespread species in the countries surrounding the Mediterranean basin. Thus, water use of this species plays a critical role in the regions water balance. Studying transpiration patterns and the mechanisms behind stomatal responses to the combined effects of changing VPD and soil moisture can help us improve estimation of forest water use in a changing climate. To improve the estimation of forest evapotranspiration in the Mediterranean basin, the objective of this thesis is to evaluate the transpiration patterns of Pinus halepensis and the role of this species in the soil-water balance under different environmental conditions. Two pine forests in the Turia river basin, eastern Spain, were monitored over a two-year period. The two locations were selected at contrasting altitudes and distances to the sea but within the same hydrological basin, to evaluate if this placement would change the relationship between environmental conditions and the water use of the pines. Sap flow measurements were obtained on a 30-minute interval together with soil moisture measurements and meteorological variables. A soil-water balance was performed on a forest plot-level using an eco-hydrological model in combination with the transpiration data, to assess the contribution of pine transpiration to actual evapotranspiration. Transpiration was dictated by changes in VPD, relative extractable water (REW) and the interaction between these two variables at both sites, indicating that the pines depended on water in the shallow soil layers, and this was restricted during large parts of the year. Except for low winter temperatures having a decreasing effect on transpiration only at the inland site, no significant differences were found in the relationship between environmental drivers and transpiration patterns between the two sites. Using a predictive model, sap flow was shown to be restricted on days of mean VPD values of 2.5 kPa, even when soil moisture levels were relatively sufficient (REW = 0.30), indicating a VPD threshold that decreases pine transpiration. This could potentially affect performance and survival of the species with predicted increases in air VPD. Transpiration levels were highly restricted throughout the first year demonstrating that physiological stresses were not limited to summer months. Using two-year old seedlings in an experiment under controlled conditions confirmed that high levels of VPD can have a decreasing effect on transpiration of P. halepensis (in response to instant changes from 1.5 kPa to 2.7 kPa), while there is an intermediate VPD range that increases transpiration (between 1.0 kPa – 1.5 kPa). This demonstrate how important it is to incorporate VPD changes when predicting forest water use under future climatic changes. Combining transpiration data with eco-hydrological modelling demonstrated that transpiration levels accounted for 62% of total ETa levels during two years of study. Interception levels where 32% of gross precipitation, representing a large water loss to the forest ecosystem. With increased frequency of drought events, soil moisture levels are predicted to become even more limited. Together with a rise in temperatures and consequently VPD, transpiration and growth are likely to be constrained.