5 pp. / This Extension Bulletin is similar to others previously completed for Tucson, Phoenix, Flagstaff, Prescott and Payson. The bulletin provides information on turfgrass consumptive use for the River Cities (Bullhead, Lake Havasu, etc.) and Kingman areas. Consumptive use is provided for each month of the year in units of inches/month and inches/day for three grass production systems: high quality overseeded turf, acceptable quality overseeded turf and acceptable quality turf with no overseeding. The bulletin concludes with a discussion on how to use incorporate this into turf irrigation management programs.

3 pp. / This publication is meant to be a short fact sheet that provides estimates of turfgrass consumptive use (of water) in the Payson area. The publication provides a brief description of the procedures used to generate the CU estimates, then presents the data both as a CU table and CU curve. The publication should prove useful for irrigation management and water resource planning.

3 pp.

14 pp. / This publication summarizes the results of a three year research study that evaluated whether the turf water duties mandated by the Arizona Department of Water Resources provide adequate water to grow acceptable quality turf in the Tucson and Phoenix areas.

An evapotranspiration system was defined as six coupled, parallel subsystems defined by five rectangular and one radial, one-dimensional diffusion equations. A block diagram and system transfer function Were developed for each subsystem and the subsystems were coupled to obtain a block diagram of the evapotranspiration system. The soil heat transfer subsystem was assumed to be defined by the diffusion equation for a homogeneous soil of infinite depth with constant diffusivity and heat transfer by conduction only. The solution of the diffusion equation was obtained in the frequency domain as the frequency response function and in the time domain as the convolution integral. The frequency response function was used as an analytical model in the form of a gain and a phase function in conjunction with time series analysis to determine the system constant. A numerical solution of the convolution integral was used to determine soil heat diffusivity from arbitrary time distributions of temperature at two depths. The system response as the temperature at a depth was computed from an arbitrary time distribution of input temperature given the diffusivity. Results from time series analysis of analytically generated temperature data gave values for diffusivity from the gain and phase function of 16.24- and 16.21-cm²/hr, respectively. The value used to generate the data was 16.2 cm²/hr. The corresponding value of diffusivity obtained from a trial and error numerical convolution was 16.3 cm²/hr. Values of numerical convolution computed temperature, obtained after 72 hours to remove a starting transient, differed from the analytically correct temperatures by less than 0.1 ° C for an 8° amplitude or a 16° range. For 50 days of 6-hour interval temperatures the 95 percent confidence interval on diffusivity was within two percent of the analytically correct value. Soil temperature data for the 10- and 15-cm depth from an experiment where cold (4° C) irrigation water was applied, including the temperature data during the time of irrigation, was analyzed by time series analysis. The value of diffusivity obtained from time series analysis and the gain function was 14.7 cm²/hr compared to a range of 15.1 to 16.9 for amplitude and phase plots and 16.6 for a finite difference solution of the diffusion equation. The value from phase was 21.61 cm²/hr which is much higher due to the time-varying effects of diffusivity or improper alignment of the two time series. Confidence intervals for diffusivity were very wide because of the short period of record and because of heat transfer by moisture during the irrigation. Numerical convolution determined values of diffusivity of 15.1-and 14.9-cm²/hr for before and after irrigation indicated some change in soil heat diffusivity with time. Numerical convolution computed temperatures were within 0.17° C of the measured temperature except during and immediately after the application of the irrigation water. The maximum error between measured and computed temperature was 3.88° C. Time series analysis can be used to determine the soil heat diffusivity from arbitrary time distributions of temperatures at two depths. Confidence limits for diffusivity can be established by certain assumptions as a measure of the adequacy with which the diffusivity has been determined. Numerical convolution can also be used to determine soil heat diffusivity by trial and error from arbitrary time distributions of temperatures measured at two depths. Simulation of soil temperatures from arbitrary time distributions of measured input can be achieved by numerical convolution.

Evapotranspiration rates of plots with vegetative cover and evaporation rates from bare soil differed during the active growing season of desert hackberry (Celtis pallida) plants but total water losses from both plots for the year were the same. Thermally induced vapor flux appeared to contribute insignificantly to moisture movement under the desert hackberry plant. The difference in measured available soil moisture was independent of location from the plant center during the growing season. During the winter months, when the plants were semidormant, soil moisture measurements had more variability and measurement locations appeared to be important due to differential rainfall input. The determined soil moisture release curve and soil water conductivity values (using an in situ technique) appeared to be representative of the conditions at the study site. A model using soil and plant parameters predicted evapotranspiration rates during the active growing season of the plants when water was not a limiting factor. Calculated results using the model were unreliable when plants were under stress -- very low soil water content. Monitoring of climatic parameters delineated only major differences in surface albedo and net radiation between plant cover and bare ground. Potential evapotranspiration estimations were high but within acceptable bounds for desert conditions. Plant diffusion resistance for the desert hackberry plant, determined from a climatological model and measured soil moisture changes, appeared to increase linearly with decreasing soil moisture until it reached a critical value, below which it rose sharply.

Revised; Originally Published: 2005 / 4 pp.

O arroz irrigado está entre os principais cereais produzidos no mundo. Determinar a evapotranspiração (ET) para as grandes áreas de arroz irrigado é um desafio devido a pouca disponibilidade de dados. Diversos Modelos de ET vêm sendo desenvolvidos com a intenção de monitorar áreas agrícolas, porém poucos estudos experimentais são realizados sobre áreas de arroz irrigado. Este trabalho tem como objetivo geral estimar a ET sobre cultivos de arroz irrigado através de um modelo que utiliza informações meteorológicas in situ (Priestley-Taylor) e outro remoto (MOD16). O Priestley-Taylor (PT) é um modelo de ET que utiliza informações de temperatura do ar e componentes relacionadas ao balanço de energia, juntamente com um parâmetro adimensional α. O modelo MOD16 foi criado para monitorar a ET em grandes áreas, utilizando informações meteorológicas de um banco de dados de reanálise juntamente com dados remotos. Ambos os métodos não apresentam calibração e validação sobre áreas de arroz irrigado no Sul do Brasil. Neste trabalho validamos estes dois modelos a partir de dois sítios experimentais com medidas de ET através da técnica de Eddy Covariance. Os resultados encontrados nesta pesquisa mostraram-se satisfatórios quando comparado o método PT com dados experimentais, recomendando-se a utilização de 1,22 do parâmetro α. A simplificação no método PT realizada a partir das componentes do balanço de energia, com substituição pela variável de radiação global através de uma regressão linear, mostrou-se válida apresentando erros poucos expressivos, e com valor de 1,18 para parâmetro α. Já o modelo de ET MOD16 mostrou-se pouco preciso sobre as áreas de arroz irrigado. A validação de ET MOD16 foi realizada sobre uma área de 3 x 3 km e pixel central, resultando em menor subestimativa do modelo para o pixel central em relação aos dados de Eddy Covariance. Além disso, a correlação foi realizada em função das variáveis ambientais, encontrando maior correlação do dado experimental com as componentes do balando de energia, enquanto o MOD16 apresentou maior correlação com a temperatura do ar. Por fim, sugerem-se melhorias na parametrização da energia disponível no modelo de ET MOD16. Além disso, a aplicação do método simplificado de PT é indicada sobre áreas de arroz irrigado. / Irrigated rice is among principal produced cereals in the world. Determining the evapotranspiration (ET) for large areas of irrigated rice is a challenge task, due to poor data availability. Several ET models have been developed with the intention of monitoring agricultural areas, however few experimental studies are accomplished on areas of irrigated rice. This study aims to estimate ET on irrigated rice crops using a model which employs meteorological information in situ (Priestley-Taylor) and one remote (MOD16). Priestley-Taylor (PT) is a model of ET that uses air temperature and related components to the energy balance as information and a dimensionless parameter α. The MOD16 model was designed to monitor ET in large areas using meteorological information obtained from the reanalysis database together with remote data. Both methods do not present calibration and validation on areas of irrigated rice in Southern Brazil. In this work we validate these two models from two experimental sites with ET measurements employing the Eddy Covariance technique. The results found in this research was satisfactory when compared to the PT method with experimental data. It was suggested 1.22 for the α parameter. The simplification in the PT method performed from the components of the energy balance, with substitution for the global radiation variable using a linear regression. It was validated with few expressive errors, with a value of 1.18 for α parameter. On the other hand, the MOD16 model did not showed good accuracy on the areas of irrigated rice. The validation of ET MOD16 was performed over an area of 3 x 3 km and central pixel, resulting in a small underestimation of the model for the central pixel in relation to Eddy Covariance data. In addition, was performed the correlation in function of the environmental variables, finding a higher correlation of the experimental data with the components of the energy balance, while the MOD16 showed a high correlation with the air temperature. Finally, it was suggested improvements in the parameterization of the available energy in the model of ET MOD16, and to indicate the application of the simplified method of PT on the areas with irrigated rice.

Evaporation and transpiration from the soil and plant, respectively, have received increasing attention from those who work with water supply, irrigation, and drainage.

The estimation of evapotranspiration (ET), a key process within the Earth's surface water and energy balance, remains an important challenge for a wide range of disciplines such as surface hydrology, irrigation management and meteorology. However, notwithstanding the considerable progress recently made in our understanding of the physical and biological processes governing ET, the accurate quantification of ET is very tricky to achieve, even at a limited spatial scale. In this study, we combine field measurements with numerical experiments to tackle issues related to the quantification of ET and the associated uncertainties for a maize cropped field using two different approaches, i.e. the agro-hydrological modelling and the soil water balance approach. For the agro-hydrological modelling, we mainly focus on the estimation of field-scale soil water content and on the identification of root water uptake parameters. With regard to the field-scale soil water content, we put forward that the within-field variability is large and that the maize crop plays a non-negligible role in the development of the soil water content patterns both at the field and at the maize row scale. For deriving root water uptake parameters (RWUP), we develop and test two different approaches, i.e. the simplified soil water balance and the inverse modelling approach. Using numerical experiments, we show that the simplified soil water balance approach produces quite accurate RWUP. On the other hand, the inverse modelling approach is only successful for some soils and for some conditions due to instability and nonuniqueness issues. For the soil water balance approach, we show that the accuracy of the local ET estimate is strongly dependent on the estimation method used to derive the bottom fluxes and that the use of pedotransfer functions is of little interest. For field-scale ET estimates, we show that the variability of ET is large both at the field scale (due to the variable crop growth) and at the maize row scale (due to the maize row layout). To produce accurate field-scale ET estimates, we suggest to scale up maize row scale ET estimates using the concept of temporal stability or using a covariant such as the Leaf Area Index. The results of our study suggest that the estimation of water fluxes or associated state variables for a row cropped field requires a two-step upscaling strategy, from the local scale to the row, then from the row to the field scale.