Seasonal Evapotranspiration Values Research Articles

Strategies of Parameter Optimization and Soil Moisture Sensor Deployment for Accurate Estimation of Evapotranspiration Through a Data-driven Method

A soil moisture data-driven method through inversely solving the Richards’ equation was tested, and proved to be a reliable alternative estimator of actual evapotranspiration (ETa) for relatively homogeneous soils in an arid region. Few studies have examined the feasibility of the method using soil moisture for soils with more heterogeneities, which may lead to biased parameters and varied root depths, and thus inaccurate estimates of ETa. We used a genetic algorithm to optimize the parameters most sensitive to ETa estimation, then estimated daily and seasonal ETa using hourly soil moisture data, measured from four sites (from surface to 2-m depth at 20-cm intervals) with different soil textures and crop species in desert-oasis farmlands in northwest China. The seasonal ETa values were 487, 574, 436, and 377 mm at the sites cropped with field maize, spring wheat, seed maize, and seed maize, respectively, in 2018. The daily rates from one site were validated against the eddy-covariance measurements, and the daily rates from all the sites were compared against the estimations from a simple water balance method, and both showed good consistency (R2 = 0.72-0.93). The inverse method has great potential for relatively accurate estimates of ETa in the middle and late growing stages but may induce a slight underestimation in the initial growing season. To determine the minimum monitoring depths of sensors for relatively accurate estimates, ETa values were estimated using soil moisture data at various observation depths, and were compared with eddy-covariance measurements and hypothetical ETa-observed depth curves. The results showed that inaccurate stratification of soil types in the profiles may cause great uncertainty in the estimates, and if texture-contrasting interlayers exist in the profiles, the lowest soil moisture sensor should be placed sufficiently deep, with all the interlayers fully included.

Improvement of seasonal runoff and soil loss predictions by the MMF (Morgan-Morgan-Finney) model after wildfire and soil treatment in Mediterranean forest ecosystems

The negative hydrological effects of wildfire are very difficult to predict in Mediterranean forest ecosystems, due the intrinsic climate and soil characteristics of these areas. Among the hydrological models simulating surface runoff and soil erosion in these environmental contexts, the semi-empirical Morgan-Morgan-Finney (MMF) model can ensure the representation of the main physical processes, while offering ease of use and limiting the number of input parameters. However, literature reports very few modelling studies using MMF in burned areas of the Mediterranean environment with or without post-fire rehabilitation measures. To fill this gap, the capacity of the MMF model to predict the seasonal surface runoff and soil loss in a Mediterranean forest was verified and improved for unburned plots and areas affected by a wildfire, with and without post-fire straw mulch treatment. The application of MMF with default input parameters (set up according to the original guidelines of the model’s developers) led to poor performance. Conversely, after introducing some changes in input data for both the hydrological and erosive components (seasonal values of evapotranspiration, reduction of the soil hydrological depth, including soil water repellency effects in burned soils, and modelling erosive precipitation only), MMF was able to predict seasonal runoff volumes and soil loss with good reliability in all the experimented conditions.This modelling experiment has shown the capacity of the MMF model to simulate the seasonal hydrological and erosion response of the experimental unburned and burned soils of Mediterranean semi-arid forests. Although more research is needed to validate the model's prediction capacity in these conditions, the use of MMF as a management tool may be suggested to predict the hydrogeological risk in these delicate ecosystems threatened by wildfire, as well as to evaluate the potential efficiency of soil treatments after fire.

Automated evapotranspiration retrieval model with missing soil-related datasets: The proposal of SEBALI

Precision Agriculture (PA) has been booming lately in alignment with the proposal of several surface energy balance algorithms. The Surface Energy Balance Algorithm for Land (SEBAL) remains one of the most validated and implemented systems worldwide. This model enables the estimation of Evapotranspiration (ET) in different vegetation settings. In Lebanon, winter cereals, including wheat, are arguably the most important crop types as they enter directly into the Lebanese diet. Yet, no recent studies were produced to estimate their water consumption, particularly with the pressing global warming trend. In this paper, a developed version of the open source SEBAL python script (i.e. Py-SEBAL), surnamed SEBAL-Improved or SEBALI, was proposed to estimate evapotranspiration for winter cereals (i.e. Wheat, Barley, Triticale) in the Bekaa plain of Lebanon with missing soil-related datasets. Main enhancements of SEBALI over py-SEBAL concern the ability to choose a random shape for the study site, the selection of Hot/Cold pixels over agricultural areas only, thus better selection process, as well as the usage of atmospherically corrected satellite images. More importantly, ET rates could be assessed in regions lacking soil-related datasets, due to the usage of the Water stress (Ws) factor.Between November 2017 and June 2018, results show that the highest ET values were in May (i.e. flowering and grain filling growth stage), with seasonal ET values significantly varying (e.g. more than 600 mm in some regions) irrespective of the spatial location of the parcels. These results were explained by the different agricultural practices, and, to a lower extent, the varied precipitations within the study area. These outputs coupled with the produced ET cereal trend could assist decision makers as well as farmers and land owners to forecast their water consumptions and to increase their yields while conserving water resources, thus enhancing the water usage efficiency. The proposed surface energy balance algorithm (i.e. SEBALI) could be portable to other climatic regions, particularly when soil-related datasets are lacking.

Evaluation of two evapotranspiration approaches simulated with the CSM–CERES–Maize model under different irrigation strategies and the impact on maize growth, development and soil moisture content for semi-arid conditions

Water deficit is the most common adverse environmental condition that can seriously reduce crop productivity. Crop simulation models could assist in determining alternate crop management scenarios to deal with water-limited conditions. However, prior to the application of crop models, the appropriate performance under different soil moisture levels should be confirmed. The objective of this study was to evaluate the capability of the CSM–CERES–Maize model to simulate the impact of different irrigation regimes on maize (Zea mays L.) growth and development, evapotranspiration and soil water content under semi-arid conditions. Data from irrigation trials that were conducted in 2008 and 2010 in northeast of Greeley, Colorado were used for this assessment. The irrigation treatments were 100, 85, 70, 55 and 40% of full crop water requirements. The daily evapotranspiration (ET) was measured using Bowen ratio-energy balance (BREB) instrumentation. The ability of the CSM–CERES–Maize model using two different ET approaches, i.e., Priestley–Taylor (PT) and FAO-56 Penman–Monteith (PM), in reproducing the experimental maize growth and development data as well as the daily and seasonal ET measured with the BREB method, and soil water content based on different water regimes was analyzed. The results showed that the model with both the PT and FAO-56 PM approach simulated phenology accurately for all irrigation treatments. The CSM–CERES–Maize model simulated both grain yield and final biomass fairly well for all irrigation levels for both ET approaches. The normalized root mean square error was less than 10.2% for grain yield and 36.8% for final biomass for the PT approach and 12.1% for grain yield and 26.0% for final biomass for the FAO-56 PM approach. The model using the PT approach provided daily and seasonal ET values that had a slightly lower accurate than those derived from the FAO-56 PM approach as compared the measured ET by the BREB method. However, the model with both two ET approached could simulate daily and seasonal ET within 12% of measured ET. There was a reasonable agreement between the simulated and observed water content for all four soil depths of the six irrigation treatments which were derived from both approaches. In addition, the model accurately simulated the fluctuation and time span of the cyclic variation of soil water. Overall, it can be concluded that the CSM–CERES–Maize model using the two different ET approaches, i.e., PT and FAO-56 PM, was able to accurately simulate crop development and yield as well as ET and soil water content in response to the different irrigation regimes under semi-arid conditions. These results also confirmed that the model has the potential for use as a tool for agricultural water management under water-limited conditions.

Analysing trends in reference evapotranspiration and weather variables in the Tons River Basin in Central India

In this study, reference evapotranspiration (ETo) has been estimated using Penman–Monteith (PM) method on monthly time step. The monthly values have been subsequently used to estimate annual and seasonal ETo values. The trend analysis has been carried out for monthly, annual and seasonal ETo values for three meteorological stations namely Allahabad, Rewa and Satna located in the Tons River Basin in Central India. Further, the trend of weather variables that affect ETo have been examined using the Mann–Kendall test after removing the effect of significant lag-1 serial correlation from the time series using trend free-pre-whitening (TFPW) method. The magnitude of trends has been calculated using Sen’s slope estimator. Almost all the months show the significant decreasing trend in ETo values at a significance level of 1, 5 and 10 %. The significant decreasing trends were also found in annual and seasonal ETo values during the period of analysis. The magnitude of decrease in annual ETo varied from −1.75 to −8.98 mm/year. On the seasonal scale, stronger decreasing trends were identified in ETo in pre monsoon and monsoon season as compare to that of winter and post monsoon season. The significant decreasing trends were found in monthly, annual and seasonal wind speed. However, significant increase was found in annual air temperature (maximum, minimum, mean and dew point temperature) and relative humidity. Using the sensitivity analysis, maximum temperature and net solar radiation was found to be the most dominant variables which influence the rate of annual ETo over all the stations.

Five methods to interpret field measurements of energy fluxes over a micro-sprinkler-irrigated mango orchard

Energy balance measurements were carried out in a mango orchard during two growing seasons in the semi-arid region of Brazil. The actual evapotranspiration (ET) was acquired by eddy correlation (EC) and Bowen ratio energy balance (BR) techniques. The daily energy balance closure in the EC measurements showed an average gap of 12%, with a root mean square error (RMSE) of 1.7 MJ m−2 d−1. Three different correction procedures were tested for closing the energy balance from the EC system: (1) the surface energy balance residual method (RES), (2) the Bowen ratio determined from the EC fluxes, the combination approach (EC_BR), and (3) a new regression energy balance closure technique (REG). All closing energy balance methods presented good correlation with the direct EC measurements, but the trends were not similar. The latent heat fluxes estimated by the BR method—λE BR—were higher than those from the direct EC measurements—λE EC. When using the RES method, the half-hour λE EC measurements represented around 88% of the λE RES values, as the uncertainties of net radiation—R n—and soil heat fluxes—G—are propagated into the RES method. The latent heat flux derived from the combination approach—λE EC_BR—also brings these uncertainties, being the agreements comparable with those for RES method. It was therefore concluded that a single correction method for EC measurements considering only the latent and sensible heat fluxes does not exist. A new way to solve the lack of energy balance closure from EC techniques was tested by means of a curve fitting, the REG method. Considering the REG corrections applied to the energy balance components involving all periods of the day and the average conditions of the two growing seasons, half-hour values of λE EC were overmeasured by 18%, H EC was undermeasured by 17%, and G values required a correction of 466%. The REG method appeared promising because it considers different weights for all energy balance components in the optimization process. Taking the REG results for the drier second growing season as a reference, it was concluded that seasonal ET values by the other methods in mango orchard ranged from 7 to 28% higher, showing that turbulent flux measurements lack accuracy for executing on-farm water-saving programmes and calibrating transient soil water flow models.

Effects of corn deficit irrigation and soil properties on water use efficiency. A 25-year analysis of a Mediterranean environment using the STICS model

This study analyses the role of variability induced by climate and soil properties (texture and total available soil water in the root zone, TAW) on the “corn deficit irrigation–water use efficiency” relation over a 25-year period, between 1981 and 2005, in three different sites located in the South of Italy. The analysis of water use efficiency was carried out by means of three indexes: crops water use efficiency (WUE ET and WUE T ) and irrigation water use efficiency (IWUE). These indexes can be obtained by calculating the ratio between the yield and the seasonal values of evapotranspiration (ET), transpiration (T) and irrigation volume (I). After its validation, the STICS model was retained to simulate the variables required to determine these indexes. Climatic variability affected the three indexes in different ways during the 25-year period studied. The dispersion around the mean values of the water use efficiency is 17% on average for the WUE (ET or T) indexes, whereas it could reach 54% for the IWUE index. This last index is only poorly reliable due to the high variability of rainfall during the corn growing season in the Mediterranean region. For the same level of soil water deficit, TAW led to an improvement (the case of the site with a high TAW and loam–clay soil texture), a stabilisation (the case of the site with a high TAW and clay soil texture) or a decrease (the case of the site with a poor TAW and clay soil texture) in WUE ET and WUE T values. For the same conditions of soil water deficit and TAW, crops water use efficiency was higher in loam textured soil than in clay soil. The results derived by analyzing three indexes (WUE ET , WUE T and IWUE) converge to the same conclusions on the “corn deficit irrigation–water use efficiency” relation observed at the three different sites. The hypotheses which may explain the differences observed in the different sites studied in terms of water use efficiency are discussed, with the presentation of some suggestions devised for corn irrigation practices.

Evapotranspiration estimates from eddy covariance towers and hydrologic modeling in managed forests in Northern Wisconsin, USA

Direct measurement of ecosystem evapotranspiration by the eddy covariance method and simulation modeling were employed to quantify the growing season (May–October) evapotranspiration (ET) of eight forest ecosystems representing a management gradient in dominant forest types and age classes in the Upper Great Lakes Region from 2002 to 2003. We measured net exchange of water vapor fluxes in a 63-year-old mature hardwood (MHW) stand, a 60-year-old mature red pine (MRP) stand, a 3-year-old young hardwood (YHW) stand, a 17-year-old intermediate hardwood (IHW) stand, a young red pine (YRP age 8) stand, an intermediate red pine (IRP age 21) stand, and two pine barren ecosystems burned 12 years (PB1) and 2 years (PB2) ago. Field data suggested that there were no significant differences in growing season (June–September) ET/precipitation ratio among all ecosystems in 2002. However, PB2 had significantly lower ET/precipitation than those of other ecosystems in 2003. The ratios were much higher for all ecosystems, up to 0.90 for IHW, during the peak summer months (June–July). PB2 was the lowest (0.64) during that period. Stand leaf area index alone did not explain ecosystem ET at the landscape scale. Seasonal ET values measured by the eddy covariance method were significantly lower than those simulated with a process-based hydrologic model, MIKE SHE. Our integration approach combined with field measurements and simulation modeling proved to be useful in providing a full picture of the effects of forest cover type change on landscape scale water balance at multiple temporal scales. The ET procedure used in the MIKE SHE model needs improvement to fully account for the effects of vapor pressure deficit on tree transpiration. Seasonal distributions of ET coincided with precipitation in the growing season, when fluxes estimated by both field and models were the highest. The simulation model suggests that removal of conifer forests in the study region may reduce ET immediately by 113–30 mm/year or about 20%, but our field data suggests that ET can recover within 8–25 years from re-growth of hardwood forests.

Evapotranspiration and canopy temperature of rice and groundnut in southeast coastal India. Crop coefficient approach and relationship between evapotranspiration and canopy temperature

Actual evapotranspiration ( ET) from rice, groundnut and bare soil was measured by micrometeorological methods along with surface temperature measurements on two experimental plots in southeast coastal India. Hourly energy balances are presented here for different stages of crop growth as well as the daily and seasonal values of ET. The following expression for estimating ET is proposed: where s(Ta) is the slope of the water vapour pressure curve, γ is the psychrometric constant, RN is the net radiation, G is the soil heat flux and C is a crop coefficient. In the case of well-irrigated crops like rice, the interest of well-calibrated C values to estimate ET is shown, but for non-permanently irrigated crops, like groundnut, C values mainly depend on the particular soil moisture conditions and, therefore, can not be proposed for general use. Finally, relationships between daily values of sensible heat and instantaneous values of canopy to air temperature differences for rice, groundnut and bare soil are presented. Experimental results were justified by an analytical interpretation of the relationship between evapotranspiration and canopy temperature, in conjunction with a succinct error analysis. The agreement between experimentally derived relationships and theoretical expectations was acceptable.

Responses of grain sorghum to variable water supply under two irrigation frequencies

Two experiments were conducted with Sorghum bicolor (L.) Moench Cv. “Pioneer 846” in a deep loam soil in the 1977 season. Experiment I consisted of two line-source sprinkler plots, one irrigated at two-day intervals (HF) and the other every 10 to 14 days (NF). In comparable treatments of both regimes, the seasonal amount of water applied was the same. Since the subsoil was very dry at planting, the different amounts of water applied led to the development of a range of water stresses from none to severe. Experiment II was conducted in an adjacent area with a fully wetted soil profile. The treatments were irrigated every week (I) and nonirrigated (NI). Applied water was measured after each irrigation. Soil water content, leaf water potential, leaf-area index, ground cover and dry-matter accumulation were measured at frequent intervals, and yields were taken at the end of the growing season. Linear relations were found between both total dry-matter production and grain yield and seasonal evapotranspiration (ET) in both HF and NF regimes. With seasonal values of ET near the potential, grain yield and dry-matter production did not differ between irrigation frequencies. At low seasonal ET values, however, the NF regime gave greater yields of dry-matter and grain than did the HF regime.