Daily Evapotranspiration Values Research Articles

2017–2019年宁夏兰山骄子葡萄园日蒸散发观测数据集

The grapevine is one of important economic crops. Accurate measurements of daily grapevine evapotranspiration (ET) measurements are essential for improving the understanding of crop water demand and optimizing water consumption efficiency. Unfortunately, there is a relative scarcity of daily grapevine ET values in China. This dataset presents daily ET values obtained through using the Bowen ratio energy balance method and the surface renewal method in Lanshan Jiaozi Vineyard on the outskirts of Yinchuan City, spanning the period from 2017 to 2019. Abnormal Bowen ratio values have been removed during the estimation of ET and the quality of each daily ET measurement has been thoroughly assessed. The dataset is freely available, with the primary goal of establishing a foundation for the efficient use of agriculture water resources. Additionally, it is aimed to assess the applicability of the surface renewal method in a highly heterogonous vineyard.

Integrating machine learning and empirical evapotranspiration modeling with DSSAT: Implications for agricultural water management

The availability of accurate reference evapotranspiration (ETo) data is crucial for developing decision support systems for optimal water resource management. This study aimed to evaluate the accuracy of three empirical models (Hargreaves-Samani (HS), Priestly-Taylor (PT), and Turc (TU)) and three machine learning models (Multiple linear regression (LR), Random Forest (RF), and Artificial Neural Network (NN)) in estimating daily ETo compared to the Penman-Monteith FAO-56 (PM) model. Long-term data from 42 weather stations in Florida were used. Moreover, the effect of ETo model selection on sweet corn irrigation water use was investigated by integrating simulated ETo data from empirical and ML models using the Decision Support System for Agrotechnology Transfer (DSSAT) model at two locations (Citra and Homestead) in Florida. Furthermore, a linear bias correction calibration technique was employed to improve the performance of empirical models. Results were consistent in that the NN and RF models outperformed the empirical models. The empirical models tended to underestimate and overestimate small and high daily ETo values, respectively, with the HS model exhibiting the least accuracy. However, calibrated PT and TU models performed comparably to the ML models. Results also revealed that using an inappropriate ETo model could lead to over-irrigation by up to 54 mm during a single crop season. Overall, ML models have proven reliable alternatives to the PM model, especially in regions with access to long-term data due to their site-independent performance. In areas without long-term data for ML model training and testing, calibrating empirical models is viable, but site-specific calibration is needed. It is important to highlight that distinct plant species exhibit varying transpiration characteristics and, consequently, have different water requirements. These differences play a pivotal role in shaping the overall impact of ETo models on crop water use.

Quantifying evapotranspiration fluxes on green roofs: A comparative analysis of observational methods

Evapotranspiration (ET) is an important process in green stormwater infrastructure (GSI) aiming to reduce urban drainage, to promote cooling and/or to contribute to an urban hydrological balance restoration closer to the natural one. However, on these structures and particularly on green roofs (GR), its evaluation remains challenging and subject to discussion. Estimates of ET by water balance, energy balance, and an ET chamber were performed on five different plots of a full-scale experimental green roof in Trappes (France). Compared to both water balance (90th percentile range of daily ET values: 0.8 mm/d to 3 mm/d) and chamber methods (90th percentile range of daily ET values: 1 mm/d to 1.5 mm/d), the energy balance (90th percentile range of daily ET values is between 1.8 mm and 3.7 mm) produces higher values, 1 to 2 times higher in cumulative values during common periods. The chamber ET displays a similar trend to the energy balance on an hourly basis, and its values remain within the same range as the water balance evaluations on a daily time-step. All three assessments consistently fell below the potential ET values estimated with the Penman-Monteith formula. Critical issues in ET estimation through experimentation have arisen. Sensible heat flux (H) significantly increases ET values when using the energy balance approach compared to the other two methods. The Water Balance method is practical, but on days following rainfall events, the Chamber method may prove more reliable, albeit more time and labour-intensive. The three methods indicated that the substrate thickness was the main contributing factor to increase ET, with well-maintained herbaceous plants providing higher ET values than sedums in thick (15 cm) substrates. In addition, the substrate's nature, especially its organic content, is another factor that promotes ET in green roofs.

Evaluation of the evapotranspiration rate of lacustrine wetland macrophytes in Lake Tana, Ethiopia

This study quantified the total evapotranspiration (ET) flux of three major types of macrophytes that cover lacustrine fringe wetlands in Lake Tana, Ethiopia during the dry season, April and May, 2022. This study was conducted to understand lacustrine wetland macrophytes' ET rates and provide an important guideline for designing their conservation and restoration plans. To assess ET rates during the peak dry season, three macrophytes of lacustrine wetlands in Lake Tana were chosen: Eichhornia crassipes (water hyacinth), Cyperus papyrus, and Echinochloa stagnina. Three replicate lysimeters for each of the three treatment types (macrophytes) and one control type (open water) were applied to measure ET. To calculate reference evapotranspiration (ETo), FAO's ETo Calculator Version 3.2 was applied. All statistical analyses were carried out using R software. The results of ET rates from wetland macrophytes (9.05mm/day) were considered to be significantly higher than open water evaporation (5.90mm/day). There was a significant difference in mean ET among the macrophytes [F (3, 488) = 194.6, p < 2e-16 ***]. In this study, crop coefficient (Kc1) (1.99 ± 0.65) referenced to FAO Penman–Monteith ETo is greater than Kc2 (1.58 ± 0.59) referenced to open water evaporation (Eow). In terms of wetland macrophyte type, E. crassipes had the maximum mean Kc values (Kc1 = 2.51±0.70 and Kc2 = 2.02±0.67). E. stagnina had the minimum mean Kc values (Kc1 = 1.52±0.32 and Kc2 = 1.19±0.24). Except for open water which strongly correlated with sunshine hours (r = 0.61) and solar radiation (r = 0.60), the correlation among daily ET values and meteorological variables was found to be weak. The result of our research indicated that the presence of floating macrophytes of E. crassipes will increase the ET flux during the dry season more than emergent macrophytes and open water surfaces. Our findings could provide an important guideline for designing conservation and restoration plans for C. papyrus and E. stagnina to reverse the spread of E. crassipes and maintaining lacustrine fringe wetlands for fish breeding ground and sediment control.

Assessment of Irrigation Efficiency by Coupling Remote Sensing and Ground-Based Data: Case Study of Sprinkler Irrigation of Alfalfa in the Saratovskoye Zavolgie Region of Russia.

Nowadays, the leading role of data from sensors to monitor crop irrigation practices is indisputable. The combination of ground and space monitoring data and agrohydrological modeling made it possible to evaluate the effectiveness of crop irrigation. This paper presents some additions to recently published results of field study at the territory of the Privolzhskaya irrigation system located on the left bank of the Volga in the Russian Federation, during the growing season of 2012. Data were obtained for 19 crops of irrigated alfalfa during the second year of their growing period. Irrigation water applications to these crops was carried out by the center pivot sprinklers. The actual crop evapotranspiration and its components being derived with the SEBAL model from MODIS satellite images data. As a result, a time series of daily values of evapotranspiration and transpiration were obtained for the area occupied by each of these crops. To assess the effectiveness of irrigation of alfalfa crops, six indicators were used based on the use of data on yield, irrigation depth, actual evapotranspiration, transpiration and basal evaporation deficit. The series of indicators estimating irrigation effectiveness were analyzed and ranked. The obtained rank values were used to analyze the similarity and non-similarity of indicators of irrigation effectiveness of alfalfa crops. As a result of this analysis, the opportunity to assess irrigation effectiveness with the help of data from ground and space-based sensors was proved.

Evapotranspiration Retrieval Using S-SEBI Model with Landsat-8 Split-Window Land Surface Temperature Products over Two European Agricultural Crops

Crop evapotranspiration (ET) is a key variable within the global hydrological cycle to account for the irrigation scheduling, water budgeting, and planning of the water resources associated with irrigation in croplands. Remote sensing techniques provide geophysical information at a large spatial scale and over a relatively long time series, and even make possible the retrieval of ET at high spatiotemporal resolutions. The present short study analyzed the daily ET maps generated with the S-SEBI model, adapted to Landsat-8 retrieved land surface temperatures and broadband albedos, at two different crop sites for two consecutive years (2017–2018). Maps of land surface temperatures were determined using Landsat-8 Collection 2 data, after applying the split-window (SW) algorithm proposed for the operational SW product, which will be implemented in the future Collection 3. Preliminary results showed a good agreement with ground reference data for the main surface energy balance fluxes Rn and LE, and for daily ET values, with RMSEs around 50 W/m2 and 0.9 mm/d, respectively, and high correlation coefficient (R2 = 0.72–0.91). The acceptable uncertainties observed when comparing with local ground data were reaffirmed after the regional (spatial resolution of 9 km) comparison with reanalysis data obtained from ERA5-Land model, showing a StDev of 0.9 mm/d, RMSE = 1.1 mm/d, MAE = 0.9 mm/d, and MBE = −0.3 mm/d. This short communication tries to show some preliminary findings in the framework of the ongoing Tool4Extreme research project, in which one of the main objectives is the understanding and characterization of the hydrological cycle in the Mediterranean region, since it is key to improve the management of water resources in the context of climate change effects.

Exploring the Influence of Seasonal Cropland Abandonment on Evapotranspiration and Water Resources in the Humid Lowland Region, Southern China

AbstractSeasonal abandonment in the previously rice‐based rotation system is increasingly prevalent worldwide particularly in southern China. Assessing the effect of this abandonment on evapotranspiration (ET) and water resources is of major importance for regional water cycle change and agricultural water management. This study analyzed the ET characterization of rice‐winter rape and rice‐winter fallow rotation systems and its relation to weather factors in a humid lowland region, southern China based on a half‐hourly ET measurement with Bowen ratio energy balance system from 2017 to 2020. Then the strategic modeling experiment combining ET and rainfall‐runoff models was used to explore the land abandoning effect on ET and water resources. The results showed that the daily ET values of the rice, rape, and fallow seasons were 3.30 ± 1.89, 1.31 ± 1.31, and 1.55 ± 1.19 mm/d, respectively. The averaged summed ET values of the rice‐winter rape and rice‐fallow rotation systems were 652.3 and 737.8 mm, respectively. Net radiation (Rn) was identified as the most critical weather factor for ET of all seasons. Air temperature and water vapor pressure deficit mainly affected ET indirectly through the path of Rn. Compared with the previously winter rape, the change in daily ET caused by seasonal abandonment was 0.13 ± 0.11 mm/d. This abandonment‐induced ET change increased the average daily storage deficit by 12.0% and groundwater depth by 4.5%, while reduced the daily runoff by 20.3%.

Evapotranspiration in the Brazilian municipalities surrounding the Itaipu Binacional reservoir: characterization process and estimation methods

Seeking to contribute with the management of water resources in the Itaipu Binacional reservoir region, this research aimed to characterize the dynamics of evapotranspiration and evaluate the performance of different mathematical methods, which determine reference evapotranspiration (ETo) from air temperature values. Fifteen municipalities were analyzed. After obtaining the data series, ETo was estimated using six methods: Camargo (C), Hargreaves-Samani (HG-S), Jensen-Haise (JH), Penman-Monteith with missing data (PMm), Thornthwaite-Camargo (TW-C) and Penman-Monteith (PM) – the latter was the reference method. The performance of the methods was analyzed by several statistical indexes. Daily ETo values ranged from 2 to 10 mm d-1, with an annual mean of 5.78 mm d-1. We also observed that it is determined predominantly by radioactive parameters, which annually represent 76% of the evapotranspiration process, while aerodynamic parameters represent 24%. Among the ETo estimation methods, HG-S and PMm were the most suitable for estimating.

INTEGRATIVE USE OF PENMAN-MONTEITH EQUATION WITH REMOTE SENSING AND GEOGRAPHICAL INFORMATION SYSTEM TECHNIQUES TO ESTIMATE EVAPOTRANSPIRATION VRIANCES IN IRAQ

This research was aimed to construct an integrative system which is capable of accurate determining and analyzing evapotranspiration rates in Iraq for long period , Since high evapotranspiration rates and extreme shortage in precipitation are the main causes of aridity, which considered principal reason for land degradation and land desertification eventually. FAO Penman-Monteith method was adopted because it's the international standard method. In this work meteorological readings of nine stations with comprehensive covering for Iraq's area were taken for every ten years in a long-term range (31 years). The daily evapotranspiration values had been calculated, then after the annual summation value determined for the years (1987, 1997, 2007, and 2017). The use of spatial analysis schemes proved that generally eighties decade of the last century had climax (Etr) values, then ETr rates rapidly decreased in whole Iraq except some anomalies. There were two reasons for this decrement, firstly air temperature value decent which increase relative humidity. Secondly wind speed rates falling (which considered the principal cause for reference evapotranspiration rates descending in this case).

Estimation of reference evapotranspiration (ETo) at Parbhani, Maharashtra

Evapotranspiration (ET) is an important parameter for climatological and hydrological studies, as well as for irrigation planning and management. The FAO Penman-Monteith method (P-M) is the method recommended by FAO-56 for estimation of ETo over a wide variety of climatic situations over the world and it requires many types of climatic data. A study has been carried out to estimate the mean daily ETo characteristics of Parbhani in Maharashtra. The results showed that, the variation of average daily ETo values over the period (1982-2017) ranged from 3.45 mm day-1 (26th December) to 10.46 mm day-1 (29th May). The weekly mean ETo varied between 3.59 mm day-1 (52nd SMW) to 10.17 mm day-1 (22nd SMW). The total ETo is highest in the month of May (292.46 mm) followed by June (244.13 mm) and lowest in December (114.47 mm) followed by January (126.14 mm). It is observed that, there is progressively decrease in the total seasonal ETo from summer season (February to May) to kharif (June to September) and rabi (October to January) seasons. The average annual ETo was 2155.85 mm.

Modeling reference evapotranspiration in island environments: Assessing the practical implications

Among the reference evapotranspiration (ETo) equations, temperature-based and radiation-based equations have been accepted as promising approaches when the available meteorological data are limited. The present paper aimed at assessing this general implication in island environments, which might be generally volatile than the interior/coastal zones. Using data from five island locations of Iran, daily ETo values were calculated by the benchmark FAO-Penman-Monteith (FAO56-PM) model, then the commonly used temperature-, radiation- and mass transfer-based ETo equations were evaluated against the benchmark values. An additional heuristic modeling of ETo was also performed through employing gene expressions programming (GEP), evaluated by k-fold testing. The obtained outcomes showed that the calibrated mass transfer-based equations and their corresponded GEP models generally surpassed the other applied models in the studied locations. This criticized the commonly accepted implication about applying temperature/radiation-based models in case of data scarcity for different locations. Nevertheless, analysis of the temporal variations of models performance among test years showed that fixing the minimum test size as 1 year for local k-fold testing (that is the case in similar studies) might be misleading as it could not show the fluctuations in modeling accuracy well. A minimum affordable size of at least one growing season was instead selected, tested and recommended in the current research.

PERFORMANCE EVALUATION OF MASS TRANSFER-BASED METHOD USING GLOBAL PERFORMANCE INDEX IN SEMIARID REGION, SAUDI ARABIA

The standard method for the estimation of reference evapotranspiration (ETo) is FAO-Penman-Monteith(FAO56-PM). However, it requires various climatic parameters which are often hard to achieve due to various reason. In order to bridge this gap an alternative equation has to be find out. The main aim of this research work was to assess the performance of the various mass transfer-based method with respect to standard FAO56-PM. Daily meteorological data from 1980 to 2018 has been used to compute reference evapotranspiration. Daily ETo values were computed. Among the computed values 70% of them were used to calibrate the mass transfer equations under study and remaining 30 % data were used to validate the calibrated equation against the standard method. The calibrated models were analysed and compared using statistical tools and ranked using Global Performance Indicator where a higher value represented a model’s better performance. The models were then arranged using GPI and it was found that Albrecht model resulted in best estimation capability. The results of this study could be used by the water management system, crop cultivators, crop advisors, researchers and students from universities and research centres. Moreover, it is beneficial for the decision maker in the vast field of agriculture, hydrology and environment.

A Simple Method for Estimating Field Crop Evapotranspiration from Pot Experiments

Pot experiments are a low-cost and easy-to-use technique for studies of soil evaporation and plant transpiration in controlled environments. However, little attention has been paid to the applicability of evapotranspiration (ET) measured in pot experiments to the field. The objective of this study was to determine whether a pot experiment can be used for measuring field ET. Evapotranspiration experiments with winter wheat and summer maize were conducted in pots and lysimeters under various water-deficit conditions. The measured ET values in the pot experiments under different water conditions were considerably different from those of the lysimeters. Causes of such differences in ET were analyzed, and a series of corrections were proposed to eliminate the effects of different crop densities, representative areas per plant, and soil moisture conditions on pot experiment results. After these corrections, the discrepancy in the total ET of wheat-maize seasons between pots and lysimeters was greatly reduced from a maximum of 117% to only approximately 10%. The relative mean square errors (RMSEs) for daily ET values also decreased from a maximum value of 4.56 mm to less than 1.5 mm for the wheat season and from a maximum value of 6.02 mm to approximately 2 mm for the maize season. Possible measures were proposed to further improve the accuracy of the corrected ET obtained from pot experiments. In sum, pot experiments can serve as a feasible tool for estimating ET in the field just with a few routine measurements at regions where large-scale weighing lysimeters, an eddy covariance device, and even meteorological data are not available. The proposed corrections can also be used for upscaling small-scale ET measurements to a large scale.

Implementation of a Two-Source Model for Estimating the Spatial Variability of Olive Evapotranspiration Using Satellite Images and Ground-Based Climate Data

A study was carried out to evaluate the potential use of the two-source Shuttleworth and Wallace (SW) model to compute the intra-orchard spatial variability of actual evapotranspiration (ET) of olive trees using satellite images and ground-based climate data. The study was conducted in a drip-irrigated olive orchard using satellite images (Landsat 7 ETM+), which were acquired on clear sky days during the main phenological stages (2009/10 growing season). The performance of the SW model was evaluated using instantaneous latent heat flux (LE) measurements that were obtained from an eddy correlation system. At the time of satellite overpass, the estimated values of net radiation ( Rn i ) and soil heat flux ( G i ) were compared with ground measurements from a four-way net radiometer and soil heat flux plates, respectively. The results indicated that the SW model subestimated instantaneous LE (W m−2) and daily ET (mm d−1), with errors of 12% and 10% of observed values, respectively. The root mean square error (RMSE) and mean absolute error (MAE) values for instantaneous LE were 26 and 20 W m−2, while those for daily values of ET were 0.31 and 0.28 mm d−1, respectively. Finally, the submodels computed Rn i and G i with errors of between 4.0% and 8.0% of measured values and with RMSE and MAE between 25 and 39 W m−2.

Modeling Evapotranspiration and Crop Growth of Irrigated and Non-Irrigated Corn in the Texas High Plains Using RZWQM

Abstract. Accurate quantification and management of crop evapotranspiration (ET) are critical to optimizing crop water productivity for both dryland and irrigated agriculture, especially in the semiarid regions of the world. In this study, four weighing lysimeters in Bushland, Texas, were planted to maize in 1994 with two fully irrigated and two non-irrigated for measuring crop ET. The Root Zone Water Quality Model (RZWQM2) was used to evaluate soil water balance and crop production with potential evapotranspiration (PET) estimated from either the Shuttleworth-Wallace method (PTSW) or the ASCE standardized alfalfa reference ET multiplied by crop coefficients (PTASCE). As a result, two water stress factors were defined from actual transpiration (AT) and were tested in the model against the lysimeter data, i.e., AT/PTSW and AT/PTASCE. For both water stress factors, the simulated daily ET values were reasonably close to the measured values, with underestimated ET during mid-growing stage in both non-irrigated lysimeters. Root mean squared deviations (RMSDs) and relative RMSDs (RMSD/observed mean) values for leaf area index, biomass, soil water content, and daily ET were within simulation errors reported earlier in the literature. For example, the RMSDs of simulated daily ET were less than 1.52 mm for all irrigated and non-irrigated lysimeters. Overall, ET was simulated within 3% of the measured data for both fully irrigated lysimeters and undersimulated by less than 11% using both stress factors for the non-irrigated lysimeters. Our results suggest that both methods are promising for simulating crop production and ET under irrigated conditions, but the methods need to be improved for dryland and non-irrigated conditions. Keywords: ET, RZWQM modeling, Stress factor, Weighing lysimeter.

Short‐ and long‐term evapotranspiration rates at ecological restoration sites along a large river receiving rare flow events

AbstractMany large rivers around the world no longer flow to their deltas, due to ever greater water withdrawals and diversions for human needs. However, the importance of riparian ecosystems is drawing increasing recognition, leading to the allocation of environmental flows to restore river processes. Accurate estimates of riparian plant evapotranspiration (ET) are needed to understand how the riverine system responds to these rare events and achieve the goals of environmental flows. In 2014, historic environmental flows were released into the Lower Colorado River at Morelos Dam (Mexico); this once perennial but now dry reach is the final stretch to the mighty Colorado River Delta. One of the primary goals was to supply native vegetation restoration sites along the reach with water to help seedlings establish and boost groundwater levels to foster the planted saplings. Patterns in ET before, during, and after the flows are useful for evaluating whether this goal was met and understanding the role that ET plays in this now ephemeral river system. Here, diurnal fluctuations in groundwater levels and Moderate Resolution Imaging Spectroradiometer (MODIS) data were used to compare estimates of ET specifically at 3 native vegetation restoration sites during 2014 planned flow events, and MODIS data were used to evaluate long‐term (2002–2016) ET responses to restoration efforts at these sites. Overall, ET was generally 0–10 mm d−1 across sites, and although daily ET values from groundwater data were highly variable, weekly averaged estimates were highly correlated with MODIS‐derived estimates at most sites. The influence of the 2014 flow events was not immediately apparent in the results, although the process of clearing vegetation and planting native vegetation at the restoration sites was clearly visible in the results.

Impact of irrigation and nitrogen fertilizer rate on soil water trends and maize evapotranspiration during the vegetative and reproductive periods

Field research was conducted in 2011 and 2012 at the University of Nebraska-Lincoln South Central Agricultural Laboratory located near Clay Center, NE to evaluate maize actual evapotranspiration (ETa) during the vegetative and reproductive growth periods for 0, 84, 140, 196, and 252kgha−1 nitrogen (N) fertilizer treatments under full irrigation (FIT), limited irrigation (75% of FIT), and rainfed settings. Daily ETa values were greatest during the early reproductive period (silking to blister growth stages) with average values of 3.62, 5.18, and 5.91mmd−1 in 2011 and 4.37, 5.92, and 6.12mmd−1 in 2012 for rainfed, 75% FIT, and FIT, respectively. Maize ETa during the vegetative period was not significantly impacted by N fertilizer rate in 2011 (P0.05=0.2357) or 2012 (P0.05=0.6341). Whereas, reproductive period ETa for FIT and 75% FIT for the pooled years significantly increased with N fertilizer rate with slopes of 0.20 and 0.17, respectively. The rainfed regression slopes were not statistically different from zero in 2012 (P0.05=0.1467) or pooled years (P0.05=0.0505). The increase in reproductive ETa with N fertilizer and irrigation resulted in a positive grain yield response with slopes of 0.021, 0.048, and 0.104 Mg ha−1mm−1 for the rainfed, 75% FIT, and FIT settings, respectively.

Pendugaan Evapotranspirasi Padi Sawah Dengan Metode Nisbah Bowen

Penelitian ini bertujuan untuk menduga nilai evapotranspirasi dengan metode Nisbah Bowen di lahan sawah. Studi kasus di Kabupaten Indramayu, dilaksanakan bulan Juni hingga September 2012. Komponen cuaca yang diukur dengan sistem Nisbah Bowen adalah radiasi neto, suhu bola basah dan bola kering, gradien suhu bola basah dan bola kering pada ketinggian antara 140 cm dan 160 cm serta pada ketinggian antara 160 cm dan 180 cm dan limpahan bahang tanah. Pengukuran setiap 30 menit mulai pukul 06.00 sampai pukul 18.00 Komponen yang diukur dengan AWS adalah radiasi, suhu, kelembaban, tekanan udara, curah hujan, arah dan kecepatan angin. Perhitungan dengan metode Nisbah Bowen kemudian dibandingkan dengan perhitungan menggunakan metode FAO Penman-Monteith. Hubungan evapotranspirasi harian hasil perhitungan dengan dua metode tersebut dianalisis dengan Korelasi (Pearson Correlation). Hasil penelitian menunjukkan evapotranspirasi harian di areal persawahan Kabupaten Indramayu pada saat periode kekeringan musim tanam II yang diduga menggunakan metode Nisbah Bowen berkisar antara antara 2,4 mm sampai 4,3 mm dengan rata-rata 3,3 mm, sedangkan evapotranspirasi harian yang diduga menggunakan metode FAO Penman-Monteith bervariasi antara 2,4 mm sampai 4,6 mm dengan rata-rata 3,5 mm. Rata-rata hasil estimasi evapotranspirasi harian dari kedua metode secara statistik tidak berbeda nyata. ©2017 dipublikasikan oleh Savana Cendana.

EQUAÇÃO DE HARGREAVES-SAMANI CALIBRADA EM DIFERENTES BASES TEMPORAIS PARA SETE LAGOAS, MG

Dados de evapotranspiração de referência (ETo) são requeridos em diversas análises relacionadas ao uso de recursos hídricos, como no manejo de irrigação, balanço hídrico de sequeiro, manejo de bacias hidrográficas, etc. O método FAO Penman-Monteith (FAO-PM) é considerado padrão para cálculo da ETo. Contudo, a aplicação deste método pode ser restringida pela falta de dados meteorológicos. Um dos métodos alternativos com menor requisição de dados é o Hargreaves-Samani (HS), o qual comumente necessita calibração local para obtenção de maior exatidão na aplicação. O objetivo deste trabalho foi avaliar o desempenho do método Hargreaves-Samani, na sua forma original e calibrado em base anual, semestral, trimestral e mensal, frente ao método padrão FAO-PM, com base em extensa série histórica de dados meteorológicos diários (86 anos), para a localidade de Sete Lagoas, MG. Calibraram-se os coeficientes e o expoente da equação de HS pela minimização do erro absoluto médio (EAM). Para avaliar a adequabilidade de aplicação de testes comparativos e para determinar o ajuste das distribuições de probabilidade de ETo, foram aplicados os testes de Kolmogorov-Smirnov e Mann-Whitney, respectivamente. A calibração do método HS anulou a tendência de superestimativa sistemática dos valores de ETo diária, comparativamente ao FAO-PM, reduzindo-se o EAM. A calibração em diferentes bases temporais acarretou a aproximação das distribuições de probabilidade de ETo calculada por meio do método HS, que não diferiram significativamente entre si, à obtida com o método FAO-PM.

Assessing reference evapotranspiration at regional scale based on remote sensing, weather forecast and GIS tools

Reference evapotranspiration (ETo) is a key component in efficient water management, especially in arid and semi-arid environments. However, accurate ETo assessment at the regional scale is complicated by the limited number of weather stations and the strict requirements in terms of their location and surrounding physical conditions for the collection of valid weather data. In an attempt to overcome this limitation, new approaches based on the use of remote sensing techniques and weather forecast tools have been proposed.Use of the Land Surface Analysis Satellite Application Facility (LSA SAF) tool and Geographic Information Systems (GIS) have allowed the design and development of innovative approaches for ETo assessment, which are especially useful for areas lacking available weather data from weather stations. Thus, by identifying the best-performing interpolation approaches (such as the Thin Plate Splines, TPS) and by developing new approaches (such as the use of data from the most similar weather station, TS, or spatially distributed correction factors, CITS), errors as low as 1.1% were achieved for ETo assessment. Spatial and temporal analyses reveal that the generated errors were smaller during spring and summer as well as in homogenous topographic areas.The proposed approaches not only enabled accurate calculations of seasonal and daily ETo values, but also contributed to the development of a useful methodology for evaluating the optimum number of weather stations to be integrated into a weather station network and the appropriateness of their locations. In addition to ETo, other variables included in weather forecast datasets (such as temperature or rainfall) could be evaluated using the same innovative methodology proposed in this study.