Reservoir evaporation in a Mediterranean climate: comparing direct methods in Alqueva Reservoir, Portugal

Alqueva Reservoir is one of the largest artificial lakes in Europe and is a strategic water storage for public supply, irrigation, and energy generation. The reservoir is integrated within the Multipurpose Alqueva Project (MAP), which includes almost 70 reservoirs in a water-scarce region of Portugal. The MAP contributes to sustainability in southern Portugal and has an important impact on the entire country. Evaporation is the key component of water loss from the reservoirs included in the MAP. Evaporation from Alqueva Reservoir has been estimated by indirect methods or pan evaporation measurements; however, specific experimental parameters such as the pan coefficient were never evaluated. Eddy covariance measurements were performed at Alqueva Reservoir from June to September in 2014 as this time of the year provides the most representative evaporation volume losses in a Mediterranean climate. This period is also the most important period for irrigated agriculture and is, therefore, the most problematic period of the year in terms of managing the reservoir. The direct pan evaporation approach was first tested, and the results were compared to the eddy covariance evaporation measurements. The total eddy covariance (EC) evaporation measured from June to September 2014 was 450.1 mm. The mean daily EC evaporation in June, July, August, and September was 3.7, 4.0, 4.5, and 2.5 mm d−1, respectively. A pan coefficient, Kpan, multivariable function was established on a daily scale using the identified governing factors: air temperature, relative humidity, wind speed, and incoming solar radiation. The correlation between the modelled evaporation and the measured EC evaporation had an R2 value of 0.7. The estimated Kpan values were 0.59, 0.57, 0.57, and 0.64 in June, July, August, and September, respectively. Consequently, the daily mean reservoir evaporation (ERes) was 3.9, 4.2, 4.5, and 2.7 mm d−1 for this 4-month period and the total modelled ERes was 455.8 mm. The developed Kpan function was validated for the same period in 2017 and yielded an R2 value of 0.68. This study proposes an applicable method for calculating evaporation based on pan measurements in Alqueva Reservoir, and it can be used to support regional water management. Moreover, the methodology presented here could be applied to other reservoirs, and the developed equation could act as a first evaluation for the management of other Mediterranean reservoirs.

Estimation of crop coefficient for Marigold (Tagetes erecta (L.)) under drip irrigated greenhouse

Crop water consumption (ETc) varies from region to region depending on crop type, growth stages, soil, and climate conditions. In order to obtain full yield and avoid unnecessary water usage, the water demand of the cultivated plants should be accurately calculated, and irrigation water should be applied in accordance with plant needs. In this, the study was carried out in field No.C3 of Central farm at Agricultural Engineering College and Research Institute, Kumulur, Trichy district to determine the growth stage-specific crop coefficient (Kc) and pan coefficient (Kp) for the greenhouse grown marigold (Tagetes erecta (L.). Since, a large area was occupied by a ClassA pan, the reduced-size evaporative pans (20 and 60 cm compared with Class A pan) was used and pan coefficient was determined as 0.93 and 0.96 respectively. A pan coefficient (Kp) was used to convert pan evaporation (Epan) to grass reference evapotranspiration (ETo). Based on the tensiometer readings, the depleted moisture content was taken to reckon the crop coefficient for different growth stage. The results revealed that crop coefficient (Kc) for marigold was observed as 0.37 during the initial stage (Kcin), 0.8 during mid-stage (Kcmid) and 0.47 (Kcfin) during the final stage. These results would be helpful for crop water requirement and irrigation scheduling for similar condition.

DESEMPENHO DE MÉTODOS DE CÁLCULO DO COEFICIENTE DE TANQUE PARA ESTIMATIVA DA EVAPOTRANSPIRAÇÃO DE REFERÊNCIA

DESEMPENHO DE MÉTODOS DE CÁLCULO DO COEFICIENTE DE TANQUE PARA ESTIMATIVA DA EVAPOTRANSPIRAÇÃO DE REFERÊNCIA ALAN DELON ANDRADE1, WEZER LISMAR MIRANDA2, LUIZ GONSAGA DE CARVALHO3, PAULO HENRIQUE FERNANDES FIGUEIREDO1, THALINE BIGHI SILVEIRA DA SILVA4 1Graduando em Engenharia Agrícola, Departamento de Engenharia, Universidade Federal de Lavras – Lavras, MG. Fone: (35)8834-3582. E-mail: [email protected]; [email protected] Agrícola, Doutorando em Recursos Hídricos em Sistemas Agrícolas, Departamento de Engenharia, Universidade Federal de Lavras – Lavras, MG. E-mail: [email protected] Agrícola, Prof. Doutor, Departamento de Engenharia, Universidade Federal de Lavras – Lavras, MG. E-mail: [email protected] em Engenharia Florestal, Departamento de Ciências Florestais, Universidade Federal de Lavras – Lavras, MG. E-mail: [email protected] 1 RESUMO Há diferentes processos aplicáveis ao adequado manejo da irrigação e dentre esses os que utilizam a estimativa da evapotranspiração de referência (ETo) como parâmetro. Assim, com este trabalho objetivou-se avaliar diferentes métodos de determinação do coeficiente de tanque (Kp) utilizado na estimativa da ETo com base em dados de evaporação do Tanque Classe “A” (TCA). Os dados meteorológicos foram coletados diariamente entre 1/1/2004 e 31/12/2013. A estimativa de ETo padrão foi realizada pelo método de Penman-Monteith-FAO (PM-FAO). Os métodos utilizados para a obtenção do Kp foram: Allen et al. (1998), Cuenca (1989), Snyder (1992), Pereira et al. (1995) e Doorenbos e Pruitt (1977). O desempenho dessas metodologias foi avaliado pela comparação entre a estimativa de ETo obtida pelo método do TCA com os diferentes valores de Kp em relação à ETo estimada pelo método de PM-FAO. Na escala mensal todas as metodologias avaliadas apresentaram um desempenho satisfatório. Para a avaliação em escala diária o melhor desempenho foi da metodologia proposta por Pereira et al. (1995).Palavras-chave: coeficiente de tanque, manejo de irrigação, agrometeorologia, Penman-Monteith-FAO ANDRADE, A. D.; MIRANDA, W. L.; CARVALHO, L. G. DE; FIGUEIREDO, P. H. F.; SILVA, T. B. S. DAPERFORMANCE OF METHODS FOR CALCULATING THE PAN COEFFICIENT FOR ESTIMATING REFERENCE EVAPOTRANSPIRATION 2 ABSTRACT There are different processes applicable to the suitable irrigation management, and among them there are those which use the reference evapotranspiration (ETo) estimation as a parameter. This research aimed to evaluate different methods for determining pan coefficient (Kp), used to estimate ETo, based on evaporation data of Class "A" pan (TCA). Daily meteorological data were collected at Principal Climatological Station, which is located at the Federal University of Lavras. The period of time analyzed was from 01/01/2004 to 12/31/2013. The standard ETo estimation was performed using Penman-Monteith-FAO (FAO-PM) method. The methods utilized to obtain Kp were: Allen et al. (1998), Cuenca (1989), Snyder (1992), Pereira et al. (1995), and Doorenbos & Pruitt (1977). The performance of these methods was evaluated by comparing the estimated ETo obtained by the PM-FAO method with ETo estimated by the TCA method with different Kp values. In the monthly scale all tested methodologies showed satisfactory performance. For the evaluation in daily scale, the best performance was the methodology proposed by Pereira et al. (1995).Keywords: pan coefficient, irrigation management, agrometeorology, Penman-Monteith-FAO