Pan Evaporimeter Research Articles

Estimation of reference evapotranspiration using some class-A pan evaporimeter pan coefficient estimation models in Mediterranean-Southeastern Anatolian transitional zone conditions of Turkey.

Reference evapotranspiration (ETo), which is used as the basic data in many studies within the scope of hydrology, meteorology, irrigation and soil sciences, can be estimated by using the evaporation (Epan) measured from the class-A pan evaporimeter. However, this method requires reliable pan coefficients (Kp). Many empirical models are used to estimate Kp coefficients. The reliability of these models varies depending on climatic and environmental conditions. Therefore, they need to be tested in the local conditions where they will be used. In this study, conducted in Kahramanmaraş, which has a semi-arid Mediterranean climate in Turkey during the July-October periods of 2020 and 2021, aimed to determine the usability levels of six Kp models in estimating daily and monthly average ETo. The Kp coefficients estimated by the models were multiplied with the daily Epan values, and the daily average ETo values were estimated on the basis of the model. The daily Epan values were measured using an ultrasonic sensor sensitive to the water surface placed on the class-A pan evaporimeter. The ultrasonic sensor was managed by a programmable logic controller (PLC). To enable the sensor to be managed by PLC, a software was prepared using the CODESYS programming language and uploaded to the PLC. The daily average ETo values determined by the FAO-56 Penman-Monteith equation were accepted as actual values. The ETo values estimated by the Kp models were compared with the actual ETo values using the mean absolute error (MAE), mean absolute percentage error (MAPE), root mean square error (RMSE) and determination coefficient (R2) statistical approaches. The Wahed & Snyder outperformed the other models in estimating daily (MAE = 0.78 mm day-1, MAPE = 14.40%, RMSE = 0.97 mm day-1, R2 = 0.82) and monthly (MAE = 0.32 mm day-1, MAPE = 5.88%, RMSE = 0.32 mm day-1, R2 = 0.99) average ETo. FAO-56 showed the nearest performance to Wahed & Snyder. The Snyder model presented the worst performance in estimating daily (MAE = 2.09 mm day-1, MAPE = 37.53%, RMSE = 2.36 mm day-1, R2 = 0.82) and monthly (MAE = 1.83 mm day-1, MAPE = 31.82%, RMSE = 1.87 mm day-1, R2 = 0.99) average ETo. It has been concluded that none of the six Kp models can be used to estimate the daily ETo in Kahramanmaraş located in the Mediterranean-Southeastern Anatolian transitional zone, and only Wahed & Snyder and FAO-56 can be used to estimate the monthly ETo without calibration.

Effect of Different Irrigation Levels and Potato Hybrids on Yield and Nutrient Uptake of the Crop under Water Stress Conditions

As the scarcity of water increases, India will face the problem of decreasing annual freshwater use per capita. Healthy and sufficient crop and food production is essential for everyone due to the population increasing globally. Drought can result in severe productivity losses, especially for crops like the potato (Solanum tuberosum) that have shallow roots. In agriculture, it's critical to keep an eye on the soil, the climate, and the water supply for a crop. The study was carried out at the research farm of Vegetable Science, Chaudhary Charan Singh Haryana Agricultural University- Hisar, India during the rabi season of the year 2018-19. The field experiment was conducted in split plot design with four irrigation levels I1 (irrigation at 20mm CPE (Cumulative Pan Evaporimeter)), I2 (irrigation at 25mm CPE), I3 (irrigation at 30mm CPE) and I4 (irrigation at 30mm CPE + 5 t/ha grass mulch) and five potato hybrids V1 (P-21), V2 (P-32), V3 (P-37), V4 (P-38), V5 (Kufri Bahar) under two different crops at 60 and 75 days. The results revealed that parameters i.e., number of leaves, total tuber yield, and nitrogen uptake by crop were higher in both 60 and 75 days of crops under irrigation level 20 mm CPE (I1) and hybrid P-38 but in water stress condition I3 gives a better yield than other irrigation levels with hybrid -38. The present study opens up new doors to the farmers and researchers for sustainable production of potatoes.

Productive and Economic Evaluation of Potato Hybrids under Different Water Stress Conditions

As the scarcity of water increases, India will face the problem of decreasing annual freshwater use per capita. Drought can cause significant output losses, particularly for crops with shallow root system like potato (Solanum tuberosum). An experiment was carried out to measure the effects of different levels of irrigation on yield parameters of different potato hybrids under water stress conditions during the winter season 2018-19 in open field conditions at the field of department of vegetable science in CCS Haryana Agricultural University, Hisar. The experiment included four irrigation levels I1 (irrigation at 20mm Cummulative Pan Evaporimeter (CPE)), I2 (irigation at 25mm CPE), I3 (irrigation at 30mm CPE) and I4 (irrigation at 30mm CPE + 5 t/ha grass mulch) and five potato hybrids under two different crops at 60 and 75 days. The results revealed that yield parameters i.e., total tuber yield, number of tubers in each grade, yield of tubers in each grade, harvest index, and biological yield were higher in both 60 and 75 days of crops under irrigation level 20 mm CPE (I1) and hybrid P-38. But, under water-stressed conditions, hybrid P-38 with an I4 schedule saves one irrigation and yields more than I3. The maximum water use efficiency (19.27 and 20.56 q/ha/mm) was attained with irrigation level I4 in 60 and 75 days of crop. In water stress conditions (I4) potato hybrid P-38 produced the highest net returns and benefit cost ratio (1.49 and 2.29). It was found that the potato hybrid P-38 with I4 was more cost-effective and produced more tubers in areas with lower water tables and less water.

Estimation of evapotranspiration from measured meteorological parameters

Five empirical equations, namely, FAO-56 Penman–Monteith, Hargreaves–Samani, Makkink, Turc, and Priestley–Taylor are utilized in the estimation of evapotranspiration for the month of May in 2018 for Trombay site in Maharashtra. Evapotranspiration from a given surface is a function of incoming solar radiation, net radiation, ground heat flux, air temperature, relative humidity, and wind speed. Daily average measurements of these parameters are utilized in the empirical equations for the estimation of evapotranspiration. These estimated values are compared with the measured data from pan evaporimeter installed at Trombay. The measured data from the pan evaporimeter are corrected using the pan coefficient Kp which in turn is also estimated using empirical equations. The average value of the pan coefficient Kp is 0.8 for the site. The average measured value of evapotranspiration is 4.7 mm/d for May 2018, whereas the values estimated using the five empirical equations range from 3.3 mm/d to 12.7 mm/d. Among the five equations, the Turc equation was found to be in the best agreement with the measured values of evapotranspiration. Such studies are useful in the estimation of groundwater recharge, latent heat flux, and agriculture meteorology.

Crop water requirement estimation using pan evaporimeter for high density apple plantation system in Kashmir region of India

Crop water requirement estimation using pan evaporimeter for high density apple plantation system in Kashmir region of India

Dry Matter Production and Nutrient Uptake of Coloured Capsicum Hybrids (Capsicum annuum var. grossum L.) as Influenced by Different Irrigation Levels under Shade Net

Aim: The experiment was aimed at evaluating the influence of different irrigation levels on dry matter production and nutrient uptake of coloured capsicum hybrids.
 Study Design: Split plot design with three replications
 Place and Duration of Study: Horticultural farm, College of Agriculture, Rajendranagar, Hyderabad during rabi 2018-19.
 Methodology: The experiment was laid out in split plot design and the treatments comprises of four irrigation levels viz., drip irrigation at 0.4, 0.6, 0.8 and 1.0 Epan as main treatments and three hybrids viz., Indra (green), Orobelle (yellow), Bomby (red) as sub treatments and replicated thrice. The recommended dose of nutrients were 100:80:60 N, P2O5 and K2O kg ha-1 and entire dose of P2O5 was applied as basal, N and K2O was applied through venturi meter as fertigation on three days interval from 9 to 153 DAT. The crop was transplanted at 45 cm × 40 cm spacing in September under a green shade net. Irrigation scheduling was done based on daily evaporation data recorded from USWB class ‘A’ pan evaporimeter. The cumulative daily evaporation during crop growth period was 737.5 mm. Quantity of water applied including special operations of 26 mm and effective rainfall during crop growth period were 245.3, 392.0, 546.5 and 698.5 mm and 58.6, 64.2, 74.6, 82.6 mm out of 127.4 mm of rainfall for 100, 80, 60 and 40 per cent irrigation treatments, respectively as per water balance method. Bed size was 7.6 m × 0.9 m.
 Results: Significantly higher yield (47.50 t ha-1) was recorded with drip irrigation at 1.0 Epan than rest of the treatments. Indra recorded significantly higher yield (40.27 t ha-1) than other two hybrids. The interaction effect between drip irrigation levels and hybrids was not significant on Dry Matter Production and N, P & K uptakes and economics of capsicum. DMP and nutrient uptake were significantly higher with drip irrigation at 1.0 Epan than 0.8, 0.6 and 0.4 Epan throughout the crop growth over other drip irrigation levels. Among hybrids, Indra recorded significantly higher DMP and nutrient uptake than other two hybrids.

Performance of a double-slope solar still for the concentration of lithium rich brines with concomitant fresh water recovery

Lithium recovery from brines has become a hot topic. The current evaporitic technology is slow, and serious environmental concern has been raised regarding the large volumes of water used, relating both to brine concentration through evaporation, and intensive pumping of fresh water needed in the fine chemical processing to produce high purity lithium carbonate.In this work, an experimental and theoretical analysis of brine desalination using a double-slope Solar Still was carried out. The Solar Still was installed right next to an existing lithium mining facility in northwest Argentina, and was tested with native high salinity lithium rich brine for a continuous year under the typical weather conditions of lithium deposits: high altitude, large thermal amplitude between day and night, strong winds, and high solar radiation. The performance of the solar still as an evaporator was compared with that of a PAN evaporimeter class A, and correlated to experimentally determined weather parameters. While the performance of the Solar Still for brine concentration was below that of open air evaporation, the Solar Still allowed for the production of an average of 2 L day−1 m−2 of distilled water, in marked contrast with current practice. Numerical simulations allowed us to quantify heat exchanges in both the Solar Still and the open air system.

Efficiency of small pan evaporimeter in monitoring evapotranspiration under poly-covered house and open-field conditions in a hot, tropical region of Nigeria

Study RegionThis study was carried out in a hot, tropical region of southwest Nigeria. Study FocusThe study aimed to evaluate the efficiency of small pan evaporimeter in estimating evapotranspiration (ET) and compare with five reference evapotranspiration (ETo) estimation models of FAO56 Penman Monteith; Modified Penman; Thornthwaite; Blaney-Criddle, and Hargreaves under poly-covered house and open-field conditions grown to maize and tomato in two contrasting seasons. Small pan evaporimeters with diameter 24.5 cm and 11 cm high were constructed and installed to measure evaporation. The ETo from the empirical models was estimated using weather data downloaded from NASA website and a mini-weather station installed in the poly-covered house. A rain gauge was also installed to measure rainfall during the growing period. New hydrological insights for the regionThe small pan evaporation significantly (p < 0.05) correlated with the reference evapotranspiration obtained from the empirical ET models. Canopy cover was the driving force responsible for the reduced pan evaporation within the crop canopy. Temperature and relative humidity are the driving forces controlling evapotranspiration in the poly-house. The inexpensive small pan could complement conventional pans, empirical ETo models, remote sensing and others for quantifying evapotranspiration, which is essential not only for irrigation but also hydrologic studies and modelling of watersheds, catchments areas, agricultural fields and landscapes in this region and similar tropical and sub-tropical environments.

Assessing the Robustness of Pan Evaporation Models for Estimating Reference Crop Evapotranspiration during Recalibration at Local Conditions

A classic method for assessing the reference crop evapotranspiration (ETo) is the pan evaporation (Epan) method that uses Epan measurements and pan coefficient (kp) models, which can be functions of relative humidity (RH), wind speed (u2), and temperature (T). The aim of this study is to present a methodology for evaluating the robustness of regression coefficients associated to climate parameters (RH, u2, and T) in pan method models during recalibration at local conditions. Two years of daily data from April to October (warm season) of meteorological parameters, Epan measurements from class A pan evaporimeter and ETo estimated by ASCE-standardized method for the climatic conditions of Thessaloniki (Greece, semi-arid environment), were used. The regression coefficients of six general nonlinear (NLR) regression Epan models were analyzed through recalibration using a technique called “random cross-validation nonlinear regression RCV-NLR” that produced 1000 random splits of the initial dataset into calibration and validation sets using a constant proportion (70% and 30%, respectively). The variance of the regression coefficients was analyzed based on the 95% interval of the highest posterior density distribution. NLR models that included coefficients with a 95% HPD interval that fluctuates in both positive and negative values were considered nonrobust. The machine-learning technique of random forests (RF) was also used to build a RF model that includes Epan, u2, RH, and T parameters. This model was used as a benchmark for evaluating the predictive accuracy of NLR models but, also, for assessing the relative importance of the predictor climate variables if they were all included in one NLR model. The findings of this study indicated that locally calibrated NLR functions that use only the Epan parameter presented better results, while the inclusion of additional climate parameters was redundant and led to underfitting.

Effect of Lockdown amid COVID-19 Pandemic on Weather Parameters of Mid Hill Region of Jammu District of J&amp;K, UT

Aim: A study was conducted in mid hill region of Jammu district, J&amp;K to analyze the impact lockdown amid covid-19 pandemic on weather parameters so as to define it as a tool to mitigate the pace of climate change.&#x0D; Methodology: Day and night temperature readings were recorded fortnightly during 22nd March to 10th June 2020 from maximum and minimum thermometer, relative humidity from dry and wet bulb thermometers in stevenson screen, rainfall values from ordinary rain gauge, evaporation readings from pan evaporimeter and soil temperature at different depth from soil thermometers.&#x0D; Results: After analyzing the data statistically using “Descriptive statistics” in MS-Excel 2010, it was observed that after the implementation of lockdown and with the beginning of unlock down the change in day temperature was -8.07% from normal mean value, night temperature was -4.44% from normal mean value, rainfall pattern was 30.00% more from normal mean value, Relative Humidity (morning) pattern was 6.94% more from normal mean value, relative humidity (evening) pattern was 20.94% more from normal mean value, evaporation pattern was 7.66% more from normal mean value. The average change in soil temperature in morning at 5 cm, 10 cm and 20 cm depth was -3.46%, -3.84% and -7.23% as compared to year 2019 (22nd March to 10th June 2019) mean value and the change in soil temperature in evening at same depths was -7.69%, -6.31% and -4.14% from year 2019 (22nd March to 10th June 2019).&#x0D; Conclusion: With the variable significant pattern observed in almost all parameters, it can be concluded that lockdown might be an effective tool in mitigating pace of climate change in future.

The Bases of Peach Tree Irrigation in the Fruit-Growing Basin from Oradea, Romania, and the Use of the Microsprinkler System

The paper presents the results obtained on preluvo-soil in Sâniob, Oradea, during 2007-2015. In order to maintain the soil water content between easily available water content and field capacity, the irrigation rate used was between 60 mm/ha and 470 mm/ha. Irrigation determined an increase of the total water consumption by 53% (712 mm/ha vs. 466 mm/ha). For the non-irrigated variant (71%) and for the irrigated one (46%), the rainfalls registered between 15 March-1 October yearly represented the main source of supplying the total water consumption, while irrigation supplied 40% of the total water consumption (with a variation range 11%-61%). The microsprinkler irrigation system led to a 30.6% yield gain, with a variation range of 15.8%-58.7%. It also determined a higher size index in comparison with the non-irrigated variant and a smaller percentage of kernels. All differences were statistically very significant. Several correlations were quantified in the soil-water-plant-atmosphere system. The parameters of the system were: pedological drought, strong pedological drought and water consumption. All correlations were statistically very significant; the best mathematical expression was the polynomial function. Four methods (Penman Monteith, Pan, Piche and Thornthwaite evaporimeter methods) were studied to determine the reference evapotranspiration (ETo) in comparison with the optimal water consumption of the peach tree. As it was cheaper and easier to use, the Pan evaporation method was recommended in the irrigation scheduling, although the Penman Monteith method could have given more accurate results in assessing the optimal water consumption.

Effect of Low Cost Drip Tape Irrigation System on Yield and Economics of Sweet Corn

A study was conducted to determine the effect of low cost drip tape irrigation system on yield and economics of sweet corn in comparison to conventional inline drip irrigation and surface irrigation systems during 2013-14 at Coimbatore, India. The treatment comprises of two drip irrigation systems with three irrigation levels viz., 75, 100 and 125% of pan evaporation (PE) from Class A Pan evaporimeter. Plant height, fresh cob length, girth, number of kernels per cob and single fresh cob weight and yield were higher at 125% PE in conventional in line drip irrigation system and it was statistically at par with drip irrigation at 125% PE in low cost drip tape irrigation system. Water saving was 36, 49 and 62% at 125, 100 and 75% PE, respectively under conventional in line drip irrigation system and drip tape irrigation system as against the surface irrigation. The cost of low cost drip tape system was 68% lower than the conventional inline drip system. The results of the research indicated that based on net income, B:C ratio and GM/TMV ratio, adoption of low cost drip tape irrigation system at 125% PE was found to be best for small and marginal farmers with substantial yield and income compared to conventional inline drip system.Bangladesh Agron. J. 2016 19(2): 71-77

MORTALITY OF TROPICAL FOREST TREE SEEDLINGS UNDER WATER AND SALT STRESS CONDITIONS

&lt;p&gt;Mortality of selected tropical forest tree species seedlings viz. &lt;em&gt;Tectona grandis, Pongamia pinnata&lt;/em&gt;, &lt;em&gt;Dalbergia latifolia&lt;/em&gt; and &lt;em&gt;Gmelina arborea&lt;/em&gt; were tested under water and salt stress conditions for 4 months under nursery stage. Water stress included moderate and severe waterlogging &amp;amp; moderate and severe drought conditions. The salt stress in the soil was maintained to 4, 8 and 12 ds/m. Pot culture experiments with twenty treatment combinations following RBD factorial design were conducted in TFRI Jabalpur nursery. The water equivalent to the field capacity of the soil was provided to the seedlings to maintain waterlogging. The drought condition in polybags was maintained according to Permanent Wilting point (PWP), which was calculated on the basis of Cumulative Pan Evaporation (CPE) values measured through Open Pan Evaporimeter. Mortality of seedlings of the species under study increased with the increase in salt concentration from 4 to 12 ds/m.&lt;em&gt; Gmelina arborea&lt;/em&gt; shown 100% mortality in 4ds/m, 8ds/m and 12ds/m concentration of salt. Cumulative effect of salt and waterlogging &amp;amp; salt and drought was found to be more prominent in &lt;em&gt;Gmelina arborea&lt;/em&gt; as compare to other three species. &lt;em&gt;Tectona grandis &lt;/em&gt;was found to be more tolerable to waterlogged followed by drought conditions&lt;em&gt;. &lt;/em&gt; Waterlogging conditions observed to be excellent for &lt;em&gt;Pongamia pinnata&lt;/em&gt; seedlings plantation shown 0% mortality. As a whole, the mortality of seedlings due to water and salt stress was found in the order &lt;em&gt;Dalbergia latifolia&lt;/em&gt; (90.95%) &amp;gt; &lt;em&gt;Gmelina arborea&lt;/em&gt; (82.50%) &amp;gt; &lt;em&gt;Tectona grandis&lt;/em&gt; (74%) &amp;gt; &lt;em&gt;Pongamia pinnata&lt;/em&gt; (35.56%). &lt;/p&gt;

Spatial Patterns and Influence Factors of Conversion Coefficients between Two Typical Pan Evaporimeters in China

Pan measurement is a reliable and efficient method for indicating the evaporative demand of the atmosphere. There are several types of pan evaporimeters worldwide, and the estimation of the conversion coefficients (Kp) between them is necessary in hydrologic research. In China, E601B pans were installed at all meteorological stations beginning in 1998. They replaced the 20 cm pans (φ20). To fully use the records from the two pans and obtain long-term pan evaporation, the spatial patterns of Kp between φ20 and E601B and the factors that influence Kp are investigated based on records from 573 national meteorological stations from 1998 to 2001. In this study, The results show that higher Kp values are found in southwestern regions and lower values are found in northeastern regions during the warm seasons (from May to September), while Kp values are lower during warm seasons than during cold seasons (from October to April the following year). In addition, net radiation was found to be the dominant climate factor that affects variations in Kp, followed by relative humidity and the vapor pressure deficit. This study can improve the benefit of not only the selection of appropriate evaporimeters by meteorological departments, but also of the study of temporal variability and trends in the evaporative demand.

Estimating the evaporation from irrigation reservoirs of greenhouses using satellite imagery

The agricultural system in south‐eastern Spain is based on intensive horticulture in greenhouses. Public and private organizations have spent substantial resources on optimizing irrigation, due to the scant annual precipitation (close to 250 mm). In order to preserve natural water resources, avoiding overexploitation and salinization aquifers, the water loss has to be minimized. Farmers save water in irrigation reservoirs, which are open to the atmosphere most of the time. In this work, the loss to evaporation from open water reservoirs was estimated in a typical agricultural greenhouse area in Almeria province, south‐eastern Spain. The data source was both a high‐resolution satellite image, and a set of climatic data from the Agro‐climatic Information Network of Andalusia (AINA) and from a Class‐A pan evaporimeter. The image was used for detecting and delineating open water bodies applying a supervised classification algorithm based on an artificial neural network. The climatic data were used to estimate the distribution of monthly evaporation. It was concluded that irrigation water reservoirs can evaporate 3.76% of the input water used for crops. If all of the water bodies were covered with shade materials and if the precipitation intercepted by the roofs of greenhouses were saved in the irrigation water reservoirs, 49.87% of water annually consumed by greenhouse crops could be saved. © 2016 American Institute of Chemical Engineers Environ Prog, 35: 1750–1757, 2016

Performance of Pongamia pinnata (L.) Pierre Seedlings in Nursery Under Salt and Water Stress Conditions

Pot culture experiments were conducted with twenty treatment combinations of salt and water stress following Randomized Complete Block Design in the nursery of Tropical Forest Research Institute, Jabalpur for one year. 4, 8 and 12 ds/m concentrations of salt in combination with moderate and severe drought &amp; moderate and severe waterlogged treatments in the soil were applied. The amount of water equal to the field capacity of the soil was given to each treatment (24.86%). The drought conditions were maintained according to Permanent Wilting point (PWP), which was calculated on the basis of Cumulative Pan Evaporation (CPE) values measured through Open Pan Evaporimeter. It was observed that height and collar diameter of P. pinnata seedlings decreased with increase in drought conditions but increased with increase in severity of waterlogging. Growth characteristics significantly decreased with increase in concentration of salts in the soil. Cumulative effect of water and salt stress was found to be more pronounced than individual stress.

Comparison of Different Methods to Estimate Mean Daily Evapotranspiration from Weekly Data at Patna, India

Estimation of evapotranspiration is necessary for efficient water management and crop planning. Fifteen different methods of ET0 estimation were employed to compute daily reference evapotranspiration for the period 2010 to 2014. In the absence of reliable open pan evaporimeter data, FAO-56 Penman Monteith method was considered as one of the reliable method of ET0 estimation. The results showed that mean weekly evapotranspiration values obtained from Penman-Monteith method were very closer to FAO-56 Penman-Monteith method and values from all the other methods except FAO- 24 Pan, Christiansen Pan and Hargreaves methods generally predicted higher values of mean weekly daily ET0 in comparison to FAO-56 Penman-Monteith method. The analysis shows that mean weekly daily ET0 estimates of combination methods resulted better ET0 estimates than radiation, and temperature and evaporation methods. Weekly ET0 values estimated by FAO-56 Penman-Monteith method were found to vary in the range of 1.3 mm/day to 6.7 mm/day. Average annual reference evapotranspiration was found as 1517.1 mm.

Dew condensation on different natural and artificial passive surfaces in a semiarid climate

In this study, five passive radiative surfaces were analyzed for dew formation in south-eastern Spain; a dew condenser (RDC), a modified Class-A pan evaporimeter, the water stored in an open pond, the water stored in a covered pond, and the suspended shade cloth cover which covered the pond. In the case of the RDC and the pan, two different modeling approaches were used to estimate dew: (i) dew was correlated with meteorological variables and (ii) dew was derived from the mass transfer equation. In the other three cases, dew formation was assessed by analyzing the difference between the dew point and the water surface temperature.The RDC was more productive than the pan as the latter cooled less overnight and also underwent interspersed processes of evaporation and condensation. In the case of the RDC, both modeling approaches gave satisfactorily estimates whilst they were less accurate for the pan. On the water bodies, the water thermal inertia usually maintained the night water surface temperature above the dew point and strongly limited the dew formation. On the contrary, dew has been proven to exist on the cover, although the low amounts of dew deposited hinder its drainage to the water.

Atmospheric evaporative demand observations, estimates and driving factors in Spain (1961–2011)

Summary We analyzed the spatio-temporal evolution of evaporation observations from Piche atmometers (1961–2011; 56 stations) and Pan evaporimeters (1984–2011; 21 stations) across Spain, and compared both measurements with evaporation estimates obtained by four physical models: i.e., Food and Agricultural Organization-56 Penman–Monteith, Food and Agricultural Organization-Pan, PenPan and Penman, based on climate data. In this study we observed a positive and statistically significant correlation between Piche and Pan evaporation measurements during the common period (1984–2011; 19 stations), mainly in summer. When evaporation observations and estimates were compared, we detected positive and statistically significant correlations with the four methods, except for winter. Among the four physical models, the FAO-Pan showed the best fitting to both Piche and Pan evaporation measurements; the PenPan model overestimated evaporation rates; and the FAO-Penman–Monteith and Penman methods underestimated evaporation observations. We also observed a better spatial agreement between Pan evaporation and estimates than that obtained by Piche measurements. Annual and seasonal trends of evaporation estimates show a statistically significant increase for 1961–2011, which do not agree with long-term Piche evaporation trends; e.g. a discontinuity was found around the 1980s. Radiative and aerodynamic driving factors suggest that this discontinuity, and the observed evaporation trends across Spain could be associated with the abrupt increase in air temperature observed during last few decades (i.e., global warming). Further investigations using available Piche evaporation observations for other regions are needed to better understand physical components influencing long-term trends of evaporation.

Evapotranspiration and water productivity of wheat under different hydrothermal regimes

A field experiment was conducted during rabi 2013–14 with three dates of sowing, D1(29th October), D2 (12th November) and D3 (28th November) and four irrigation levels, I1 (Irrigation at CRI stage), I2 (irrigation at CRI and Flag leaf emergence stage), I3 (irrigation at crown root initiation, flag leaf emergence and soft dough stage) and I4 (recommended 4 post sowing irrigations) in randomized block design. Evapotranspiration computed with soil moisture depletion method and Papadakis method was higher under D1 (374.9 mm and 492.7 mm) as compared to D2 (352.7mm and 480.2mm) and D3 (346.5 mm and 443.0 mm) whereas with USDA open pan evaporimeter and modified Jenson and Haise method, it was higher in D2 (340.2 mm and 423.5 mm) as compared to D1 (326.6 mm and 409.8 mm) and D3 (334.2 mm and 409.4 mm). Water productivity was higher under D1 followed by D2 and D3. The crop coefficient was also higher under D1 (1.16) as compared to D2 (1.04) and D3 (1.03). Higher water productivity with regard to grain and straw yield was observed in D2I3 (14.02 kg/ha/mm) followed by D2I2 (13.85 kg/ha/mm) and lowest in D3I4 (9.77 kg/ha/mm).