Evaluation of Potential Evapotranspiration Based on CMADS Reanalysis Dataset over China

Potential evapotranspiration (PET) is used in many hydrological models to estimate actual evapotranspiration. The calculation of PET by the Food and Agriculture Organization of the United Nations (FAO) Penman–Monteith method requires data for several meteorological variables that are often unavailable in remote areas. The China Meteorological Assimilation Driving Datasets for the SWAT model (CMADS) reanalysis datasets provide an alternative to the use of observed data. This study evaluates the use of CMADS reanalysis datasets in estimating PET across China by the Penman–Monteith equation. PET estimates from CMADS data (PET_cma) during the period 2008–2016 were compared with those from observed data (PET_obs) from 836 weather stations in China. Results show that despite PET_cma overestimating average annual PET and average seasonal in some areas (in comparison to PET_obs), PET_cma well matches PET_obs overall. Overestimation of average annual PET occurs mainly for western inland China. There are more meteorological stations in southeastern China for which PET_cma is a large overestimate, with percentage bias ranging from 15% to 25% for spring but a larger overestimate in the south and underestimate in the north for the winter. Wind speed and solar radiation are the climate variables that contribute most to the error in PET_cma. Wind speed causes PET to be underestimated with percentage bias in the range −15% to −5% for central and western China whereas solar radiation causes PET to be overestimated with percentage bias in the range 15% to 30%. The underestimation of PET due to wind speed is offset by the overestimation due to solar radiation, resulting in a lower overestimation overall.

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Potential Evapotranspiration Reduction and Its Influence on Crop Yield in the North China Plain in 1961–2014

Advances in Meteorology ◽

10.1155/2020/3691421 ◽

2020 ◽

Vol 2020 ◽

pp. 1-10 ◽

Cited By ~ 1

Author(s):

Wanlin Dong ◽

Chao Li ◽

Qi Hu ◽

Feifei Pan ◽

Jyoti Bhandari ◽

...

Keyword(s):

Wind Speed ◽

Relative Humidity ◽

Crop Yield ◽

North China Plain ◽

North China ◽

Potential Evapotranspiration ◽

The North ◽

The North China Plain ◽

Sunshine Hours ◽

Humidity Index

Climate change has caused uneven changes in hydrological processes (precipitation and evapotranspiration) on a space-temporal scale, which would influence climate types, eventually impact agricultural production. Based on data from 61 meteorological stations from 1961 to 2014 in the North China Plain (NCP), the spatiotemporal characteristics of climate variables, such as humidity index, precipitation, and potential evapotranspiration (ET0), were analyzed. The sensitivity coefficients and contribution rates were applied to ET0. The NCP has experienced a semiarid to humid climate from north to south due to the significant decline of ET0 (−13.8 mm decade−1). In the study region, 71.0% of the sites showed a “pan evaporation paradox” phenomenon. Relative humidity had the most negative influence on ET0, while wind speed, sunshine hours, and air temperature had a positive effect on ET0. Wind speed and sunshine hours contributed the most to the spatiotemporal variation of ET0, followed by relative humidity and air temperature. Overall, the key climate factor impacting ET0 was wind speed decline in the NCP, particularly in Beijing and Tianjin. The crop yield in Shandong and Henan provinces was higher than that in the other regions with a higher humidity index. The lower the humidity index in Hebei province, the lower the crop yield. Therefore, potential water shortages and water conflict should be considered in the future because of spatiotemporal humidity variations in the NCP.

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Empirical Equations to Estimate Evapotranspiration in Mosul City

Tikrit Journal of Engineering Sciences ◽

10.25130/tjes.27.4.10 ◽

2020 ◽

Vol 27 (4) ◽

pp. 98-102

Author(s):

Haqqi Yasin ◽

Luma Abdullah

Keyword(s):

Wind Speed ◽

Relative Humidity ◽

Air Temperature ◽

Reference Evapotranspiration ◽

Sunshine Duration ◽

Food And Agriculture ◽

Food And Agriculture Organization ◽

Daily Data ◽

Daily Sunshine ◽

Measured Wind Speed

Average daily data of solar radiation, relative humidity, wind speed and air temperature from 1980 to 2008 are used to estimate the daily reference evapotranspiration in the Mosul City, North of Iraq. ETo calculator software with the Penman Monteith method standardized by the Food and Agriculture Organization is used for calculations. Further, a nonlinear regression approach using SPSS Statistics is utilized to drive the daily reference evapotranspiration relationships in which ETo is function to one or more of the average daily air temperature, actual daily sunshine duration, measured wind speed at 2m height and relative humidity

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Prediction of Biome-Specific Potential Evapotranspiration in Mongolia under a Scarcity of Weather Data

Water ◽

10.3390/w13182470 ◽

2021 ◽

Vol 13 (18) ◽

pp. 2470

Author(s):

Khulan Batsukh ◽

Vitaly A. Zlotnik ◽

Andrew Suyker ◽

Paolo Nasta

Keyword(s):

Potential Evapotranspiration ◽

Aridity Index ◽

Crop Coefficient ◽

Weather Data ◽

Gobi Desert ◽

Area Index ◽

Food And Agriculture ◽

Food And Agriculture Organization ◽

Practical Guidelines ◽

Specific Potential

We propose practical guidelines to predict biome-specific potential evapotranspiration (ETp) from the knowledge of grass-reference evapotranspiration (ET0) and a crop coefficient (Kc) in Mongolia. A paucity of land-based weather data hampers use of the Penman–Monteith equation (FAO-56 PM) based on the Food and Agriculture Organization (FAO) guidelines to predict daily ET0. We found that the application of the Hargreaves equation provides ET0 estimates very similar to those from the FAO-56 PM approach. The Kc value is tabulated only for crops in the FAO-56 guidelines but is unavailable for steppe grasslands. Therefore, we proposed a new crop coefficient, Kc adj defined by (a) net solar radiation in the Gobi Desert (Kc adjD) or (b) leaf area index in the steppe region (Kc adjS) in Mongolia. The mean annual ETp obtained using our approach was compared to that obtained by FAO-56 guidelines for forages (not steppe) based on tabulated Kc values in 41 locations in Mongolia. We found the differences are acceptable (RMSE of 0.40 mm d−1) in northern Mongolia under high vegetation cover but rather high (RMSE of 1.69 and 2.65 mm d−1) in central and southern Mongolia. The FAO aridity index (AI) is empirically related to the ETp/ET0 ratio. Approximately 80% and 54% reduction of ET0 was reported in the Gobi Desert and in the steppe locations, respectively. Our proposed Kc adj can be further improved by considering local weather data and plant phenological characteristics.

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Evaluation of the FAO Penman–Montheith, Priestley–Taylor and Hargreaves models for estimating reference evapotranspiration in southern Malawi

Hydrology Research ◽

10.2166/nh.2012.224 ◽

2012 ◽

Vol 44 (4) ◽

pp. 706-722 ◽

Cited By ~ 23

Author(s):

Cosmo Ngongondo ◽

Chong-Yu Xu ◽

Lena M. Tallaksen ◽

Berhanu Alemaw

Keyword(s):

Wind Speed ◽

Relative Humidity ◽

Vapour Pressure ◽

Reference Evapotranspiration ◽

Climate Variables ◽

Limited Data ◽

Full Data ◽

Data Intensive ◽

Food And Agriculture ◽

Food And Agriculture Organization

This study evaluated the performance of the Food and Agriculture Organization (FAO) Penman–Monteith (PM) reference evapotranspiration (ET0) method for various limited data scenarios in southern Malawi. The study further evaluated the full data PM method against the radiation-based Priestley–Taylor (PT) and the temperature-based Hargreaves (HAG) methods, which are less data-intensive approaches commonly used to estimate ET0 in data-scarce situations. A comprehensive daily climate dataset observed at the Nchalo Sugar Estate in southern Malawi for the period 1971–2007 was the basis of the study. The results suggested that lack of data on wind speed and actual vapour pressure did not significantly affect the PM ET0 estimates. However, the estimation of radiation using various combinations of observed wind speed and relative humidity all resulted in significant deviations from the PM ET0. Further, the HAG and PT methods significantly underestimated the PM. However, the PM method computed with estimated climate variables instead of observed climate variables still outperformed both the PT and HAG methods if their original parameters and estimated radiation were used. Thus, new monthly parameters for the PT and the HAG methods are proposed for more accurate daily ET0 estimates.

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Modification of FAO Penman–Monteith equation for minor components of energy

Hydrology Research ◽

10.2166/nh.2018.093 ◽

2018 ◽

Vol 50 (2) ◽

pp. 607-615

Author(s):

Arman Varmaghani ◽

William E. Eichinger ◽

John H. Prueger

Keyword(s):

Energy Equation ◽

Minor Components ◽

Net Radiation ◽

Obukhov Length ◽

Available Energy ◽

Food And Agriculture ◽

Food And Agriculture Organization ◽

Monteith Equation ◽

Energy Components

Abstract The conventional Food and Agriculture Organization of the United Nations (FAO) Penman–Monteith (P-M) equation requires knowledge of the available energy to estimate reference evapotranspiration (ETo); however, it is common to ignore the minor energy components (MECs). This study was conducted to determine the effect of not including the MECs in the FAO P-M equation. Fifteen-min micrometeorological records of four sites (covered with corn, soybeans, and prairie) in central Iowa, USA, during the years 2007–2012 were investigated. The major/minor components of the energy equation were either measured or estimated by in-situ eddy covariance instruments. It was discovered that, on average, the MECs accounted for at least 13% of daily net radiation, leading to 27% decrease in daily ETo. Therefore, an equation is introduced to estimate MECs as a function of net radiation, air temperature, and Monin–Obukhov length; and another equation is regressed to roughly estimate daily MECs as a function of net radiation and day of the year. The findings in this study suggest a fundamental modification of FAO P-M formula by considering the inclusion of MECs in the energy term.

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SENSITIVITY ANALYSIS OF A FAO PENMAN MONTEITH FOR POTENTIAL EVAPOTRANSPIRATION TO CLIMATE CHANGE

Jurnal Teknologi ◽

10.11113/jt.v79.8377 ◽

2017 ◽

Vol 79 (7) ◽

Author(s):

Nor Farah Atiqah Ahmad ◽

Muhamad Askari ◽

Sobri Harun ◽

Abu Bakar Fadhil ◽

Amat Sairin Demun

Keyword(s):

Climate Change ◽

Sensitivity Analysis ◽

Wind Speed ◽

Solar Radiation ◽

Graphical Method ◽

Potential Evapotranspiration ◽

Peninsular Malaysia ◽

Percentage Change ◽

Cameron Highlands ◽

Tropical Climates

Sensitivity of the FAO Penman-Monteith (FPM) potential evapotranspiration (PET) model under tropical climates has been studied in the present study. A total of 17 meteorological stations covering Peninsular Malaysia starting from 1987-2003 were used as model inputs. A sensitivity analysis (SA) was carried out using the graphical method for temperature, wind speed and solar radiation within the possible range of ±20% with increments of 5%. From the comparison done on the sensitivity of PET to climatic change, the Kuala Krai station gave the highest percentage change in terms of temperature (±6%). The highest percentage change for wind speed (±2%) and solar radiation (±17%) were shown at the Alor Setar and Kuala Krai stations, respectively. The Alor Setar station had the lowest percentage change for temperature (±0.3%) and solar radiation (±9.9). The lowest percentage change of wind speed (± 0.2%) was observed at the Kuala Krai station. PET percentage changes have a positive correlation to the percentage change of all climatic variables except for the Cameron Highlands station. Results revealed that solar radiation has the most significant effect on PET (±14%), followed by temperature (±4%) and wind speed (±1%). Taken together, these results suggest that solar radiation plays an important role in estimating PET in Peninsular Malaysia.

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How Ångström–Prescott Coefficients Alter the Estimation of Agricultural Water Demand in South Korea

Water ◽

10.3390/w10121851 ◽

2018 ◽

Vol 10 (12) ◽

pp. 1851

Author(s):

Hanseok Jeong ◽

Rabin Bhattarai ◽

Syewoon Hwang ◽

Jae-Gwon Son ◽

Taeil Jang

Keyword(s):

South Korea ◽

Global Solar Radiation ◽

Water Requirement ◽

Agricultural Water ◽

Reference Crop Evapotranspiration ◽

Agricultural Water Management ◽

Food And Agriculture ◽

Food And Agriculture Organization ◽

Reference Crop ◽

Monteith Equation

The Food and Agriculture Organization (FAO) Penman–Monteith equation, recognized as the standard method for the estimation of reference crop evapotranspiration (ET0), requires many meteorological inputs. The Ångström–Prescott (A-P) formula containing parameters (i.e., a and b) is recommended to determine global solar radiation, one of the essential meteorological inputs, but may result in a considerable difference in ET0 estimation. This study explored the effects of A-P coefficients not only on the estimation of ET0, but also on the irrigation water requirement (IWR) and design water requirement (DWR) for paddy rice cultivation, which is the largest consumer of agricultural water in South Korea. We compared and analyzed the estimates of ET0, IWR, and DWR using the recommended (a = 0.25 and b = 0.5) and locally calibrated A-P coefficients in 16 locations of South Korea. The estimation of ET0 using the recommended A-P coefficients produced significant overestimation. The overestimation ranged from 3.8% to 14.0% across the 16 locations as compared to the estimates using the locally calibrated A-P coefficients, and the average overestimation was 10.0%. The overestimation of ET0 corresponded to a variation of 1.7% to 7.2% in the overestimation of the mean annual IWR, and the average overestimation of the IWR was 5.1%. On average, the overestimation was slightly reduced to 4.8% in DWR estimation, since the effect of A-P coefficients on the IWR estimation decreased as the IWR increased. This study demonstrates how the use of A-P coefficients can alter the estimation of ET0, IWR, and DWR in South Korea, which underscores the importance of their proper consideration in agricultural water management.

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Lysimeter-Based Water Use and Crop Coefficient of Drip-Irrigated Potato in an Arid Environment

Agronomy ◽

10.3390/agronomy9110756 ◽

2019 ◽

Vol 9 (11) ◽

pp. 756 ◽

Cited By ~ 1

Author(s):

Alataway ◽

Al-Ghobari ◽

Mohammad ◽

Dewidar

Keyword(s):

Water Use ◽

Irrigation Schedule ◽

Crop Coefficient ◽

Arid Environment ◽

Crop Evapotranspiration ◽

Food And Agriculture ◽

Food And Agriculture Organization ◽

Use Efficiency ◽

Monteith Equation

The determination of the water requirements and crop coefficient (Kc) of agricultural crops helps to create an appropriate irrigation schedule, and with the effective management of irrigation water. The aim of this research was to estimate the water requirement, Kc, and water-use efficiency (WUE) of potato using non-weighing-type lysimeters in four regions of the Kingdom of Saudi Arabia (Qassiem, Riyadh, Al-Jouf, and Eastern). Our results clearly show that the accumulated values of the measured crop evapotranspiration of potato derived from the lysimeters were 573, 554, 592, and 570 mm, while the accumulated values of the predicted crop evapotranspiration from Penman-Monteith equation based on FAO (Food and Agriculture Organization) were 651, 632, 672, and 647 mm for the Qassiem, Riyadh, Al-Jouf, and Eastern regions, respectively. The Kc values of potato obtained from the lysimeters were Kc initial (0.58, 0.54, 0.50, and 0.52), Kc middle (1.02, 1.05, 1.13, and 1.10), and Kc end (0.73, 0.74, 0.74, and 0.75) for the Qassiem, Riyadh, Al-Jouf, and Eastern regions, respectively. Based on the amount of water used and the yield achieved, the highest WUE (3.6 kg m−3) was observed in the Riyadh region, while the lowest WUE (1.5 kg m−3) was observed in the Al-Jouf region.

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Water balance of the basin of Mandali/ east part of Iraq

Iraqi Journal of Physics (IJP) ◽

10.30723/ijp.v13i26.283 ◽

2019 ◽

Vol 13 (26) ◽

pp. 51-57

Author(s):

Qusai Y. AL-Kubaisi

Keyword(s):

Data Analysis ◽

Wind Speed ◽

Relative Humidity ◽

Water Balance ◽

Potential Evapotranspiration ◽

East Part ◽

Class A ◽

The North ◽

Water Recharge ◽

Water Surplus

Mandali Basin is located between latitudes (33◦ 39' 00" and 33◦54' 55") to the north and longitudes (45ο 11' 00" and 45ο 40' 00") to theeast; to the east of Diyala province at the Iraqi-Iranian border; thebasin area is approximately 491 km2.From the study of climate reality of the basin between 1990-2013and assessment of the basic climate transactions, it was foundthat the annual rate of rainfall is 253.02 mm, the relative humidity(44.4%), the temperature (21.3 ◦C), wind speed (2.08 m /sec.),sunshine (8.27 h/day) and evaporation of the basin class (a) (271.98mm) and corrected potential evapotranspiration (80.03 mm). Theresults of the data analysis show that, there are three basic periods ofclimate variability wet period, semi wet and dry period.This study shows that, there is water surplus of 60.87% of therainfall amount which is equivalent to 154.03 mm, the amount ofrunoff is 7.47 mm, and the amount of water recharge is 146.56mm.

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Influence of Meteorological Factors on the Potential Evapotranspiration in Yanhe River Basin, China

10.22541/au.161606525.58625543/v1 ◽

2021 ◽

Author(s):

yu luo ◽

Peng Gao ◽

Xingmin Mu

Keyword(s):

Wind Speed ◽

Relative Humidity ◽

Solar Radiation ◽

River Basin ◽

Air Temperature ◽

Hydrological Cycle ◽

Meteorological Factors ◽

Potential Evapotranspiration ◽

Sensitivity Coefficients ◽

The Impact

Potential evapotranspiration (ET) is an essential component of the hydrological cycle, and quantitative estimation of the influence of meteorological factors on ET can provide a scientific basis for studying the impact mechanisms of climate change. In the present research, the Penman-Monteith method was used to calculate ET. The Mann-Kendall statistical test with the inverse distance weighting were used to analyze the spatiotemporal characteristics of the sensitivity coefficients and contribution rates of meteorological factors to ET to identify the mechanisms underlying changing ET rates. The results showed that the average ET for the Yanhe River Basin, China from 1978–2017 was 935.92 mm. Save for a single location (Ganquan), ET increased over the study period. Generally, the sensitivity coefficients of air temperature (0.08), wind speed at 2 m (0.19), and solar radiation (0.42) were positive, while that of relative humidity was negative (-0.41), although significant spatiotemporal differences were observed. Increasing air temperature and solar radiation contributed 1.09% and 0.55% of the observed rising ET rates, respectively; whereas decreasing wind speed contributed -0.63%, and relative humidity accounted for -0.85%. Therefore, it was concluded that the decrease of relative humidity did not cause the observed ET increase in the basin. The predominant factor driving increasing ET was rising air temperatures, but this too varied significantly by location and time (intra- and interannually). Decreasing wind speed at Ganquan Station decreased ET by -9.16%, and was the primary factor underlying the observed, local “evaporation paradox.” Generally, increases in ET were driven by air temperature, wind speed and solar radiation, whereas decreases were derived from relative humidity.

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