Variation Of Reference Evapotranspiration Research Articles

Assessing the effect of climate change on spatiotemporal variations in reference evapotranspiration across Iraq

Assessing the effect of climate change on spatiotemporal variations in reference evapotranspiration across Iraq

Global evapotranspiration from high-elevation mountains has decreased significantly at a rate of 3.923 %/a over the last 22 years

Clarifying the responses of human activities and climate change to the water cycle under variable environments is crucial for accurately assessing regional water balance. An analysis of the changes in actual evapotranspiration and its driving factors was conducted in the global high-elevation mountains during the period from 2001 to 2022. Utilizing 18 formulas for calculating evapotranspiration, which are based on comprehensive, temperature, radiation, and mass transfer, and then simulated the variations in reference evapotranspiration. Furthermore, we optimized the ET simulation model based on the most effective simulation results and projected future changes using scenario simulation data. Our findings reveal that: 1) ET at high-elevation mountains has significantly decreased at an average rate of 3.923 %/a, with monthly values ranging from 31.179 to 33.652 mm and an average of 32.646 mm; 2) The radiation-based model of Irmark-Allen is particularly well-suited for simulating ET at high-elevation mountains, with precision analysis and the Taylor diagram confirming its superior simulation performance. After optimizing the model using the method of least squares, the value of R2 before and after the optimization were 0.633 and 0.853, respectively. 3) An upward trend in ET under both SSP245 and SSP585 scenario in future simulation projections. Attribution analysis has identified Vapor Pressure Deficit as the key positive driver influencing the change of ET in global high-elevation mountains. Structural equation modeling further reveals that variations in net radiation and precipitation play a significant role in altering evapotranspiration rates. Meanwhile，The water balance analysis reveals that ET has been declining from 2001 to 2022. This phenomenon can be largely attributed to the substantial decline in vapor pressure deficit, the rise in the Normalized Difference Vegetation Index signifying increased vegetation cover, and the reduction in shallow soil moisture during the same period. These factors collectively explain the notable decrease in ET observed in high-elevation mountains.

Sensitivity of the Penman–Monteith Reference Evapotranspiration Equation to Meteorological Variables for Puerto Rico

Spatiotemporal variations in reference evapotranspiration (ETo) are sensitive to the meteorological data used in its estimation. The sensitivity of the ASCE standardized ETo equation to meteorological variables from GOES-PRWEB dataset was evaluated for the island of Puerto Rico. Island wide, ETo is most sensitive to daily mean relative humidity (RHmean), followed by solar radiation, daily maximum (Tmax) and minimum (Tmin) air temperatures, and wind speed with average absolute relative sensitivity coefficients (SCs) of 0.98, 0.57, 0.50, 0.27, and 0.12, respectively. The derived SCs guided the prioritization of bias correction of meteorological data for ETo estimation from two downscaled climate models (CNRM and CESM). The SCs were applied to evaluate how meteorological variables contribute to model errors and projected future changes in ETo from 1985–2005 to 2040–2060 at irrigated farms in the south. Both models project a 5.6% average increase in annual ETo due to projected increases in Tmax and Tmin and a decrease in RHmean. Despite ETo being most sensitive to relative changes in RHmean, the contributions from RHmean, Tmax, and Tmin to future changes in ETo are similar. CESM projects increases in ETo in March, November, and December, increasing the potential for crop water stress. Study limitations are discussed.

Spatial and Temporal Variation in Reference Evapotranspiration and Its Climatic Drivers in Northeast China

Reference evapotranspiration (ET0) is an important component of the global water cycle, and its long-term change directly influences the regional water supply and demand balance. Under the background of global change, investigating spatiotemporal trends in ET0 and its response to climate change is of great importance for the conservation and rational utilization of water resources. Based on daily climate data from 91 meteorological stations during 1960–2017 in Northeast China, this study calculated ET0 using the Penman-Monteith method and analyzed its spatiotemporal change trends and primary driving factors. The results show the following: (1) During 1960–2017, the annual ET0 in Northeast China showed a nonsignificant upward trend at a rate of 1.45 mm/10a. A mutation point of ET0 was detected in 1993. From 1960 to 1993, ET0 experienced a significant decrease (p < 0.1), while annual air temperature showed a significant upward trend (p < 0.01), which indicated the appearance of an evaporation paradox. This was because the remarkable drop in wind speed and sunshine duration played a great role in the reduction of ET0. From 1994 to 2017, the evaporation paradox disappeared. (2) ET0 trend in Northeast China was significantly and positively related to altitude. In the lower altitude regions (<500 m), ET0 generally decreased, while in the higher altitude areas (>500 m), ET0 displayed an upward trend. (3) Based on the results of multiple regression analysis, relative humidity was the primary driving factor for ET0 trends in Northeast China during 1960–2017. At diverse altitudes, the primary climatic factors influencing ET0 were different. In high-altitude areas (>500 m), the change in ET0 was mainly influenced by relative humidity, while wind speed was the primary driving factor at low altitudes (<500 m).

Spatiotemporal Variations in Reference Evapotranspiration and Its Contributing Climatic Variables at Various Spatial Scales across China for 1984–2019

Reference evapotranspiration (ET0) is of great significance in studies of hydrological cycle, agricultural water resources, and hydrometeorology. The present study collected daily meteorological data at 536 meteorological stations in China from 1984 to 2019, calculated daily ET0 using the FAO Penman–Monteith equation, analyzed the spatial distribution and temporal variation characteristics of ET0 and meteorological variables at four different spatial scales (continental, regional, provincial, and local), and discussed the sensitivity of ET0 to the meteorological variables and the contribution rates of the meteorological variables to the ET0 variations. The results showed that ET0 increased at 406 out of the 536 stations (75.7%), with the trends being significant at 65 stations at the 5% significance level, and 147 at the 1% significance level. The slope calculated using Sen’s method and linear trend method showed that the annual ET0 at the continental scale increased by approximately 12 mm/decade. Most of the stations showed decreasing trends in relative humidity (Hm), sunshine duration (SD), and wind speed at 2 m height (U2) while increasing trends in the maximum air temperature (Tmax) and minimum air temperature (Tmin). ET0 was most sensitive to Hm (sensitivity coefficient, St = −0.66), followed by Tmax (St = 0.29), SD (St = 0.18), U2 (St = 0.16), and Tmin (St = 0.07). Most of the stations showed increasing trends in St for Hm (56.16%), Tmax (72.95%), Tmin (87.31%), and U2 (90.49%), and decreasing trends for SD (69.78%). The variations in Hm, Tmax, and Tmin increased the ET0 at most of the stations (82.28%, 98.13%, and 69.03%, respectively). The variations in SD and U2 decreased ET0 at most of the stations (66.04% and 56.34%, respectively). Some ET0 characteristics in a few regions can be well described using a single spatial scale. However, most regions exhibited significantly different ET0 characteristics across spatial scales. The results of this project can provide reference for hydrological analysis and agricultural water management under climate change conditions and provide data and information for other hydrology-related applications.

Effect of Elevation on Variation in Reference Evapotranspiration under Climate Change in Northwest China

Through its effects on water and energy cycles, elevation plays an important role in modulating the spatial distribution of climatic changes in mountainous regions. A key hydrological indicator, reference evapotranspiration (ET0) reflects the maximum amount of water transferred to the atmosphere from the land surface. The current scarcity of information regarding elevation’s impact on variation in ET0 under climate change limits our understanding of the extent to which elevation modulates interactions between ET0 and climate change and of the attendant processes involved. Drawing upon long-term (1960–2017) meteorological observations from 84 stations in Northwest China (NWC), we examined (i) spatial and temporal variations in ET0; (ii) the sensitivity and contribution of air temperature (T), sunshine duration (SD), relative humidity (RH), and wind speed (WS) to ET0; (iii) the existence of a relationship between elevation and ET0 trends; and (iv) the major factor in controlling this relationship by using attribution analysis. Overall, annual ET0 in NWC showed a declining trend between 1960 and 2017, though at a change point in 1993, the trend shifted from a decline to a rise. A significant correlation between temporal change in ET0 and elevation confirmed the existence of a relationship between elevation and ET0 variation. The effect of elevation on changes in ET0 depended mainly on the elevation-based tradeoff between the contributions of T and WS: WS was the primary factor contributing to the decrease in ET0 below 2000 m, and T was the dominant factor contributing to the increase of ET0 above 2000 m. The rate of reduction in WS declined as elevation increased, thereby diminishing its contribution to variation in ET0. The present study’s results can serve to guide agricultural irrigation in different elevation zones under NWC’s evolving climatic conditions.

Temporal variations in reference evapotranspiration in the Tarim River basin, Central Asia.

Reference evapotranspiration (ET0) is important for agricultural production and the hydrological cycle. Knowledge of ET0 can aid the appropriate allocation of irrigation water in arid regions. This study analyzed the trends in ET0 over different timescales in the Tarim River basin (TRB), Central Asia. ET0 was calculated by the Penman-Monteith method using data from 1960–2017 from 30 meteorological stations located in the TRB. The Mann-Kendall (MK) test with trend-free prewhitening and Sen’s slope estimator were applied to detect trends in ET0 variation. The results showed that the mean ET0 decreased at a rate of 0.49 mm·10 a-1 on an annual timescale. The mean ET0 exhibited a decreasing trend in summer and increasing trends in other seasons. The effects of climatic factors on ET0 were assessed by sensitivity analysis and contribution rate analysis. Maximum temperature (Tmax), relative humidity (RH) and wind speed (WS) showed important effects on ET0. However, WS, which decreased, was the key element that induced changes in ET0 in the TRB. This work provides an important baseline for the management of agricultural water resources and scientific planning in agriculture.

Reference evapotranspiration change in Heilongjiang Province, China from 1951 to 2018: The role of climate change and rice area expansion

It is of great significance to study the variation in reference evapotranspiration (ETo) and the factors that influence it to ensure the sustainable and efficient utilization of water resources. In this study, the spatio-temporal changes in ETo and rice areas as well as the relationship between them in Heilongjiang Province, China, from 1951 to 2018 were analysed by using trend, correlation and contribution analyses. The results showed that rice area expansion is an important factor affecting ETo changes. ETo in Heilongjiang Province decreased during the study period. The areas with high ETo in the Songnen and Sanjiang Plain showed a gradually shrinking trend. Climate change and rice area expansion both contributed to the decline in ETo. The decreases in sunshine duration and average wind speed in Heilongjiang Province were the main reasons for the decrease in ETo. Rice area in Heilongjiang province continued to increase at a rate of 0.54 × 105 ha yr−1. The expansion of rice area in Sanjiang Plain was the largest, followed by Songnen Plain. In response to the rice area expansion, the rise in average temperature slowed down, the average relative humidity was increased, while wind speed was reduced, which directly lead to the decrease in ETo. The effects of the transformation of different land types into rice fields on ETo were different. The cumulative effects of wetlands and dry fields conversion to rice fields on ETo were 7.67 mm yr−1 and − 20.15 mm yr−1 in Sanjiang Plain respectively.

Analysis of variation in reference evapotranspiration and its driving factors in mainland China from 1960 to 2016

Understanding the variation in reference evapotranspiration (ETo) is vital for hydrological cycles, drought monitoring, and water resource management. With 1507 meteorological stations and 130 radiation-measured stations, the annual and seasonal ETo were calculated at each site from 1960 to 2016 in mainland China. The phenomenon of coefficient ‘a’ being less than 0.25 and coefficient ‘b’ being greater than 0.50 in the Angstrom–Prescott model occurred in almost the whole country, except for a small area of western and northeastern China. Moreover, the Xiao’s method was more applicable to calculate the net longwave radiation (R nl) and then improve the estimation accuracy of ETo. The annual ETo varied from 538.8 to 1559.8 mm and had a high-value center located in the plateau and desert of northwestern China and a low-value center located in Northeast China and near the Sichuan Basin. The spatial distribution of seasonal ETo was roughly similar to that of annual ETo, except for that in winter when ETo was high in the south and low in the north. In mainland China, the annual ETo decreased by 21.2 mm decade−1 because of the declining sunshine duration before 1993 and increased by 21.1 mm decade−1 due to the decreased relative humidity (RH) after 1993. Generally, the abrupt change of ETo mainly occurred in the southern China rather than northern China (except for Qinghai Tibet Plateau). Basically, the dominant driving factors of annual and seasonal ETo were RH and/or T max after the abrupt change in most parts of China.

Variation in Reference Evapotranspiration over the Tibetan Plateau during 1961–2017: Spatiotemporal Variations, Future Trends and Links to Other Climatic Factors

Reference evapotranspiration (ET0) is a key factor in the hydrological cycle and energy cycle. In the context of rapid climate change, studying the dynamic changes in ET0 in the Tibetan Plateau (TP) is of great significance for water resource management in Asian countries. This study uses the Penman–Monteith formula to calculate the daily ET0 of the TP and subsequently uses the Mann–Kendall (MK) test, cumulative anomaly curve, and sliding t-test to identify abrupt change points. Morlet wavelet analysis and the Hurst index based on rescaled range analysis (R/S) are utilized to predict the future trends of ET0. The Spearman correlation coefficient is used to explore the relationship between ET0 changes and other climate factors. The results show that the ET0 on the TP exhibited an increasing trend from 1961 to 2017, with the most significant increase occurring in winter; an abrupt change to a tendency to decrease occurred in 1988, and another abrupt change to a tendency to increase occurred in 2005. Spatially, the ET0 of the TP shows an increasing trend from east to west. The change trend of the ET0 on the TP will not be sustainable into the future. In addition, the mean temperature has the greatest impact on the ET0 changes in the TP.

Temporal trends of climatic variables and water footprint of rice and wheat production in Punjab, India from 1986 to 2017

AbstractThe agriculture sector is vulnerable to climate change and related changes in the hydrological cycle. In order to understand the changes in climatic variables and their implications for agricultural water consumption, the present study aims to analyse the temporal variability of climatic factors and water footprint (WF) of rice and wheat during the period 1986–2017 in Ludhiana, Punjab. Further, it aims to identify the dominant climatic factors that cause variation in reference evapotranspiration (ETo) and WF of rice and wheat. WF was estimated using CROPWAT, and Path analysis was used to determine the dominant climate variables. Temporal trends of climate variables were analysed using the Mann–Kendall test. The total WF of both rice and wheat shows a significant declining trend over the past 32 years. Sunshine duration and wind speed were the dominant factors influencing the variability of total WF of rice and wheat, respectively, whereas rainfall strongly influenced the green and blue WF of rice and wheat. Rainfall had a high variability, and consequently, irrigation water requirement was highly fluctuating. This indicates the significant impact of present and projected erratic pattern of precipitation on agriculture due to climate change and reiterates the importance of adaptive measures like rainwater harvesting and capacity building.

Spatiotemporal variation in reference evapotranspiration and its contributing climatic factors in China under future scenarios

AbstractGlobal climate change is likely to affect reference evapotranspiration (ET0), which is important for agricultural water resources and food security. Analysis of ET0 changes is also important for understanding climate change and its impacts on hydrology. In this study, ET0 was calculated from 2020 to 2099 in nine agricultural regions and the entire country of China utilizing the Penman–Monteith method based on bias‐corrected climate data from the global climate models MIROC‐ESM‐CHEM, NorES1‐M, IPSL‐CM5A‐LR, GFDL‐ESM 2M and HadGEM2‐ES under future climate change scenarios. The spatiotemporal characteristics of seasonal and annual ET0 and climatic variables were analysed based on the Mann–Kendall test with trend‐free prewhitening (TFPW‐MK) and Sen's slope estimator. Sensitivity coefficient and multivariate regression were used to identify factors controlling the change in ET0. The results showed that seasonal and annual air temperature and precipitation both increased under all climate scenarios, and the majority of relative humidity and wind speed values showed downward trends during 2020–2099. The lowest annual ET0 values were found in the NECR and QTR, and the SCR had the maximum ET0. Both the TFPW‐MK and slope statistics showed an upward trend of seasonal ET0 during 2020–2059 under all scenarios. During 2060–2099, seasonal ET0 values showed a slight and nonsignificant downward trend under RCP 2.6, while upward trends were produced in other scenarios. Areas with high ET0 values were located in the SCR, GXR and HHHR, while low ET0 values mainly occurred in the NECR and QTR. The ET0 for the four seasons in the SCR was higher than that in the other regions, and the summer ET0 was the highest compared with that in the other seasons overall. For the attribution assessment, Tavg is the main controlling variables to ET0 trends under the interaction of multiple climatic factors though RH is the most sensitive.

Assessing Climate Change Impact on Future Reference Evapotranspiration Pattern of West Bengal, India

Considering the importance of reference evapotranspiration (RET) in agriculture, hydrology and meteorology, the research problem was taken to assess the RET during winter season under projected climatic situation of West Bengal, India. The Penman-Monteith method was used in the study as it is the most accurate method of estimating RET. However, validation of the output of the equation was done with the help of observed data set. The data analysis was carried out using NCAR Command Language (NCL). The result clearly shows that the reference ET of the study area will be increased in the tune of 13% to 32% in the year 2050 compared to present RET level. Analysis of actual rainfall data shows a decreasing trend of winter rainfall in the study region. The projected rainfall data also follows the same pattern. Thus, the combination of low rainfall and higher ET value will demand more irrigation requirement for winter crops in West Bengal. The temporal changes of RET on decadal basis and spatial variation of RET for each decade have been observed and discussed in the paper.

Determination of seasonal variation in reference evapotranspiration using regression analysis

In the study, variability in reference evapotranspiration (ET0) from Southeastern Anatolian Project (GAP) area was investigated with linear regression method. For the purpose, seasonal ET0 time series were formed from monthly reference evapotranspiration (ET0). The ET0 data sets of three sites showed a statistically significance decreasing trend while there was upward trend in some seasons of two sites. But, variation in all seasonal ET0 time series of Kilis site was not detected.

Variations of the Reference Evapotranspiration and Aridity Index Over Northeast China: Changing Properties and Possible Causes

Temporal and spatial variations in reference evapotranspiration (ET0) and aridity index (AI) can be used as important indexes for understanding climate change and its effects on ecosystem stability. Thus, in this work, we comprehensively investigated 71 meteorological stations in Northeast China from 1965 to 2017 to analyze the spatial-temporal variation and trend of ET0 and AI using the nonparametric Mann–Kendall test, the linear regression, and the Morlet wavelet methods. The results elucidated that ET0 for Northeast China as a whole exhibited a decrease at a rate of −1.97 mm/yr, AI declined at a rate of −0.01/yr during 1965–2017, and approximately 94% stations showed a decrease trend. Spatially, the high values of AI and ET0 were primarily at the western part of the study area except for the Heilongjiang province, and the stations showing low values were mainly distributed in the central and eastern part. The decreasing trends for AI were more obvious in the eastern part compared with the western part over the study region. The abrupt changes in AI occurred in 2005 and 2007, whereas only one abrupt change for ET0 occurred in 1995. For annual ET0, there were periods of 3, 7, 11, and 15 yr, and there existed periods of 1, 7, 11, and 13 yr for annual AI. The correlation coefficients implied wind speed and precipitation were the dominant meteorological factors resulting in the ET0 and AI decrease, respectively. Additionally, the change of the Indian summer monsoon index (ISMI) may also contribute to the weakened AI in the study area. Nevertheless, further investigation is still required to clarify the mechanisms for AI and ET0 variations in the future.

Variation of reference evapotranspiration and its teleconnection with multiple large‐scale climate oscillations in the Yangtze River Delta, China

Evapotranspiration is a key factor in regional hydrological processes and water resources management. Long‐term variation of evapotranspiration affects the regional climate wet/dry tendency and agricultural production profoundly. Thus, reference evapotranspiration (ET0) values for 46 meteorological stations in the Yangtze River Delta (YRD) were calculated for 1957–2014 using the FAO‐Penman–Monteith (FAO‐PM) method. The variation patterns of ET0 values were determined based on the principal component analysis (PCA) method. In addition, the methods of cross wavelet transform (CWT), Kendall tau‐b correlation coefficient determination and cross‐correlation method were applied in the assessment of the correlation between ET0 values and large‐scale climate oscillations, such as the North Atlantic Oscillation (NAO), the Pacific Decadal Oscillation (PDO), the Oceanic Niño3.4 Sea Surface Temperature Index (NINO) and the Indian Ocean Dipole (IOD). Annual ET0 patterns for three dominant geographic subregions of the YRD (the southeastern, northwestern and mid‐eastern) were determined. There were only several discontinuous lower timescale bands between the three change patterns of annual ET0 and climate oscillations. In seasonal scale, the temporal patterns of ET0 changed simultaneously with the NAO, NINO and PDO in spring, the PDO in summer and the NAO in winter. The monthly ET0 was mostly influenced by the NAO and IOD in January, the IOD in February, the IOD and NINO in March, the NINO in June, the PDO in July to October, the NINO, IOD and NAO in October and the NINO in December. The lag times for the ET0 changes were about 0–5 months for the NAO and NINO, 1–2 months for the PDO and 4 months for the IOD.

Variations in Reference Evapotranspiration and Associated Driving Forces in the Pearl River Delta of China during 1960–2016

Variations in Reference Evapotranspiration and Associated Driving Forces in the Pearl River Delta of China during 1960–2016

Potential Impacts of Climate Variation on Potato Field Evapotranspiration: Field Experiment and Numerical Simulation of Potato Water Use in an Arid Site

AbstractClimate change would significantly affect crop evapotranspiration processes. Many studies have been conducted for various crops. However, there is a lack of sufficient observational evidence on how climate change would influence potato evapotranspiration. In this paper, an experimental potato field in Maowusu Desert, northwest of China, was used to investigate the effect of climate change on potato evapotranspiration. Temporal variations in reference evapotranspiration (ET0) were comprehensively investigated during 1954–2013, which shows that annual temperature and ET0 had significant increasing trends in the past 60 years. Meanwhile, an experimental crop of potato was grown in Maowusu Desert to investigate water‐soil‐air‐plant‐human nexus in 2016, and a HYDRUS‐1D model for the unsaturated flow in a potato field was calibrated and validated with measured soil water tensions and soil water contents at various depths during the potato growing periods from 8 to 16 August 2016 and from 6 September to 3 October 2016, respectively. The model computed the actual potato evapotranspiration (ETa) as 183 mm during the whole growing period from 5 June to 3 October 2016. The groundwater contribution to potato water use was calculated to be 320 mm during the growing season in 2016. As the atmospheric temperature increases, the reference crop evapotranspiration increases, the actual potato evapotranspiration increases too. The actual potato evapotranspiration increase with temperature increase will lead to a bigger water resource pressure in this area. The study results provide the basis for managing crop irrigation in the region in the future.

Assessing the Monthly Variation of Reference Evapotranspiration of Nsukka, Enugu State, Nigeria

Assessing the Monthly Variation of Reference Evapotranspiration of Nsukka, Enugu State, Nigeria

Temporal variations in reference evapotranspiration in Hubei Province, China, from 1960 to 2014

Reference evapotranspiration (ET0) plays a critical role in irrigation planning and is also important for hydrological cycle, environmental, and other studies. Thus, this research examined the trends in ET0 on seasonal and annual timescales in Hubei Province, China. ET0 was estimated using the Penman Monteith method (P-M) at 16 meteorological stations located in different areas of Hubei Province during the period 1960–2014. The trends in seasonal and annual ET0 were investigated using the Mann-Kendall test and Sen’s slope estimator. The periodicities of ET0 in different regions were investigated using wavelet analysis. The major meteorological factors affecting ET0 were investigated using partial correlation analysis and the contribution rate method. The results showed, on a seasonal timescale, that in spring, ET0 increased in all geographic zones. In summer, ET0 decreased in all geographic zones. In autumn and winter, ET0 displayed no significant changes in any of the geographic zones. On an annual timescale, ET0 decreased in all geographic zones, and the magnitudes of the negative trend in annual ET0 were 2.58–10.04 mm 10a−1. In the five geographic zones, the periodic characteristics of ET0 were identical; the significant wavelet power spectra of ET0 had 3–7, 13–17, and 24–32-year modulations in variation. Among the meteorological factors, sunshine hours were the major climate element that influenced the variability in ET0. The results will provide important references for scientific planning for agriculture, water resource allocation, and water-saving irrigation.