Annual Evapotranspiration Values Research Articles

Enhancing references evapotranspiration forecasting with teleconnection indices and advanced machine learning techniques

After precipitation, reference evapotranspiration (ETO) plays a crucial role in the hydrological cycle as it quantifies water loss. ETO significantly impacts the water balance and holds great importance at the basin level because of the spatial distribution of managing water resources. Large scale teleconnection indices (LSTIs) play a vital role by influencing climatic variables and can be pivotal in determining ETO and its predictive variables. This study aimed to model and forecast annual ETO in Iran’s basins by utilizing LSTIs and employing various machine learning models (MLMs) such as least squares support vector machine, generalized regression neural network, multi-linear regression (MLR), and multi-layer perceptron (MLP). Initially, climate data from 122 synoptic stations covering six and 30, main and sub basins were collected, and annual ETO values were computed using the Food and Agriculture Organization 56 (PMF 56) Penman–Monteith equation. The correlations between these values and 37 LSTIs were examined within lead times ranging from 7 to 12 months. Through a stepwise approach, the most influential predictor indices (LSTIs) were selected as input datasets for the MLMs. The findings revealed the significant influence of factors such as carbon dioxide (CO2), Atlantic multidecadal oscillation, Atlantic Meridional Mode, and East Atlantic on annual ETO. Overall, all MLMs performed well in terms of the Scatter Index during both training and testing phases across all sub-basins. Furthermore, the MLP and MLR models displayed superior performance compared to other models in the training and testing evaluations based on various assessment metrics.

Eddy covariance measurement-based differences in annual evapotranspiration between forests and grasslands in China.

Annual evapotranspiration (AET), the total water vapor loss to the atmosphere during a year, is a vital process of global water cycles and energy cycles. Revealing the differences in AET values and spatial variations between forests and grasslands would benefit for understanding AET spatial variations, which serves as a basis for regional water management. Based on published eddy covariance measurements in China, we collected AET values from 29 forests and 46 grasslands, and analyzed the differences in AET values and spatial variations between forests and grasslands in China. The results showed that forests had a significant higher AET (645.98 ± 232.73 kgH2O m-2 yr-1) than grasslands (359.31 ± 156.02 kgH2O m-2 yr-1), while the difference in AET values between forests and grasslands was not significant after controlling mean annual precipitation (MAP) relating factors. The effects of latitude and mean annual air temperature (MAT) on AET spatial variations differed between forests and grassland, while AET of forests and grasslands both exhibited increasing trends with similar rates along the increasing MAP, aridity index (AI), soil water content (SW), and leaf area index. The comprehensive effects of multiple factors on AET spatial variations differed between forests and grasslands, while MAP both played a dominating role. The effects of other factors were achieved through their close correlations with MAP. Therefore, forests and grasslands under similar climate had comparable AET values. AET responses to MAP were comparable between ecosystem types. Our findings provided a data basis for understanding AET spatial variation over terrestrial ecosystems of China or globally.

Assessment of Interannual Variability of Moistening of Siberian Territory According to Observational Data

The article discusses the features of large-scale spatial and temporal variability of moistening (potential evapotranspiration, precipitation, potential evapotranspiration coefficient) in the Siberian part of Russia for the period 1981–2015. The All-Russian Research Institute of Hydrometeorological Information—World Data Center (RIHMI-WDC) archive has served as a source of initial information. Due to the rare network of stationary meteorological stations in most of Siberia, only 32 stations located mainly in the valleys of large rivers have been used for calculations. To estimate potential evapotranspiration, the modified method of M.I. Budyko has been used. A comprehensive delimitation of Siberia has been carried out by the interannual fluctuations of characteristics of moistening, being well divided into four regions, three of which encompass the basins of the largest rivers: the Ob, the Yenisei, the Lena and the fourth region represents the Baikal region. Analysis of the trends shows that the evapotranspiration in Siberia is growing only in the Ob basin and the Baikal region. Precipitation, excluding the Baikal region, is also increasing in the Yenisei and Lena basins. As for the potential evapotranspiration coefficient, a significant trend refers only to the Baikal region due to the rapid increase in evaporation. The modeling of the annual values of the characteristics of moistening for the selected regions has been carried out using the decision trees method. For 4-branch trees, the coefficient of determination R2 describes about two-thirds of the variance of the original variable (0.57–0.73). In the models of annual evapotranspiration values, the main predictor is the air temperature. In precipitation models, the contribution of local and external circulation factors to interannual precipitation fluctuations is equal.

A Comparison of SSEBop-Model-Based Evapotranspiration with Eight Evapotranspiration Products in the Yellow River Basin, China

Accurate evapotranspiration (ET) estimation is important in understanding the hydrological cycle and improving water resource management. The operational simplified surface energy balance (SSEBop) model can be set up quickly for the routine monitoring of ET. Several studies have suggested that the SSEBop model, which can simulate ET, has performed inconsistently across the United States. There are few detailed studies on the evaluation of ET simulated by SSEBop in other regions. To explore the potential and application scope of the SSEBop model, more evaluation of the ET simulated by SSEBop is clearly needed. We calculated the SSEBop-model-based ET (ETSSEBopYRB) with land surface temperature product of MOD11A2 and climate variables as inputs for the Yellow River Basin (YRB), China. We also compared the ETSSEBopYRB with eight coarse resolution ET products, including China ETMTE, produced using the upscaling energy flux method; China ETCR, which is generated using the non-linear complementary relationship model; three global products based on the Penman–Monteith logic (ETPMLv2, ETMODIS, and ETBESS), two global ET products based on the surface energy balance (ETSEBS, ETSSEBopGlo), and integrated ET products based on the Bayesian model averaging method (ETGLASS), using the annual ET data derived from the water balance method (WB-ET) for fourteen catchments. We found that ETSSEBopYRB and the other eight ET products were able to explain 23 to 52% of the variability in the water balance ET for fourteen small catchments in the YRB. ETSSEBopYRB had a better agreement with WB-ET than ETSEBS, ETMODIS, ETCR, and ETGLASS, with lower RMSE (88.3 mm yr−1 vs. 121.7 mm yr−1), higher R2 (0.49 vs. 0.43), and lower absolute RPE (−3.3% vs. –19.9%) values for the years 2003–2015. We also found that the uncertainties of the spatial patterns of the average annual ET values and the ET trends were still large for different ET products. Third, we found that the free global ET product derived from the SSEBop model (ETSSEBopGlo) highly underestimated the annual total ET trend for the YRB. The poor performance of the land surface temperature product of MOD11A2 in 2015 caused the large ETSSEBopYRB uncertainty at eight-day and monthly scales. Further evaluation of ET based on the SSEBop model for site measurements is needed.

Environmental and biophysical controls of evapotranspiration from Seasonally Dry Tropical Forests (Caatinga) in the Brazilian Semiarid

Seasonally dry tropical forests are among the most important biomes regarding regional and global hydrological and carbon fluxes. Thus, the objective of this study was to evaluate the seasonal and interannual variability of evapotranspiration (ET) and its biophysical control and characteristics (surface conductance—Gs; decoupling coefficient—Ω; ratio between actual evapotranspiration and equilibrium evapotranspiration—ET/ETeq) in a preserved Caatinga Biome environment during two dry years in the Northeast Brazil region. A study on this subject with this level of detail in this biome is unprecedent. Measurements were carried out using an eddy covariance system during the period from 1st January 2014 to 31st December 2015. The lowest ET values were observed in the dry season of both experiment years (0.3 and 0.2 mm day−1) as a consequence of poor water availability, which favored partial stomatal closure and reduced Gs values (0.22 and 0.13 mm s−1). The opposite occurred in the wet season, when ET (2.6 and 1.7 mm day−1) and Gs (3.74 and 2.13 mm s−1) means reached higher values. Regarding annual values, differences between total annual rainfall in both years is the most probable cause for the differences observed in annual ET values. In 2014, annual ET was of 473.3 mm while in 2015 it was 283.4 mm, which incurred in an overall decrease in Gs, Ω and ET/ETeq values. Leaf senescence and extremely low Gs values during the dry season suggest that the trees of the Caatinga Biome are more resilient regarding the use of water and are avoiding water stress caused under low water availability

Spatio-temporal patterns of evapotranspiration based on upscaling eddy covariance measurements in the dryland of the North China Plain

Accurate evapotranspiration (ET) estimation is important for understanding hydrological cycle and water resources management in the cropland. Based on eight flux sites within the North China Plain (NCP) and the surrounding area, which were integrated together for the first time, we applied support vector regression method to develop ET dataset for the cropland in NCP from 1982 to 2015 with 1/12° spatial resolution and eight-day temporal interval. The mean annual ET over cropland within NCP was 575 mm yr−1 with a non-significant increasing trend. In wheat season, the seasonal ET increased significantly at the rate of 1.28 mmyr−2 with a mean value of 238 mmyr−1; in maize season, the mean value of seasonal ET was 221 mmyr−1 with a decreasing trend of −0.95 mmyr−2. The comparatively high mean annual ET values occurred primarily in the well irrigated area near the Taihang Mountains, irrigation districts along the Yellow River and the humid region. The attribution analysis which combined multiple regression with the first difference method revealed that human activities dominated ET trend at annual scale as well as in wheat season, with relative contributions of 52% and 56%, respectively. While in maize season, ET trend was mostly controlled by climate change with relative contribution of 77%. Among the climate factors, in wheat season, the significantly increasing air temperature was the principal climatic cause of ET increase which was partly offset by the significantly decreasing wind speed; while in maize season, the significant ET decline was primarily resulted from the significantly decreasing net radiation and wind speed. Compared with our ET dataset, the four widely used global or national ET datasets significantly underestimated ET in wheat season, especially in the extensively irrigated areas, suggesting that local observations are crucial for regional studies.

Relationship between Evapotranspiration and water Availability in the Tropical Regions: A Case Study of a South Western City in Nigeria

The understanding of the impacts of evapotranspiration on water supply in time and space is critical to a purposeful water management effort. A study was conducted to examine annual water balance situation in the humid tropical city of Ogbomoso, Oyo State, Nigeria. A thirty-year rainfall and temperature data (1977-2006) were collected from NIMET Office for this purpose. Annual evapotranspiration values were empirically determined using temperature data and Thornthwaite’s model. The study revealed that the major determinant of water balance is the availability of water at the surface which is majorly supplied by green surface and rainfall. Evapotranspiration rate was found to be relatively constant and high above 1000 mm annually ranging from 1249.7 mm in 1980 to 1112.87 mm in 2004 while annual rainfall total varies over the study period of 30 years ranging from 697.1 mm in 2002 to 1595.5 mm in 1998. Results showed that effort should be directed towards urban reforestation and or aforestation, planting of shade trees and other related measures that will encourage water availability for evapotranspiration process for improvement on water balance in the study area.

Biophysical regulation of evapotranspiration in semiarid croplands

Water vapor exchange is a key component in terrestrial surface water balance. However, the biophysical regulation processes that control evapotranspiration (ET) in semiarid farmland areas have not been fully resolved. In this study, seasonal and interannual variances in ET and their environmental controls from 2009 to 2011 were investigated in a semiarid, rain-fed farmland using eddy covariance. One moderately dry year (2010) and two extremely dry years (2009 and 2011) were observed; however, 2009 (an extremely dry year) had the same weather condition as that of 2010 (a moderately dry year), and 2011 set out as different from the other two years. The results indicated that the maximum daily ET in the 2009 (4.4 mm d−1) and 2010 (4.7 mm d−1) growth seasons was higher than that in 2011 (3.0 mm d−1). Cumulative annual ET values were 310.6, 318.0, and 210.2 mm in 2009 to 2011, which were 109%, 96%, and 72% of the precipitation (PPT) received, respectively. The contribution of PPT in summer to the annual ET was more than that in autumn, and the extremely dry climate during the pregrowth stage and early spring period restricted the annual ET in 2011. The lowest annual ET in 2011 was caused by low daytime ET rather than nighttime ET. The strong power relationship (R2 = 0.85) between the decoupling coefficient (Ω) and the canopy conductance (gc) indicated that ET was sensitive to gc, and gc control on ET increased as the day progressed. The physiological controls of ET were associated closely with soil moisture, and drought had a strong effect on the ET response to environmental factors, such as incoming shortwave radiation and vapor pressure deficit. These results have important potential implications for understanding and modeling water cycle feedback to the increasing drought climate in the Loess Plateau characterized by serious soil and water loss.

Lysimetric Evaluation of the APEX Model to Simulate Daily ET for Irrigated Crops in the Texas High Plains

Abstract. The NTT (Nutrient Tracking Tool) was designed to provide an opportunity for all users, including producers, to run complex simulation models, such as APEX (Agricultural Policy Environmental eXtender), with the associated required databases. The APEX model currently nested within NTT provides estimates of the changes in nitrogen (N), phosphorus (P), and sediment losses that are associated with management practices specified by the user. Five methods (Penman-Monteith, Penman, Priestley-Taylor, Hargreaves-Samani, and Baier-Robertson) for determining potential evapotranspiration (PET) are available as inputs for estimating actual ET. This study was conducted to evaluate the accuracy of the ET values obtained from the five PET equations currently available in APEX using both onsite measured climate data and data from the NTT standard databases. The mean daily, monthly, and annual ET values predicted by each of the equations in APEX for a lysimeter field at the USDA-ARS Conservation and Production Research Laboratory at Bushland, Texas, was compared to values measured for the 2001-2010 period. APEX generally underestimated ET with all PET methods (mostly during growing seasons) at both the daily and monthly levels but overpredicted for years when cotton was grown as the major cash crop due to overprediction of leaf area index during the senescing stage for cotton. The underprediction of ET in growing seasons was possibly from underprediction of rainfall due to estimation of rainfall for missing data. Overall, APEX was able to adequately (R2 = 0.82 and NSE = 0.80) predict mean monthly ET for major crops grown in the semi-arid Texas High Plains region. These results should reinforce confidence in APEX’s ability to simulate ET accurately for fully irrigated farms. ET predictions with the Hargreaves-Samani and Priestley-Taylor methods, which require limited data compared to the Penman and Penman-Monteith methods, were similar (p > 0.05, one-way ANOVA), with mean errors within 8.7% for measured weather data and 12.6% for NTT-generated weather data for both methods. This is encouraging because of the limited availability of measured climate data for the majority of locations in the world, including the U.S. Keywords: APEX, Evapotranspiration (ET), Irrigation, Lysimeters, NTT, Semiarid regions.

Evaluating Landsat 8 evapotranspiration for water use mapping in the Colorado River Basin

Abstract Evapotranspiration (ET) mapping at the Landsat spatial resolution (100 m) is essential to fully understand water use and water availability at the field scale. Water use estimates in the Colorado River Basin (CRB), which has diverse ecosystems and complex hydro-climatic regions, will be helpful to water planners and managers. Availability of Landsat 8 images, starting in 2013, provides the opportunity to map ET in the CRB to assess spatial distribution and patterns of water use. The Operational Simplified Surface Energy Balance (SSEBop) model was used with 528 Landsat 8 images to create seamless monthly and annual ET estimates at the inherent 100 m thermal band resolution. Annual ET values were summarized by land use/land cover classes. Croplands were the largest consumer of “blue” water while shrublands consumed the most “green” water. Validation using eddy covariance (EC) flux towers and water balance approaches showed good accuracy levels with R2 ranging from 0.74 to 0.95 and the Nash–Sutcliffe model efficiency coefficient ranging from 0.66 to 0.91. The root mean square error (and percent bias) ranged from 0.48 mm (13%) to 0.60 mm (22%) for daily (days of satellite overpass) ET and from 7.75 mm (2%) to 13.04 mm (35%) for monthly ET. The spatial and temporal distribution of ET indicates the utility of Landsat 8 for providing important information about ET dynamics across the landscape. Annual crop water use was estimated for five selected irrigation districts in the Lower CRB where annual ET per district ranged between 681 mm to 772 mm. Annual ET by crop type over the Maricopa Stanfield irrigation district ranged from a low of 384 mm for durum wheat to a high of 990 mm for alfalfa fields. A rainfall analysis over the five districts suggested that, on average, 69% of the annual ET was met by irrigation. Although the enhanced cloud-masking capability of Landsat 8 based on the cirrus band and utilization of the Fmask algorithm improved the removal of contaminated pixels, the ability to reliably estimate ET over clouded areas remains an important challenge. Overall, the performance of Landsat 8 based ET compared to available EC datasets and water balance estimates for a complex basin such as the CRB demonstrates the potential of using Landsat 8 for annual water use estimation at a national scale. Future efforts will focus on (a) use of consistent methodology across years, (b) integration of multiple sensors to maximize images used, and (c) employing cloud-computing platforms for large scale processing capabilities.

“ET-CALCULATOR” A NEW MODEL TO ROBUSTLY CALCULATE EVAPOTRANSPIRATION IN EGYPT

The Penman-Monteith (P-M) equation is widely recommended to calculate evapotranspiration (ET) because of its detailed theoretical base and its accommodation of small time periods. Thus, there is a need to develop a model to easily calculate ET and can be used by extension workers. The objective of this research is to use evaluate the MS Excel sheet capability to develop a program to calculate ET values in the Governorates of the Nile Delta and Valley. A model was developed called “ET-Calculator”. The model uses P-M equation to calculate ET. Weather parameters of 17 governorates in the Nile Delta and Valley were input (maximum and minimum temperature, mean of relative humidity, wind speed and solar radiation), as well as the elevation above sea level in order to calculate ET values. To test the validity of the model, the estimated ET values by ET-Calculator model were compared to the estimated ET values by BISm model. Closeness of both estimated ET values to each other was tested by Root Mean Square Error per observation (RMSE/obs) and Willmott index of agreement (d). The results indicated that ET-Calculator model estimated monthly and annual ET values in all governorates similar to the ET values estimated by BISm model, where RMSE/obs values were low and d values were high. These results implied that the presence of friendly and easy use program to calculate ET, such as ET-Calculator facilitate the calculation of water requirements for crops by extension workers and could improve the current situation of agricultural water management in Egypt.

Temporal pattern of aridity index in Iran with considering precipitation and evapotranspiration trends

AbstractThe knowledge of aridity is needed to explain landscape characteristics and the rational utilization of water resources. With global warming, an increase in aridity is expected for many parts of the world. This study was undertaken to analyse monthly and annual aridity index (IA), utilizing ratio of precipitation (P) over reference evapotranspiration (ETo), at ten stations located in critical agricultural regions in Iran. The Kendall and Spearman tests with considering serial correlation effect were used for analysis. An increase in aridity, as the P/ETo index decreased, was found during the study period, and the increase was more obvious in the semi‐arid region of Iran than in the humid region. The increase of aridity was caused by the concurrent occurrences of negative P trends and positive ETo trends. The results indicated the lowest numbers of the negative IA trends in the July series and the highest numbers in the January, February and March series. According to the Theil–Sen's estimator, the annual P of the semi‐arid and humid regions decreased at the average rates of (−)22.87 and (−)6.24 mm year−1 per decade respectively, whereas the annual ETo values in the semi‐arid and humid regions increased by (+)11.42 and (+)6.82 mm year−1 per decade, respectively. Copyright © 2012 Royal Meteorological Society

Long-Term Eddy Covariance Monitoring of Evapotranspiration and Its Environmental Factors in a Temperate Mixed Forest in Northeast China

AbstractOn the basis of eddy covariance measurements, the results of three years (2005–2007) of direct evapotranspiration (ET) measurements over a mixed temperate forest in Northeast China are presented. The diurnal and seasonal variations in ET and its main driving factors were analyzed. Annual ET values for the forest were 437, 506, and 632 mm in 2005, 2006, and 2007, respectively. The contribution of ET during the dormant season was not negligible, ranging from 17 to 23% of the annual ET for the study years. On an annual course, the increase in ET is associated with the increasing air temperature (Ta) and plant growth in late April and early May, peaking in July or August with monthly mean rates of 2.9 mm day−1 (July 2005), 3.4 mm day−1 (July 2006), and 3.8 mm day−1 (August 2007). Priestley-Taylor parameter α also varied seasonally, with its minimum and maximum values occurring in the dormant and growth seasons, respectively. During the growth season, the values of α were generally between 0.6 and 0...

A simple irrigation scheduling approach for pecans

Abstract Pecans are a major crop in New Mexico's Lower Rio Grande Valley (LRGV). It is estimated that New Mexico is responsible for about 21% of the world's pecan production ( Lillywhite et al., 2007 ). Currently, approximately 12,000 ha of pecan orchards at various stages of growth consume 45% of the area's irrigation water. Pecan evapotranspiration (ET) varies with age, canopy cover, soil type, crop density and method of water management. Intense competition for the LRGV's limited water supply has created a serious need for better water management through improved irrigation scheduling. Annual pecan ET ranges from as low as 500 mm to as high as 1400 mm. Diversity of the pecan crop coefficient ( K c ) and ET makes the task of irrigation scheduling for this crop very complicated. Using remote sensing technology and field ET measurements, a simple relationship was developed to relate crop coefficient and ET to canopy cover. This relationship is then used in combination with climate data to calculate daily and weekly water requirements for each orchard. The difference between annual ET values estimated from canopy cover and values measured with an eddy covariance flux tower ranged from 2 to 5%. The average ratio of estimated monthly ET values over measured ET values was 1.03 with the standard error of the estimate ranging from 10 to 20 mm/month. This methodology provides a simple tool that farmers can use to schedule irrigation of pecan orchards. Even though the methodology was developed for irrigation scheduling in the LRGV, it can be used in other locations by transferring the reference crop coefficients using K c –GDD relationships.

Evapotranspiration from a Mixed Deciduous Forest Ecosystem

The objectives of this paper were to determine evapotranspiration (ET) from an oak-beech dominated forest ecosystem in Belgrad Forest near Istanbul, Turkey by using catchment water balance method and compare it with potential evapotranspiration (PET) computed by using Thornthwaite method. Data, in this study, were derived from a long-term hydrological research conducted in Belgrad Forest. Long-term stream flow measurements (1979–1995) were conducted with concrete sharp-crested V-notch weirs instrumented with automatic water level recorders in two close experimental watersheds. ET values of the watersheds were determined by using water balance equation. Average annual ET values from the old growth oak-beech forest ecosystem during the monitoring period of 17 years were around 833.20 mm for W-I and 752.07 mm for W-IV whereas PET estimated according to Thornthwaite method was found to be 726.14 mm. In other words, 79.68%, and 71.93% of mean annual precipitation evaporated from W-I and W-IV, respectively while 69.45% of precipitation evaporated according to Thornthwaite method. PET estimated with Thornthwaite method differed significantly only from W-I whereas W-I and W-IV had similar ET values.

Impact and consequences of evapotranspiration changes on water resources availability in the arid Zhangye Basin, China

Evapotranspiration (ET) plays an important role in the hydrological cycle and it is essential to estimate ET accurately for the evaluation of available water resources. This is most important in arid and semi‐arid regions. In this paper, the long‐term changes in daily ET in the semi‐arid Zhangye Basin in northwest China and its impact factors were studied. The spatial distribution of ET was assessed by using the Surface Energy Balance System (SEBS). Cloud‐free National Oceanic and Atmospheric Administration Advanced (NOAA) Very High Resolution Radiometer (AVHRR) September images over the Zhangye Basin from 1990 to 2004 were used in combination with SEBS to estimate ET at a spatial resolution of 1.1 km. This daily ET was converted to a monthly ET (for September) using daily pan evaporation values from a meteorological station in the study area. Spatial aggregation of all pixels yielded the total monthly ET for the whole study area. Subsequently, the monthly ET was extrapolated to annual ET values using the pan evaporation data. The results were validated with ground‐based measurements on the water balance for the whole Zhangye Basin. The annual ET increased gradually from 23.7×108 m3 in 1990 to 26.9×108 m3 in 2004 for the Zhangye Basin. The main cause appeared to be change in vegetation.

Evapotranspiração e coeficientes de cultivo de cafeeiros em fase de formação

A quantificação do consumo hídrico das culturas é fundamental para diversas aplicações na agricultura. Neste estudo, lisímetros de pesagem instalados em Londrina (PR), foram usados para determinar a evapotranspiração (ET) de cafeeiros da cultivar IAPAR 59, não irrigado e irrigado por aspersão e gotejamento, durante dois anos após a implantação da lavoura. O coeficiente de cultivo (Kc) foi obtido nos tratamentos irrigados a partir da razão entre ET e a evapotranspiração de referência (ETo) estimada pelo método Penman-Monteith. Os valores de ET e Kc dos tratamentos analisados variaram em função do método de irrigação, frequência de chuvas, demanda da atmosfera e evolução da área foliar. O tratamento irrigado por aspersão foi aquele com os maiores valores médios anuais de ET (3,1 e 3,4 mm dia-1 para o primeiro e segundo ano, respectivamente), seguido do gotejamento (2,9 mm dia-1 para o segundo ano) e do não-irrigado (2,2 e 2,5 mm dia-1 para o primeiro e segundo ano, respectivamente). O valor médio anual de Kc foi maior para o tratamento irrigado por aspersão (0,99 e 1,03 para o primeiro e segundo ano, respectivamente) e menor para o irrigado por gotejamento (0,92 para o segundo ano).

An integrated hydrological and meteorological approach for the simulation of terrestrial evapotranspiration / Une approche hydrologique et météorologique intégrée pour la simulation de l'évapotranspiration terrestre

Terrestrial evapotranspiration (ET) plays an important role in determining water and heat balances in the water cycle between the land surface and the atmosphere. In the present research a dynamic approach is developed to simulate actual ET distribution for large-scale spatial and temporal scales based on an integration of meteorological and hydrological methods. The method developed has been used to examine the impacts of climate change, complex land cover features, and soil moisture on actual ET. The distribution characteristics of actual ET demonstrate that ET in eastern China is greater than that in western China, and that ET is greater in low-latitude regions of China than in high-latitude regions. Actual monthly and annual ET values in most regions show an increasing tendency from the year 1991 to 2000, especially in arid and semi-arid regions. The results of the present study also confirm that soil moisture is one of the critical factors that affect regional ET in China. It is demonstrated that the integrated hydrological-meteorological approach is effective for simulating actual ET on large spatial and temporal scales.