Evapotranspiration Measurements Research Articles

Estimating the value of satellite-derived measurements of evapotranspiration to inform irrigation scheduling in California almond orchards

Estimating the value of satellite-derived measurements of evapotranspiration to inform irrigation scheduling in California almond orchards

A review on models, products and techniques for evapotranspiration measurement, estimation, and validation

AbstractIn this review study, the major available methods for measurement and estimation of evapotranspiration (ET) are discussed briefly while explaining the latest developments. The best available validation methods are also reviewed and explained. It highlights the importance of accurate ET quantification in managing water resources, evaluating climate change impacts, and supporting crop water requirement management. Measurement methods such as scintillometry, lysimetry, and the eddy covariance (EC) flux method are presented. Additionally, hydrological models are discussed as estimation approaches for actual and potential ET. The paper explores various ET estimation products, particularly those based on remote sensing techniques. Specifically, methods like Mapping EvapoTranspiration at high Resolution with Internalized Calibration (METRIC), Simplified Surface Energy Balance Operational (SSEBop ET), Moderate Resolution Imaging Spectroradiometer (MOD16), Surface Energy Balance Algorithm for Land (SEBAL), Global Land Surface Evaporation: Amsterdam Methodology (GLEAM), Satellite Application Facility on Land Surface Analysis (LSA‐SAF), and Global Land Data Assimilation System (GLDAS) are described. The integration of machine learning (ML) with EC and remote sensing is investigated, with a comprehensive discussion of different ML approaches. Validation methods including the EC method, water balance method‐derived ET (WBET), and statistical techniques are explained. Overall, this review paper provides a comprehensive overview of ET quantification, covering measurement techniques, estimation approaches, remote sensing methods, and the integration of ML. The insights gained from this review contribute to a profound knowledge of ET dynamics and helps those sectors dealing with drought monitoring, water resource management and climate change assessments.

Actual and reference evapotranspiration for a natural, temperate zone fen wetland – Upper Biebrza case study

Evapotranspiration is the key and predominant component of the water balance in wetlands. Direct evapotranspiration measurements are challenging in wetlands due to their remoteness and high surface water level. This article describes the actual (ETa and reference evapotranspiration (ET0) from a cultivated wet meadow located in the Biebrza National Park – the largest national park in north-east Poland, Central Europe. The data were sourced from a micrometeorological station equipped with an eddy covariance system to measure heat and vapour fluxes and such meteorological elements as radiation balance components, air temperature and humidity. The values of directly measured ETa were presented daily in the context of available energy and ET0. Daily sums of ETa ranged from below 0.2 mm in winter to 6.5 mm in summer. The share of daily sums of ETa in the ET0 usually ranged from 50 to 60%, with extreme values from 10 to 170%. Aside from giving more insight into Biebrza wetlands’ functioning, the actual data produced in this study may be used instead of indirect methods, which were used the most in modelling wetlands areas.

Improved 30‐m Evapotranspiration Estimates Over 145 Eddy Covariance Sites in the Contiguous United States: The Role of ECOSTRESS, Harmonized Landsat Sentinel‐2 Imagery, Climate Reanalysis, and Deep Neural Network Postprocessing

AbstractThis study developed and evaluated 30‐m daily evapotranspiration (ET) estimates using the Priestley‐Taylor Jet Propulsion Laboratory (PT‐JPL) model with ECOSTRESS, Moderate MODIS, harmonized Landsat Sentinel‐2 (HLS) imagery, ERA5‐Land reanalysis, and eddy covariance measurements. The new daily 30‐m ET showed significantly improved performance (overall, r = 0.8, RMSE = 1.736, KGE = 0.466) at 145 EC sites over contiguous United States compared to the current 70‐m ECOSTRESS ET (overall, r = 0.485, RMSE = 4.696, KGE = −0.841). A deep neural network postprocessing model trained with ET measurements from EC sites further improved the performance on test sites that were not used for model training (overall, r = 0.842, RMSE = 0.88, KGE = 0.792). The 30‐m ET estimation biases were significantly related to the biases in the upwelling longwave (RUL) and downwelling shortwave radiation (RDS) inputs, with ET estimates driven by MODIS radiation showing higher biases compared to those driven by ERA5‐Land radiation. The error diagnosis using random forest indicates that ET biases tend to be larger under higher ET estimates, and RUL and RDS were the primary contributors to the high bias at the higher ET ranges, with partial dependence plots revealing that the estimation biases tend to be higher under more humid environment, denser vegetation covers, and high net radiation conditions. In conclusion, higher spatial resolution satellite imagery of vegetation characteristics and higher temporal resolution radiation data, combined with continent‐wide EC measurements and deep learning, provided substantial added value for improving ET estimations at the field scale (30‐m).

Measurement and estimation of evapotranspiration in a maize field: A new method based on an analytical water flux model

Quantifying evapotranspiration (ET) in rainfed cropping systems can be challenging due to complicated interactions among site-specific soil, plant, and management factors. In Northeast China, ET and soil water status in maize fields often display strong spatial and temporal variations due to the changes in tillage practice, planting pattern, and maize plant density. Previous studies have shown that near-surface soil water content (θ) observations at multiple scales provide the potential to estimate surface soil water fluxes. In this study, we introduced a new method to estimate daily field ET by using a soil water flux model mainly based on the time-series of θ at a depth of 2.5 cm. The new method required a calibration of soil water diffusivity with maximum net water flux in the near-surface soil layer, which was related to precipitation redistribution below the canopy. Finally, the new method was evaluated using observed ET values over a 2-year period in a maize field, where independent measurements of soil water evaporation (E) and transpiration (T) were made with heat-pulse sensors and sap-flow gauges, respectively. Field observations showed that E dominated water loss during the seedling stage (16% of total ET). As the canopy was fully developed, E sharply decreased to a value of 0.4 mm d−1, and T accounted for about 89% of ET since the silking stage. The new method to estimate ET performed well in drying periods, while it tended to underestimate ET in wet periods with substantial infiltration into the surface layer. On rain-free days, the ET values estimated with the new method matched well with the measured E+T values, with R2 and RMSE values of 0.85 and 1.93 mm d−1. Therefore, the new approach provides an effective way to quantify maize ET.

Validation and field application of a low-cost device to measure CO2 and evapotranspiration (ET) fluxes

Abstract. Mitigating the global climate crisis and its consequences, such as more frequent and severe droughts, is one of the major challenges for future agriculture. Therefore, identifying land use systems and management practices that reduce greenhouse gas (GHG) emissions and promote water use efficiency (WUE) is crucial. This, however, requires accurate and precise measurements of carbon dioxide (CO2) fluxes and evapotranspiration (ET). Despite that, commercial systems to measure CO2 and ET fluxes are expensive and thus often exclude research in ecosystems within the Global South. This is especially true for research and data of agroecosystems in these areas, which are to date still widely underrepresented. Here, we present a newly developed low-cost, non-dispersive infrared (NDIR)-based CO2 and ET flux measurement device (∼ EUR 200) that provides reliable, accurate and precise CO2 and ET flux measurements in conjunction with manually operated closed chambers. To validate the system, laboratory and field validation experiments were performed, testing multiple different low-cost sensors. We demonstrate that the system delivers accurate and precise CO2 and ET flux measurements using the K30 FR NDIR (CO2) and SHT31 (RH, relative humidity) sensor. An additional field trial application demonstrated its longer-term stability (> 3 months) and ability to obtain valid net ecosystem C balances (NECBs) and WUE. This was the case, even though environmental conditions at the field trial application site in sub-Saharan Africa were rather challenging (e.g., extremely high temperatures, humidity and rainfall). Consequently, the developed low-cost CO2 and ET flux measurement device not only provides reasonable results but also might help with democratizing science and closing current data gaps.

2017–2019年宁夏兰山骄子葡萄园日蒸散发观测数据集

The grapevine is one of important economic crops. Accurate measurements of daily grapevine evapotranspiration (ET) measurements are essential for improving the understanding of crop water demand and optimizing water consumption efficiency. Unfortunately, there is a relative scarcity of daily grapevine ET values in China. This dataset presents daily ET values obtained through using the Bowen ratio energy balance method and the surface renewal method in Lanshan Jiaozi Vineyard on the outskirts of Yinchuan City, spanning the period from 2017 to 2019. Abnormal Bowen ratio values have been removed during the estimation of ET and the quality of each daily ET measurement has been thoroughly assessed. The dataset is freely available, with the primary goal of establishing a foundation for the efficient use of agriculture water resources. Additionally, it is aimed to assess the applicability of the surface renewal method in a highly heterogonous vineyard.

Changes in evapotranspiration, transpiration and evaporation across natural and managed landscapes in the Amazon, Cerrado and Pantanal biomes

Land-use and land-cover change (LULCC) can dramatically affect the magnitude, seasonality and main drivers of evaporation (E) and transpiration (T), together as evapotranspiration (ET), with effects on overall ecosystem function, as well as both the hydrological cycle and climate system at multiple scales. Our understanding of tropical ecosystem responses to LULCC and global change processes is still limited, mainly due to a lack of ground-based observations that cover a variety of ecosystems, land-uses and land-covers. In this study, we used a network of nine eddy covariance flux towers installed in natural (forest, savanna, wetland) and managed systems (rainfed and irrigated cropland, pastureland) to explore how LULCC affects ET and its components in the Amazon, Cerrado and Pantanal biomes. At each site, tower-based ET measurements were partitioned into T and E to investigate how these fluxes varied between different land-uses and seasons. We found that ET, T and E decreased significantly during the dry season, except in Amazon forest ecosystems where T rates were maintained throughout the year. In contrast to Amazon forests, Cerrado and Pantanal ecosystems showed stronger stomatal control during the dry season. Cropland and pasture sites had lower ET and T compared to native vegetation in all biomes, but E was greater in Pantanal pasture when compared to Pantanal forest. The T fraction of ET was correlated with LAI and EVI, but relationships were weaker in Amazon forests. Our results highlight the importance of understanding the effects of LULCC on water fluxes in tropical ecosystems, and the implications for climate change mitigation policies and land management.

Using foliar δ13C from high‐Andean plants (Silala River basin) as a measure of potential evapotranspiration through water use efficiency

AbstractThe water‐dependent nature of arid ecosystems is closely related to the coupling between energy input through photosynthesis and the loss of water through transpiration (Tr), which can be expressed as water use efficiency (WUE). The relationship, however, between environmental factors and plant physiology in controlling evapotranspiration is not well understood in high‐altitude arid environments. Here, we review the use of carbon isotope fractionation (δ13C) to indirectly track fluctuations in WUE and the use of the portable chamber method to partition landscape actual evapotranspiration (ETa) into Tr and bare soil evaporation (Ebs) in the alluvial deposits of the Silala River, a high elevation watershed located in northern Chile. Landscape ETa was also measured with Eddy covariance (EC) systems in the basin's riparian wetland and alluvial hillslope deposits. Carbon isotope results were consistent with what is known from the literature regarding these high‐elevation ecosystems. WUE, as estimated by carbon isotope discrimination values, decreased in summer (the wet season), and increased in winter at all sites. These results were consistent with the EC measurements. Changes in WUE were much greater in the valley wetlands than along the hillslopes, most likely due to a large drop in available soil moisture along the valley bottom during the dry season. Portable chamber results obtained during summer and winter field campaigns showed that at the landscape scale, hillslope ETa was mainly dominated by bare soil evaporation; and ETa partitioning into Tr and Ebs had a seasonal change.This article is categorized under: Engineering Water > Methods Science of Water > Hydrological Processes

Comprehensive accuracy assessment of long-term geostationary SEVIRI-MSG evapotranspiration estimates across Europe

This study quantifies the accuracy of evapotranspiration (ET) estimates from the Spinning Enhanced Visible and Infrared Imager (SEVIRI) geostationary sensor onboard the Meteosat Second Generation (MSG) satellites, along seven key dimensions, i.e., diurnal cycle, daily, intra-annual, inter-annual, ecosystem, climate zone, and products intercomparison. In situ measurements were collected at 54 eddy covariance (EC) sites to evaluate the accuracy of SEVIRI actual ET products (diurnal and daily SEVIRI-ETa) as well as reference ET (daily SEVIRI-ET0) covering the period from 2004 to 2018 across Europe. SEVIRI-ETa is produced by the Tiled ECMWF Surface Scheme of Exchange processes at the Land surface (TESSEL) model, while SEVIRI-ET0 is estimated by a combination of a thermodynamically-based and an atmospheric boundary layer model. This evaluation is further separated according to the land cover heterogeneity of the SEVIRI pixels across all 54 EC sites, using MODIS land cover data. The Root Mean Squared Error (RMSE), along with the Kling-Gupta efficiency (KGE) and their respective decompositions, were employed to quantify the errors.For diurnal SEVIRI-ETa estimates, we found that the KGE (RMSE [mm hour−1]) varied between −1.6 (0.04) to 0.8 (0.14), with a median value of 0.26 (0.07). Higher accuracy for diurnal SEVIRI-ETa was obtained in the summer and during the mid-day time. For daily SEVIRI-ETa, the KGE (RMSE [mm day−1]) varied between −0.88 (0.43) to 0.93 (1.79), with a median value of 0.6 (0.77) and for daily SEVIRI-ET0 the KGE (RMSE [mm day−1]) varied between 0.51 (0.40) to 0.94 (1.50), with a median value of 0.77 (0.57). For daily SEVIRI-ETa, intra-annual accuracy was low from January to March, increased in the mid-year, and then began to decline from November to December. Although accuracy remained relatively stable during the middle of the year, it varied considerably in the winter period. In the inter-annual dimension, the mid-year positive KGE values and distributions changed over time from 2004 to 2018. In spatial dimensions, the highest accuracy was in peat and grassland ecosystems, and the lowest in cropland ecosystem, with similar patterns observed in the boreal snow fully humid warm summer and warm temperate fully humid hot summer climate zones. Regarding SEVIRI-ET0 results, similar to SEVIRI-ETa, intra-annual accuracy was low in the first quarter of the year and the last one but high in the mid-year. In the inter-annual dimension, unlike SEVIRI-ETa, almost an identical pattern was observed for the mid-year positive KGE values, demonstrating only a slight change in SEVIRI-ET0 accuracy during 2004–2018. However, the highest accuracy was found in crop ecosystem, while the lowest was in forest ecosystem, reflecting similar trends in the warm temperate fully humid hot summer and warm temperate summer dry hot summer climate zones. The observed range of median RMSE changed between 0.4 and 1.5 mm day−1, also suggests a reasonable accuracy for SEVIRI-ET estimates in all spatial domains.Our results showed that the main trends in the accuracies (median KGEs) of SEVIRI-ET (both ETa and ET0) remained similar in separated homogeneous and heterogeneous sites and were comparable to combined sites among the dimensions. Through error decomposition, we discerned that SEVIRI-ET estimates performed particularly well in explaining inter-annual and spatial variabilities. Furthermore, the intercomparison of ET products revealed that SEVIRI satellite-derived ETa exhibited the strongest correlation with in situ ET measurements across all ecosystem types and climate zones, outperforming other products (such as MODIS, PML, GLEAM, and BESS). The ET estimates from other products exhibited lower standard deviation errors and were in closer agreement with the in situ measurements. This study provides the first comprehensive evaluation of the accuracy of SEVIRI diurnal and daily ET products across Europe, which may serve as a stimulus for further optimized selection of these products by potential users for various applications.

Estimation of crop evapotranspiration and crop coefficient for coriander using Portable Automatic Closed Canopy Chamber

An experiment was carried out to determine crop evapotranspiration and crop coefficient of Coriander crop by using Portable Automatic Closed Canopy Chamber (PACCC), Micro-Lysimeter (MLs) and field water balance (FWB) methods. The results revealed that there was no significant difference in the coriander crop evapotranspiration measured by the MLs inside and outside the PACCC and no significant difference among the crop evapotranspiration measured by the PACCC, MLs and FWB at 95 percent confidence level was found. It is indicating that, there are no effects of the change in micro-climate for a short period of 2 minutes in the chamber and on the plant physiological processes. During validation of PACCC, the average crop coefficients measured by MLs were varied from 0.66 to 1.26 for coriander crop. However, the stage wise crop coefficients of corianders measured by FWB were varied from 0.67 to 1.28 during field testing of PACCC. The result showed that the PACCC can be used for measurement of crop evapotranspiration in the field condition.

Calibration and validation of solar radiation-based equations to estimate crop evapotranspiration in a semi-arid climate

The Abtew and Jensen-Haise solar radiation-based equations were used to estimate evapotranspiration, considering the limited climatic data in many locations. Both equations were proven to successfully predict the potential evapotranspiration (ETO) compared with the standard Penman–Monteith (PM) method in two Mediterranean countries. Calibration of the constant coefficient k of the Abtew equation showed substantial differences compared to recommended values (1.22 vs. 0.53), with the highest values observed during September (1.46). Validation of ETO measurements using calibrated Abtew equation against the PM method indicated a high correlation coefficient (r2 = 0.97, RMSE = 0.61). Further, evapotranspiration requirements, using the calibrated empirical equation, were calculated for olives (449 mm) and citrus (807 mm) showing a good agreement with recommended values for dry climate regions. Therefore, the tested equations could be safely used to predict frequencies and doses of irrigation in semi-arid climates, considering limited climatic data availability.

Using Ensembles of Machine Learning Techniques to Predict Reference Evapotranspiration (ET0) Using Limited Meteorological Data

To maximize crop production, reference evapotranspiration (ET0) measurement is crucial for managing water resources and planning crop water needs. The FAO-PM56 method is recommended globally for estimating ET0 and evaluating alternative methods due to its extensive theoretical foundation. Numerous meteorological parameters, needed for ET0 estimation, are difficult to obtain in developing countries. Therefore, alternative ways to estimate ET0 using fewer climatic data are of critical importance. To estimate ET0 with alternative methods, difference climatic parameters of temperatures, relative humidity (maximum and minimum), sunshine hours, and wind speed for a period of 20 years from 1996 to 2015 were used in the study. The data were recorded by 11 meteorological observatories situated in various climatic regions of Pakistan. The significance of the climatic parameters used was evaluated using sensitivity analysis. The machine learning techniques of single decision tree (SDT), tree boost (TB) and decision tree forest (DTF) were used to perform sensitivity analysis. The outcomes indicated that DTF-based models estimated ET0 with higher accuracy and fewer climatic variables as compared to other ML techniques used in the study. The DTF technique, with Model 15 as input, outperformed other techniques for the most part of the performance metrics (i.e., NSE = 0.93, R2 = 0.96 and RMSE = 0.48 mm/month). The results indicated that the DTF with fewer climatic variables of mean relative humidity, wind speed and minimum temperature could estimate ET0 accurately and outperformed other ML techniques. Additionally, a non-linear ensemble (NLE) of ML techniques was further used to estimate ET0 using the best input combination (i.e., Model 15). It was seen that the applied non-linear ensemble (NLE) approach enhanced modelling accuracy as compared to a stand-alone application of ML techniques (R2 Multan = 0.97, R2 Skardu = 0.99, R2 ISB = 0.98, R2 Bahawalpur = 0.98 etc.). The study results affirmed the use of an ensemble model for ET0 estimation and suggest applying it in other parts of the world to validate model performance.

Evaluation of the storage and evapotranspiration terms of the water budget for an agricultural watershed using local and remote-sensing measurements

The understanding of the water budget components, especially evapotranspiration and the amount of water stored in the watershed, is key to water resources management and hydrological modeling in general. In this work, we present the analysis of 13 hydrological years’ measurements of discharge, precipitation, evapotranspiration, and soil moisture over two agricultural watersheds in Eastern Nebraska, United States. These data were used to investigate several facets of the hydrological water budget: water- and energy-balance closures, water budget residues (here, the water budget residue is the remaining imbalance after all water budget terms have been considered; see Eq. (13)), storage in the unsaturated and saturated soil layers, and the evapotranspiration derived from the water budget. Remote-sensing data were also used to assess the spatial variability of net radiation and soil moisture over the basins. Adjusting the eddy-covariance measured evapotranspiration to close the energy budget agreed, in the long term, with the water budget evapotranspiration estimates. The evapotranspiration estimated with storage calculated with soil moisture measurements and recession analysis presented the best agreement with the (adjusted) measured evapotranspiration, but considering only either the vadose zone or the saturated zone for storage estimates still produced reasonable results. We found considerable variability in soil moisture over the basins in the final period of the growing season, coinciding with the time of the year when water budget residues were largest.

Satellite-based assessment of water use and leaf area efficiencies of dryland conifer forests along an aridity gradient

Dryland forests worldwide are increasingly threatened by drought stress due to climate change. Understanding the relationships between forest structure and function is essential for managing dryland forests to adapt to these changes. We investigated the structure-function relationships in four dryland conifer forests distributed along a semiarid to subhumid climatic aridity gradient. Forest structure was represented by leaf area index (LAI) and function by gross primary productivity (GPP), evapotranspiration (ET), and the derived efficiencies of water use (WUE = GPP/ET) and leaf area (LAE = GPP/LAI). Estimates of GPP and ET were based on the observed relationships between high-resolution vegetation indices from VENμS and Sentinel-2A satellites and flux data from three eddy covariance towers in the study regions between November 2015 to October 2018. The red-edge-based MERIS Terrestrial Chlorophyll Index (MTCI) from VENμS and Sentinel-2A showed strong correlations to flux tower GPP and ET measurements for the three sites (R2cal > 0.91, R2val > 0.84). Using our approach, we showed that as LAI decreased with decreasing aridity index (AI) (i.e., dryer conditions), estimated GPP and ET decreased (R2 > 0.8 to LAI), while WUE (R2 = 0.68 to LAI) and LAE increased. The observed global-scale patterns are associated with a variety of forest vegetation characteristics, at the local scale, such as tree species composition and density. However, our results point towards a canopy-level mechanism, where the ecosystem-LAI and resultant proportion of sun-exposed vs. shaded leaves are primary determinants of WUE and LAE along the studied climatic aridity gradient. This work demonstrates the importance of high-resolution (spatially and spectrally) remote sensing data conjugated with flux tower data for monitoring dryland forests and understanding the intricate structure-function interactions in their response to drying conditions.

Remote sensing of daily evapotranspiration and gross primary productivity of four forest ecosystems in East Asia using satellite multi-channel passive microwave measurements

Satellite multi-channel passive microwave observations provide valuable information of canopy vertical structure and vegetation water content, while their potential in the simultaneous estimation of forest evapotranspiration (ET) and gross primary productivity (GPP) has not been explored. This study combined satellite multi-channel microwave Emissivity Difference Vegetation Indices (EDVIs) from 6.9 to 36.5 GHz with the Penman-Monteith (PM), Priestley-Taylor (PT) and light use efficiency (LUE) models to estimate daily ET and GPP over four forest ecosystems in East Asia. In-situ measurements of daily ET, GPP and meteorological variables from ChinaFLUX network (2003 to 2010) were used to calculate and validate the method. An exponential relationship was found between EDVIs and canopy conductance across the forests. By inverting EDVIs-based LUE model coupled with PM and PT models when canopy carbon uptake and water content reached a maximum in growing seasons, the maximum LUE (EDVI-LUEmax) was derived and found to agree with other independent studies. Site validations showed that the EDVI-based method performed a good simultaneous estimation of daily ET and GPP at a tropical forest and three sub-tropical and temperate forests (R2 of 0.64 to 0.94 and RMSE of −11.7% to 19.6% for ET, R2 of 0.39 to 0.73 and RMSE of 31.2% to 50.4% for GPP). The modeled relationship between GPP and ET also agreed that from in-situ measurements. The results were also found to correlate with microwave frequencies. In-situ ET and GPP showed a stronger correlation with EDVI at 18.7 and 36.5 GHz than that at 10.7 and 18.7 GHz across the forests. EDVI-LUEmax of a temperate mixed forest increased as EDVI incorporated lower frequency microwave emissions from deeper canopy layers, which reduced the negative bias in GPP estimation. Overall, this study demonstrated the potential of multi-channel microwave measurements in estimating ET and GPP with the potential effects of vegetation vertical structure.

A review of the Artificial Intelligence (AI) based techniques for estimating reference evapotranspiration: Current trends and future perspectives

Reference Evapotranspiration (ETo) is a complex, dynamic and non-linear hydrological process. Accurate estimation of ETo has long been an eminent topic of interest in the research community for its importance in effective planning and sustainable water resource management. Although the FAO-56 Penman-Monteith (PM) equation has been accepted as a standard equation for ETo measurement, the primary concern that inhibits the applicability of this equation is the requirement for all the climatological variables, which might not be available at a given location. Owning to the remarkable success and accuracy achieved by Artificial Intelligence (AI) in almost every sphere, scientists have proposed the usage AI models for ETo prediction as an alternate to the conventional methods. This comprehensive review will serve to raise awareness regarding the various state-of-the-art standalone AI frameworks, along with capturing the intriguing developments in the advanced AI space such as the hybrid and ensemble models, evolutionary models and a range of optimization techniques. The results from the publications published over the last 15 years (2007–2022) for ETo prediction using AI under varied agro-climatic scenarios have been analysed and synthesized. The advantages and disadvantages of the established AI techniques have been discussed in each subsection. Some of the derived insights and major findings are discussed along with the future research recommendations. This review will not only provide a research vision for the novice researchers in the applicability of the aforementioned techniques, in context of ETo prediction, but also be helpful as a compilation of the AI modelling studies for ETo prediction for the established water resource engineers and hydrologists.

Grain for Green Project May Not Threaten Ecosystem Sustainability by Degrading Water Availability in Humid Karst Landscapes

AbstractGrain for Green project could result in high evapotranspiration (ET), exacerbate water shortage, and intensify conflicts in water demand between ecosystems and humans in many water‐limited areas. However, it is still unclear how vegetation restoration would influence ET in humid karst regions where abundant precipitation but quick leakage. Particularly, it is challenging that existing ET measurement methods are not applicable simultaneously for various ecosystems in such highly heterogeneous and fragmented landscapes. To solve this issue, this study, for the first time, develops a new ET measurement system, by integrating multi‐techniques, to quantify ET for multiple vegetation restoration types and identify their controlling factors in a humid karst region for three consecutive years. The results show that (a) for different succession stages during natural restoration, the ET of secondary forest (680 ± 7 mm yr−1) > shrub (564 ± 16 mm yr−1) > grass (546 ± 12 mm yr−1) > cropland (513 ± 8 mm yr−1) (P < 0.05); (b) ET of all ecosystems are far less than that of precipitation (1,059 ± 63 mm yr−1) but closer to potential ET (849 ± 11 mm yr−1), and soil moisture has been maintained at >0.20 cm3cm−3 in the growing season; (c) solar radiation and vapor pressure deficit are the two predominant factors on the ET (P < 0.01), while there is no significant relationship between ET and soil moisture (P > 0.05). The results suggest that vegetation restoration returned from cropland in humid karst regions increased ET but may not induce water scarcity for vegetation sustainability, at least under normal climatic conditions.

Stress coefficients for hybrid bermudagrass in the transition zone

AbstractThe use of drought tolerant turfgrass cultivars is desirable due to greater water use efficiency and sustained acceptable turfgrass quality during times of drought stress. Crop coefficients (Kc) have traditionally been utilized to assist in reducing irrigation by comparing reference evapotranspiration (ETo) to actual evapotranspiration (ETa) of specific crops. However, Kc values are most relevant during times of nonlimiting conditions and do not quantify the amount turfgrasses restrict evapotranspiration (ET) under moderate drought stress. Stress coefficients (Ks) estimate water needs while maintaining minimally acceptable turfgrass quality. The objective of this study was to derive Ks values for four bermudagrass (Cynodon spp.) cultivars managed in the transition zone. Direct measurements of actual evapotranspiration were made through weighing lysimetry during a 2‐year field study. Experimental units were allowed to naturally dry down near wilting point and maintained at a steady level of soil moisture to calculate Ks for each cultivar. A lower Ks value indicates increased turfgrass tolerance to water stress; whereas a Ks value ≥1 suggests higher soil moisture levels are required to sustain turfgrass quality. ‘TifTuf’, ‘Latitude 36’ and ‘Tifway’ were the best performing cultivars with mean Ks values of 0.747, 0.766, and 0.796, respectively. ‘Celebration’ had the highest Ks value of 0.944. The results indicate certain bermudagrass cultivars can maintain quality with less soil water, and the reduced water requirements may be used to schedule efficient irrigation applications.

Measurement of actual evapotranspiration in a páramo ecosystem using portable closed chambers: Comparison between giant rosettes, tussock grasses and shrubs

AbstractThe páramos are Neotropical alpine tundra‐like ecosystems that play a crucial role as biodiversity hotspots and also act as water sources for the inter‐Andean regions and cities. Improving our understanding of hydrological processes, here evapotranspiration, is crucial, especially in the context of global changes. In páramos, most research have focused on estimating potential evapotranspiration (ETo) using the Penman–Monteith method. Only a few studies have quantified actual evapotranspiration using mostly the Eddy covariance method (EC) or volumetric lysimeters. Importantly, these studies focused only on tussock grass communities, and none have addressed the effect of other plant communities specific to páramos on the actual evapotranspiration of this ecosystem. In this research, portable closed chambers were installed for the first time in a páramo (in Los Nevados National Park, between 3900 and 4100 masl) to quantify actual evapotranspration (ETa) in March and May 2019 in three representative plant communities of the páramo (giant rosettes, shrubs and tussock grasses). The ETa rates measured were then compared with ETo estimated using the Penman–Monteith method. Also, environmental factors of solar radiation, temperature and relative humidity were recorded and their influence on ETa variation was analysed. Our results indicate that ETa daily rates were very low with a high daily variation (0.290 ± 0.266 mm day−1). The shrubs showed higher ETa rates even though differences among communities were not significant. ETo rates calculated via the Penman–Monteith method were significantly higher (1.017 ± 0.468 mm day−1) than those measured using the portable chambers. Portable closed chamber is a promising method to assess ETa at small spatial and time scales and under controlled environment; however, they should be improved to enable ETa measurements on longer time periods. This study confirms the highly variable and low evapotranspiration rate of the páramo vegetation, here confirmed across different plant communities and underlines the importance of solar radiation and temperature, which were positively correlated with evapotranspiration rates.