Daily Evapotranspiration Rates Research Articles

Application of surface energy balance Algorithm for land (SEBAL) for mapping spatiotemporal evapotranspiration over various climatic zones of Pakistan

To address the emerging issues of water scarcity in a hydrological realm, estimation of evapotranspiration (ET) at spatiotemporal scale is essential. It is crucial for understanding climate change, particularly for Pakistan's ongoing water resource management policy under the United Nations' Sustainable Development Goals (SDGs), where water is given top priority. In situ techniques can quantify ET, but with a small spatial footprint, it cannot accurately depict its regional distribution. Therefore, geospatial techniques and data, especially high resolution satellite imagery, estimate ET for large heterogeneous surfaces. The Surface Energy Balance Algorithm for Land (SEBAL) was employed in this study to estimate the spatiotemporal distribution of ET in various climatic zones of Pakistan using Landsat 8 images. A total of 48 satellite images were processed for six study sites (Skardu, Kalam, Peshawar, D.I. Khan, Quetta and Tando Jam) for the summer months from 2013 to 2020. Accuracy of SEBAL-based ET was evaluated with ground-based ET. The model performs well with daily rate of ET under southern desert hot climate of Tando Jam with highest pearson’s correlation coefficient (r) of 0.89, lowest root mean squared difference (RMSD) and mean bias error (MBE) of 0.42 mm/day and 0.26 mm/day, respectively. The steppe-hot and extremely humid climate of Peshawar follow Tando Jam, with r value of 0.82, RMSD value of 0.76 mm/day, and MBE value of 0.40 mm/day. Central desert hot climate of Dera Ismail Khan(D.I. Khan) has the lowest (though still better) r value at 0.74, while the other two indices (RMSD and MBE) do not differ significantly from other sites. A high RMSD (0.84 mm/day) for the daily ET rate is recorded in Skardu's northern, cold, snowy climate; the rest of the indices are comparable to D.I. Khan region. In Kalam, the ET rate for various land uses was calculated and was found highest for snow cover (4.66 to 6.45 mm/day), followed by forest cover (3.69 to 5.79 mm/day), and open water body (3.25 to 5.25 mm/day). The SEBAL model exhibitedtremendous potential to be applied under a range of climatic conditionsin this study. Evapotranspiration can provide vital information for monitoring hydrological extremes (droughts and floods), environmental protection, planning climate-resilient agriculture, combating climate change, and sustainable management of water resources.

Influence of vegetation type and climatological conditions on evapotranspiration from extensive green roofs

Evapotranspiration (ET) is the key hydrologic process governing the capacity of a green roof to retain rainfall as it regenerates available water storage space in the green roof substrate (soil) between rainfall events. In this field study, the impact of climatological conditions, vegetation type, and substrate depth on ET rates were evaluated from experimental, modular extensive green roofs installed in three climate regions in Canada: Calgary AB (Prairies), London ON (Great Lakes/St. Lawrence), and Halifax NS (Atlantic/ Maritime). Daily ET rates and cumulative ET over two field seasons were quantified for two substrate depths (10 and 15 cm), substrate only treatments (no vegetation), and four vegetation treatments (monoculture treatments of Sedum spurium, Sporobolus heterolepis, and Aquilegia canadensis, and a mixed species treatment consisting of the three aforementioned species). 73 %, 67 % and 33 % of the cumulative rainfall was returned to the atmosphere via ET over the two field seasons in Calgary, London and Halifax, respectively. Importantly, ET rates were shown to be a strong function of substrate moisture content as well as atmospheric forcing with the relative importance of each varying between the different cities. ET rates were typically greater in the mixed species treatment in comparison to the three monoculture treatments (Sedum spurium, Sporobolus heterolepis, and Aquilegia canadensis) and for deeper substrate depths, although ET rate enhancement with substrate depth was comparatively small. This study provides valuable insights on the impact of climatological conditions and green roof design parameters (i.e., vegetation type and substrate depth) on ET rates.

Actual Evapotranspiration in Clay Soil on Three Slope Zones in Volcanic Slope of Mt. Sumbing, Central Java-Indonesia

Background: Soil physical properties have not been widely discussed as the main factor of evapotranspiration. This study aimed to see the relationship between land and soil physical factors on the evapotranspiration rate that occured at each slope position. Methods: Sampling and measurements were carried out on three slope zones in a landscape, i.e. the upper slope (erosion zone), the middle slope (transition zone) and the lower slope (deposition zone). The soil sampling was carried out to analyze the soil physical properties. The evapotranspiration rate was measured using a modified chamber in two measurement periods. It was carried out throughout the day since the sun started shining the land until sunset or until the sunlight were blocked by rain clouds. Result: The average daily evapotranspiration rate was 0.17 mm hr-1 with the lowest value was 0.02 mm hr-1 and the highest 0.62 mm hr-1. Slope position and slope arrangement were the key factors influencing other controlling factors for the rate of evapotranspiration, including vegetation and soil physical properties.

Radiation estimation and crop growth trajectory reconstruction by novel algorithms improve MOD16 evapotranspiration predictability for global multi-site paddy rice ecosystems

Reliable estimations in evapotranspiration (ET) of paddy rice ecosystems by satellite products are critical because of their important roles in regional hydrological processes and climate change. However, the NASA MODIS ET products (MOD16A2) and its derivatives do not have good correlations with all global paddy rice ET observations. In this research, MOD16 model sensitivity analyses and parameter optimization strategies were conducted in order to solve the problem. Results suggested that underestimation of daily net radiation (Rn) in overcast conditions and less satisfactory reconstruction of field-scale leaf area index (LAI) growth trajectory from the start date of field flooding and transplanting (FFTD) to the end of growing seasons by MODIS coarse vegetation index were identified as two major causes. A Light and Temperature-Driven Growth model and a Phenology-based LAI temporal Smoothing method fusion algorithm (LTDG_PhenoS) and an improved Rn estimation method were introducted and evaluated in paddy rice fields in South Korea, Japan, China, Philippines, India, Spain, Italy, and the USA from 2002 to 2019. The LTDG_PhenoS algorithm considers Landsat and MODIS EVI observations and meteorological data as input variables and 30-m LAI daily time series as outcomes. Introducing the global cloudy index algorithm resulted in improved estimations of daily Rn under all-sky conditions, with a significant decrease of root mean square error (RMSE) from 1.87 to 1.11 MJ m−2 day−1. The LTDG_PhenoS algorithm well reconstructed crop LAI growth dynamics from the FFTD to the end of rice growing seasons, with a substantial decline of RMSE from 1.49 to 0.27 m2/m−2. The FFTD estimations by the LTDG_PhenoS algorithm had an R2 of 0.97 and a small RMSE of less than 12-days. Daily ET rates estimated by novel algorithms had a substantial decline in RMSE from 2.88 to 0.90 mm day−1.

Estimation of sub‐annual inter‐catchment groundwater flow using short‐term water balance method

AbstractPredicting inter‐catchment groundwater flow (IGF) is essential because IGF greatly affects stream water discharge and water chemistry. However, methods for estimating sub‐annual IGF and clarifying its mechanisms using minimal data are limited. Thus, we quantified the sub‐annual IGF and elucidated its driving factors using the short‐term water balance method (STWB) for three forest headwater catchments in Japan (named here catchment A, B and As). Our previous study using the chloride mass balance indicated that annual IGF of catchment A (49.0 ha) can be negligible. Therefore, we calculated the daily evapotranspiration (ET) rate using the Priestley–Taylor expression and the 5‐year water balance in catchment A (2010–2014). The sub‐annual IGF of the three catchments was then calculated by subtracting the ET rate from the difference between rainfall and stream discharge during the sub‐annual water balance periods selected using the STWB. The IGF rates of catchment B (7.0 ha), which is adjacent to catchment A, were positive in most cases, indicating that more groundwater flowed out of the catchment than into it, and exhibited positive linear relationships with rainfall and stream discharge. This suggested that as the catchments became wetter, more groundwater flowed out of catchment B. Conversely, the IGF rates of catchment As (5.3 ha), included in catchment A, were negative in most cases, indicating that more groundwater flowed into the catchment than out from it, and exhibited negative linear relationships with rainfall and stream discharge. Given the topography of the catchments studied, infiltration into the bedrock was the probable reason for the IGF outflow from catchment B. We hypothesized that in catchment As, the discrepancy between the actual hydrological boundary and the surface topographic boundary could have caused an IGF inflow. This study provides a useful tool for determining an IGF model structure to be incorporated into rainfall‐runoff models.

Interannual Variability and Seasonal Dynamics of Evapotranspiration of Arundo donax L. and Populations of its Biological Control Agent (Tetramesa romana)

Giant reed (Arundo donax L.), a woody grass native to the Mediterranean, has become a cause of concern for national water security in its invaded range of the arid southwestern United States, Australia, New Zealand, and South Africa. The main objective of this study was to provide the first, landscape-level estimates of water use by giant reed. The study utilized the eddy covariance method to quantify evapotranspiration (ET) throughout the 2014 and 2015 growing seasons along the Rio Grande River in Eagle Pass, Texas. We monitored ET concurrently with the implementation of a biological control program targeting giant reed. Daily ET rates were strongly associated with the phenology of giant reed, as estimated by degree day accumulation. Monthly ET was higher in each month of the active growing season (May–October) of giant reed in 2014 than in 2015. Consequently, seasonal (DOY 121-304) ET was substantially higher in 2014 (842 mm) than in 2015 (625 mm) even though the 2015 growing season was wetter. Cumulative rainfall from May to October was 188 and 264 mm in 2014 and 2015, respectively. Our study indicated that the reduction in ET could be attributed to the presence of specialist insect biological control agent, the stem-galling arundo wasp (Tetramesa romana). In 2015, we observed a 28.6% (May), 53.5% (June), and 44% (July) increase in the number of arundo wasps captured in sticky traps from the previous year. Additional studies are needed to quantify conservation and economic benefits of the biological control program in the Rio Grande Basin.

Seasonal and Interannual Variations in the Surface Energy Fluxes of a Rice–Wheat Rotation in Eastern China

AbstractQuantitative knowledge of the water and energy exchanges in agroecosystems is vital for irrigation management and modeling crop production. In this study, the seasonal and annual variabilities of evapotranspiration (ET) and energy exchanges were investigated under two different crop environments—flooded and aerobic soil conditions—using three years (June 2014–May 2017) of eddy covariance observations over a rice–wheat rotation in eastern China. Across the whole rice–wheat rotation, the average daily ET rates in the rice paddies and wheat fields were 3.6 and 2.4 mm day−1, respectively. The respective average seasonal ET rates were 473 and 387 mm for rice and wheat fields, indicating a higher water consumption for rice than for wheat. Averaging for the three cropping seasons, rice paddies had 52% more latent heat flux than wheat fields, whereas wheat had 73% more sensible heat flux than rice paddies. This resulted in a lower Bowen ratio in the rice paddies (0.14) than in the wheat fields (0.4). Because eddy covariance observations of turbulent heat fluxes are typically less than the available energy (Rn − G; i.e., net radiation minus soil heat flux), energy balance closure (EBC) therefore does not occur. For rice, EBC was greatest at the vegetative growth stages (mean: 0.90) after considering the water heat storage, whereas wheat had its best EBC at the ripening stages (mean: 0.86).

Development of a Pilot Soil-Water Balance Model for Determination of Probability of a Working Day for Rice Harvesting

Abstract The probability of a working day is the ratio of workable days to the total available days in a working season for the intended operation. Soil moisture is the most important limiting factor in terms of rice harvesting. Therefore, to determine the PWD for this operation, a model was developed to estimate the soil moisture based on soil-water balance. To calibrate and validate the model, the soil moisture was monitored in the paddy field of the University of Guilan during the rice harvest seasons in 2017 and 2018. The calibration process was performed by applying a decreasing ratio, i.e. the senescence factor (α), at a daily evapotranspiration rate compared to that of previous day. At the validation stage, the simulated soil moisture contents were compared with measured values, which indicated a good model accuracy (NRMSE = 6.53%) of the soil moisture estimation. Therefore, this model can be used for the rice harvesting operation feasibility evaluation and PWD calculation.

Estimated seasonal daily evapotranspiration rates for a horizontal subsurface flow constructed wetland

We measured the daily evapotranspiration on a horizontal sub-surface flow constructed wetland in Hódmezővásárhely, Hungary. The main focus of our research was the seasonality of evapotranspiration in this CW. We measured the water balance of the CW and searched days when no precipitation, no inlet or outlet impacted on the water balance of the constructed wetland, only the evapotranspiration. had impact on the water balance. The results show that in spring the evapotranspiration rates were between 18-42,6 mm/day, in summer 12,3-42,3 mm/ day and in autumn the values were 13,6-22,7 mm/day. The highest hourly evapotranspiration was 16,3% of the daily evapotranspiration. This value was 415 % of the average, hourly hydraulic load that can significantly affects on the effluent concentration. The results also show the morning and evening condensation which has two main effects. On the other hand, the water balance of the CW is increased, which results the decrease of the concentration of wastewater.

Evapotranspiration estimation using a modified Priestley-Taylor model in a rice-wheat rotation system

The rice-wheat rotation system is one of the largest agricultural production systems worldwide. Accurate estimation of evapotranspiration (ET) in the rice-wheat rotation system is critical to enhance efficient irrigation management and water use. The variation of ET for a rice-wheat rotation system during 2015–2018 and its controlling meteorological factors was investigated using the Bowen ratio energy balance and path analysis methods. A modified Priestley–Taylor (PT) model considering soil water stress for soil evaporation (E) (fsw), and plant temperature constraint (deviation of air temperature from optimum for the crops used, ft), leaf senescence for transpiration was developed. The results showed that the diurnal variation of ET rate in different months exhibited a single peak curve with the maximum ET rates of 0.90 and 0.42 mm h−1 for rice and winter wheat, respectively. The total ET of the rice-wheat rotation system over the whole growing season was 765–841 mm, of which 63–67% was consumed by the rice field. The average daily ET rate over the whole growing season was 3.27–4.13 and 1.50-1.65 mm d−1 for rice and winter wheat, respectively. The results of ET partitioning showed that E accounted for 23–32% of the seasonal ET for rice and 48–51% for winter wheat. The ET partitioning of rice and winter wheat was closely linked to leaf area index (LAI). The ratio of E/ET reduced exponentially for rice with the increase of LAI, while it reduced linearly for winter wheat. The path analysis showed that the net radiation (Rn) was the dominant meteorological factor affecting short-term ET of the rice-wheat rotation system through the direct effect. The water vapour pressure deficit (VPD), another important factor influencing ET, showed mainly an indirect effect on ET through path of Rn and had a greater impact on ET for rice than that for wheat. The modified PT model could estimate ET for rice and winter wheat reasonably, with linear regression coefficient of 0.93–1.09 and coefficient of determination of 0.92−0.96. The model was sensitive to the fsw or ft.

Comment on “A hybrid approach combining the FAO-56 method and the complementary principle for predicting daily evapotranspiration on a rainfed crop field’ by D. Kim et al.

Kim et al. (2019) proposed to scale the generalized complementary-relationship-obtained daily evapotranspiration (ETGCR) rate by the wet-environment ET value (ETw) as an index (Ks) of soil water stress but they did not tie their index-values to any soil moisture data. With daily measurements from the same study area (Mead, Nebraska) and period (2002–2012) it is demonstrated that there indeed exists a statistically significant near-linear relationship between Ks (=ETGCR/ETw) and the volumetric soil water content (VWC) when scaled by its maximum observed value, a proxy for field capacity (FC). The soil moisture data therefore support, with increasing reliability as the length of the averaging period grows, the employment of ETGCR/ETw as a practical indicator of soil water stress, the latter here defined as VWC/FC.

Increasing Evapotranspiration on Extensive Green Roofs by Changing Substrate Depths, Construction, and Additional Irrigation

Urban environments are characterized by dense development and paved ground with reduced evapotranspiration rates. These areas store sensible and latent heat, providing the base for typical urban heat island effects. Green roof installations are one possible strategy to reintroduce evaporative surfaces into cities. If green roofs are irrigated, they can contribute to urban water management and evapotranspiration can be enhanced. As part of two research projects, lysimeter measurements were used to determine the real evapotranspiration rates on the research roof of the University of Applied Sciences in Neubrandenburg, Germany. In this paper, we address the results from 2017, a humid and cool summer, and 2018, a century summer with the highest temperatures and dryness over a long period of time, measured in Northeast Germany. The lysimeter measurements varied between the normal green roof layer (variation of extensive green roof constructions) and a special construction with an extra retention layer and damming. The results show that the average daily evapotranspiration rates can be enhanced from 3 to 5 L/m2/day under optimized conditions. A second test on a real green roof with irrigation was used to explain the cooling effects of the surface above a café building in Berlin.

Predictive Evapotranspiration Equations in Rain Gardens

Current stormwater control measure (SCM) design often does not include the dynamic process of evapotranspiration (ET) for vegetated systems. This study compared two reference ET equations with a three-year data set from rain garden weighing lysimeters. The outcome was a tool to incorporate ET into SCM design. The weighing lysimeters at Villanova University, located in southeastern Pennsylvania, were used to measure water budget parameters for three scenarios: sandy loam with UO, sand with an unconstricted outflow (UO), and sand with internal water storage (IWS). The two ET models explored were the ASCE Penman-Monteith equation (a robust model) and the Hargreaves equation (a simple model). Estimated ET values from these two equations, both with and without modifications for water availability and crop presence, were compared and calibrated (if modified) with observed data. Comparisons and calibrations were performed on a daily and storm basis to explore the applicability of the two ET models for continuous and storm approaches. The observed ET was 28%–52% of inflow over the continuous three-year period and 16–30 mm on a storm scale, making ET a significant part of the lysimeters’ water budget. Due to the experimental nature of the lysimeters, 12 of the 36 study months had additional simulated runoff, such that a smaller ET as a percentage of inflow was expected in the rain garden SCM’s water balance. The Hargreaves and ASCE Penman-Monteith equations without modification provided an adequate estimate for rain garden ET for all systems at the storm scale. Modifications to ET estimations produced by both equations through crop coefficients and a soil moisture extraction function provided a good model for storm-scale ET by reducing errors and increasing efficiencies for all weighing lysimeter types. Evapotranspiration estimates from both unmodified equations provided, at best, a marginally better estimate than the average observed rate for continuous daily rain garden ET. The application of crop coefficients and a soil moisture extraction function to both equations reduced errors in ET estimates and increased the equations’ predictive power (Nash-Sutcliffe efficiency) for all weighing lysimeter types. Both equations with modifications on a daily scale produced good ET estimates for the IWS system. For both equations, crop coefficients were found in an expected range for UO systems (0.3–1.5) but were high in the IWS system (1.6–2.0). Soil moisture extraction functions were not needed to calibrate the IWS equations on the storm scale. Both the Hargreaves equation and the ASCE Penman-Monteith equation provided an adequate model (especially with modifications) to incorporate ET into a design-storm approach to SCM design. Use of both predictive models on a daily scale has potential use in continuous simulation, as in most cases the ET estimations predicted by the equations provided a better estimate than the average of the observed daily ET rates.

Water use and photosynthesis of Dendrobium Sonia ‘Earsakul’ under water deficit stress

Dendrobium Sonia ‘Earsakul’ orchids in three developmental stages (plantlet, mature, flowering) were exposed to water deficit stress for 7 d. The average daily evapotranspiration rate (ET) ± SD under the well-watered condition was lowest in the plantlet stage (10.51 ± 1.96 mL/d). The ET of the mature and flowering stages was 45.80 ± 6.90 mL/d and 50.97 ± 7.23 mL/d, respectively. However, the ET was not significantly different between the mature and flowering stages. Under the water-limited condition, the ET values of all stages for the orchid were continuously depleted from the well-watered control at the 2nd day in the plantlet stage and the 3rd day of the mature and flowering stages after withholding water. The CO2 exchange rate (CER) of the water-stressed plant substantially decreased compared to the control due to strong decreases in the stomatal conductance (gs) and the transpiration rate (TR) in all developmental stages. In addition, water deficit stress led to a substantial decline in the water use efficiency (WUE) in the plantlet stage while the WUE of the mature and flowering stages remained similar to the control. However, the water deficit stress induced increased Ci/Ca in the plantlet stage. Moreover, shrinking of the stressed pseudobulb was seen in the plantlet and flowering stages but leaf wilting occurred only in the stressed plant of the plantlet stage. These results demonstrated that water deficit stress led to decreased photosynthesis in Den. Sonia ‘Earsakul’ due to stomatal limitation.

Effects of Surface and Subsurface Drip Irrigation on the Yield, Vegetative Growth and Water Productivity of Onions

Summary The objective of this study, conducted in the northern Serbian province of Vojvodina, was to analyze the effect of surface and subsurface drip irrigation (with drip lateral placement depths of 0.05 and 0.1 m) on the yield and water productivity of onions (Allium cepa L., var. ‘Holandski žuti’). The irrigation applied was scheduled on the basis of the water balance method. The daily evapotranspiration rate was computed using the reference evapotranspiration (ETo) based on the Hargreaves equation and the crop coefficient (kc). The irrigation rate was 30 mm, whereas the amount of water added by irrigation during the season was 150 mm. According to the results obtained, the onion yield under irrigated conditions was significantly higher than that under non-irrigated (control) conditions. Differences in the yield obtained using surface and subsurface irrigation were non-significant. The amounts of water used for evapotranspiration under irrigated and non-irrigated conditions were 363 mm and 220 mm, respectively. The value of the surface irrigation yield response factor (Ky) was 0.62, whereas the values of the subsurface irrigation yield response factor (Ky) were 0.61 (0.05 m) and 0.79 (0.1 m). Consequently, onions grown from sets proved moderately sensitive to water stress under regional climate conditions and could be grown without irrigation. The value of the irrigation water use efficiency (Iwue) ranged from 3.55 to 4.97 kg m−3, whereas the value of the evapotranspiration water use efficiency (ETwue) ranged from 3.72 to 5.22 kg m−3. The highest yield of onions was obtained using a drip lateral placement depth of 0.1 m, which is recommended for high-yielding onion production.

Evapotranspiration Rates of Turf Bermudagrasses under Nonlimiting Soil Moisture Conditions in Oklahoma

Due to limited water availability and increasing water costs, it is essential to identify and utilize turfgrasses with reduced water use rates. The objective of this study was to evaluate the evapotranspiration rates of bermudagrass (Cynodon spp.) genotypes under nonlimiting soil moisture conditions in the field at Stillwater, OK. Evapotranspiration rates of 10 bermudagrass genotypes were determined using mini‐lysimeters with calcined clay as rooting media. Daily evapotranspiration (ET) rates were measured before dawn by weighing the mini‐lysimeters from August to September in 2013, 2014, and 2015. A significant genotype × year effect was found. Therefore, data were analyzed separately for each year. Within years, the genotype × date effect was significant only in 2014. In 2013, ‘TGS_U3’, ‘TifTuf’, and ‘Premier’ used more water than OKC 1302, OKC 1163, ‘Latitude 36’, ‘Tifway’, and OKC 1131. In 2014, TifTuf, ‘Celebration’, Tifway, and OKC 1302 used more water than Premier, TGS_U3, ‘NorthBridge’, OKC 1163, and OKC 1131. In 2015, TifTuf, Celebration, and Latitude 36 used more water than Premier, OKC 1302, OKC 1163, OKC 1131, and NorthBridge. TifTuf ranked consistently in the group of genotypes with the highest ET rates, whereas OKC 1131 ranked consistently in the group of genotypes with lowest ET rates in 2013, 2014, and 2015. The differences in ET rates show the potential for breeding programs to develop bermudagrass cultivars with lower ET rates, which may result in reduced overall ET requirements.

A field-modeling study for assessing temporal variations of soil-water-crop interactions under water-saving irrigation strategies

Simulation models are useful tools that may help to improve our understanding of soil-water-plant interactions under innovative water-saving irrigation strategies. In this study, the HYDRUS-2D model was applied to evaluate the influence of deficit irrigation (DI) and partial root-zone drying (PRD) on maize water extractions during two cropping cycles of 2010 and 2011. The model was calibrated and validated using measured soil water content data (expressed as equivalent water depths). Reliable estimates of soil water content were provided by HYDRUS-2D, with root mean square error and mean bias error values of 2.3–5.11 and 1.63–4.93mm, respectively. Root water uptake and maize grain yields were reduced by 13.2–28.8% and 13.6–52.8%, respectively, under different water-saving irrigation treatments compared to full irrigation. However, different root and water repartitions in the PRD treatment with a 25% reduction in the irrigation depth (PRD75) improved soil water utilization and consequently, crop growth. Increased root water uptake (2.2–4.4 times higher than in other treatments) from the 60–100cm soil depth in the PRD75 treatment maintained a favorable daily evapotranspiration rate, resulting in no significant reduction in maize grain yield compared to full irrigation. Consequently, a 15.7–85% increase in water use efficiency for maize cultivation under PRD75 ensured 25% water savings without threatening food security in the study area. It can be concluded that HYDRUS-2D can be successfully used to optimize water management under local water-stress conditions.

OPTIMIZING IRRIGATION AND DRAINAGE RATES IN SRI PADDY FIELDS

A quantified study to optimize furrow irrigation and drainage rates for SRI paddy fields has been carried out over three different planting seasons. It is very crucial to maintain soil conditions where the water level sustains soil moisture at around saturation and air-entry values. In the present study we report on a simulator program which applies a saturated water flow equation in one dimension for which boundary conditions at both ends formed water rates (Neumann type). A spreadsheet optimization using an imbedded Solver in MS Excel was employed alongside the simulation. Daily rainfall, evapotranspiration and percolation rates as sink-source functions were incorporated into the equations. Our study shows that optimizing irrigation and drainage rates gives an effective water level for SRI paddy fields within a range of -5 to 0 cm for all planting seasons. The highest value for irrigation rate within the furrow was about 6 mm per day, while the optimizing drainage rate was about 0.5 mm per day. Water table profiles are significantly affected by planting season. Our study confirmed that conserving drained water from one planting season is desirable to provide sufficient irrigation water for the next planting season.

Regional evapotranspiration from a wetland in Central Europe, in a 16-year period without human intervention

Regional evapotranspiration (ET) for Fenéki “Pond” (FP, Kis-Balaton wetland, Hungary) was estimated using weighted canopy areas of five macrophyte classes and open water over an uninterrupted period without any human intervention between 1997 and 2012. In addition to the dominant common reed (Phragmites australis), the cover ratio of the other four plant groups and open water was monitored. The different cover categories of the wetland were separated using images with surface interpretation using the maximum likelihood classification method. Although the annual cover ratio for any class only changed slightly by 1–2%, this wetland was not considered to be in equilibrium, since species turnover (sedge-grass) was observed during this study. Reference ET was calculated by the widely accepted Penman–Monteith (FAO-56) formula from the data of a nearby climate station. Of the five macrophyte classes studied, crop coefficients (as the ratio of measured and reference ET) of three groups were measured locally with a lysimeter. To process the 16-year long ET time series, the means of six-season long Kc values were applied. As the open water of FP was frequently covered by seaweed (Ceratophyllumdemersum), a special evaporation (E) was defined using seaweed settled “A” pans. Compared to evaporation of standard “A” pan, the seasonal average evaporation was 7% higher in “A” pans containing seaweed (C.demersum). Annual and seasonal mean ET totals fluctuated depending on environmental conditions (air temperature) and the type of macrophyte. The range of macrophytes’ 16-year annual mean ET varied from 876.8±54.58mm year−1 (dominant common reed) to 662.8±41.57mm year−1 (woody deciduous, Salix fragilis, Alnus glutinosa, Populus tremula) with a weighting average of 802.1±50.4mm year−1 for the regional ET of FP. The average winter ET sum was 17.1±1.19% with a range of 15.7±1.09–20.7±1.43% for common reed and woody deciduous, respectively. The annual mean ET totals were highly correlated with mean daily ET rates of different macrophyte classes. Seasonal daily average ET rates of different macrophyte classes varied between 4.0±0.26mm day−1 and 2.9±0.19mm day−1 in common reed and woody deciduous, respectively. The long-term weighted daily mean ET rate for FP was 3.6±0.24mm day−1. The highest ET/E ratio of 1.09 was for common reed, in an agreement with previous observations, but was lowest in woody deciduous (0.81). In addition to classic statistical approaches, monthly ET data were also used for modeling purposes (ARIMA models). The projected monthly regional ET values supported earlier observed seasonal patterns likely due to peculiarities in wetland water supply. Instead of exclusively using dominant species to estimate regional ET, more accurate results were possible by extending the ET approach to include several macrophyte species. Neglecting the smaller-scale differences in macrophyte, ET could cause more than a 10% overestimation in the regional ET sum. The SARIMA(1,0,0)(0,1,1)12 model contributed positively to the existing information about the ET of the study site. The projected monthly regional ET values retained the earlier observed seasonal pattern until 2020.

Evaluating the complementary relationship of evapotranspiration in the alpine steppe of the Tibetan Plateau

AbstractThe complementary relationship (CR) of evapotranspiration allows the estimation of the actual evapotranspiration rate (ETa) of the land surface using only routine meteorological data, which is of great importance in the Tibetan Plateau (TP) due to its sparse observation network. With the highest in situ automatic climate observation system in a typical semiarid alpine steppe region of the TP, the wind function of Penman was replaced by one based on the Monin‐Obukhov Similarity theory for calculating the potential evapotranspiration rate (ETp); the Priestley‐Taylor coefficient, α, was estimated using observations in wet days; and the slope of the saturation vapor pressure curve was evaluated at an estimate of the wet surface temperature, provided the latter was smaller than the actual air temperature. A symmetric CR was obtained between the observed daily actual and potential evapotranspiration. Local calibration of the parameter value (in this order) is key to obtaining a symmetric CR: α, wet environment air temperature (Twea), and wind function. Also, present symmetric CR contradicts previous research that used default parameter values for claiming an asymmetric CR in arid and semiarid regions of the TP. The effectiveness of estimating the daily ETa via symmetric CR was greatly improved when local calibrations were implemented. At the same time, an asymmetric CR was found between the observed daily ETa and pan evaporation rates (Epan), both for D20 aboveground and E601B sunken pans. The daily ETa could also be estimated by coupling the Epan of D20 aboveground and/or E601B sunken pan through CR. The former provided good descriptors for observed ETa, while the latter still tended to overestimate it to some extent.