Reference Crop Evapotranspiration Research Articles

Crop water requirement for wheat under different conservation practices in the semi arid region of India

Experiments were conducted during Rabi 2014–15 and 2015–16 at research farm of ICAR- Indian Agricultural research Institute, New Delhi to study crop water requirement for wheat under different conservation practice along with conventional practice using single crop coefficient, dual crop coefficient and water balance methods. The field experiment was carried out with seven treatments i.e. conventional tillage (CT), permanent narrow-bed without residue (PNB), permanent narrow-bed with residue (PNB+R), permanent broad-bed without residue (PBB), permanent broad-bed with residue (PBB+R), zero tilled flat bed without residue (ZT), zero tilled flat bed with residue (ZT+R) arranged in a randomized block design (RBD) with three replications. Adjusted single and dual crop coefficient values for semi-arid climate of Delhi were calculated with the help of FAO-56 method. The reference crop evapotranspiration ET0, was estimated using FAO Penman–Monteith equation. Results showed that estimated reference evapotranspiration and pan evaporation had good correlation at R2 value of 0.89 for wheat crop. The adjusted value of single and basal crop coefficient had initially lower value, increase during development phase reached maximum during mid stage and then decline during late stage. Soil evaporation coefficient Ke was low except during irrigation and precipitation events. The value of crop evapotranspiration was found to be more value during mid season stage with respect to different treatments. The crop evapotranspiration (ETc) and actual evapotranspiration (ETa) were found higher values under CT, ZT and ZT+R treatments because they had flood irrigation. PNB, PNB+R, PBB and PBB+R had less value due to furrow irrigation. Water productivity had maximum values under PBB+R treatment and lowest value under conventional treatment. PBB+R treatment had 23–27% higher value in wheat as compared to corresponding value in conventional treatment. Since dual crop coefficient method consider the effect of soil evaporation and crop transpiration both therefore the value calculated by it are more reliable as compared to single crop coefficient. Therefore dual crop coefficient method is useful for determine water stress in crop, daily evapotranspiration losses, water need of crop and for irrigation scheduling in the crop for optimum use of irrigation water. Among all treatments, PBB+R showed better water productivity than other treatments. Thus, PBB+R management practice could be adopted by farmers for improving water productivity in semi-arid region of India.

Water requirement of rice crop using CROPWAT model for Dehradun district, Uttarakhand

Management of water resources with optimal utilization results in fulfilling the constraint of inadequate water availability. Determination of crop water requirement is the first step in planning and effective utilization of irrigation water which curtaining the impact developed due to water stress condition. In the present study crop water requirement (CWR) and irrigation requirement was computed for rice in Dehradun district using CROPWAT simulation software by taking into account different local climatic parameter which influencing reference crop evapotranspiration (ET0) and thus affecting crop production. Penman–Monteith method was used to calculate ET0 and the United States Department of Agriculture (USDA) soil conservation method was used to estimate the effective rainfall. The ET0 varied from 1.43 (January) to 5.28 (May) mm/day and annual mean was 3.1 mm/day. The average annual rainfall value was 1718 mm and out of which 977.3 mm was effective rainfall. The crop water requirement and net irrigation water requirement (NIR) for rice crop was estimated to be 559.5 mm and 288.7 mm, respectively. The values of CWR and NIR were maximum in June and minimum in October. The net scheme irrigation requirement was scheduled to be maximum in June (190.6 mm/month), minimum in October month and zero in the month of July, August and September. The actual irrigated area was found to be 18.92 km2 for which net irrigation demand was maximum in the month of June (3.61 MCM) followed by October month (0.12 MCM). Total net irrigation demand for actual irrigated area was 5.47 MCM. The computation of crop water requirement, NIR, and total net irrigation demand using CROPWAT has proved to be an effective tool for proper management of water resources in water stress condition.

Estimation of Reference Crop Evapotranspiration in Northwest China

Based on the daily meteorological data from 1956 to 2011 in Northwest (NW) China and the Penman-Monteith (PM) equation, the regional reference crop evapotranspiration (ET0) is estimated. The ET0 variations in time series and spatial distributions are analyzed. The trend analysis, Mann-Kendall (M-K) test, wavelet analysis, stepwise regression and EOF analysis methods are used to investigate the spatiotemporal variability of ET0 and its contributing climatic factors, the mutation of ET0, the period of ET0, and the main influencing meteorological factors, respectively. Major conclusions are obtained as follows: (1) In the past 56 years, the trend of average annual ET0 time series in the NW China is significantly reduced, the differences exists in different seasons, i.e., the trends of ET0 in spring (-0.26mm/a), summer (-0.72mm/a) and autumn (-0.31mm/a) are decreased, respectively, the ET0 in winter is slowly increased (0.02mm/a). (2) The region which ET0 decreased most is located at the field from Kumul to Hotan (from northeast to southwest). ET0 has a sharply decrease around the 1980s, with a multiple-time scale nesting complex structure in the period. The first, second and third EOF models account 36.84%, 13.87% and 9.04% for the explained variance, respectively. The summer EOF model is the main contributor to the annual first model. (3) The upward trend of mean surface air temperature (T) and the decreased trend of sunshine duration (SD), relative humidity (RH) and wind speed at 2 m high (U2) induce ET0 to decline. The variability of annual ET0 rate is most influenced by the variations of U2, followed by SD, RH and T, which is influenced by various climatic variables. The investigation of spatiotemporal variability of ET0 and its contributor meteorological factors may help us better understand how ET0 responds to regional climate change.

Evaluation of uncertainty in evapotranspiration values by FAO56-Penman-Monteith and Hargreaves-Samani methods

Methods of calculating evapotranspiration are subject to uncertainty. It is important to evaluate their uncertainty. Using 54 years of data, this study evaluated the uncertainty values of monthly reference crop evapotranspiration calculated with the FAO-56 Penman-Monteith and Hargreaves-Samani methods. The objective of this study was to determine the range of variation in the results of each method. It was found that for both methods, the bandwidth uncertainty obtained with 95% confidence interval was more in warm months than in cold months, and the mean and variance by the Hargreaves-Samani method were always less than by the FAO-56 Penman-Monteith method. The uncertainty value of the FAO-56 Penman-Monteith method was more than of the Hargreaves-Samani method, because the number of parameters used in the FAO-56 method was more than in Hargreaves-Samani method which increased uncertainty resources.

Study of the fractal nature of evapotranspiration time series from agricultural regions of Northern Karnataka

Multifractal detrended fluctuation analysis (MFDFA) renders valuable insights pertaining to the randomness, inner regularity and long range correlations in the time series data. We applied this technique to assess the fractal behaviour and inherent correlations of the potential and reference crop evapotranspiration data collected from two regions of Karnataka, viz., Belgaum and Raichur. The annual periodic nature of the evapotranspiration data series was removed using seasonal trend decomposition method and it was seen that all the decomposed series consisted of long-term persistence. The multifractal behaviour in the evapotranspiration series at the two stations were seen owing to the strong dependency of generalised Hurst exponent H(q) on the values of q. We also tested for the reduction in the dependence of h(q) on q by shuffling the evapotranspiration time series and it is indicative of the fact that the multifractality is responsible for the correlation characteristics and also the probability density function of the evapotranspiration data series. The two regions, Belgaum and Raichur vary considerably in climatic and geomorphic conditions and this difference is evident in their corresponding evapotranspiration data as fractal properties. This is depicted by the values of the generalised Hurst exponent H(q) obtained using MFDFA technique.

ESTIMATING OF EVAPOTRANSPIRATION USING ARTIFICIAL NEURAL NETWORK

This study investigates the application of artificial neural networks (ANNs) on the prediction of daily grass reference crop evapotranspiration (ET0) and compares the performance of ANNs with the conventional method (Penman–Monteith). The use of ANNs was examined number of hidden layers and the activation function were also tested. The best ANN architecture for estimation of daily ET0 was obtained for different data set for Nubaria. Using these data, the networks were trained with daily climatic data (maximum and minimum temperature, dew point and wind speed) as input and the Penman– Monteith (PM) estimated ET0 as output. The analysis was carried out with MATLAB software. Feed forward one-layer networks with sigmoid function were used. Performance evaluation of the models have been carried out by calculating root mean square error (RMSE), The network were selected based on maximized R and R2 value and minimized RMSE values which were 0.98, 0.957 and 0.44 mm/day, respectively in testing. The optimal ANN (4-12-1) for Nubaria regions showed a satisfactory performance in the ET0 estimation. These ANN models may therefore be adopted for estimating ET0 in the study area with reasonable degree of accuracy.

Calculation of reference crop evapotranspiration in Shaanxi province based on ANFIS

Calculation of reference crop evapotranspiration in Shaanxi province based on ANFIS

Comparing of Generalized Linear Models, Random Forest and Gradient Boosting Trees in Estimation of Reference Crop Evapotranspiration (Case Study: The Sistan Plain)

Comparing of Generalized Linear Models, Random Forest and Gradient Boosting Trees in Estimation of Reference Crop Evapotranspiration (Case Study: The Sistan Plain)

Reference crop evapotranspiration database in Spain (1961–2014)

Abstract. Obtaining climate grids describing distinct variables is important for developing better climate studies. These grids are also useful products for other researchers and end users. The atmospheric evaporative demand (AED) may be measured in terms of the reference evapotranspiration (ETo), a key variable for understanding water and energy terrestrial balances and an important variable in climatology, hydrology and agronomy. Despite its importance, the calculation of ETo is not commonly undertaken, mainly because datasets consisting of a high number of climate variables are required and some of the required variables are not commonly available. To address this problem, a strategy based on the spatial interpolation of climate variables prior to the calculation of ETo using FAO-56 Penman–Monteith equation was followed to obtain an ETo database for continental Spain and the Balearic Islands, covering the 1961–2014 period at a spatial resolution of 1.1 km and at a weekly temporal resolution. In this database, values for the radiative and aerodynamic components as well as the estimated uncertainty related to ETo were also provided. This database is available for download in the Network Common Data Form (netCDF) at https://doi.org/10.20350/digitalCSIC/8615 (Tomas-Burguera et al., 2019). A map visualization tool (http://speto.csic.es, last access: 10 December 2019) is available to help users download the data corresponding to one specific point in comma-separated values (csv) format. A relevant number of research areas could take advantage of this database. For example, (i) studies of the Budyko curve, which relates rainfall data to the evapotranspiration and AED at the watershed scale, (ii) calculations of drought indices using AED data, such as the Standardized Precipitation–Evapotranspiration Index (SPEI) or Palmer Drought Severity Index (PDSI), (iii) agroclimatic studies related to irrigation requirements, (iv) validation of climate models' water and energy balance, and (v) studies of the impacts of climate change in terms of the AED.

Influence of the accuracy of reference crop evapotranspiration on drought monitoring using standardized precipitation evapotranspiration index in mainland China

AbstractReference crop evapotranspiration (ET0) estimation accuracy strongly affects the accuracy of drought monitoring using the standardized precipitation evapotranspiration index (SPEI). The FAO56 Penman–Monteith (the reference method here), Irmak, Berti, Priestley–Taylor, and Valiantzas methods were used to compute ET0 and subsequently SPEI at 1‐, 3‐, and 12‐month timescales during 1961–2016 at 763 weather stations in China. The spatiotemporal variations in the climatic variables and ET0, D (=P − ET0) and SPEI with five ET0 estimators (hereafter SPEIPM, SPEIIRA, SPEIPT, SPEIMHS, and SPEIVal) were investigated. The cumulative frequency and periods (using the Morlet wavelet analysis) of the annual SPEIs were analyzed. The results showed that, corresponding to the P, ET0, and D, drought severity was characterized by large seasonal and regional differences using SPEIPM, SPEIIRA, SPEIPT, SPEIMHS, or SPEIVal, especially in northwestern China, the Inner Mongolia region, and the Qinghai–Tibetan Plateau (P < 500 mm/yr). Additionally, the effects of the different ET0 equations on the minimum SPEI and frequency values were large in these drier subregions but generally small in other regions. Meanwhile, an increased ET0 prediction accuracy did not automatically lead to an improved SPEI accuracy in regions P > 500 mm/yr. With respect to the averaged values for Subregion 1 (P < 134 mm/yr), although the vibration intensities and spectra were visually similar for different SPEIs, the periodical signals differed. Regional climatic conditions have a significant impact on the SPEI estimates in regions characterized by P (<500 mm/yr); we therefore suggest that the ET0 equations for drought analysis with SPEI should be carefully selected.

Time-Lag Effect Between Sap Flow and Environmental Factors of Larix principis-rupprechtii Mayr

A time lag between sap flux density (Js) and meteorological factors has been widely reported, but the controlling factors of the time lag are poorly understood. To interpret the time lag phenomenon systematically, thermal dissipation probes were placed into each of eight trees to measure the Js of Larix principis-rupprechtii Mayr. in the Liupan Mountains in Northwest China. Meteorological factors, including vapor pressure deficit (VPD), solar radiation (Rs) and air temperature (Ta), were synchronously measured with Js, and the dislocation contrast method was used to analyze the time lag between Js and the meteorological factors. The analysis indicated the following for the whole experimental period. (1) The time lag between Js and VPD (TLV) and the time lag between Js and Rs (TLR) both exhibited different patterns under different weather conditions, and Js could precede Rs on dry days. (2) Both TLV and TLR varied with the day of the year (DOY) throughout the experimental period; namely, both exhibited a decreasing tendency in September. (3) Reference crop evapotranspiration (ETref) had a greater influence on the time lag than the other meteorological factors and directly controlled the length and direction of TLV and TLR; relative extractable water (REW) modified the relationship between ETref and time lag. (4) The regression analysis results showed differences between the time lags and the environmental factors (ETref and REW) within different ranges of REW. Namely, TLR was better determined by ETref and REW when REW < 0.38, while TLV was better correlated with ETref and REW in the absence of soil water limitations (REW > 0.38). This project provided an important opportunity to advance the understanding of the interaction between plant transpiration and meteorological factors in a changing climate.

Identification and remediation countermeasures of the Agriculture water problem in Qilu lake basin

In this paper, based on the characteristic of natural geography, hydrometeor, ecological environment and the development of economic and society on the Qilu Lake Basin, making full use of a lot previous data, including field measured data, investigation data, planning reports and historical materials, to study and analyze the evolution population, arable land, irrigation area, agricultural planting, the water surface of lake of Qilu Lake since 1280 A.D. The test was carried out in the variation trend of Qilu Lake’s precipitation, average temperature, relative humidity, reference crop evapotranspiration, water resources, and other factors during 1950∼2016. The results show that water resources shortage phenomenon of Qilu Lake Basin can be traced back to 400 years ago. Social progress and increasing population have promoted the continuous improvement of the agricultural replanted pattern, the large consumption of water resources and the pollution of agricultural non-point sources have caused the deterioration of the water environment of the Qilu Lake. Additionally, lake water appears three times greatly atrophy was caused by the reclaiming land from lakes and climate warming, and the fragility of water ecology is intensifying. The integration of resources should be combined with the system of lake-leader, then taking some measures like that saving water and reducing wastewater, reducing agricultural replanting index, delineation of ecological red line and management and protection of water coastline, water trans-valley project form other river basin, allocation of water resources and monitoring and control of water resources and so on. The adoption of these measures will gradually repair the water ecology, improve the water environment, improve the carrying capacity of water resources, and realize the green and beautiful countryside.

Groundwater use and rapid irrigation expansion in a changing climate: Hydrological drivers in one of the world’s food bowls

In recent decades, increased groundwater use enabled a large areal increase in irrigated dry season crops in northwest Bangladesh. Concurrent declining groundwater levels across the region are of great concern for food security. A water balance model approach that considered changes in irrigated agriculture was implemented to assess changes over the long-term to three five-year evaluation periods (1985–1989, 1998–2002 and 2011–2015) and seasonally (annual, dry season and wet season). The model used two different methods that explicitly capture changes in irrigation to compute and compare actual evapotranspiration (ETa). The first method used MODIS satellite data to estimate a crop coefficient based on vegetation indices (at 500 m spatial resolution) scaled by reference crop evapotranspiration (ETref). The second method used a crop coefficient approach based on survey data of crop areas at the district level and subsequently scaled by ETref. Both methods yielded very similar results at the district level, with correlation coefficients between 0.75 and 0.89. The maximum difference between the monthly averages was only of 5.4%. Notwithstanding the observed overall increase in irrigated areas, estimated overall mean annual ETa is similar through the analysis (ca. 1100 mm) and district-level trends were mixed (some increasing and some decreasing) showing in some districts a weak association between ETa and the related declining groundwater level. From the water balance, it is inferred that both the groundwater extraction (by pumping for irrigation and capillary rise to supply roots) and the groundwater recharge reduced from 1998–2002 to 2011–2015, and with deeper groundwater in later years, much of the irrigation water supply is by soil water storage rather than by groundwater. As highlighted in this paper, there are other factors aside crop expansion that may have contributed to the groundwater decline, thus a single policy or management change such as restricting groundwater extraction for irrigation may alone be inadequate to reverse declining groundwater trends.

Spatiotemporal trends in reference evapotranspiration over South Korea

The universal phenomena of global warming caused by climate change have direct linkage with different hydro-meteorological variables which in turn affect the evaporative demand of the atmosphere. Therefore, this study evaluated the seasonal and spatial changes in reference crop evapotranspiration (ETo) during last 4.7 decades and identified the forcing mechanism behind the seasonal changes in ETo using a stepwise regression equation. To remove the effect of serial correlation, the modified Mann–Kendall test was adopted together with Sen's slope and linear regression method to identify and compare the spatial and temporal trends between Thornthwaite, Hargreaves and FAO Penman–Monteith (FAO-PM) methods. Results indicate that the annual average ETo value is higher along the south and east coastal areas and lower along the northwest side of South Korea. The highest number of stations with significant increasing trends was detected in Thornthwaite and significant decreasing trend in FAO-PM method. Spatial and temporal correlation analysis showed the existence of strong correlation between Hargreaves and FAO-PM methods with the Pearson r value ranging from 0.84 to 0.98 and R2 of 0.8. Wind speed is found to be the most influencing climatic variable, especially in autumn, early winter and early summer, and maximum temperature during spring and late summer.

Sensitivity analysis of the reference crop evapotranspiration in a humid region.

This study examined the sensitivity of reference crop evapotranspiration (ET0) to climatic variables in a humid region in Iran. ET0 was estimated using the FAO-56 Penman-Monteith (PMF-56), Blaney-Criddle (BC), and Hargreaves-Samani (HG) methods. Sensitivity analysis was performed by two distinct methods which were (i) changing the value of a certain climatic parameter in a range between ± 20% of its long-term mean with an increment of 5%, and calculating the percentage of change in ET0, while the other parameter values were kept constant; and (ii) calculating the sensitivity coefficients (SCs) for each of the climatic variables. For each of the climatic parameters, the Iso-SC maps were plotted using the Arc-GIS software. Results indicated that the most sensitive parameter for ET0 was the maximum air temperature (Tmax) by PMF-56 and HG methods. Increasing Tmax up to 20% led to an increase in ET0 between 8.5 and 15%, at the selected stations by PMF-56. In contrast, the less sensitive parameter for ET0 was the minimum air temperature (Tmin) for PMF-56 and Tmean for HG. For PMF-56, increasing the minimum relative humidity (RHmin) to 20% led to a decrease in ET0 in the range between 0.5 and 5%. The highest values of SC in the cases of Tmax and Tmin were found to be equal to 0.8 and 0.53, respectively. Similarly, the SC in the case of RHmin varied between - 0.29 and - 0.0038. This range for wind speed was between 0.06 and 0.22 and in the case of sunshine hours it was between 0.272 and 0.385. These findings would be useful in the scientific management of water resources in the region.

Investigate the possible reduction of mine water ingress by introducing tree plantations: Case study of Cooke 4 mine (South Africa)

Continuous influxes of groundwater into underground mine workings require a significant financial investment related mainly to the high costs of pumping of large volumes of water ingress, consequently mines become unprofitable. An innovative alternative to pumping methods with the purpose to reduce water volumes, is the establishment of deep rooted, high water-use vegetation covers to act as “artificial pumps”. Hydraulic control is one of the leading applications of plant-based strategies for remediating and managing groundwater systems by introducing plantations in selected areas with high ingress potential. This study investigates the impact of plantation introduction on the reduction of effective groundwater recharge. A temperature-based field model was formulated to determine daily ET from measured and observed leaf and air temperature. Results were compared to the FAO (Food and Agricultural Organisation) Penman-Monteith reference crop ET (Evapotranspiration) model and the Shuttleworth-Wallace models in order to validate the predictions of the field model. The developed field model was then used to predict monthly ET values for the Cooke 4 study area (Gemsbokfontein West compartment) to determine the possible reduction of pumping volumes. The area chosen for the proposed plantation was selected based on groundwater levels and the agricultural potential. A water balance for the study area has been developed through the use of the SVF (Saturated Volume Fluctuation) method and inflows to the study area has been modelled as head dependent by using a conductance term.

Evapotranspiration and crop coefficient of basil determined by weighing lysimeters

ABSTRACT The basil (Ocimum basilicum) crop is of great importance for trading as fresh or dried condiment for human consumption and essential oil for pharmaceutical and cosmetic industries. Water excesses and deficits can affect biomass production of plants, making it necessary to use the correct amount of water for each crop. Considering that determinations of water consumption and cultivation coefficients for medicinal plants are scarce, the aim of this study was determining evapotranspiration and crop coefficients of basil using lysimeters. The crop evapotranspiration was determined by weighing lysimeters for the replacements of 100, 75 and 50% of the maximum daily evapotranspiration. The reference crop evapotranspiration was estimated by the Penman-Monteith equation. Crop evapotranspiration for the 49 day cycle was 471, 352 and 236 mm, and daily rates ranged from 4.8 to 9.4; 4 to 8.1 and 3.7 to 7.4 mm/day, for the replacements of 100, 75 and 50% of the maximum daily evapotranspiration. Crop coefficients varied from 1.5 to 2.8 and were related to the days after transplanting, leaf area index, cover ratio and cumulative degrees-day.

Scaling Up Sap Flow Measurements from the Stem Scale to the Individual Scale for Multibranched Caragana Korshinskii on the Chinese Loess Plateau

The traditional heat balance method for measuring plant sap flow (SF) becomes troublesome and uneconomic for multibranched shrub species if all their stems are used for the measurement. The objectives of this study were to explore specific relationships between stem-scale SF and plant morphological traits and then to scale up SF measurements from the stem scale to the individual scale for Caragana korshinskii Kom., a dominant shrub species on the Chinese Loess Plateau. Sap flow was measured for twenty-one stems from three representative individuals from July to September 2018 during the rainy season. The results indicated that the stem-scale SF in C. korshinskii presented a positive linear correlation with the stem base diameter (SBD), stem length (SL), primary branch numbers in the stem (PBN), and estimated stem biomass (W). The SBD-based statistical models performed well in estimating the stem-scale SF, with an R2 value of 0.9726 and root mean squared error (RMSE) of 2.5389 g h−1. Over the canopy projection area, the individual-scale transpiration flows for the three selected C. korshinskii were 1.91, 1.10, and 1.59 mm·d−1. In addition, stem-scale SF was positively and linearly correlated with air temperature, photosynthetically active radiation, vapor pressure deficit, reference crop evapotranspiration, and variable transpiration. This study sheds light on morphological and meteorological influences on stem-scale SF and has made contributes to the accurate and rapid estimation of the plant sap flow from easily available morphological traits for multibranched shrub species in semiarid regions. Limitations, however, may exist for the established model when it is used to estimate SF of C. korshinskii during the water-limited dry season. Our study deserves further exploration of a more general model to have a better estimation of SF for C. korshinskii in both dry and rainy seasons.

Using a lysimetric station to determine the irrigation water requirements for chufa crop (Cyperus esculentus var. sativus)

Chufa, also known as tigernut, is a typical irrigated crop in Valencia, Spain, where it is traditionally cultivated for its tubers. Its cultivation uses large amounts of water, in the order of 10,000 m3 ha(‑1) year‑1. During the last years, the research team in which this study has been developed, has carried out several studies leading to improve the irrigation water use efficiency in chufa. Although these improvements are considerable, they are not definitive, as the water requirements of the crop are still unknown. To know these needs, it would be recommended to determine the crop evapotranspiration (ETc). The experiment was carried out on an experimental plot of the Universitat Politecnica de Valencia, included in the traditional cultivation area. This plot includes a lysimetric station (Smart Field Lysimeter) which allows determining the daily ETc. In addition, the plot is equipped with a meteorological station, which provides the necessary parameters for the determination of the daily reference crop evapotranspiration (ETo) through the FAO-56 Penman-Monteith method. Relating the values of ETc and ETo, the crop coefficient (Kc) values corresponding to the different growth stages, has been estimated from the data obtained during the crop cycle. Considering the crop development, the length of the four growth stages were considered as 21, 76, 43 and 29 days for initial, development, mid-season and late season stages, respectively. The single Kc values for the initial, mean and end of the late season stages were established as 0.25, 1.43 and 0.75, respectively. The use of these Kc values will allow adjusting irrigation water doses to water requirements, thus reducing the volume of water applied and improving the irrigation application efficiencies in chufa crop.

Performance of Various Forms of the Palmer Drought Severity Index in China from 1961 to 2013

Abstract A topic of ongoing debate on the application of PDSI is whether to use the original version of the PDSI or a self-calibrating form, as well as which method to use for calculating potential evapotranspiration (PET). In this study, the performances of four forms of the PDSI, including the original PDSI based on the Penman–Monteith method for calculating PET (ETp), the PDSI based on the crop reference evapotranspiration method for calculating PET (ET0), the self-calibrating PDSI (scPDSI) based on ETp, and the scPDSI based on ET0, were evaluated in China using the normalized difference vegetation index (NDVI), modeled soil moisture anomalies (SMA), and the terrestrial water storage deficit index (WSDI). The interannual variations of all forms of PDSI agreed well with each other and presented a weak increasing trend, suggesting a climate wetting in China from 1961 to 2013. PDSI-ET0 correlated more closely with NDVI anomalies, SMA, and WSDI than did PDSI-ETp in northern China, especially in northeastern China, while PDSI-ETp correlated more closely with SMA and WSDI in southern China. PDSI-ET0 performed better than PDSI-ETp in regions where the annual average rainfall is between 350 and 750 mm yr−1. The spatial comparability of scPDSI was better than that of PDSI, while the PDSI correlated more closely with NDVI anomalies, SMA, and WSDI than did scPDSI in most regions of China. Knowledge from this study provides important information for the choice of PDSI forms when it is applied for different practices.