基于温度信息和历史阈值的蒸散发预报及修正

蒸散发（ET_c）是陆面和大气之间物质与能量交换的关键要素,其精准预报对于制定合理的灌溉计划和提高水分利用效率至关重要。本文以华北平原冬小麦和夏玉米为研究对象,在作物充分供水条件下,重点考虑了温度对作物生长的影响,发展了基于温度效应的作物系数（K_c）和参考作物蒸散发（ET_o）估算模型,构建了ET_c预报模型（简称：M_T）;考虑极端天气情况的不确定性影响,通过构建历史阈值修正函数进一步发展了M_T模型,形成了M_T-threshold模型,并以涡度相关法实测值为依据,验证了M_T-threshold模型在1~15 d预见期的适用性。结果表明：基于温度效应的K_c预报值与实测值拟合效果较好,1~15 d预见期内具有较好的适用性;率定后Hargreaves-Samani模型的ET_o估算效果较好,1~15 d预见期的预报准确率均在72%以上,且冬小麦生长季的预报效果优于夏玉米生长季;M_T模型在1~7 d预见期具有较好的适用性（预报准确率>83%）;M_T-threshold模型在1~15 d预见期的预报效果有明显提升,1~7 d预见期的预报精度提高2%以上,预报精度均在86%以上;8~15 d预见期预报准确率提高8%以上,预报精度均在80%以上。因此,基于温度预报信息及作物生长历史阈值能够较好的实现ET_c短中期预报。     

Estimation of Crop Coefficient and Evapotranspiration of Wheat (Triticum aestivum) in an Irrigation Command Using Remote Sensing and GIS

Remote sensing and Geographical Information System (GIS) techniques were used to estimate actual crop evapotranspiration of wheat crop grown in Tarafeni South Main Canal (TSMC) irrigation command of West Bengal State in India. The area under wheat crop was clipped from landuse/land cover map generated from Indian Remote Sensing Satellite P6 (IRS P6) image of January, 2004 for winter season 2003–04. The IRS P6 image and four wide field sensor (WiFS) images for different months of winter season were used to determine the Normalized Difference Vegetation Index (NDVI) and Soil Adjusted Vegetation Index (SAVI) for area under wheat crop. The relationship between vegetation indices and crop coefficients (K_c) of wheat for corresponding months were developed. Based on these developed regression equations crop coefficient maps were generated for each month of wheat crop season. Monthly reference crop evapotranspiration (ETo) was estimated based on FAO-56, Penman–Monteith method. ETo was combined with spatially distributed K_c maps of different months of wheat crop season to generate crop evapotranspiration (ET_c) maps of each month. The crop water demand of wheat estimated using spatially distributed ET_c maps for months of December 2003, January 2004, February 2004, March 2004 (1st Fortnight) and March 2004 (2nd Fortnight) were found to be 3.98, 8.14, 4.66, 2.49, and 1.21 million cubic meter (MCM) respectively. Based on crop evapotranspiration the total crop water demand of wheat crop in irrigation command of TSMC was estimated as 20.48 MCM.     

Evaluating and Calibrating Reference Evapotranspiration Models Using Water Balance under Hyper-Arid Environment

This research investigates five reference evapotranspiration models (one combined model, one temperature-based model, and three radiation-based models) under hyper-arid environmental conditions at the operational field level. These models were evaluated and calibrated using the weekly water balance of alfalfa by EnviroSCAN to calculate crop evapotranspiration (ET_c). Calibration models were evaluated and validated using wheat and potatoes, respectively, on the basis of weekly water balance. Based on the results and discussion, the FAO-56 Penman-Monteith model proved to be superior in estimating ET_c with a slight underestimation of 2 %. Meanwhile, the Hargreaves-Samani (HS) model (temperature-based) underestimated ET_c by 20 % and the Priestley-Taylor (PT) and Makkink (MK) models (radiation-based) had similar performances underestimating by up to 35 % of the measured ET_c. The Turc (TR) model had the lowest performance compared with other models, demonstrating values underestimated by up to 60 % of the measured ET_c. Local calibration based on alfalfa evapotranspiration measurements was used to rectify these underestimations. The surprisingly good performance of the calibrated simple HS model, with a new coefficient 0.0029, demonstrated its favorable potential to improve irrigation scheduling. The MK and PT models were in third and fourth rank, respectively, reflecting minor differences between one another. The new coefficients obtained for the MK and PT models were 1.99 and 0.963, respectively. One important observation was that the calibrated TR model performed poorly, with an increase in its coefficient from 0.013 to 0.034 to account for hyper-arid environmental conditions; moreover, it required additional seasonal calibration to adequately improve its performance.     

应用双作物系数模型估算温室番茄耗水量

准确估算作物耗水量对于合理利用有限的水资源和制定合理的灌溉制度至关重要。本文利用3个生长季的西北地区日光温室番茄水量平衡计算耗水资料,率定和验证双作物系数模型SIMDual Kc在日光温室条件下的适用性。结果表明耗水模拟值与实测值有较好的一致性。模型估算的平均标准误差为0.55 mm·d-1,平均绝对误差为0.44 mm·d-1。模型估算的番茄初期、中期和后期的基础作物系数分别为0.50、0.85和0.55。番茄生育初期蒸发占耗水的比例最大为22.8%;发育期最小,仅为3.2%。3年全生育期总蒸发量占总耗水量的比例平均为5.9%,表明温室生产中植株蒸腾为耗水最主要部分。     

Evaluation of Reference Crop Evapotranspiration Equations in Various Climates

Evapotranspiration is one of the most important elements for quantifying available water since it generally constitutes the largest component of the terrestrial water cycle. This study evaluated four models (Makkink, Turc, Priestley–Taylor and Hargreaves) commonly used to estimate monthly reference crop evapotranspiration (ET_o) values. The main aim of this study was to determine the model used to estimate ET_o with small data requirements and high accuracy for twelve synoptic stations in four climates of Iran. The results showed that the Turc model was the best suited model in estimating ET_o for cold humid and arid climates. The Hargreaves model turned out to be the most precise model under warm humid and semi-arid climatic conditions. In contrast, the Makkink model presented the poorest estimates in all of the climates exception for cold humid environment. In cold humid climate, the Hargreaves model was the least accurate model in estimating ET_o. In general, the results obtained from this study revealed very clearly that the Makkink and Priestley–Taylor models estimated ET_o values less accurately than Turc and Hargreaves models for the all climates.     

Assessment of the Performance of a Distributed Code in Relation to the ETp Estimates

This article is a preliminary report of a research activityfocusing on the effects of the crop potentialevapotranspiration (ET_p) generation methods on boththe performance of a distributed catchment model as well ason the magnitude of its main effective parameters. Thereferred effects were assessed on the basis of theindependent Multi-Calibration (MC) of the distributed modelfor which three different ET_p scenarios were generatedas follows: (A) FAO-24 standard approach;(B) FAO-24 approach but used with coefficients of the wind function and of the Stefan-Boltzmann equation selected according to local conditions; and (C) FAO-56 standard approach. ET_p was estimated as a function of the reference crop evapotranspiration (ET_o) by means of the k _c-ET_o approach. For assessing the performance of theestimation approach, the ET_o outputs of the three scenarioswere compared to local ET_o constraints derived from a previous research. The outputs of scenario B and scenario C showed a close agreement with the local ET_o constraints. Their effect on the performance of the hydrological model alsoseemed to be comparable. The output of scenario A producedhigher estimates than the outputs of the other two scenarios, inthe order of 200 mm per year. The best model performance was obtained by using the estimates of scenario A. The research alsorevealed the weak dependency of the model effective parametersinspected in this preliminary research on the ET_pestimating methods.     

黄土高原北部淤地坝区域土壤水分模拟及水分有效性——以六道沟流域为例

为揭示黄土高原北部淤地坝区域土壤水分变化特征及其有效性,以黄土高原北部六道沟流域的一处淤地坝区域为研究区,基于实测的水文、气象数据,利用Penman公式和Penman-Monteith公式分别推求参考作物的蒸散发以及草地蒸散发,并对水分有效性进行评估;基于非饱和土壤水分运动方程式(Richards formula)构建了一维土壤水分计算模型,并对土壤水分进行模拟。结果表明:计算时段内,研究区的水分有效性参数值受同期表层土壤含水量和蒸散发的影响较大;淤地坝区域的水分有效性参数均值(0.31)比坡面均值(0.17)大;构建的一维土壤水分模型模拟精度较高,实测值与模拟值之间的相关系数以及模型的纳什效率(Nash-Sutcliffe efficiency(NSE))系数在0.90以上。研究结果可为黄土高原北部淤地坝区域蒸散发和土壤水分运动的深入研究提供基础数据和方法上的借鉴。     

Spatio-temporal Calibration of Blaney–Criddle Equation in Arid and Semiarid Environment

Estimates of reference evapotranspiration (ET_o) are widely used in irrigation engineering to define crop water requirements. A major drawback to application of the FAO Penman-Monteith is the relatively high data demand which unfortunately, for many locations; such meteorological variables are often incomplete and/or not available. Alternatively, the Blaney–Criddle (BC) equation is a simpler method for ET_o estimation. In this study, the BC equation was calibrated using three methods: spatially calibration at each station for the whole period (ET_o-BC_S); two periods calibration (ET_o-BC_S2); and spatial and temporal calibration at each station for each month (ET_o-BC_S,T) using twelve stations a cross Jordan. The calibration coefficient of BC equation (a, b) were determined at all stations. The results of the calibration methods showed that: (1) the spatial calibration of BC had the highest RMSE, and ME and Lower R² comparing to spatial and temporal calibration and two periods calibration. (2) Improvement was achieved for the BC equation when considering the spatial and temporal calibration for all months at each station. The values of a were negative for all months of any station. The higher values of a are coincided with cold or low temperature months while the high values coincided with high month temperature. The b values were positive for the whole stations and months. As the a values, it seems that b values had higher values in warm months than the cold one. A relatively good improvement could be obtained using two periods calibration instead of one period. The maps of a and b clearly show that a and b varied considerably in the study area and being aware of the spatial temporal variations of climatologically parameters is important in managing the limited water resources. Knowing the spatial temporal changes of such parameters, accurate calculations of ET_o can be achieved which will lead to precise and elevate water resources management in the arid region such as Jordan.     

基于AquaGIS模型的盈科灌区制种玉米农业用水效率分析

盈科灌区是黑河流域中游绿洲典型灌区之一,该灌区农业用水效率较低,农业用水矛盾十分突出。制种玉米是灌区主要种植作物,研究制种玉米的优化灌溉制度对实现该区域农业用水可持续发展具有十分重要的意义。利用分布式作物模型AquaGIS模型,基于盈科灌区土壤质地的空间变异性对该灌区制种玉米灌溉制度进行了优化,提出了适合灌区实际配水情况的最佳灌溉制度。通过灌溉制度优化,灌区制种玉米蒸散发量减少36~53mm,水分生产率WPET增加5%左右,灌溉水生产率WPI增加25%~48%,极大地提高了灌区农业用水效率。同时,对该灌区不同水文年灌溉制度进行优化,综合对比灌区制种玉米WPET、WPI和产量,其中丰水年灌溉3次、平水年灌溉4次、枯水年灌溉5次可以实现农业用水效率最高,为灌区高效节水灌溉提供理论指导。     

Groundwater Use for Irrigation and its Productivity: Status and Opportunities for Crop Intensification for Food Security in Bangladesh

Bangladesh has a large and growing population that will demand more food and place greater pressure on resources. Dry season irrigated Boro rice production is important for national food security. Dry season irrigation mainly uses groundwater, but the extent of its use is not well known. We assessed groundwater use and water productivity of Boro in the northwest region of Bangladesh using remote sensing based energy balance modelling, crop classification and secondary statistics. The energy balance modelling shows a large spatial variation in the actual evapotranspiration (ET_a) from about 325 to 470 mm, with an overall spatial average of 365 mm during dry season. The estimated values of ET_a correspond well with independent values from field and regional scale soil and water balance modelling results. From spatial estimates of ET_a and effective rainfall, we computed regional net groundwater use for Boro production in 2009 as 2.4 km³. Groundwater is being used unsustainably in some areas, and a spatial time series (1990 to 2010) of pre- and post-monsoon groundwater depth changes in the northwest region of Bangladesh suggests that, with the current level of groundwater use, falling groundwater levels may pose a long term threat to the sustainability of irrigated agriculture in much of the region. Boro water productivity varies from 0.95 to 1.35 kg/m³, allowing the identification of high performing “bright” and low performing “hot” spots and the development of strategies to reduce crop yield/productivity gaps and ensure future food security.     

Assessment of Water Availability and Consumption in the Karkheh River Basin,Iran—Using Remote Sensing and Geo-statistics

This study was conducted to assess water availability and consumption in the Karkheh River Basin in Iran using secondary data and freely available satellite data. Precipitation was estimated using geo-statistical techniques while a Surface Energy Balance approach was selected for evapotranspiration estimation. The spatial distribution of actual evapotranspiration (ET_a) for the Karkheh Basin has been estimated by use of 19 cloud free Moderate Resolution Imaging Spectroradiometer (MODIS) images, which cover a complete cropping year from November 2002 to October 2003. ET_a estimates were compared to potential crop evapotranspiration (ET_p) estimates for two predominantly irrigated wheat areas in Upper and Lower Karkheh. Differences were found to be 12.5% and 11.7% respectively. Results of the ETa and precipitation estimates reveal that for the study period, the Karkheh Basin received 18,507 × 10⁶m³ as precipitation while ET_a is estimated at 16,680 × 10⁶m³. Estimated outflow from the basin for the study period only is 7.8% of the precipitation and indicates that water is a very scarce resource in the Karkheh basin. The basin has been divided in sub-basins to allow for more detailed analysis and results indicate that water balance closure at sub-basin scale ranges from 7.2% to 0.6% of the precipitation. This suggests that the water balance is sufficiently understood for policy and decision making.     

An Integrated Assessment of the Impacts of Changing Climate Variability on Agricultural Productivity and Profitability in an Irrigated Mediterranean Catchment

Climate change is likely to have a profound effect on many agricultural variables, although the extent of its influence will vary over the course of the annual farm management cycle. Consequently, the effect of different and interconnected physical, technical and economic factors must be modeled in order to estimate the effects of climate change on agricultural productivity. Such modeling commonly makes use of indicators that summarize the among environmental factors that are considered when farmers plan their activities. This study uses net evapotranspiration (ET_N), estimated using EPIC, as a proxy index for the physical factors considered by farmers when managing irrigation. Recent trends suggest that the probability distribution function of ET_N may continue to change in the near future due to changes in the irrigation needs of crops. Also, water availability may continue to vary due to changes in the rainfall regime. The impacts of the uncertainties related to these changes on costs are evaluated using a Discrete Stochastic Programming model representing an irrigable Mediterranean area where limited water is supplied from a reservoir. In this context, adaptation to climate change can be best supported by improvements to the collective irrigation systems, rather than by measures aimed at individual farms such as those contained within the rural development policy.     

作物需水量与灌溉制度模拟

从作物需水量的基本概念出发，以水量平衡原理为基础，建立了模拟农田根层土壤水循环的计算机模型-ISAREG.这一模型具有多种功能，可模拟根层土壤水分变化，评价给定的灌溉制度，计算作物需水量和灌溉需水量，也可用以制订多种供水限制条件下的优化灌溉制度．用望都灌溉试验站的小麦、玉米、棉花3种作物两年的试验观测资料对上述模型进行了验证．     

Simulation supported scenario analysis for water resources planning: a case study in northern Italy.

The work presents the results of a comprehensive modelling study of surface and groundwater resources in the Muzza-Bassa Lodigiana irrigation district, in Northern Italy. It assesses the impact of changes in land use and irrigation water availability on the distribution of crop water consumption in space and time, as well as on the groundwater resources. A distributed, integrated surface water-groundwater simulation system was implemented and applied to the study area. The system is based on the coupling of a conceptual vadose zone model with the groundwater model MODFLOW. To assess the impact of land use and irrigation water availability on water deficit for crops as well as on groundwater system in the area, a number of management scenarios were identified and compared with a base scenario, reflecting the present conditions. Changes in land use may alter significantly both total crop water requirement and aquifer recharge. Water supply is sufficient to meet demand under present conditions and, from the crop water use viewpoint, a reduction of water availability has a positive effect on the overall irrigation system efficiency; however, evapotranspiration deficit increases, concentrated in July and August, when it may be critical for maize crops.     

考虑气象因子不确定性的参考作物蒸散量预报方法

参考作物蒸散量(ET0)的准确预测预报对于制定作物灌溉制度与实时灌溉调度具有重要意义,然而气象因子的不确定性极大的影响着ET0的预测精度.因此本研究采用马尔科夫蒙特卡罗模拟与自适应采样算法相结合的方法(AM-MCMC)对气象因子的不确定性进行修正,以气象站实测ET0作为标准值,利用径向基神经网络(RBF)模型建立气象因...     

Multiple Linear Correlation Analysis of Daily Reference Evapotranspiration

An accurate estimation of reference evapotranspiration (ET₀) is of paramount importance for many studies such as hydrologic water balance, irrigation system design and management, crop yield simulation, and water resources planning and management. Simple regression techniques, may sometimes, provide adequate estimation of ET₀. Implementation of regression methods considering all the predictor variables may, however, lead to overfit and consequent reduction in the predictive capability. The regression models for ET₀ have been developed in the present study for Tirupati, Nellore, Rajahmundry, Anakapalli and Rajendranagar regions of Andhra Pradesh, India by following step-wise procedure, eliminating superfluous predictor variables based on statistical criteria. The sunshine hours, wind velocity, temperature and relative humidity influenced ET₀ in the study area. The linear regression models developed in terms of predictor variables may conveniently be applied in the regions selected for the present study and, in the regions with similar climatic conditions for satisfactory ET₀ estimation.     

Framework for Standardizing Less Data-Intensive Methods of Reference Evapotranspiration Estimation

Evapotranspiration is one of the vital components of water cycle and its accurate estimation is the key to sustainable management of irrigation water. The FAO Penman-Monteith (FAO-PM) method is recommended as the standard method for computing reference evapotranspiration (ET_o) as well as for evaluating other indirect methods. However, due to the lack of weather data such as radiation, relative humidity and wind speed in many regions of the world, especially in developing countries, the FAO-PM method is difficult to use. To address this issue, a fairly robust methodology is proposed in this study to standardize two popular less data-intensive (temperature-based) ET_o methods, viz., Hargreaves-Samani (HS) and Penman-Monteith Temperature (PMT) against the FAO-PM method. To achieve this goal, the daily and monthly biases of these two methods were adjusted using the weather data of 14 locations for the 1979–2003 period. Subsequently, the performance of the standardized (de-biased) less data-intensive methods were verified using salient statistical and graphical indicators for the 2004–2013 period. The results indicated that the HS and PMT methods underestimate ET_o on a monthly time step by 9.62 and 14.77%, respectively. However, the performances of these methods significantly improve after the standardization. The estimates of ET_o by the standardized less data-intensive methods were found to be in close agreement with those by the standard FAO-PM method, thereby suggesting the usefulness and applicability of the proposed framework in data-scarce situations irrespective of agro-climatic conditions.     

Assessment of Blaney-Criddle Equation for Calculating Reference Evapotranspiration with NOAA/AVHRR Data

Reference evapotranspiration (ET₀) data are desirable for assessing crop water requirements and irrigation needs. A large number of methods have been developed for assessing ET₀ from meteorological data. In several places of the world, the existing network of weather stations is insufficient to capture the spatial heterogeneity of this variable The purpose of this work is to investigate whether it is possible to attain reliable estimation of ET₀ only on the basis of the remote sensing-based surface temperature (T_s) data by Blaney-Criddle (B-C) model under a semi arid environment of Iran. This study has assumed that the daytime surface temperature at the cold pixel obtained from the AVHRR/NOAA sensor can be used instead of air temperature in the Blaney-Criddle (BC) equation for ET₀ estimation in irrigated area. For this purpose, 61 NOAA- AVHRR satellite images acquired between June and September in 2004 and 2005 and weather data measured at two weather located in two irrigation regions with sugar cane located in Khuzestan plain in the southwest of Iran were used to calibrate and test the B-C model. The FAO-56 Penman–Monteith model was used as a reference model for assessing the performance of the calibrated BC model. The results show that calibrated B-C model provided close agreement with the reference values, with an average RMSE of 1.0 mm day^?1and a R² of 0.91.     

覆膜滴灌下枸杞耗水规律研究

通过大田枸杞滴灌和传统畦灌对照处理试验,研究了覆膜滴灌下枸杞耗水规律、水分利用效率和产量的变化规律,结果表明,枸杞覆膜滴灌生育期内耗水量相比传统畦灌平均减少了34%,生育期内灌溉定额相比传统畦灌平均节约了52%。当覆膜滴灌枸杞耗水量为612 mm时,枸杞的水分效率和干果产量达到最优组合水平。     

河套灌区套种模式下田间灌水有效性评价

针对河套灌区典型的套种模式以及地下水位较浅的情况,基于SPAC系统应用土壤水动力学理论定量分析了作物生育期内大气水、灌溉水、作物水、土壤水和地下水的相互转化关系。应用FAO推荐的Penman-Monteith法及双作物系数法,对小麦套种玉米、小麦套种向日葵模式的实际腾发量进行了计算。从动态观点出发,在时间尺度上考虑深层渗漏量和根系层储水量对作物的有效性,对灌区田间灌溉水的有效性进行了评价。结果表明:小麦套种玉米的实际腾发量为635.8 mm,小麦套种向日葵的实际腾发量为428.2 mm;小麦套种玉米灌溉水利用率为91.9%,小麦套种向日葵的灌水利用效率为88.4%。