新疆玛纳斯河流域玉米田蒸散量的估算研究

根据新疆乌兰乌苏农试站１９８７－１９８８年的试验资料,选用Ｐｒｉｅｓｔｌｅｙ和Ｔａｙｌｏｒ的农田蒸散力,作物生物学特性函数和农田土壤水分有效性函数,应用数理统计方法建立了新疆玛纳斯河流域玉米田蒸散量估算模型。该模型只需常规气象资料和农业气象资料,计算简便,具有较高的精度,便于在干旱区推广使用。     

Calibration of Hargreaves–Samani and Priestley–Taylor equations in estimating reference evapotranspiration in the Northwest of Iran

Accurate estimation of reference evapotranspiration (ET_o) is essential for water resources management and irrigation systems scheduling, especially in arid and semiarid regions such as Iran. In the present research, constant coefficients of Hargreaves–Samani (C_H–S) and Priestley–Taylor (C_P–T) equations were locally calibrated to estimate the ET_o based on the FAO–Penmen–Monteith (PM) method as standard method. For this purpose, meteorological data of eight synoptic stations located in the northwest of Iran were used during the period of 1997–2008. The outcomes showed that the values of C_H–S and C_P–T were 0.0026 (instead of 0.0023) and 1.68 (instead of 1.26), respectively. Also, at stations with high wind speed, the values of calibrated coefficients of C_H–S and C_P–T were maximum. Then, the estimated ET_o values using adjusted C_H–S and C_P–T coefficients were compared to the obtained actual ET_o values by PM method using root mean square error and mean bias error indices. The results indicated that the new calibrated H–S and P–T equations have good agreement with the PM method for estimation of the ET_o. Moreover, the equation of Ravazzani et al. was calibrated in the studied region. It was concluded that in general, the mentioned equation was shown better performance than original H–S equation.     

Priestley-Taylor与Penman法计算参照作物腾发量的结果比较

利用北京气象站50年的气象资料，对两种常用的计算参照作物腾发量的公式——Priestley-Taylor和Penman方法的计算结果进行了比较。年值序列比较显示，Priestley-Taylor结果远小于Penman结果，前者比后者低15%～31%，两者最大相差378.3 mm，最小相差150.9 mm，多年平均相差255.9 mm。对历年逐月序列分析显示，两种方法在7、8月份的结果十分接近，没有显著差异，但其它月份均存在显著差异。造成这种显著差异的原因，既有降雨的影响，又有Penman中空气动力学项的影响，而后者的影响可能更大些。空气动力项与辐射项之比与两种方法的吻合程度呈显著负相关。该比值越大，两种方法的吻合程度越差；反之，吻合程度越好。     

豫北地区参考作物需水量计算方法比较与评价

[目的]比较豫北地区参考作物需水量的计算方法。[方法]利用新乡站点连续47年气象资料,采用Hargreaves公式和Priestley Taylor公式计算参考作物需水量,以Penman-Monteith公式计算结果作为对照,用统计学方法对Hargreaves公式和Priestley Taylor公式计算结果进行对比评价。[结果]Hargreaves公式和Priestley Taylor公式计算结果均与Penman-Monteith公式结算结果呈线性关系,相关系数分别为0.946 1和0.922 2,拟合度分别为98%和97%。[结论]在豫北地区可以用Hargreaves公式和Priestley Taylor公式代替Penman-Monteith公式计算参考作物需水量,并且Hargreaves公式比Priestley Taylor公式计算更精准。     

Evaluation and calibration of simple methods for daily reference evapotranspiration estimation in humid East China

The current study aims to improve the performance of simple methods for the estimation of daily reference evapotranspiration (ET₀) in humid East China, namely Priestley–Taylor 1972 (P-T 1972), Hargreaves–Samani 1985 (H-S 1985) and Turc 1961 (TU 1961). These methods were evaluated and calibrated based on well-watered grass lysimeter experiments. The FAO-56 Penman–Monteith equation (FAO-56 PM) is the best method, and the radiation-based methods (TU 1961 and P-T 1972) perform much better than the temperature-based method (H-S 1985). In the simple methods, the coefficients are calibrated to: 1.34 for P-T 1972; 0.0186, 23.47 and 17.06 for TU 1961; and 0.0027 and 0.449 for H-S 1985. The locally calibrated TU 1961 and P-T 1972 perform much better than the original, with either the observed ET_0r or the ET_0c obtained by FAO-56 PM as standard. However, local calibration does not significantly improve the performance of the H-S 1985 method. In humid East China, FAO-56 PM is the best method for daily ET₀ calculation. TU 1961, especially if locally calibrated, is the optimal choice as a simple substitute for FAO-56 PM when solar radiation is available. Otherwise, serious local calibration is strongly recommended before applying H-S 1985 for daily ET₀ estimation.     

A New Simple Method to Determine Crop Coefficients for Water Allocation Planning from Satellites: Results from Kenya

Crop coefficient K_c is defined as theratio of crop potential and grass referenceevapotranspiration. This paper discussesthe estimation of crop potentialevapotranspiration from remote sensing datato deduce spatial variable and regionalscale crop coefficients. Maps of cropcoefficients avoid the need to frequentlyuse remote sensing data because grassreference evapotranspiration obtained fromroutine weather data describe the shorterterm day-to-day variation. The new methodis based on the simplified Priestley &Taylor equation for cropevapotranspiration. It is argued that thisis justified for humid conditions and thecalculation procedure is validated withfield data collected from irrigatedvegetables in Kenya. The method isthereafter applied to Landsat-TM satellitedata covering the Lake Naivasha Basin,Kenya, and the spatially variable cropcoefficients are determined. This simpletechnique improves the planning ofirrigation water resources because K_cestimations based on satellite imagesreveal the real agricultural practicesbetter than expected acreage data andtabulated K_c-values published in theinternational literature.