干旱荒漠草原应用Penman-Monteith与Penman修正式计算ET0的偏差分析

甘肃天祝草原位于我国西北干旱荒漠草原,应用天祝县二道墩试验站2005年的实测气象资料,利用Penman-Monteith公式和Penman修正式计算参考作物腾发量(ET0)并进行了比较。Penman修正式计算的参考作物腾发量ET0值略小于Penman-Monteith公式计算的值,最大绝对偏差0.5 mm/d。分析发现生育期辐射项ETrad是导致参考作物腾发量ET0产生偏差的主要原因。2种方法计算的空气动力项ETaero差别较小,最大绝对偏差不超过0.2 mm/d。导致计算偏差的原因在于2种公式采用了不同的辐射项和空气动力学项计算公式和参数。2个公式计算的参考作物腾发量具有显著的线性相关性。     

豫西北几种ET_0计算方法的比较及Hargeaves公式的修正

根据豫西北地区30年的气象资料,选用辐射法中的Makkink公式和Priestley-Taylor公式以及温度法的Hargreaves公式和McCloud公式计算了ET0,并以Penman-Monteith公式为标准,分别对各公式年值和旬均值的绝对误差、相对误差和累计误差进行分析,结果显示Hargreaves公式的精度最高。为了进一步提高Hargreaves公式的应用精度,建立了线形回归方程,并对其进行了修正。     

(A)ngstr(o)m-Prescott系数选取对参考作物蒸散量的影响-以黄河中游站点为例

利用黄河中游三个站点近50a的气象资料,研究了(A)ngstr(o)m-Prescott系数不同取值对参考作物蒸散量的影响.结果显示,当ngstrm-Prescott系数as和bs分别相差56%和93%时,引起的ET0差异月值在0.6%～26.2%,年值在173.1～197.4mm(18.2%～21.9%).ngstrm-Prescott系数不同取值对ET0的影响程度随地点而变化,即随海拔和日照时数的增加,对ET0的影响程度相应增大.因此在高海拔和高辐射地区,应对ngstrm-Prescott系数进行校正.尽管FAO56 PM推荐的(A)ngstr(o)m-Prescott系数在世界各地广泛应用,但依据本文结果尚不能确定其在中国能否直接使用.随着辐射数据的不断积累,有必要对这些系数进一步研究、验证和校正.     

参考作物腾发量长期年际变化规律及其机理探讨

运用Penman-Monteith方法,对北京昌平、开封惠北及湖北团林3个灌排试验站的近几十年参考作物腾发量(ET0)进行计算,结果显示,惠北及团林站年均ET0在近几十年呈现随时间而下降的趋势,而昌平站年均ET0则随时间而上升。ET0与同步气象资料变化分析表明,ET0的上述变化是由于气象环境变化所引起,其中相对湿度是最主要原因,其次为温度及日照时数。对昌平站,由于相对湿度的降低和风速的增加,ET0表现出上升的趋势;对惠北及团林站,由于相对湿度的增加和日照时数的减少,ET0表现出下降的趋势。     

Variation in reference crop evapotranspiration caused by the Ångström-Prescott coefficient: Locally calibrated versus the FAO recommended

Accurate estimation of the reference crop evapotranspiration (ET₀) is investigated due to its critical role in affecting calculation of crop water use and efficiency in agricultural ecosystems. The main emphasis in this paper is to clarify the possible uncertainty in the estimation of ET₀ associated with using un-calibrated Ångström-Prescott (A-P) coefficients. We first calibrated the coefficients using long-term data records from 34 sites in the Yellow River basin in China, and then applied these coefficients to estimate short wave irradiance (R_s) and ET₀ at 16 sites to evaluate the difference in ET₀ between the FAO recommended and the locally calibrated. We found that the direct use of the FAO recommended coefficients significantly affected the estimation of ET₀ at most sites, which differed from −3% to 15% at daily scale and from −4% to 16% at monthly scale from the locally calibrated ones. These differences are comparable with or larger than those caused by some alternatives of the FAO recommended algorithms for net irradiance or vapor pressure, which further highlights the importance of using the locally calibrated coefficients. The degree of difference in ET₀ showed a significant threshold relation with altitude and longitude in such a way that relatively small impact lies around 2233 m and 98°E, and away from these, the effect begins to increase. Given the large overestimation in water use as a consequence of the significant overestimation in ET₀ associated with the direct use of the FAO coefficients, especially in those high yield production areas with altitude <1200 m, we developed several relationships between the A-P coefficient a, b, (a + b) and other easily obtainable factors (altitude, longitude and air temperature). A three-step procedure was recommended in applying these relations, which was (1) determine if calibration is needed or not for a given location; (2) estimate one of the A-P coefficients, either a or b if calibration is needed; (3) estimate the remaining coefficient using relations of (a + b) due to its higher coefficient of determination. In summary, we have revealed the errors and areas that are most affected when using the un-calibrated coefficients, and discussed the consequence of such error on agricultural production, and proposed practical solutions to avoid large errors. These results are intended to make the research community aware of such errors so that more appropriate choice of these coefficients is made. We hope that similar assessment will be done in other climates, contributing to managing water resources efficiently in water basins.     

Determination of growth-stage-specific crop coefficients (KC) of maize and sorghum

A ratio of crop evapotranspiration (ET_C) to reference evapotranspiration (ET_O) determines a crop coefficient (K_C) value, which is related to specific crop phenological development to improve transferability of the K_C values. Development of K_C can assist in predicting crop irrigation needs using meteorological data from weather stations. The objective of the research was conducted to determine growth-stage-specific K_C and crop water use for maize (Zea Mays) and sorghum (Sorghum bicolor) at Texas AgriLife Research field in Uvalde, TX, USA from 2002 to 2008. Seven lysimeters, weighing about 14 Mg, consisted of undisturbed 1.5 m × 2.0 m × 2.2 m deep soil monoliths. Six lysimeters were located in the center of a 1-ha field beneath a linear-move sprinkler system equipped with low energy precision application (LEPA). A seventh lysimeter was established to measure reference grass ET_O. Crop water requirements, K_C determination, and comparison to existing FAO K_C values were determined over a 3-year period for both maize and sorghum. Accumulated seasonal crop water use ranged between 441 and 641 mm for maize and between 491 and 533 mm for sorghum. The K_C values determined during the growing seasons varied from 0.2 to 1.2 for maize and 0.2 to 1.0 for sorghum. Some of the values corresponded and some did not correspond to those from FAO-56 and from the Texas High Plains and elsewhere in other states. We assume that the development of regionally based and growth-stage-specific K_C helps in irrigation management and provides precise water applications for this region.     

基于Penman-Monteith公式的关中地区作物系数研究

通过对基于Penman-Monteith公式的作物系数研究,为Penman-Monteith公式在关中地区的推广应用提供参考。采用联合国粮农组织(FAO)先后推荐的Penman修正式与Penman-Monteith公式,计算关中地区30个气象站1961~2001年的参照作物腾发量,确定关中地区冬小麦和夏玉米基于Penman-Monteith公式的作物系数,比较分析基于Penman修正式与基于Penman-Moneith公式的作物系数的差异。在关中地区,冬小麦基于Penman修正式与基于Penman-Moneith公式的作物系数有显著差异;而夏玉米的没有显著差异。在关中地区推广应用Pen-man-Monteith公式计算作物需水量时,目前正在使用的基于Penman修正式的冬小麦作物系数需要校正;而夏玉米作物系数无须校正。     

咸阳地区参考蒸散量变化特征及敏感性分析

为了研究咸阳地区作物参考蒸散量变化特征及其影响因素,利用1981—2012年咸阳地区的气象资料,根据Penman-Monteith公式计算参考蒸散量(ET_0),分析咸阳地区的ET_0及主要气象因子的变化趋势,并通过响应曲线和敏感矩阵分析咸阳地区ET_0对气温、日照时数、风速、相对湿度等的敏感性。结果表明:(1)咸阳地区年平均日ET_0整体上处于基本稳定状态,在以2.37 mm/d为平均值、±0.3 mm/d的范围内波动;(2)咸阳地区的年平均气温、最高气温及最低气温均呈显著增长趋势,平均风速与平均相对湿度呈下降趋势;(3)咸阳地区多年日平均参考蒸散量年际变化以及四季变化趋势不明显;(4)气温、日照时数、平均风速的变化与日ET_0呈正比关系,而平均气压和平均相对湿度与日ET_0呈显著负相关,并且平均相对湿度对日ET_0的影响最为明显。该结果对确定咸阳地区的作物需水量有重要指导意义。     

沈阳市灌区水田耗水量的试验与计算

对沈阳市十个主要水田灌区进行了两方面研究:彭曼-蒙特斯公式水田需水量的计算、水田渗漏量的试验和计算。最后得出沈阳市十个主要灌区的水田需水量、渗漏量和耗水量结果,为灌区工程的规划、设计和管理提供依据。     

参考作物腾发量计算方法的应用比较

应用陕西杨凌地区2001～2002年的气象数据,对3种不同类型的参考作物腾发量计算公式进行比较,用这些公式计算日ETo值,并以FAO 56 Penman-Moteith公式为标准,比较3种方法计算结果的相异性和相关性,并探讨了以简化的ETo公式为基础进行参考作物腾发量的预报.