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1.
The standardized ASCE Penman–Monteith and FAO-56 equations were used to estimate reference evapotranspiration (ET0) using estimated and measured net radiation (Rn) and soil heat flux (G), based on hourly and daily meteorological data. The estimates were evaluated against lysimeter measurements. The results indicate that using measured or estimated values of Rn and G can have significant effect on the accuracy of the ET0 estimations, especially when calculations were made on an hourly basis. The FAO-56 version performed very well during the irrigation season on a daily basis. The use of measured Rn and G did not improve ET0 estimation on a daily basis, therefore, the use of estimated Rn and G appears to be dependable when calculations are based on 24-h weather data. When daily ET0 was calculated from hourly estimations, the results were different depending on the version used. The ASCE version was more accurate, especially when Rn and G were measured. Therefore, measurement of Rn and G may have potential to improve estimation only when daily ET0 is calculated from hourly estimations. The PM FAO-56 version was always a little less accurate than the ASCE version. For hourly calculations, using a constant surface resistance (as in FAO-56 version), the PM method underpredicted for high evaporative demand and vice versa. The ASCE version performed better than PM FAO-56 version when Rn and G were measured and estimated. Therefore, ASCE version tended to provide quite accurate values of hourly ET0, even using estimated values of Rn and G. As conclusion, the methods proposed by FAO-56 for estimating Rn and G tended to produce accurate estimates for daily and hourly ET0 under semiarid conditions and can be used with some degree of confidence for estimating ET0. In addition, results suggest that the ASCE standardized equation on an hourly basis improved the accuracy of ET0 estimation with respect to the FAO-56 version. 相似文献
2.
参考作物腾发量计算方法的适用性研究 总被引:1,自引:1,他引:0
选用5种方法,利用陕西6站的气象资料,计算了各站逐日ET0。并以FAO56 Penman-Monteith(P-M)法为标准,对其它方法进行评价。结果表明,在陕西6地区,5种方法计算的ET0变化趋势基本相同,但数值上有一定差异,所有的差异随ET0的增大而增大。Hargreaves法计算结果差异性较小,适用性较好;1948Penman和Priestley-Taylor二方法估值较FAO24 Penman法更接近P-M法的计算结果;缺气象资料时,Priestley-Taylor法可获得较好估值,且更适用于湿润地区;FAO24 Penman法也能获得较好结果,但其估值精度低于Priestley-Taylor法,一般不宜采用。同时分析了P-M法计算的ET0值和水面蒸发量之间的关系,为利用水面蒸发资料估算陕西6地区ET0值提供参考。 相似文献
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Shingo Kawai Kyoko Okita Kazuhiro Sugishita Ai Tanaka Hideo Ohash 《Journal of Wood Science》1999,45(5):440-443
A modified synthetic method for phenolic56l8133101k/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-O-4 lignin substructure model dimers was developed involving protection of the phenolic hydroxyl group of acetophenons with benzoyl chloride, bromination with 4-dimethylaminopyridiniumbromide perbromide, condensation with phenols in the presence of 18-crown-6-ether, condensation with paraformaldehyde, reduction with NaBH4 and debenzoylation. This method results in shorter reaction times and increasing yields without the application of strict anhydrous and drastic conditions or chloric solvents. This alternative route could be applied to the56l8133101k/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-O-4 dilignol syntheses of four combinations of guaiacyl and syringyl derivatives. 相似文献
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L.G. Hou H.L. Xiao J.H. Si S.C. Xiao M.X. Zhou Y.G. Yang 《Agricultural Water Management》2010,97(2):351-356
Based on successive observation, fifteen-day evapotranspiration (ETc) of Populus euphratica Oliv forest, in the extreme arid region northwest China, was estimated by application of Bowen ratio-energy balance method (BREB) during the growing season in 2005. During the growing season in 2005, total ETc was 446.96 mm. From the beginning of growing season, the ETc increased gradually, and reached its maximum value of 6.724 mm d−1 in the last fifteen days of June. Hereafter the ETc dropped rapidly, and reached its minimum value of 1.215 mm d−1 at the end of growing season. The variation pattern of crop coefficient (Kc) was similar to that of ETc. From the beginning of growing season, the Kc value increased rapidly, and reached its maximum value of 0.623 in the last fifteen days of June. Afterward, with slowing growth of P. euphratica, the value dropped rapidly to the end of growing season. According to this study, the ETc of P. euphratica forest is affected not only by meteorological factors, but by water content in soil. 相似文献
8.
利用FAO-56 Penman-Monteith法计算四川省4个分区1960—2010年逐月的潜在蒸散量(ET0),采用贡献率法分析ET0近50 a来变化成因。结果表明:整个四川省、四川盆地和盆周山地日照时数和风速下降对ET0的负贡献超过平均、最高和最低气温上升以及相对湿度下降对ET0的正贡献,使ET0呈下降趋势;川西北高原平均、最高和最低气温上升以及相对湿度下降对ET0的正贡献超过风速和日照时数下降对ET0的负贡献,使ET0呈上升趋势;川西南山地平均、最低气温、日照时数和风速的下降对ET0的负贡献超过了最高气温上升和相对湿度下降对ET0的正贡献,使ET0呈下降趋势。四川省和四川盆地日照时数下降是ET0下降的主要原因,盆周山地和川西南山地风速下降是ET0下降的主要原因,川西北高原最低温度上升是ET0上升的主要原因。 相似文献
9.
Castor and maize are the most commonly cultivated crops in the Rajendranagar region of Andhra Pradesh, India. The study aims to develop a crop coefficient (Kc) models for these crops, using Lysimeter measured daily crop evapotranspiration (ETc) data and daily reference evapotranspiration (ET0) computed using FAO-56 Penman-Monteith (PM) method. Kc values obtained using relationship Kc = ETc/ET0, crop coefficient curves were derived as a function of days after sowing and polynomial model was fitted. The performances of the models were tested using performance indicators. The models performed well for both the crops. These models can, therefore, be used for estimating Kc values of castor and maize crops for any day after sowing in the study region. 相似文献
10.
Chinese urban migrants' sense of place: Emotional attachment,identity formation,and place dependence in the city and community of Guangzhou 总被引:2,自引:0,他引:2
In this paper, we study urban migrants' sense of place in Guangzhou, China, focusing on the structural relations between place attachment, identification and dependence as the three key place dimensions. Through both quantitative structural equation modelling and qualitative analysis of in‐depth interviews data, our research suggests that migrants' sense of place demonstrates complex relationships between the three registers of emotional attachment, identity formation and functional dependence. The construction of sense of place is also related to the personal experiences of living as urban ‘outsiders’. Our research also reveals a striking difference between the city and community levels in terms of the ways in which migrants' sense of place is constructed. Urban migrants tend to exploit the functional utilities of microscopic urban spaces to meet their demands for recreation, education and socialisation. On the other hand, their sense of place to the city is largely compromised by their attachment to the hometown and conditioned by their personal identification to the city. 相似文献