安徽省参考作物蒸散模型参数化

模型参数优化是准确估算参考作物蒸散(reference crop evapotranspiration,ET0)的关键问题之一。该研究基于安徽省81个地面气象站点1961—2011年逐日气象数据和合肥、武汉、南京、杭州和南昌5个辐射站1993—2011年的逐日辐射数据,评估日尺度的净长波辐射、气压和水汽压模型在安徽地区的适用性;并结合已有研究获得的最优逐日太阳辐射参数化估算模型,建立安徽省本地化逐日ET0模型的最优参数化方案,探讨模型参数优化对ET0估算的影响。结果表明:7种净长波辐射估算参数化方案中,邓根云法的精度最高,在安徽地区的适用性优于其他方案,建议作为安徽本地化方案使用;FAO56 Penman-Monteith公式中推荐的气压估算模型和基于实测平均气温和相对湿度估算水汽压的模型在安徽省基本适用,但该研究认为在资料能够获取的情况下直接使用实测值为最优。与基于实测资料计算的ET0相比,该研究建立的本地化最优模型估算的ET0在日、月和年尺度上的相对误差分别为15.5%、9.05%和6.12%,能较好地适用于安徽地区。FAO56 Penman-Monteith公式推荐的参数化方案由于高估了安徽地区的太阳辐射,低估了净长波辐射,导致其与基于实测资料计算的ET0值相比,在日、月和年尺度上高估ET0达40.0%以上,不推荐安徽地区直接使用。研究可为安徽省准确估算作物需水量、农业旱涝评估和合理调度水资源等提供依据。

Parametrization of reference crop evapotranspiration model in Anhui Province

Model parameter optimization is one of key issues to accurately estimate reference crop evapotranspiration (ET0). This study evaluated feasibility of different methods for estimation of net long-wave radiation, air pressure and vapor pressure and established optimal parameters for ET0 estimation in Anhui Province. The data collected included daily observations of 81 meteorological stations in Anhui Province from 1961 to 2011 and daily observed radiation data of Hefei, Wuhan, Nanjing, Hangzhou and Nanchang radiation stations from 1993 to 2011. Seven different net long-wave radiation methods were Brunt method, Penman method, Bepлянд method, FAO24 and FAO56 PM method, Deng Genyun method and Tong Hongliang method. The net long-wave radiation calculated based on radiation balance equation was considered as standard value. Vapor pressure was estimated based on 2 methods: 1) daily maximum and minimum temperature; and 2) mean air temperature. They were compared with measured vapor pressure. Air pressure was estimated by FAO56 PM method, which was compared with measured air pressure. Furthermore, the optimal parameterization scheme of ET0 for Anhui Province was established by combining the results and the previous optimal daily solar radiation parameterized model. Finally, the effect of parameter optimization on the ET0 estimation was analyzed. Results showed that the net long-wave radiation over Anhui Province was underestimated by all these 7 methods with the mean absolute relative errors almost larger than 30%. The mean absolute relative error and root mean square error of the Deng Genyun method was 24.8%-31.3% and 1.44-1.93 MJ/(m2·d) for the 5 stations, which were less than those of the other 6 models. In addition, the Tong Hongliang method was also better than the others. Both were good for Anhui Province. Due to a large value of air pressure, estimators of air pressure based on FAO56 PM model had smaller errors in most areas of Anhui. The vapor pressure calculated based on mean air temperature and relative humidity was better than that based on maximum and minimum temperature. The former had mean absolute relative error of 2.0% and root mean square error of 0.04 kPa. The errors in plain stations were smaller than at stations located at mountain. Though the empirical air pressure and calculated vapor pressure estimation models were suitable in Anhui Province except 3 mountain stations, the measured values were still recommended if possible, especially for high latitude. The mean absolute relative errors between the standard values of ET0 values calculated by measured values and that by the optimal model were 15.5%, 9.05% and 6.12% at the daily, monthly and annual scale, respectively, indicating that the optimal model was applicable in Anhui Province. The FAO56 PM model overestimated the solar radiations and underestimated the net long-wave radiations in Anhui Province, resulting in that an overestimation of ET0 up to 40.0% at all daily, monthly and annual scales. Thus, a recommended scheme for ET0 estimation in Anhui Province was Caowen modified method for solar radiation, Deng Genyun method for net long-wave radiation, and measured values for air and vapor pressure.