相对湿润度指数在农业干旱监测业务中的应用

The Application of Relative Humidity Index to Agricultural Drought Monitoring

该文介绍相对湿润度指数在逐日滚动的农业干旱监测业务中应用的处理方法。文中采用联合国粮农组织推荐的方法进行潜在蒸散的计算和作物系数订正,提出了作物根区可吸收土壤总有效含水量的概念,并替代作物根区土壤总有效含水量进行水分胁迫条件下的作物系数订正,观察济南站2008年1—5月冬小麦实际蒸散量的计算结果,发现在蒸发强烈的春季,水分胁迫效果明显;提出了复合相对湿润度指数、区域综合相对湿润度指数等概念,对相对湿润度指数进行应用上的演化,解决了干旱演变过程中存在的前期土壤水分盈亏的累积影响问题,实现了县域内农业干旱状况的综合评定,并突破单种作物生长季的局限,实现了农业干旱的周年监测。通过对山东省114个测墒站2008年2月28日—12月8日人工测墒与区域综合相对湿润度指数的干旱等级对比,3048组有效数据中,2012组数据吻合,总吻合率为66%,其中,黄河、东平湖、微山湖灌溉区及鲁西北大部吻合率在50%以下;中东部地区多在70%以上;从全年情况来看,春季吻合率较低,夏季吻合率较高。

Relative humidity index and corresponding methods are introduced to deal with daily agricultural drought monitoring. The method recommended by FAO is used to calculate the potential evapotranspiration and rectify the crop coefficient. When rectifying the crop coefficient under soil water stress condition, the absorbable total available soil water in the root zone is used to replace the total available soil water in the root zone. Because the lat- ter causes higher results, which means water stress seldom occurs. Actually, most of the roots are located in shallow layer, only a small part of major roots extends to deep layer. For example, the roots of winter wheat can be 1.0 m deep before winter, but 80%-85% of the roots are in the soil shallower than 0.4 m. Therefore, if water stress occurs in the upper soil, the winter wheat＇s growing will be limited despite e- nough water in the deeper soil, because 15~//00--20~//00 of the roots in deeper soil can＇t absorb enough water for transpiration. So it＇s necessary to consider the water absorbing capacity of the crop root, that＇s why the absorbable total available soil water in the root zone is used. When calculating the relative humidity index, steady rule can＇t be reflected reasonably in any individu- al period, because the former field water balance affects the current soil water condition. By summing up the weighted relative humidity index during different period of time, the combined relative humidity index is evolved, and it can well reflect the cumulative affection of former field water balance. The relative humidity index of single crop reflects the soil water condition on one kind of crop, regional combined relative humidity index is evolved by summing up the combined relative humidity index of single crop weighted on its planting area. With this method, agricultural drought monitoring can step over single crop growing season, so and agricultural drought can be monitored throughout the whole year. There are 114 stations for soil moisture manual observation in Shandong Province. From 28 Feb 2008 to 8 Dec 2008, manual observation is carried out every ten days, and 3048 groups of data are available. The comparison shows that for 2012 groups of data, drought degree calculated from relative humidity index is coincident with observation, reaching 66%. The accuracy is lower than 50% in most of west-north area of Shandong, the irrigation district of the Yellow River, the Dongping Lake, and the Weishan Lake. On the other hand, the accuracy is mostly greater than 70% in east-central of Shandong and some other districts. Among the whole period, the degree of coincident is lower in spring than that in summer.