南方水稻生育期降雨预报准确率评价及节水灌溉策略分析

以江西省赣抚平原灌区为例,收集了中央气象台2012—2015年的三季早稻和晚稻生育期内未来7 d降雨预报数据和实际观测降雨数据,采用正确率、漏报率、空报率、TS评分及ROC对降雨预报准确率进行评价,在此基础上提出相应的节水灌溉策略.结果表明:水稻生育期晴雨预报正确率达76.3%,早稻的漏报率总体低于晚稻,空报率高于晚稻,小雨TS评分相差较小,中雨及以上量级降雨晚稻明显小于早稻;1~7 d预见期的ROC下的面积都大于0.5,表明命中率大于虚警率,都有正的预报价值,可用于灌溉管理.返青期、乳熟期和黄熟期早稻的正确率为80.1%~88.6%,如果预报结果在小雨及以上量级可不灌或少灌;分蘖前期、分蘖后期、拔节孕穗期和抽穗开花期的正确率稍低,为64.9%~77.2%,此期间如果遇连续无雨和小雨预报可按照需水量进行灌溉,如果预报2~3 d内有中雨或以上降水则应减少灌溉量;早稻与晚稻相比虽然预报的准确度较低,但降雨预报次数和实际降雨次数更多,尤其遇到中雨及以上量级预报时,可适当减少每次灌溉的水量.考虑降雨预报的准确度进行灌溉决策既可充分利用天然降雨,又可避免灌水浪费,从而达到节水增效的目的.

Accuracy assessment of rainfall forecast and analysis on water-saving irrigation strategies during rice growing seasons in South China

Increasing effective rainfall is one of strategies for saving irrigation water, unfortunately there is an uncertainty in future rainfall, thus accuracy assessment of rainfall forecast is necessary for effective rainfall use. Taking the Guanfu Plain Irrigation District as an example, we collected 7-day lead time rainfall forecast data in three seasons of early and late rice(2012—2015)from the National Meteorological Centre of China, and the observed rainfall data, then analyzed the forecast accuracy by using correct forecast rate, threat score(TS), false alarm rate(FAR), missing alarm rate(MAR)and receiver operating characteristic(ROC)curve. Furthermore, strategies for increasing effective rainfall are proposed based on the accuracy assessment. The results show that the correct forecast percentage of rain/no rain during the rice growing seasons has reached 76.3%, the MAR is lower but the FAR is higher in the early rice season than in the late rice season. The difference in TS for light rain during the early and late rice seasons is not significant; for middle and above rainfalls, however, the TS in the late season is lower than in the early season. The areas under the ROC are greater than 0.5 for all 1-7 days lead time, implying that the correct forecast percentage is higher than the FAR and all the forecasts are positive, thus the correct forecast percentage can be used in irrigation management. The correct forecast percentage is ranged from 80.1% to 88.6% in the re-greening, milk-maturing and yellow-maturing stages of early rice. Thus if a light rain or above is forecasted, then there should be no or less irrigation. The correct forecast percentage is slightly lower and ranged from 64.9% to 77.2% in the early tillering, late tillering, jointing/booting, and heading/flowering stages. Therefore, if a continuous clear day or slight rain is forecasted, then irrigation should be applied according to the crop requirement. However, if a medium or above rainfall in 2-3 days is forecasted, then irrigation amount should be reduced. Although the accuracy in the early rice season is lower than in the late rice season, the forecasted and actual rainfall events are even more in the early rice season, so that the irrigation amount can be decreased if a medium or above rainfall is forecasted. After a decision on irrigation amount is made by taking an account of rain forecast accuracy, not only natural rainfall will be utilized sufficiently but also water wasting can be avoided to achieve the water saving goal.