GPM近实时降水产品在青藏高原的多尺度精度评价

Multi⁃Scale Accuracy Evaluation of GPM Precipitation Products over the Qinghai⁃Tibet Plateau

为了定量评价GPM近实时降水产品在青藏高原的精度,以中国气象局提供的地面降水资料作为参考,采用多种统计指标分析GPM卫星时代GSMaP和IMERG的近实时卫星降水产品(GSMaP-NRT、GSMaP-MVK;IMERG-Early、IMERG-Late)在青藏高原的适用性。结果表明:①IMERG在青藏高原表现出的降水时空分布明显优于GSMaP,IMERG-Late最佳。卫星产品在夏季精度最好,冬季最差,夏季相关系数均在0.6以上,相对偏差(RB)明显低于其他季节。GSMaP高估了青藏高原各个季节的降水(RB>0),而IMERG则表现出低估降水现象。②卫星产品在两江流域、南部流域的精度明显优于其他地区,IMERG呈现出的相关系数、均方根误差和相对偏差空间分布明显优于GSMaP,IMERG在青藏高原大部分地区的误报率低于GSMaP,在地形更为复杂的羌塘高原、柴达木盆地等区域命中率也较好,表现出更稳定的探测降水事件精度。③卫星降水对不同等级降水的探测能力存在差异,降水强度越大,卫星产品的命中率越低,误报率随之增大。IMERG的ETS指数在各个降水等级上均优于GSMaP,其中IMERG-Late最好。整体上,IMERG在青藏高原表现出更好的反演降水精度,具有一定的应用潜力,GSMaP的精度表现很差,不适用于青藏高原。

In order to quantitatively evaluate the applicability of near real⁃time versions of both GSMaP and IMERG precipitation products(GSMaP⁃NRT,GSMaP⁃MVK,IMERG⁃Early and IMERG⁃Late)over the Qinghai⁃Tibet Plateau(QTP)in China,six statistical indices were used to systematically analyze the characteristics of these products,benchmarked by a set of ground⁃based dataset of China Meterological Ad⁃ministration(CMA).The results show that a)the spatial and temporal distribution of IMERG near real⁃time products is significantly better than that of GSMaP,of which IMERG⁃Late is the best.All satellite products have the best accuracy in summer,the correlation coefficients(Corr)are all above 0.6,relative bias(RB)is significantly lower than that of the other seasons and the winter is the worst.GSMaP products overestimate precipitation in all seasons(RB>0)over QTP,of which winter is the most severe(RB>200%).In contrast,IMERG shows underestimated precipitation over QTP,with RB indices of about-15%and-50%in summer and winter respectively.b)The accuracy of all satellite products in the two major river basins and the southern river basins are significantly better than that of other regions.The spatial distribution of root mean square error(RMSE)and RB of IMERG(Early,Late)are significantly better than that of GSMaP.GSMaP has a high hit rate in the two major river basins and the southern watersheds(POD>0.7),but its false alarm rate is also relatively larger and the false alarm rate of IMERG(Early,Late)in most parts of the QTP is lower than that of GSMaP,showing more stable accuracy in detecting precipitation events.c)Satellite products have different detection capabilities for different levels of precipitation.The greater the intensity of precipitation,the lower the hit rate of satellite products and the higher the false alarm rate.From the perspective of the ETS index,the IMERG is superior to GSMaP in each precipitation level and the IMERG⁃Late performs the best.Overall,IMERG products perform better and have certain application potential over QTP.On the contrary,due to the poor accuracy of GSMaP products,it is not recommended to use it for carrying out precipitation application research.