Advancements in 0-6 Hour Blended Quantitative Precipitation Forecasting Technique for South China
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摘要: 为进一步提升0~6 h定量降水预报(Quantitative Precipitation Forecast,QPF)精度,首先对CMA-GD (R3)和CMA-GD(R1)逐时降水进行相位和强度订正,并基于自适应融合方程实现融合;其次,对双偏振雷达水平反射率因子(ZH)和差分传播相移率(KDP)两个参数进行外推,在基于多年雨滴谱资料对广东降水进行时空划分并分别拟合降水反演关系式的基础上实现降水反演;最后,基于动态权重融合技术实现双偏振雷达外推预报和模式预报的融合,并对影响预报精度的不同模式融合方案和基于不同高度CAPPI参数外推方案两个关键因素进行分析。结果表明:(1) 弱降水时(雨强 < 5 mm·h-1),三种融合方案产品各区域和预报时次各有优劣,当雨强≥ 5 mm·h-1时,双偏振雷达外推与两个模式融合产品(QPF_Blending)较单模式融合(QPF_R1和QPF_R3)的最优评分至少提升15%以上,且雨强越大,提升越明显;(2) 内陆地区(距离海岸线130 km以外的区域)使用高度过低或过高的CAPPI会对第1 h QPF精度产生明显影响,但总的来说使用3 km高度的CAPPI外推预报的QPF精度最高;(3) 改进后的0~6 h QPF产品在各预报时效和降水量级上ETS或TS评分都明显提升,雨强≥1 mm·h-1时TS评分提升率达20.4%,随着雨强增大,提升率也越大。研究成果有效支撑了华南0~6 h强降水预报预警业务,对防灾减灾有重要意义。Abstract: To further improve the accuracy of 0-6 quantitative precipitation forecast (QPF), this study applied phase and intensity corrections to hourly precipitation data from the CMA-GD (R3) model and the CMA-GD (R1) model, followed by blending achieved based on an adaptive blending equation. Secondly, extrapolation was performed on two dual-polarization radar parameters: horizontal reflectivity (ZH) and specific differential propagation phase shift (KDP). Based on the spatiotemporal classification of precipitation in Guangdong using multi-year disdrometer data and the fitting of precipitation retrieval relationships, precipitation retrieval was realized. Finally, dynamic weighting blending technique was used to blend dual-polarization radar extrapolation with model forecasts. Key factors affecting forecast accuracy, such as different model blending schemes and extrapolation schemes based on different constant-altitude plan-position-indicator (CAPPI) parameters at varying heights, were analyzed. The results show that: (1) For weak precipitation (rainfall intensity < 5 mm · h-1), the three model blending schemes exhibited varying performance across different regions and forecast times. However, for rainfall intensities ≥ 5 mm · h-1, the dual-polarization radar extrapolation combined with two model blending products (QPF_Blending) outperformed single-model blending products (QPF_R1 and QPF_R3) by at least 15%, with greater improvements observed for higher rainfall intensities. (2) In inland areas (beyond 130 km from the coastline), the use of CAPPI parameters at excessively low or high altitudes significantly impacted the accuracy of 1-hour QPF. Overall, CAPPI extrapolation at a height of 3 km yielded the highest QPF accuracy. (3) The improved 0-6 hour QPF products showed significant improvements in equitable threat score or threat score (TS) at various forecast lead times and precipitation levels, with a TS score improvement rate of 20.4% when the rainfall intensity was higher than 1 mm · h-1, and the improvement rate increased with increasing rainfall intensity. These findings effectively support the operational forecasting and warning of heavy rainfall within 0-6 hours in South China, which is of great significance for disaster prevention and mitigation.
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表 1 CMA-GD(R3)和CMA-GD(R1)
模式类型 CMA-GD(R3) CMA-GD(R1) 预报范围 96.60~122.76 °E,16.60~30.76 °N 107.2~118.8 °E,18.2~26.8 °N 预报时效 30 h 6 h 预报时次 逐时更新 逐12 min更新 空间分辨率 0.03 ° × 0.03 ° 0.01 ° × 0.01 ° 时间分辨率 1 h 12 min 表 2 QPF_R3、QPF_R1和QPF_Blending的0~6 h预报时效的平均评分
评分标准 QPF 量级/(mm·h-1) ≥0.1 ≥1 ≥5 ≥10 ≥20 ≥25 ≥30 ≥50 TS QPF_R3 0.471 0.341 0.127 0.079 0.048 0.038 0.033 0.008 QPF_R1 0.455 0.338 0.131 0.083 0.049 0.038 0.033 0.008 QPF_Blending 0.369 0.289 0.137 0.102 0.079 0.067 0.055 0.027 FAR QPF_R3 0.269 0.509 0.820 0.892 0.934 0.949 0.957 0.991 QPF_R1 0.265 0.491 0.810 0.884 0.932 0.949 0.957 0.991 QPF_Blending 0.412 0.583 0.800 0.847 0.871 0.890 0.908 0.956 PO QPF_R3 0.431 0.472 0.695 0.769 0.850 0.869 0.876 0.951 QPF_R1 0.456 0.498 0.702 0.771 0.850 0.869 0.876 0.951 QPF_Blending 0.502 0.516 0.696 0.763 0.831 0.856 0.880 0.936 Bias QPF_R3 0.779 1.075 1.695 2.143 2.281 2.598 2.879 5.265 QPF_R1 0.740 0.988 1.564 1.983 2.217 2.566 2.872 5.255 QPF_Blending 0.847 1.162 1.518 1.554 1.306 1.304 1.309 1.455 表 3 QPF_1.5、QPF_2.0、QPF_2.5和QPF_3.0的0~6 h预报时效的平均评分
评分标准 QPF 量级/(mm·h-1) ≥0.1 ≥1 ≥5 ≥10 ≥20 ≥25 ≥30 ≥50 TS QPF_1.5 0.352 0.245 0.126 0.092 0.066 0.055 0.047 0.024 QPF_2.0 0.356 0.249 0.126 0.092 0.068 0.056 0.047 0.023 QPF_2.5 0.353 0.246 0.125 0.092 0.068 0.057 0.048 0.023 QPF_3.0 0.369 0.289 0.137 0.102 0.079 0.067 0.055 0.027 FAR QPF_1.5 0.493 0.655 0.813 0.859 0.892 0.910 0.922 0.962 QPF_2.0 0.490 0.653 0.813 0.858 0.888 0.907 0.920 0.962 QPF_2.5 0.491 0.655 0.814 0.857 0.886 0.902 0.918 0.960 QPF_3.0 0.412 0.583 0.800 0.847 0.871 0.890 0.908 0.956 PO QPF_1.5 0.465 0.544 0.724 0.794 0.856 0.878 0.894 0.940 QPF_2.0 0.460 0.533 0.719 0.792 0.854 0.878 0.896 0.945 QPF_2.5 0.466 0.539 0.725 0.795 0.857 0.878 0.898 0.948 QPF_3.0 0.502 0.516 0.696 0.763 0.831 0.856 0.880 0.936 Bias QPF_1.5 1.055 1.322 1.474 1.458 1.332 1.350 1.359 1.580 QPF_2.0 1.061 1.344 1.500 1.462 1.299 1.311 1.300 1.449 QPF_2.5 1.049 1.335 1.482 1.436 1.250 1.248 1.245 1.294 QPF_3.0 0.847 1.162 1.518 1.554 1.306 1.304 1.309 1.455 表 4 QPF_OLD和QPF_Blending的0~6 h预报时效的平均评分
评分标准 QPF 量级/(mm·h-1) ≥0.1 ≥1 ≥5 ≥10 ≥20 ≥25 ≥30 ≥50 TS QPF_OLD 0.350 0.24 0.124 0.089 0.044 0.025 0.014 0.000 QPF_Blending 0.369 0.289 0.137 0.102 0.079 0.067 0.055 0.027 FAR QPF_OLD 0.523 0.676 0.806 0.816 0.784 0.792 0.792 1.000 QPF_Blending 0.412 0.583 0.800 0.847 0.871 0.890 0.908 0.956 PO QPF_OLD 0.433 0.518 0.744 0.854 0.948 0.973 0.985 1.000 QPF_Blending 0.502 0.516 0.696 0.763 0.831 0.856 0.880 0.936 Bias QPF_OLD 1.191 1.488 1.323 0.795 0.242 0.131 0.071 0.001 QPF_Blending 0.847 1.162 1.518 1.554 1.306 1.304 1.309 1.455 -
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