甘肃榆中2025年“8·7”暴雨事件极端性特征和环境条件研究

Study on the extreme characteristics and environmental conditions of the heavy rainfall event in Yuzhong, Gansu on August 7, 2025

摘要

2025 年 8 月 7—8 日，甘肃榆中县遭遇历史罕见极端降水，榆中兴隆山气象观测站 15 h 降水量达 220.2 mm，达该站年平均降水量的 56%，极端降水诱发严重山洪，造成严重的人员伤亡和经济损失。基于气象观测站降水、探空、ERA5 再分析和 GIIRS 卫星数据，利用诊断分析、降水极端性指标和热力参数，分析“8·7”事件的降水实况、动力和水汽条件、降水极端性特征及关键热力参数演变。结果表明：(1) “8·7”事件持续时间长、累计降水量大、短时雨强大、局地性强。榆中县共出现 15 站次短时强降水，其中兴隆山站出现连续 6 h 的短时强降水；甘肃省内 16 个降水量达 100 mm 以上的大暴雨站点有 4 个出现在榆中县。(2) 500 hPa “两槽一脊”型与西北太平洋副热带高压 (以下简称副高) 边缘共同维持高能高湿环境；700 hPa 切变线是主要的动力抬升系统，配合充沛的水汽输送与马衔山地形抬升，是“8·7”事件的有利条件。(3) 甘肃省中部 78 站过程降水量、37 站小时雨强及 79 站短时强降水频次均突破建站以来 8 月历史极值，且空间分布不均。榆中县和临夏回族自治州东部为“8·7”事件强中心，兴隆山等站日降水量超 100 mm，达日雨量历史极值 2 倍。(4) 事件发生前多个强对流参数均突破近 10 a 95% 的极端阈值，说明大气存在极端不稳定能量；同时，可降水量在多个时次持续超过近 10 a 年 95% 分位数，且副高边缘的西南急流与地形抬升形成了稳定的“水汽-能量”输送带，这种“高位势不稳定”与“异常充沛水汽”的时空耦合，加之地形对切变线的阻挡和辐合作用加强，是降水突破历史极值的核心成因。(5) 基于 GIIRS 卫星数据，提出了副高边缘型环流背景下局地突发性极端降水的关键预报判据：当卫星反演的关键热力参数 (如 CAPE、SI) 突破历史极端阈值，且地形辐合作用显著时，可有效指示极端降水的发生。该判据为西北复杂地形区局地突发性极端降水的预报提供了更为精细的量化依据。

Abstract

On August 7-8, 2025, Yuzhong County of Gansu Province suffered historically rare extreme precipitation. A cumulative rainfall of 220.2 mm was recorded at the Xinglong Mountain meteorological station in Yuzhong within 15 hours, accounting for 56% of the local annual average precipitation. The extreme torrential rain triggered severe flash floods, resulting in heavy casualties and substantial economic losses. Based on precipitation observations, radiosonde data from Yuzhong, ERA5 reanalysis datasets and GIIRS satellite retrievals, this study adopts diagnostic analysis, precipitation extremity indices and thermodynamic parameters to investigate the observed rainfall characteristics, dynamic and water vapor conditions, extreme precipitation signatures, and evolutionary features of key thermodynamic parameters associated with this event. The main conclusions are as follows. (1) This extreme rainfall event was characterized by long duration, enormous cumulative precipitation, intense short-duration rainfall rates and prominent local concentration. A total of 15 hourly extreme rainfall records were observed across Yuzhong County, with continuous short-duration heavy rainfall lasting 6 consecutive hours at Xinglong Mountain station. Among the 16 meteorological stations across Gansu Province that recorded total rainfall exceeding 100 mm (heavy torrential rain), four stations were located within Yuzhong County. (2) A two-trough-one-ridge circulation pattern at 500 hPa combined with the periphery of the Western Pacific Subtropical High (WPSH) sustained an environment with high convective available potential energy and abundant moisture. The shear line at 700 hPa served as the primary dynamic lifting trigger. Favourable synoptic conditions for this extreme rainfall were jointly established by ample water vapor transport and orographic lifting induced by the Maxian Mountain terrain. (3) For central Gansu, the total event rainfall at 78 stations, hourly rainfall intensity at 37 stations, and frequency of short-duration heavy rainfall at 79 stations all broke the all-time August records since station establishment, accompanied by highly heterogeneous spatial distribution. The core heavy rainfall centers were situated in Yuzhong County and eastern Linxia Hui Autonomous Prefecture. Daily rainfall at stations including Xinglong Mountain surpassed 100 mm, twice their historical maximum values. (4) Multiple severe convective parameters exceeded the 95th percentile extreme threshold of the past decade prior to the event, indicating extremely unstable atmospheric energy. Meanwhile, atmospheric precipitable water persistently exceeded the 95th percentile of the past decade at multiple hours. The southwest jet stream along the edge of the WPSH, coupled with orographic lifting, formed a steady transport channel for integrated water vapor and convective energy. The spatiotemporal coupling of extremely high potential instability and abnormally abundant moisture, further intensified by terrain-induced blocking and convergence acting on the shear line, constituted the core physical mechanism driving record-breaking precipitation. (5) Based on GIIRS satellite retrievals, this study proposes quantitative key forecasting criteria for localized sudden extreme precipitation under the circulation regime along the WPSH periphery: extreme precipitation is highly likely to occur when satellite-retrieved key thermodynamic parameters (e.g., CAPE, Showalter Index) exceed historical extreme thresholds and pronounced terrain convergence exists. The proposed criteria provide refined quantitative references for forecasting localized sudden extreme precipitation over complex terrain in Northwest China.

关键词

极端暴雨 / 甘肃榆中 / 小时雨强 / 强对流参数 / 卫星遥感

Key words

extreme precipitation / Yuzhong County, Gansu / hourly rainfall intensity / convective parameters / satellite remote sensing

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基金资助

国家自然科学青年基金项目(42205083)

中国气象局创新发展专项(CXFZ2025Q012)

甘肃省科技重点研发计划(26YFFA040)

中国气象局复盘总结专项(FPZJ2025-136，FPZJ2025-140)

甘肃省气象局人才专项(2627rczx-B-JCRC-01，2425rczx-B-QNBJRC-07)

甘肃省科技计划项目(22JR5RA753，25JRRA1108，23JRRA1329)

甘肃省气象局创新团队(GSQXCXTD-2024-01)