Spatiotemporal Characteristics of Rainfall over Different Terrain Features in the Middle Reaches of the Yangtze River Basin during the Warm Seasons of 2016–20

Abstract

Based on hourly rain gauge data during May–September of 2016–20, we analyze the spatiotemporal distributions of total rainfall (TR) and short-duration heavy rainfall (SDHR; hourly rainfall ⩾ 20 mm) and their diurnal variations over the middle reaches of the Yangtze River basin. For all three types of terrain (i.e., mountain, foothill, and plain), the amount of TR and SDHR both maximize in June/July, and the contribution of SDHR to TR (CST) peaks in August (amount: 23%; frequency: 1.74%). Foothill rainfall is characterized by a high TR amount and a high CST (in amount); mountain rainfall is characterized by a high TR frequency but a small CST (in amount); and plain rainfall shows a low TR amount and frequency, but a high CST (in amount). Overall, stations with high TR (amount and frequency) are mainly located over the mountains and in the foothills, while those with high SDHR (amount and frequency) are mainly concentrated in the foothills and plains close to mountainous areas. For all three types of terrain, the diurnal variations of both TR and SDHR exhibit a double peak (weak early morning and strong late afternoon) and a phase shift from the early-morning peak to the late-afternoon peak from May to August. Around the late-afternoon peak, the amount of TR and SDHR in the foothills is larger than over the mountains and plains. The TR intensity in the foothills increases significantly from midnight to afternoon, suggesting that thermal instability may play an important role in this process.

摘 要

利用地面自动站逐小时降水观测数据,针对不同的地形特征(山区(≥ 400 m)、山麓(100 ~ 400 m)和平原(0 ~ 100 m)),分析了2016–20年暖季(5~9月)长江中游地区总降水和短时强降水(小时降水量≥20 mm)的整体特征、空间分布差异及日变化演变特征。对于山区、山麓和平原,总降水和短时强降水的雨量均在6月或7月达到峰值,短时强降水对总降水的贡献率在8月达到峰值(雨量为23%;频次为1.74%)。山麓降水中总降水量高、且短时强降水雨量贡献高,山区降水中总降水频次高、但短时强降水雨量贡献低,平原降水的总降水频次和雨量均较低、但短时强降水的雨量贡献高。整体来看,总降水(雨量和频次)的大值区多分布在山脉附近的山区和山麓站,短时强降水(雨量和频次)则集中分布在山脉附近的山麓或平原站。在日变化方面,山区、山麓和平原的总降水和短时强降水均表现为强度有明显差异的双峰特征(弱清晨峰值和强午后峰值),且从5到8月具有从清晨降水逐渐向午后降水转变的特征。在午后峰值时刻,总降水和短时强降水的雨量均具有山麓高于山区和平原的特征,且山麓地区从夜间到午后的总降水强度增幅显著,表明午后的热力不稳定对山麓地区的降水增强有重要作用。