The Climatic Characteristics Of Rainstorms In Huaihe River Basin And Circulation Patterns

Huaihe River Basin is one of the most flood-prone areas in China. Rainstorms are the direct causes of flooding. It’s extremely necessary to study rainstorms of Huaihe River Basin.Floods are closely related to heavy rainfall processes. There are many previous studies about every heavy rainfall process in Huaihe River Basin, including the characteristics of precipitation of heavy rainfall processes, the causes and the large-scale circulation background for strong precipitation, the influence of synoptic systems in different latitudes on rainstorms such as blocking high, the West Pacific subtropical high, tropical circulation system, the relationship between upper-level jet stream, low-level jet stream and rainstorms, moisture channel and moisture source of rainstorm processes. However, previous research for rainstorms of Huaihe River Basin mostly focuses on the case study of rainstorm process or flood year, there are few studies which from a point of climate view to comprehend characteristics of rainstorms in Huaihe River Basin, and little systematic analysis on large-scale circulation background and synoptic systems for every heavy rainfall process in Huaihe River basin.In this thesis the climatically statistical characteristics of rainstorms are studied by the trend analysis, EOF and REOF based on the daily precipitation datasets at753stations over China from1961to2009, especially DEOF method has been applied to study the temporal and spatial characteristics of rainstorm precipitation and rainstorm days in Huaihe River Basin. Results show:(1) there are3extreme centers for average annual rainstorm precipitation in Huaihe River Basin, which lie at west Shandong, northeast Jiangsu and south Henan. There is the most rainstorm precipitation in1991and the least in1966. Trend analysis reveals that in the last50years the annual rainstorm precipitation in the north of the upstream shows significant upward trend, while the rest areas have no significant trends.(2) EOF analysis shows that the variation of rainstorm precipitation exhibits general feature pattern, south-north pattern and east-west pattern, while DEOF analysis reveals that there are two meaningful patterns:anti-phase variation of Huainan and Huaibei, three zonal areas from north to south of Huaihe River Basin displaying a pattern of "-+-".(3) REOF analysis shows that the distribution of rainstorm precipitation could be divided into4patterns:South pattern, Central pattern, Northeast pattern and Northwest pattern. The4patterns obviously display inter-decadal variations, and performance different characteristics.(4) The temporal-spatial variations of rainstorm days are very similar to that of rainstorm precipitation.The persistent rainstorm processes with the time scale from a week to ten days directly cause severe flooding in Huaihe River Basin. In this thesis, by using the NCEP/NCAR reanalysis data and historical synoptic maps, the characteristics of the general atmospheric circulation for26concentrated rainstorm processes from8flood years are analyzed, then the typical circulation patterns leading to rainstorm processes in Huaihe River Basin have been concluded. Finally,6kinds of typical circulation patterns are refined, namely Meiyu type, Jianghuai cyclone type, Jianghuai sheer line type, Warm sheer line type, Deep trough type and Typhoon rainstorm type. Meiyu type is the most important circulation pattern and has greatest influence on flood since its frequent occurrences and lasting the longest days. The most important feature of Jianghuai sheer line type is the establishment of the saddle-shaped circulation field. The processes of warm sheer line generally occur in the period of subtropical high northward jumping, and the precipitation often has a quasi-zonal distribution. Deep trough type has a stable situation, which may cause severe and persistent rainstorms under certain conditions. Jianghuai cyclone type has a short duration, and the rain belt moves along with the cyclone leading to a weaker influence on Huaihe River Basin than other types. The rain belt of typhoon northward type usually lies at Shandong and northern part of Jiangsu. In addition, landed typhoons generally have a great impact on Guangdong, Fujian, Zhejiang and Jiangxi, not on Huaihe River Basin.