Spatial-temporal Variation Characteristics Of Heavy Rainfall In Summer And Its Relation With Circulation In Dongting Lake Basin

Based on daily precipitation for 91 stations over the period 1961-2013 in Dongting Lake basin,the corresponding NCEP/NCAR reanalysis data(U-wind,V-wind,specific humidity and 500 hPa potential height),and monsoon index(East Asian Summer Monsoon Index(EASMI),South China Sea Summer Monsoon Index(SCSSMI)and characteristic quantity of Western Pacific Subtropical High,researching the the relationship of heavy rainfall with circulation in summer.Using the singular value decomposition(SVD)to analyze the relationship of heavy rainfall with 500 hPa potential height in Dongting basin in summer;Using the wavelet coherence and cross-wavelet transform to research the relationship of heavy rainfall with characteristic quantity of Western Pacific Subtropical High(intensity(II)?area(AI)?western ridge point(WRPI)?north boundary(NBI)?ridge-line index(RI))and SCSSMI?EASMI in summer.Researching the circulation variation characteristics of regional heavy precipitation days finally.The results are as following:(1)According to characteristics of the temporal variation of heavy precipitation in Dongting lake basin in summer,it showed that whether it was heavy precipitation amount,heavy precipitation days or heavy precipitation intensity,its tendency rate was positive and upward trend during 1961-2016.According to the Morlet wavelet analysis,it showed that heavy rainfall amount,intensity,days had quasi-periodicity of30 years in summer.(2)According to characteristics of the spatial variation of heavy precipitation in Dongting lake basin in summer,it showed that the heavy precipitation amount,intensity,days had a significant increasing trend during 1961-2106 in the central region of Dongting lake basin.So,the probability of flood disasters in the central region of Dongting lake basin increased.(3)According to the relationship of precipitation with 500 hPa potential height in Dongting lake basin in summer,it showed that when the 500 hPa potential height of the northern of the Ural Mountains and the Yellow Sea region raised(fell)and other regions fell(raised),the heavy precipitation amount and heavy precipitation days fell(raised)in most areas of the Dongting Lake Basin,while the heavy precipitation days and heavy precipitation amount raised(fell)in a small part of Southeast Dongting basin in summer.When the 500 hPa potential height of the northern of the Ural Mountains and the Yellow Sea increased(decreased)and other areas decreased(increased),the heavy precipitation intensity in most areas of the Dongting Lake Basin was weaker(stronger),while that the Zhuzhou and Liuyang was stronger(weaker).(4)According to the relationship of heavy rainfall in Dongting lake basin in summer with the western pacific subtropical high,East Asian monsoon and South Asian monsoon,Generally speaking,it showed that the cross-wavelet spectrum of precipitation amount,heavy precipitation intensity,heavy precipitation days with area,intensity and western ridge point index in Dongting Lake Basin had more strips,but less coherent ones in summer.Heavy precipitation days and heavy precipitation amount had two common high power spectral bands with East Asian summer monsoon index.There was only one cross-spectral band between precipitation intensity and East Asian summer monsoon index.The cross-wavelet spectrum of South China Sea summer monsoon index and summer heavy precipitation amount,heavy precipitation days and heavy precipitation intensity had a common high power spectral band,which was a 1-4-year period from 1993 to 1997.(5)According to the trait of 500 hPa potential height,water vapor transport flux,700 hPa wind field and water vapor transport divergence of regional of heavy precipitation day,they were beneficial to the formation of regional heavy precipitation.Froming North China to Dongting Lake basin was affected by low-pressure trough on the day of heavy rainfall in summer;Water vapor sources are more abundant;Cyclonic eddies and negative vapor flux divergence over the heavy rainfall area of Dongting Lake Basin.