Study on the relationship between typical drought/flood years in autumn flood season in Hanjiang River basin and preceding sea surface temperature

Based on pentad precipitation data from 16 meteorological observing stations in Hanjiang River Basin in the autumn flood season from September to October during 1961-2010, this paper has calculated the precipitation concentration degree (PCD) and precipitation concentration period (PCP). Combined with time series of PCD and precipitation anomalous percentage in the autumn flood season, typical drought/flood years were determined. Meanwhile, using sea surface temperature (SST) and 500 hPa height field data from NCEP/NCAR in the same period, the relationship between these typical years and SST was discussed by composite and correlation analysis method. The results show that there are three SST key areas located in Indian Ocean, equatorial middle Pacific and North Pacific respectively. When the SST in these sea areas show anomaly, the main synoptic systems, including India-Burma trough, Baikal trough, East Siberia high and Ural Mountains high, influencing autumn rainfall in Hanjiang River Basin change accordingly, which lead to anormaly of PCD and rainfall, and then initiate drought and flood disaster in Hanjiang River Basin. Anomaly of preceding SST in the three key sea areas can be regarded as a precursor signal to judge the amount of precipitation and the strength of PCD in the autumn flood season in Hanjiang River Basin to a certain extent.