Characteristics Of Spatial And Temporal Variations Of Extreme Precipitation During The Pre-flood And Post-flood Seasons In Fujian

Based on the precipitation data from52meteorological stations in Fujian Province and NOAA ERSST data (2°×2°) from1961-2009, the characteristics of spatial and temporal variations of extreme heavy rain during the pre-flood and post-flood seasons were analyzed, together with the flood anomalies related to the SSTA, using Empirical Orthogonal Function (EOF) decomposition, Singular Value Decomposition (SVD)and Correlation Analysis and extreme heavy rainfall definition methods. Results are shown as follows:(1) The threshold value of extreme heavy rainfall is a good indicator for the contributions during pre-and post-flood seasons in Fujian Province. During period of1961-2009, the extreme heavy rainfall exhibits a strong northwest-southeast difference both in pre-and post-flood seasons. In the pre-flood season, the extreme heavy rainfall, the total rainfall, the extreme rainfall and the index of heavy rainfall intensity show high values in the seaside regions but low in continent regions. The opposite conditions occur in the post-flood season. Therefore, the spatial distribution of rainfall can be well depicted by the extreme heavy rainfall;(2) The total extreme rainfall and extreme heavy rainfall show decreasing/increasing trends in the pre/post-flood seasons from1961to2009. The total rainfall and extreme heavy rainfall in the pre-flood have almost no changes, however, a clear increasing trend of extreme precipitation strength occurs in both the pre-and post-flood seasons, which suggest the possible increases of severe meteorological disasters;(3) The variation of extreme rainfall in pre-flood season mainly occurs in North-Fujian Province, especially in the cross-boundary of Fujian and Jianxi, where the extreme rainfall occurs more frequent and in much stronger strength. In pre-flood season, the anomaly high values are located over the whole Minjiang River domain, which leads more easily to the flood disaster there. In the post-flood season, the anomaly high values move to the middle of Fujian Province, which largely weakens the extreme weather and disaster in the northern part; (4) The extreme rainfall in Fujian Province in pre-and post-flood season is obvious related to the sea surface temperature (SST) in the former winter, with strong spatial distribution and index different influence. The key region affected the extreme rainfall in the pre-flood season is located over the central Pacific and the middle-east equatorial Pacific regions (the El Nino monitoring regions), with the largest negative correlation coefficients there, In the post-flood season, the SSA is most closely related to the extreme rainfall strength, with the highest values occur over the north Indian and central Pacific regions;(5) The anomaly of extreme rainfall is strongly affected by the anomaly of SST in the former winter. The positive anomaly over the middle-east equatorial Pacific or El Nino corresponds to the anticyclone wind anomaly over the Mongol in the pre-flood season, the cyclone wind anomaly over the east Chinasea region at850hPa, which results in the anomaly low/high values of extreme rainfall over the south/north of Fujian Province. While the negative anomaly or La Nina occurs, the opposite conditions happen;(6) The extreme precipitation strength is closely related to the SST anomaly. When the positive anomaly of SST or El Nino occurs, the southerly anomaly appears over the east continent of China at850hPa in the post-flood season, and then results in the strengthen of extreme rainfall strength over most of the Fujian regions; while the negative SST anomaly corresponds to the weakened extreme rainfall strength.