Abstract:

Re-establishing a current rule on the grading of drought and flood in Nanjing from 1470 to 2012, based on historical drought and flood grades data in Nanjing from 1470 to 1950, monthly precipitation data from Nanjing National Basic Meteorological Station from 1951 to 2012 and the drought and flood grades standards for precipitation classification in "Chinese Map Collection of Drought and Flood Distribution in the Past Five Hundred Years". Morlet wavelet analysis and moving mean t-test were used as the research methodology to analyze the evolution characteristics of the drought and flooding grade series in Nanjing from 1470 to 2012. The result showed that between 1470 and 2012, it experienced 160 years of drought, 167 years of flooding and 216 years of normal conditions in Nanjing. Severe floods, severe droughts occur frequently and intensively. The occurrence of droughts and floods in Nanjing showed distinct phases. Drought dominated from 1470 to 1554, 1625 to 1652, and 1912 to 2012. From 1653 to 1805 and from 1849 to 1912, the normal dominated. Between 1806 and 1848 there was a significant alternating pattern of droughts and floods, and the region had experienced more droughts than floods over the past century. The drought and flood levels in Nanjing also exhibit multi−scale periodic oscillations, with the most significant oscillations occurring on time scales of 2−8y and 10−20y. Following these, there were long-period oscillations on the scales 64y, 32y, and 16y. At the present, the Nanjing region had entered a period of oscillation within the 2−8y period. In different time series, significant drought−flood mutations occurred around the years in 1554, 1615 and 1914, characterizing the climatic evolution of dry periods-pluvial periods-dry periods. Since the 20^th century, the duration of moderate flood in Nanjing had been shortened by a trend towards aridity. 

Key words: Drought and flooding, Reconstruction, Evolutionary characteristics, Trend