兰州地区500余年来旱涝变化规律分析

旱涝是影响兰州及其周边地区的频发性自然灾害。利用兰州地区1470—2008年间旱涝等级序列，借助累积距平法、滑动T检验和小波分析等方法，研究了500余年来兰州地区旱涝变化分布特征与发展规律。结果表明:兰州地区旱涝演变存在1580—1721年、1757—1789年、1891—1930年的3个显著干旱阶段和1533—1580、1721—1757年、1789—1891、1953—1961年的4个显著洪涝阶段，且旱多于涝；兰州地区旱涝序列存在年代际尺度和百年尺度的突变；不同时间尺度上正负相位交替出现，波动明显，兰州地区旱涝变化的第一、二、三主周期分别为108 a、39 a和13 a；1951—2008年，由于气温升高、降水减少，兰州地区旱涝气候变化表现为干旱化趋势。

Analysis on the Variation of Drought & Flood Grades from 1470 to 2008 in Lanzhou Area

Drought and flood are the main natural disasters surrounding Lanzhou area. We described the variation characteristics of drought & flood grades of Lanzhou area from 1470 to 2008 by performing the manners of accumulative departure analysis, running T-test and Morlet wavelet analysis. Results showed that the drought & flood severity has 3 obvious drought stages and 4 flood stages nearly the 539 years. The frequency of drought is larger than flood. There are two abrupt changeson 100-year scale and 14 abrupt changes on decadal scale in Lanzhou area. Positive and negative phrase appear alternately during different time scales. The major cycles of drought & flood grades transformation are 108 years, 39 years and 13 years, respectively. With the rising temperatures and decreasing precipitation, the drought & flood had been showing the dry trend from 1951 to 2008.