1957－2007年云南省森林火险变化

Change trends of forest fire danger in Yunnan Province in 1957-2007.

当前以变暖为主要特征的气候变化已对全球林火的发生产生重要影响。本文基于日气象数据(气温、降水量、空气相对湿度、风速),按照加拿大火险天气指数的计算方法,计算了云南省1957—2007年间每日的森林火险天气指数,分析了该省50年来森林火险的变化趋势。结果表明:云南省的火险期为上年11月至当年6月,持续期约8个月;林火数据(林火数量、过火面积和受害森林面积)与火险天气指数的相关性显著,半腐层湿度码(DMC)的火险期平均值和火险期严峻度(SSR)可作为不同火险期火险状况比较的良好指标。1957—2007年云南省森林火险状况呈现2种变化趋势:1)总体上周期性变化趋势明显,在周期性变化的同时呈上升趋势,表现为1991—2007年的火险状况比1961—1990年的火险状况略有升高;2)1991—2007年各火险期火险状况的波动性下降,火险状况异常严峻的火险期数量比1961—1990年减少。

Climate wanning has already made great impact on forest fires. Based on the daily meteorological data （temperature, precipitation, relative humidity, and wind speed）, and by using the Canadian Fire Weather Index calculation formula, the daily forest fire weather indices （FWIs） of Yunnan Province in 1957-2007 were calculated, and through the statistical analysis of FWIs, the forest fire trends in this province over the past 50 years were studied. In the past 50 years, the forest fire season in Yunnan Province was from previous year November to current year June, lasting 8 months. Fire data （fire numbers, burned area, and burned forest area） had significant relationships with fire weather indices. The average daily duff moisture code （DMC） in whole fire season and the seasonal severity rating （SSR） were the good indices to evaluate the fire danger conditions among different fire seasons. The forest fire danger in Yunnan Province in 1957-2007 showed two change trends. One showed a clear cyclical change and a weak upward trend, i. e. , the fire danger conditions in 1991-2007 was slightly severer than that in 1961- 1990 ; and the another was that the fluctuation of forest fire danger conditions among different fire seasons decreased in 1991-2007, and the number of abnormal severe fire seasons was less than that in 1961-1990.