Study on climatie characteristics of forest in Gansu and the its connection with forest fire danger

Chinese. 为保护和发展甘肃省现有森林，改善自然资源匮乏、生态环境脆弱的局面提供参考依据。 利用甘肃林区1971～2003年气象要素、1988～2003年森林火灾及1990～2001年植被指数资料，采用统计分析方法对甘肃11个主要林区的气候特征及变化进行了分析，并对林区气象条件与火险的关系进行了研究。甘肃林区气温自东南向西北、由盆地向高山逐渐递减，各林区气温在1971～2003年总体呈上升趋势；林区降水量自东南向西北递减，且逐年呈下降的趋势。各林区相对湿度的年变化有春低秋高和冬低秋高2种类型，蒸发量具有明显的季节变化特征；在3～10月植物生长期，干旱现象明显，近十几年来干旱状况较严重。气象要素及干旱指数与森林火险密切相关。在气温高、湿度大、降水量多、干旱指数高的季节，火灾发生率较低，而在天气寒冷、空气干燥、降水量稀少、干旱指数低的季节，火灾发生率较高。相对湿度、平均气温、最低气温、最高气温、降水量等气象要素及干旱指数，可用于甘肃森林火险的预警工作。

English. Reference is provided in order to protect the forest in Gansu, and to improve natural resources and environment. Using the data of forest meteorological factors from 1971 to 2003, forest fire from 1988 to 2003 and NDVI from 1990 to 2001 in Gansu province, the characteristics and changes of forest climate were analyzed, and the connections between meteorological condition and fire danger were studied too. The result shows that the forest temperature in Gansu decreases gradually from southeast to northwest and from basin to mountain, and tends to increase from 1971 to 2003. The forest precipitation also decreases from southeast to northwest, and tends to decrease year after year. The relative humidity is lowest in spring and highest in autumn, or lowest in winter and highest in autumn, and the evaporation changes clearly within a year. The drought is severe from March to October every year, which becomes more and more serious in the latest ten years. The meteorological factors and drought index are in close connection to forest fire danger. The forest fire frequency is lower when the temperature and humidity are higher, and precipitation is abundant, whereas is higher when it is colder and drier. It is feasible to apply humidity, temperature, precipitation and drought index to the fire danger forecast model of Gansu.