An analysis of index of dryness/wetness for growth season during past 70 years in western Guanzhong -- Taking Yangling as a case

The index of dryness/wetness and the grade of dryness/wetness based on method of Bhalme and Mooley are calculated for growth season (March to October)during past 70 years at Yangling. The result shows that the frequency of various grades of dryness is bigger than that of wetness in several months during growth season. The frequency of serious dryness is 5% from April to May and September to October, while the frequency of middle dryness is 10% from March and April and June and August. The frequency of middle serious dryness is 9.9%~12.1% and 11.2%~30.0% higher than that of middle serious wetness during 1930s~1940s and 1970s~1990s respectively, while the frequency of middle serious wetness is 3.5%~7.5% higher than that of middle serious dryness during 1950s~1960s. The index series of dryness/wetness has a phenomenon of climatic jump in 1952 and 1976.