Changes of Meteorological Disasters and Their Impacts on Grain Crop Yield in Ningxia

The data of annual precipitation,hail occurrence,frost-free period from 23 meteorological stations in 1961-2004 in Ningxia,and the data of the grain crop yields,such as rice,wheat,corn and potato,total grain grain crop yields and area affected by disaster in 1991-2006 were used to analyze the variability of important meteorological disasters and their impacts on grain crop yield in Ningxia.The results indicated that the drought index increased with fluctuation.The intensity and frequency of drought increased,and the impacts of drought increased.The degree and the area of hail occurrences increased,though the annual average occurrence showed a declining trend.The frost-free period lengthened,and the frost period shortened.The main meteorological disaster affecting crop and grain crop yield was drought.The impacts of cold and hail disasters varied according to their distribution and occurrence time.The crop growing period and geographic distribution of the crop planting was related to the impacts of cold and hail disasters.