| Based on the analysis of soil water equilibrium relationship, this thesis brings forward 5 drough evaluation indices: water deficiency index, withering index, water consumption index, comprehensive index and drought index. Using the drought index, the crop production in Ledou mountainous area during 19611999 is classified. The results show that the frequency of extremely heavy drought, heavy drought, middling drought, light drought and rainy year was 1 a, 3 a, 19 a, 11 a and 5 a respectively, and the corresponding probability was 2.6%, 7.69%, 48.72%, 26.21% and 12.82%. In the dry-farming region of east Qinghai, there is anextrusive inconsistency between crop demand and water consumption, and the occurrence rate of drought disasters is very high, which is changeful and is difficult to forecast and control. |