Primary analysis of drought and waterlogging law in north china

Abstract

According to the drought and waterlogging disaster statistics over the last 30 years (1950–1979), the annual average area suffering from drought was about 300 million mu (1 mu=1/ 15 ha) in the whole country, among which about 100 million mu were disastrous areas where the output reduced more than 30%. and the annual lost grains totalled about 5 billion kg. The waterlogging disaster was less than drought disaster. The area suffering from waterlogging was about 100 million mu, among which 60 million mu were disastrous. Drought and waterlogging disasters affect directly the development of the national economy. So it is important to study drought and waterlogging variations, especially the drought and waterlogging variation laws of the areas where the disasters frequently occur.

The historical literatures and recent observation data reveal the fact that there existed drought and waterlogging variations. For example, the occurrence frequency of the outstanding and severe drought years in north China is higher than that of the Loess Plateau. The analysis of the annual rainfall variations of Beijing Station shows that the period of 1914–1948 was low-water in this region, the frequency and length of the negative-run were more than those of the period of 1949–1986, the most negative-run length was 6 years, and the frequency of positive-run was only 1 (2 years). The period of 1949–1986 was plentiful water period in this region. The frequency of positive-run was 3 times, lasting 3 years for the longest. The variatons of annual runoff are similar to the variations of annual rainfall on the whole. In addition, the climatic factors affecting the drought and waterlogging variations are analyzed. The long-term observed data of rainfall and runoff in North China are fully collected, and the temporal and spatial variation laws of drought and waterlogging are analyzed by Markov’s autoregressive equation and run-theory, and quantitative indexes are given.