Analysis and Gray Prediction of Rainfall in Well Irrigation Area

The variation pattern of precipitaion over Taiyuan Basin well irrigation area was analyzed on basis of annual precipitaion series(1957-2007),using moving average method for trend test and moving t test method for abrupt test.The result showed:(1)the annual precipitation series demonstrated a significant decrease trend over the study area;(2)An abrupt change was found in 1985,with the statistics t value being maximun at a significant level of 0.001.In addition,from 1954 to 2007,the monthly precipitation of statistical results showed a very uneven distribution of rainfall during the years,71.23% of precipitation concentrated in months June to September,1.49% concentrated in December,January and February;monthly precipitation fluctuate strongly,in December CV was 1.4,in January 1.09,and in February CV was1.08,which all suggested strong variability.Finally,the gray system GM(1,1)of the decomposition model: long-term trend of precipitation amount,periodic fluctuation of E(ti),and random variation of R(t)were used to forecast precipitation in the irrigation area.The accuracy was improved using proven model,the forecast data could be the basic data to predict the groundwater volume in the irrigation area and provide a scientific basis for the development and protection of water resources.