Regularities of Monthly Variations of the Ili River Runoff and Its Forecasting

Abstract

Analysis of fluctuations in the time series of Ili River runoff monthly values for 1971-1994 was carried out using the method of “Periodicities” on the posts located 164 km upper and 37 km lower Kapchagayskaya Dam. The analysis revealed in fluctuations of each of them nine harmonics with the periods’ length larger than 1.5 years. The revealed sinusoids and repeating successions of runoff annual cycle’s mean monthly values were applied in different runoff prediction schemes for months and totally for 1995. Training forecasts’ results were estimated by the new independent data. Runoff regulation by the reservoir causes some reduction of its mean value, smoothing and losing its annual cycle rhythm. Long term periods are revealed more distinctly in the runoff variation lower the dam. In spite Kapchagayskaya Dam influence the harmonics with the same periods of 25 and 35 months were revealed in both time series among other sinusoids. Possibly they are more reliable, and it is more expedient to apply them for future runoff estimation comparing with sinusoids whose periods were proved only in one of time series. The Ili River runoff in 1995 upper the dam was extreme small. Lower the dam the runoff was close to the mean value of its time series. By the maj ority of applied predictions’ schemes results for the runoff upper the dam were better its estimations for future by the mean value of time series. Forecast’s mistake lower the dam was smaller than its acceptable value. Therefore, the forecasts computed by these schemes for months and for the annum at total could be estimated as satisfactory and quite acceptable.