Abstract
In cold and snowy regions as in Hokkaido, snowmelt amounts are the most important resource for supplying water for irrigation. However, there are little meteorological and hydrological data in mountainous catchment areas. For the Toppu basin sites around the higher mountains, it is difficult to design a rainfall-runoff process from the rainfall of the rain gauge station nearest the basin. Some rainfall-runoff method is required to solve the water-balance problem in situations were data is not sufficient. The autoregressive (AR) method used herein is very powerful to inversely estimate rainfall and snowfall amounts at higher altitudes from the discharge output in the rainfallrunoff process.
The main results of the present study are summarized as follows:
i) In the current catchment area study, the response characteristics in both the winter and summer seasons were well reproduced by the identical AR process.
ii) The seasonal correction factors for precipitation between the catchment and the lowest rain gauge station were estimated. The correction factor was 2.2 in summer and fall, and 2.7 for the other seasons.
iii) The seasonal correction factors estimated by the AR method corresponded well with the factors which was derived from the coaxial method between the discharge and rainfall.
The filter-separation autoregressive method was found to be useful for the runoff analysis in the Toppu basin.
