Seasonal and Annual Water Balance of Agricultural Land in Tokachi, Hokkaido, Japan

Soil water balance determines the accumulation and leaching of solutes in the surface soil. In cold regions, where agricultural land is covered with snow in winter, the soil water balance has not been as thoroughly investigated as in warm regions due to the difficulty of conducting continuous and accurate winter field observation in cold environments. In this study, annual water balance at Tokachi, Hokkaido, Japan was evaluated including snow-covered periods using a comprehensive hydrometeorological observation system developed for cold region application. During the period from October 20, 2004 to October 19, 2005, the ground was covered with snow for a total of 130 days. Annual precipitation during the study period was 799 mm and estimated evaporation was 591 mm. During the snow-covered period, precipitation was 260 mm, accounting for only 32.5% of the annual precipitation; however, precipitation excess was large (236 mm) due to very small evaporation (24 mm), and the bulk of it infiltrated rapidly during the four-week snowmelt period. This observation suggests that the leaching of soil solutes occurs almost exclusively during the snowmelt period, and that the agricultural soil environment in this region is strongly affected by the water balance in the snow-cover period.