Stream water temperature difference between coniferous and deciduous forest

Amount of solar radiation input into ground surface has a strong influence on underground heat condition. Stream water temperature is a gross index of underground heat condition of a watershed. As for stream water temperature of forest covered watershed, the effect of riparian forest on direct solar radiation input on stream water, and the effect of deforestation on stream water temperature have been studied. However, there is a few studies which deal with the impact of forest type difference on heat condition of a watershed. Thus, we measured stream water temperature of adjacent watersheds of which forest types are different; i.e. coniferous and deciduous forest. As a result, significant stream water temperature pattern difference between coniferous and deciduous forest was observed. While stream water temperature of coniferous forest was significantly lower than that of deciduous forest during the period of winter season (from the end of October to the start of May), tendency was converted during the period of summer season (from June to the end of October). No significant difference was found in the annual temperature amplitude of both forest types. We conducted numerical modeling study to explore the mechanism of stream water temperature difference. The result suggested that difference of snow cover pattern due to the leaf abscission of deciduous forest might play an important role in deciding stream water temperature during the winter season.