Analysis of stream water temperature changes on different forest type watersheds; cases study at field measurements in kochi region and comparing with other regions in Japan

The changes in stream water temperature help to identify the mechanism that generates the initial response as direct inputs of solar radiation or air temperature and rainwater or discharge of groundwater.The objective is to clarify the stream water temperature changes on different forest type watersheds. A total of 23 events at 16 streams at Aichi, Kochi, Mie and Tokyo were chosen for analysis.Water level and temperature (Tw) were measured at the interval of 5 minutes from January 2004 to December 2005. We used air temperature data (Ta) at the nearest AMeDAS stations to the respective streams. The specific discharge (Qs) was calculated from water level data. In particular, field measurements also have been done at Kochi 3 (broadleaf) and Kochi 8 (bad managed hinoki) at the interval of 30 minutes from June 2005 to November 2006. Based on field measurements, soil temperatures (Ts) at Kochi 8 were smaller than those at Kochi 3 at 50 cm (0.9oC and 1.70C, respectively) and 70 cm depths (0.80C and 0.90C, respectively), indicating smaller proportions of precipitation infiltrated into the ground compared with broadleaf forest. Stream water temperature fluctuation expressed by Rms Tw/Rms Ta at broadleaf and hinoki were 0.18 ± 0.04 and 0.24 ± 0.11, respectively. In addition, the values of |ΔTw| at broadleaf and bad managed hinoki watersheds (2.0 ± 1.0oC and 1.9 ± 0.7oC, respectively) were significantly larger than those at well managed hinoki watersheds (1.3 ± 0.5oC), possibly suggesting the difference in flow path proportion.