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Poster Session 2
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Land Cover Change and Long-Term Fluctuation of Evapotranspiration in Okutama
4. Conclusion
From hydrological and satellite data, annual water budget and evapotranspiration in the upper Tama River were analyzed to conclude the next items.
- From satellite data in 1984 and 1997, forest area increased from 92.8 % to 97.2 %, while agricultural fields decreased from 2.9 to 1.5 %.
- As a result of long-term water budget from 1959 to 1997, annual precipitation was constant, annual evapotranspiration increased moderately, but runoff ratio decreased in trend. It seems to be caused by forest constitution change or the increase of forest area and the decrease of paddy fields.
- As a result of short-term water budget, monthly evapotranspiration changed with corresponding to seeding, mid-term drying, and final drying in paddy fields. Therefore, the fluctuation of the monthly evapotranspiration may be the results of agricultural water use change with the policy of paddy field reduction.
Acknowledgement
The authors thank Waterworks Bureau in Tokyo Metropolitan Government for their hydrological data. We also greatly appreciate to Dr. Genya Saito, Mr. Naoki Ishituka, and Dr. Takuhiko Murakami at National Institute of Agro-Environmental Sciences, and Ms. Ikuyo Makino at Tokyo Institute of Technology for their cooperation.
References
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Aoyama, T., H. Nishikawa, and H. Murai, Journal of Remote Sensing Society of Japan, 20, 2, 539-551, 1990.
- Kazama, S., T. Tada, and M. Sawamoto, Annual Journal of Hydraulic Engineering, 40, 323-328, 1996.
- Sado, K. and R.Wei, Annual Journal of Hydraulic Engineering, 40, 323-328, 1996.
- Sado, K., Journal of Japan Society of Hydrology & Water Resources, 9, 2, 188-197, 1996.
- Waterworks Bureau, Tokyo Metropolitan Government, Annual Report of Ogouchi Reservoir Management, 1959-1997.
- Meteorological Agency, Meteorological Monthly, 1968-1997.
- Suzuki, M., Journal of Japan Society of Forest, 67, 4, 115-125, 1985.
- Kotoda, K., Estimation of River Basin Evapotranspiration, Environmental Research Center, The University of Tsukuba, 1986.
- Statistics and Information Department, Economic Affairs Bureau, Ministry of Agriculture and Forestry, Agricultural Field Area Statistics, 1973-1999.
- Makino, I., S. Ogawa, and G. Saito, Annual Journal of Hydraulic Engineering, 44, 283-288, 1999.
Table 1 Satellite data used
| Satellite | Date |
| LandsatTM | 1984/10/26; 1997/10/30 |
Figure 1 Okutama and its observation stations
Table 2 Land cover area rate in Okutama using LandsatTM (Unit:%)
| Year | Forest | Urban Area | Grass | Paddy Field | Vegetable Field | Water |
| 1984 | 92.8 | 0.4 | 2.6 | 2.1 | 0.8 | 1.3 |
| 1997 | 97.2 | 1.0 | 0 | 1.0 | 0.5 | 1.3 |
Figure 2 Agricultural area ratio in Okutama
Table 3 Annual mean hydrological observation results
| Period | Precipitation | Discharge | Evapo-
transpiration | Runoff ratio |
| 1958-1967 | 1550mm | 1060mm | 490mm | 0.68 |
| 1968-1977 | 1582 | 1067 | 515 | 0.67 |
| 1978-1987 | 1551 | 1013 | 538 | 0.64 |
| 1988-1997 | 1658 | 1135 | 524 | 0.67 |
Table 4 Annual mean evapotranspiration with water balance, pan evaporation, and Penman's method
| Period | Water Balance | Pan Evaporation | Penman's method |
| 1968-1977 | 515mm | 760mm | 655mm |
| 1978-1987 | 538 | 768 | 662 |
| 1988-1997 | 524 | 792 | 683 |
Figure 3 Water balance in Okutama
Figure 4 Runoff ratio in Okutama
Figure 5 Monthly evapotranspiration in Okutama
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