VEGETOS: 植物研究の国際ジャーナル

Characteristics of Runoff Variation and its Response to Forest Cover Change in Three Gorges Reservoir Area

R Wang, Y J Wang, Y Q Wang and H L Zhang

Characteristics of Runoff Variation and its Response to Forest Cover Change in Three Gorges Reservoir Area

In this paper, the average annual rainfall and runoff presented fluctuation trends in Three Gorges Reservoir Area was studied. To assess impact of forest coverage changes on runoff in Three Gorges Reservoir Area accurately, we selected rainfall time series, runoff time series and forest coverage rate as the research objects from 1955 to 2011 in Three Gorges Reservoir Area. In this study, we borrow the methods of Mann-Kendall time series trend analysis and double mass curve to quantitatively evaluate the response of runoff on forest coverage and the results showed that the average annual rainfall and runoff presented fluctuation have the trends，Rainfall and runoff average values were 1161.8mm, 38.58 billion m3 respectively, amplitudes were 744.0mm, 43.89 billion m3, and coefficients of variation were 13.4%, 26.1% from 1955 to 2011 in Three Gorges Reservoir Area. The results shows that the reservoir area runoff have four stages：the first one is that the reservoir area runoff had the same decreasing trend as precipitation before 1965. the second one is that annual runoff was from a decreasing trend to increasing trend, and achieved a significant increasing trend in 1983-2002. . the third one is that the extent of an upward trend began to decrease from 2003, and became a decreasing trend by 2011. the last one is that forest coverage changes have experienced from a small reduction to a substantial increase in Three Gorges Reservoir Area from 1950 to the present. When the forest coverage was low level (<24%), decreasing forest cover reduced water yield, whereas increasing runoff, but the degree of impact was limited. Finally, as the forest cover reached a high level (>24%), increasing forest reduced river runoff.