嘉陵江流域年径流量的变化及其原因

以嘉陵江的资料为基础,探讨了年径流量的变化及其原因,分析了水土保持措施减少径流的效应。以1956-1980年作为人类活动较弱的“基准期”,而以1981-2000年为人类活动较强的“措施期”,分别给出了回归方程。计算表明,降水减少导致的年减水量占年平均总减水量的84.3%,水利水土保持措施导致的年减水量占年平均总减水量的15.7%。人类活动对年径流的影响是依赖于年降水量的,降水偏少年减水量较大,降水偏多年减水量较小,超过某一临界值之后,年径流量不但不会减少,反而会增加。计算表明,这一临界年降水量为1 000 mm。年径流系数的变化和年径流量的变化相似,1980年以前无趋势性变化,1980年后有减小的趋势。人类活动对年径流系数的影响同样是依赖于年降水量的,降水偏少年径流系数的减小较显著,降水偏多年径流系数的减小不明显,甚至还可能增大。

Temporal Variation in Annual Water Yield of the Jialingjiang River and the Formative Causes

Based on data from the Jialingjiang River,the temporal variation in annual water yield and the formative cause have been studied,and the water reduction effect of soil and water conservation has been analyzed.The periods 1956-1980 and 1981-2000 were taken as the "baseline" period and the period with measures,and a regression equation between annual water yield and areal average precipitation has been established for the above two periods,respectively.Using the two equations,the water reduction by the decreased precipitation has been estimated as 84.3% and that by soil and water and conservation measures as 15.7%.The effect of human activity on water yield is dependent on annual precipitation.During the years with higher precipitation,the water reduction is lower,and during the years with lower precipitation,the water reduction is higher.When the annual precipitation exceeds a certain threshold,the water reduction may become negative.The temporal variation in annual runoff coefficient(R_c) is similar to that in water yield.Before 1980,no trend could be seen,but after 1980,the annual runoff coefficient tended to decrease.The effect of human activity on runoff coefficient is also dependent on annual precipitation.During the years with higher precipitation,the reduction in R_c is lower,and during the years with lower precipitation,the reduction in R_c is higher.When the annual precipitation exceeds a certain threshold,the R_c might increase.