长江上游森林影响流域水文过程模拟分析

Simulations and analysis on the effects of forest on the hydrological processes in the upper reaches of Yangtze River

用森林流域水文模型(FCHM)模拟分析长江上游森林植被变化下的平通河流域和刘家河流域森林水文过程。可知随着两个流域森林覆盖率(FR)的提高,林冠截留量的增加和土壤入渗能力的改善,使得径流成分比例也随之发生变化,地表径流Rf逐渐减少,快速流转换为慢速流,因此延迟了流域降水汇流时间,洪峰流量得以削减。以平通河为例,当该流域全部被森林覆盖以后,则流域百年一遇的设计洪水标准可由非森林地时的4520m3/s降到3380m3/s,因此森林的存在可大大提高流域的防洪能力;而两个流域又由于区域结构等条件的不同,使得流域径流成分所占比例不同。其中平通河流域径流成分主要以浅层径流Rs和深层径流Rp为主,而刘家河流域径流成分主要以壤中流Ri为主,且都随森林覆盖的增加而有所增加。不同的径流成分为流域蒸散发带来了不同的水分条件,因此流域蒸散发量随着森林覆盖率的增加各有不同的变化趋势。其中平通河流域随着森林覆盖率的增加,流域蒸散发总量将由非森林地时候的373.3mm减少至289.3mm,根据水量平衡原理,该流域径流总量则会增加,呈流域径流正效应(23.7%);而后者流域则相反,随着森林覆盖率的增加,流域蒸散发总量反而会逐步增加,则流域径流总量会随之减少,呈流域径流负效应(-8.6%)。

By applying of forest watershed hydrological model（FCHM）,this paper simulated the forest hydrological effects in Pingtong and Liujia watersheds of the upper reaches of Yangtze River.With the increase of forest cover（FR）,the canopy interception and soil infiltration capacity were improved;as a result,the surface runoff（Rs） decreased and rapid flow converted into slow flow,and the time period needed for runoff accumulation delayed,so that the flood peak was alleviated.For example,with forest cover,the flooding control criteria for Pingtong watershed decreases to 3380m^3 /s from 4520m^3 /s（without forest cover）.indicating the existence of forest can enhance the flooding control capacity of the watershed.The different characteristics of the two watersheds,the major runoff components in Pingtong watershed are shallow runoff（Rs） and deep runoff（Rp）,but are dominated by interflow（Ri） in Liujia watershed.All of these components increase with the increasing FR.The different runoff components brought different moisture conditions,as the result,the evapo-transpiration show different trends with the increase of FR.In Pingtong watershed,with the increase of FR,the evapo-transpiration decreased from 373.3 mm to 289.3 mm but runoff went up,resulting in a positive effect of 23.7%.In Liujia watershed,higher FR resulted in the increase of the evapo-transpiration and the decrease of runoff,resulting in a negative effect of-8.6%.