Study On Rainfall Redistribution Process In Different Forests In Three Gorges Reservoir Area

In this study,three types of forests,including warm coniferous forest,coniferousdeciduous mixed forest and deciduous broad-leaved forest,were selected as the studied slopes in the Dalaoling Nature Reserve.Aiming to analyze and evaluate the effects of different types of forest canopy on precipitation redistribution in the Three Gorges Reservoir area.We not only conducted continuous field monitoring test of throughfall,stemflow and canopy interception in three forest lands,but analyzed the correlation between rainfall features and forest characteristics affecting precipitation redistribution.We purposed to reveal the influence mechanism of different forests on the rainfall input process,so as to provide reference for the ecological construction and vegetation protection of the Three Gorges Reservoir Area.The results are shown as follows:(1)From April 8,to November 15,2018,a total of 65 rainfall events occurred in the study area,with a total rainfall of 1145 mm.The rainfall in the study area is mainly light rain of<10 mm,which accounts for 52%of the total rainfall events,however,the rainfall composition only accounts for 8.9%.The heavy rains and torrential rain with single rainfall above 50 mm occurred for 5 times,and the rainfall accounts for 40%of the total rainfall,with more heavy rains.(2)The redistribution of rainfall in three forests showed different characteristics.During the study period,the corresponding penetration rate,stemflow rate and canopy interception rate of warm coniferous forest,coniferous-deciduous mixed forest and deciduous broad-leaved forest were 62.8%,6.9%,28.5%,72.8%,2.7%,24.5%,75.7%,3.4%and 20.8%,respectively.The throughfall and the throughfall rate of the three kinds of forests all increased rapidly with the increase of the rainfall,and then tended to be stable,and all increased with the increase of the maximum rainfall intensity within 30 minutes.The stemflow and stemflow rate also fluctuated with the increase of rainfall level,and first increased and then decreased with the increase of rainfall intensity.The average stemflow rate of the warm coniferous forest was the highest,and the stemflow rate of the deciduous broad-leaved forest was the fastest.The canopy interception rate of the 3 frosts decreased with the increase of rainfall,and decreased with the increase of maximum rainfall intensity within 30 min.Canopy interception rate of deciduous broad-leaved forest did not fluctuate much under different rainfall levels and rainfall intensity.Overall,canopy interception capacity of warm coniferous forest>coniferousdeciduous mixed forest>deciduous broad-leaved forest.(3)The correlation analysis showed that there was a linear relationship between forest throughfall,stemflow and canopy interception and the rainfall outside the forest,and that there was a logarithmic relationship between the rainfall outside the forest and the penetration rainfall and canopy interception.It was found by fitting that the minimum rainfall required for the production of penetrating rain in warm coniferous forest,coniferous and coniferous-deciduous mixed forest and deciduous broad-leaved forest was 1.90mm,1.46mm and 0.86mm,respectively,and the minimum rainfall required for the production of stemflow was 4.45mm,2.53mm and 2.01mm,respectively.The results of correlation analysis showed that the canopy interception rate of the three types of woodlands was significantly negatively correlated with rainfall,duration of rainfall and maximum rainfall intensity within 30 min(α=0.01).Under the same rainfall conditions,the differences of DBH,tree height,canopy thickness and canopy width did not cause significant differences in canopy interception rates in the same forest land,but there were significant differences among different forest lands.Under the same DBH,tree height,canopy thickness and canopy width level,there was no significant difference in canopy interception rates between warm coniferous forest and coniferous-deciduous mixed forest,but both of them were significantly larger than deciduous broad-leaved forest.(4)After the occurrence of the rain event outside the forest,the rain in the three forests land(penetration and stemflow)has a certain delay in the time of production and termination.The lag time of the rain in the forest is deciduous broad-leaved forest<warm coniferous forest<coniferous-deciduous mixed forest.When the rain outside the forest was terminated,the delay time of the rain inside the forest of the three kinds of forest was shown as deciduous broad-leaved forest<coniferous and broad-leaved mixed forest<warm coniferous forest.With the increase of the rainfall intensity,the delay effect of the rain inside the forest was weaker and weaker,and even the rain inside the forest ended before the rain outside the forest.With the increase of the rainfall intensity,the delay effect of the rain inside the forest was weaker and weaker,and even the rain inside the forest ended before the rain outside the forest.The correlation analysis of rain delay time in forest and rainfall factors outside forest showed that the delay time of rain in three kinds of forest was negatively correlated with average rainfall intensity and positively correlated with rainfall duration.At the same time,the delay time of penetration rainfall is negatively correlated with the rainfall and rainfall intensity in the first hour during a single rainfall field.The maximum rainfall intensity at 30 min had a significant effect on the termination of penetration rain.