Analysis On The Characteristics Of Forest Change And Runoff And Sediment Change In The Amazon Basin

The Amazon basin has the largest tropical rain forest in the world.In the past few decades,under the interference of human activities and climate change,the tropical forests in the Amazon basin have been decreasing.It is very important to understand the forest loss pattern and the change of forest structure in the Amazon basin for the effective protection and management of forests.Based on the long time series of land use / cover data,meteorological data,water and sediment data,this paper uses Mann Kendall trend analysis,hot spot analysis,Pettitt test of forest fragmentation model to analyze the temporal and spatial distribution characteristics of forest loss and forest degradation,as well as the change trend of climate factors and water and sediment in the Amazon basin,and uses the elasticity based water and heat model The contribution of each factor to the change of water and sediment is quantified by the balance coupling equation and the diagnostic attribution method of sediment identity.The main conclusions are as follows.(1)The proportion of forest area in the Amazon basin decreased continuously from 1992 to2018,and the forest reduction rate decreased significantly from 2003 to 2018.The cultivated land increased by 3.23%.The newly increased cultivated land mainly came from forest,and other land use / cover types had little change.Although the total area of forest loss decreased,the small area(< 50ha),"moderate" and "serious" forest loss increased significantly.The spatial distribution of forest loss gradually spread from the southeast to the whole basin,and new forest loss hotspots appeared in Peru and Ecuador.(2)From 1992 to 2018,the number of forest patches in the Amazon basin increased year by year,and the number of forest patches less than 50 ha increased significantly..The proportion of "internal forest" representing the forest integrity in the watershed is more than60%,but the proportion of "internal forest" gradually decreases,and the proportion of "marginal forest","patch forest","transitional forest" and "hole forest" gradually increases.The forest as a whole is relatively complete,but has a trend of gradual fragmentation.Forest fragmentation mainly occurs in the non-forest edge and river coastal areas,which is consistent with the spatial distribution of forest loss.(3)The temperature,precipitation and potential evapotranspiration(PET)of the Amazon basin showed an increasing trend from 1985 to 2015.The temperature and precipitation passed the significance test of 0.05,and the seasonal variation of climate factors was small.From 1985 to 2015,the annual runoff increased significantly(P < 0.05),while the annual sediment concentration and sediment transport decreased insignificantly.The seasonal variation of water and sediment is also small.(4)The contribution rate of precipitation to runoff increase was 117.62%,and that of pet to runoff increase was-9.74%.In the landscape composition and fragmentation components,the proportion of woodland was significantly negatively correlated with runoff,and significantly positively correlated with "patch forest" and "transitional forest".The contribution rate of underlying surface parameters to runoff increase was-7.88%.It shows that forest loss and degradation will increase river runoff,but the main reason for the increase of runoff is still the increase of precipitation.The contribution rate of sediment concentration to sediment reduction is 53.76%,the contribution rate of runoff coefficient to sediment reduction is 33.87%,and the impact of precipitation is 12.37%.