Thereasonsforthechangesarecomplex.Itisclearthatpollutionoftheairandwaterbyfactoriesisaffectingtheenvironment.Treesandothervegetationdie,andsosoiliseroded.themoretreesthatdie,thelesswaterisheldintheearth.theneedforwoodforfuelandbuildingsleadstofurtherdeforestation,whichcausesfurthersoilerosion.Localfarmersfinditmoreandmoredifficulttomakealiving.theyendupusinginefficientfarmingmethods,whichagainleadstosoilerosion.