Tornado is a climate change that is density independent factor, and will exert influence on the size of population, no matter what is the density of that population. While on the other hand their are density dependent factors, whose effect become intense as the size of that particular population increases e.g. spread of a certain disease in an area will be more where people are living in close proximity.
Rivers are large bodies contained of water which always move from the higher part to the lower. Over years It could change landscape of a land through erosion by slowly scrapping the land it passed through
