What I know is Niuling, which is a watershed. After Lingshui, it is tropical to the south and subtropical to the north. It can also clearly feel the difference in climate. Because I often go to Sanya from Wanning, I can find it magically several times. It is raining in the north, and it will be clear after passing the Niuling Tunnel, and it will not rain. If you take the old national road, Niuling's Panshan Road is the worst to walk.