The Xisha archipelago is located in tropical regions.It is sultounded by oceans and with a climate of high in temperature and plenty in rainfall.The islands are composed of coral reefs

whose modem landforms are developed after a subside in tectonic movement and an uplift followed.Islands are narrow in area.Particular environment developes particular hydrology which is characterised by that surface water storages are rare

surface runoff is difficult to develope and deep groundwater is connected with salt water

thus fresh water resource is scarece thought rainfall is abundant.With the increasing human activities

questions are brought out for island development such as how to imporove hydrologic conditions so as to provide enough fresh water resource

to improve the ecosystem and to keep continuous developement for environment and economic.