Rice production in Tsiwm ie likely to dccreaee because of two major thre8tzx an increase in the industrial demand on water resourcea and cheaper imported rice resulting from the free trade policy which will be enforced when Taiwan joins the World Trade Organh&ion. A &h&age in rice paddy acreage raisea environmental concerna, espechdly in relation to water conwrwatlon. Besides rice production, the existence of paddy ffelde promotes groundwater rech8rge and r&ediatea floods. Unlike rice production, the v&e of the environmental consen&ion is dillicult to quantify. In thii study, the eRecta of paddy fields on groundwater recharge end flood rem&r&ion have been inveatlgated. To aseem the long-term signiicance of them e&&s, the study taam developed a model baaed on hydrologic equilibrium. Thii model describea the performauce of wrrter recharge Bnd detention.
According to a case study, the amount of runoff from a rice paddy field ie about 27% of the amount of the precipitation. This percentage is signiiicantly lower than that of the runoff from 8 dry f8rming field, which is normally as high aa 55% of the precipitation. In this case, the amount of ewapotranspiration from a rice paddy field end that from a dry farming field are 56% and 31%, respectively. In this rxae, the amount of recharge from a rice paddy field, 17%, is higher than that from 8 dry f8rmhrg field, which ia 14%. Clearly, 8 sign&ant increase in runoff end a decrease in groundweter recharge can be expected when a rice peddy Reid is converted to other ums. The second analyeia includes an event-based simulation study regarding the effects of rice paddy fields on the flood peak. Attributed to ita superior detention c8pacity, a paddy field typically hae a much lower flood peak, about one third of a dry farm field. These positive elfecta of rice paddy iields on runoff should be considered in making decisiona about the reduction of rice cultivation.