The submodel ”UPLAND” of the Peatland Hydrologic Impact Model (PHIM) was described and applied at the Lienhuachih Experimental Watershed No. 3, a 3.34-ha natural hardwood watershed located in central Taiwan, for simulating hydrographs and estimating water yield. Judging from the fitness of hydrographs and water yield between simulated and observed values, the simulations of daily resolution, but not for hourly, were accepted with 95% confidence. The results indicate that PHIM is reliable for estimating annual streamflow hydrographs and for determining the effects of land use changes on water yield for small watersheds in central Taiwan.