The impact of landscape changes on weather modification in western Australia in summer was studied. A three-dimensional spectral model was used to simulate limited-area weather modification by changing surface conditions, such as surface wetness, roughness, and albedo. Using global analysis data sets as the initial and boundary conditions, comparative simulations were made for original and modified surface conditions in a nearly 500¿500 km region on January 14 and 22, 1990. For those two days, precipitation naturally occurred under convective atmospheric conditions. The simulation results show that the net precipitation (i.e., increased precipitation minus increased evaporation) increased significantly in the modified region when we changed surface conditions from bare soil to forests. Also, we did sensitivity studies of the effect of the evapotranspiration efficiency β, roughness z0, and albedo on precipitation, sensible and latent heat fluxes, and precipitation patterns during the day. We did sensitivity studies for 0.1<β<0.8, 0.010<2.00 m, and albedo from 0.05 to 0.25. Our simulations indicate that for z0=1.0 m and albedo of 0.15, increasing β from 0.1 to 0.8 increased precipitation from 9.1 to 14.6 mm on January 14 and 4.4 to 8.5 mm on January 22. For z0=1.0 m and β=0.60, decreasing albedo from 0.25 to 0.05 increased precipitation from 12.8 to 16.1 mm on January 14 and 7.6 to 8.1 mm on January 22. Precipitation varied when z0 was increased from 0.01 to 0.5 m but changed insignificantly for further increases in z0 above 0.5 m. ¿ 2000 American Geophysical Union