Stream channel geometry data were collected on 18 small watersheds in the West and sediment yield data were obtained for 673 small watersheds across the United States. Regression analysis was used to test what effects precipitation modification might have on these watershed parameters. No consistent changes of stream channel geometry between watershed areas were obtained, but the results indicated that the stream channel at a given location would adjust significantly in response to increases in precipitation (amounting to 14% annually). This response would probably initiate increased stream channel erosion. Sediment yield will increase substantially in semiarid regions with increasing precipitation until about 27 inches mean annual precipitation; at this point vegetation growth as a result of increased precipitation will begin to reduce sediment yield. Significant changes in stream channel geometry and sediment yield may result in sufficient economic damage to nullify many of the beneficial effects of weather modification.