Estimating the direct precipitation on channel and waterbodies in Iran

Channel precipitation can be defined as rainfall and throughfall intercepted by the flowing stream channel and waterbodies, that without contribution to infiltration, subsurface flow, and ground water, incorporated into stream flow. Contributions of channel precipitation were studied in main river basins of Iran. The annual isohyetal map of the study area was converted to raster format and the average rainfall which falls on the streams and water-bodies surface were calculated, and converted to volumetric amount. The results indicated that streams and water-bodie's areas constitute 1.5 percent of the total country area. The results show that the amount of channel precipitation is 7.74 billion cubic meters, which represents 1.85% of total annual precipitation. The spatial pattern of volumetric ratio of channel precipitation indicates that its amount varies in different basins of Iran.