Quantifying Critical Area and Investigating its Relationship with the Physio-Climatic Characteristics of the Second and Third Order River Basins in Iran

If the channel network map of a region is not suitable for the purpose of modeling water and solute transport processes, the underlying river network should be extracted by the relating algorithms given the critical area as the input. The goal of this study was to (1) extract the critical area in the second and third order river basins in Iran, and (2) investigate the relationship between the critical area and physio-climatic characteristics of the basins with the aim of determining the most dominant factors controlling the critical area. To this end, the closest critical area to reality was determined by minimizing the difference between the drainage density of the extracted river networks using the D8 method and the one known as the base map of the river networks. Results indicate that the spatial resolution of the digital elevation model between 30 m to 200 m does not impose significant impact on the magnitude of the estimated critical area. Also, direct relationship holds between the critical area and the soil permeability and erosion rate, while the correlation is negative between the critical area and the vegetation density. Critical area is smaller and larger in the temperate and warmer climates, respectively. Furthermore, increase in the average slope and the average annual precipitation height decreases the critical area. Nevertheless, the correlation between the critical area and the studied physio-climatic quantities is insignificant, highlighting the need to determine the critical area of a given river basin using approaches other than physical-mathematical relationships.