DEM-based passive flooding analysis method integrating hydraulic gradient and early warning water level

The invention discloses a DEM-based passive inundation analysis method integrating hydraulic gradient and early warning water level. The method comprises the following steps: inputting a DEM, extracting a river network system, and dividing river reach by taking a reservoir, a dam and a hydrometric station as nodes; sampling points are extracted from all the river reaches according to given intervals, and the samples with insufficient intervals are end points; combining all the extracted sampling points, and outputting point locations and water level attribute layers thereof; calculating the water level of each adopting point through a formula; performing spatial interpolation on the water level of the sampling point, and outputting a water level map layer; the water level map layer and the DEM are superposed to output the submerged area map layer and the water depth grid, the huge error of continuous submerging is remarkably improved, meanwhile, the whole analysis and calculation process can be achieved without complex hydrological model calculation and more parameters, the application range is wide, calculation is fast, and the method is suitable for large-scale popularization and application. The defect of large upstream and downstream errors caused by cutting the digital elevation model by using a horizontal plane with an infinitely extended water level point in the existing passive submerging method is avoided.