Causes and dynamic change characteristics of the 2022 devastating floods in Pakistan

In 2022, a catastrophic flood triggered by the extreme precipitation in Sind Province, Pakistan. To better understand the comprehensive response of water vapor, rainfall, topography, and flood, the source of water vapor for the flood was calculated by the NCAR Command Language (NCL) application. Simultaneously, the Global Precipitation Measurement (GPM) data was collected from NASA for overlay analysis with water vapor observations. In addition, a digital elevation model (DEM) was also obtained to analyze the impact of topography on flood inundation. Importantly, multi Sentinel-1 data was used to monitor the long-term changes in flood inundation area. The extreme precipitation is dominated by water vapor continue transferred by southwest monsoon, especially impacted by the occurrence of cyclone. Simultaneously, influenced by the steep terrain that located in the north and west of Pakistan, the extreme precipitation first occurred in Islamabad and its adjacent area, subsequently in Punjab Province, and finally concentrated in Sind Province. The surface runoff induced by rainstorm converged in the junction of Sind and Punjab Province with the pattern of fire hose effect. Subsequently, the flood in Indus River in the Sind Province overflow into the low-lying area along the bank of Indus River due to the terrain of Indus River in these regions has the characteristics of over ground river, and the flood flow capacity is lower than that in northern of Pakistan. In addition, the long-term changes in the flood inundation area can be summarized into four stages: increase slowly period (In June), increase slightly period (In July), increase rapidly period (Between August and the beginning of September), rapidly decline period (After September 15, 2022). Importantly, a conceptual model of disaster caused by the fire pipe effect is summarized based on the comprehensive response of water vapor, rainfall, and topography.