Performance of the GPM IMERG and CMORPH Gridded Precipitation and Rain on Grid Approaches to Reproduce the Pluvial Flood of 2022 in Lower Indus Basin, Pakistan

Hydrological extreme events are exacerbated by global climate change. The root cause of climate change is mainly attributed to increased emission of Green House Gases (GHGs) and increased fossil fuel use. Although Pakistan contributes nominal in GHGs emissions, it is one of the most vulnerable countries facing climate-related disasters. These disasters include heatwaves, weather abnormalities, and hydrological extremes such as drought and flood events. Frequent and unprecedented rainfall caused fluvial 2010 and pluvial 2022 devastating floods in Pakistan. Anthropogenic activities in natural floodways have multifold the extremities of floods. This study presents the comparison of two gridded precipitation data (CMorph and IMERG) with high temporal (half-hourly) and spatial resolution (8-10Km) and the use of direct rainfall modeling (DRM) or rain on grid (ROG) approach to reproduce pluvial flood 2022 in lower Indus basin in Sindh Pakistan. Both the precipitation datasets were able to reproduce the pluvial flood 2022 flood with reasonable accuracy. Results indicate that gridded precipitation and DRM approach can be used for the modeling of pluvial floods (urban and flash floods) for probabilistic flood mapping. However, IMERG precipitation data was able to produce a more realistic flood extent as compared to CMorph when both were compared with SAR-extracted flood extent. The estimated stream flow or gridded precipitation forecast can be directly used as Rain on Grid in Hec-RAS to produce flood hazard maps. The study also highlights the possibility of utilizing the Global Forecast System (GFS), Weather Research Forecasting (WRF) predictions for flood forecasting, and early warning systems that can be developed for a country like Pakistan. The study can be useful for government departments, National Disaster and Management Authority (NDMA), and other agencies involved in flood fighting and flood prevention to make an early and well-informed decision before the disaster strike, thus can reduce the loss of life and property. The methodology can be useful in transforming flood management from reactive to proactive.