Update of Early Warning Indicators of Flash Floods: A Case Study of Hunjiang District, Northeastern China

Geomorphology-Based Analysis of Flood Critical Areas in Small Hilly Catchments for Civil Protection Purposes and Early Warning Systems: The Case of the Feltrino Stream and the Lanciano Urban Area (Abruzzo, Central Italy)

This work is based on a drainage basin-scale geomorphological investigation combined with flood modeling. It is focused on the assessment of flood critical areas for the implementation of a geomorphology-based urban Early Warning System (EWS) in the urban area of Lanciano and the Feltrino Stream basin (a minor coastal basin of the Abruzzo hills, Central Italy). This area was investigated by combining: pre-existing geological, geomorphological, and hazard data and new detailed field surveys and mapping of geomorphological and hydrographical features (superficial and buried natural and urban stream network). The study was integrated with 2D flood numerical modeling for verifying the expected flooded areas and calibrating the critical areas. All the collected data were integrated into a geodatabase, and an expert-based approach through a geomorphology-based matrix allowed us to define the main categories of flood critical areas. The assessment of the critical areas supported the emplacement of a network of rainfall, temperature, and flood gauges. The geodatabase, the derived critical areas, and the gauge network contributed to set up an urban EWS, integrated with the regional forecast-based warning system. This system provides combined forecast-based, rainfall threshold-based, and flood monitoring-based alerts for floods. It incorporates communication tools for civil protection management. Finally, the EWS provides a tool for civil protection purposes and for the management of flood critical areas and the mitigation of the related risks by local authorities and will be integrated with sensors related to other hazards (i.e., landslides, wind, etc.).

Application of the GPM-IMERG Products in Flash Flood Warning: A Case Study in Yunnan, China

NASA’s Integrated Multi-Satellite Retrievals for Global Precipitation Measurement (IMERG) is a major source of precipitation data, having a larger coverage, higher precision, and a higher spatiotemporal resolution than previous products, such as the Tropical Rainfall Measuring Mission (TRMM). However, there rarely has been an application of IMERG products in flash flood warnings. Taking Yunnan Province as the typical study area, this study first evaluated the accuracy of the near-real-time IMERG Early run product (IMERG-E) and the post-real-time IMERG Final run product (IMERG-F) with a 6-hourly temporal resolution. Then the performance of the two products was analyzed with the improved Rainfall Triggering Index (RTI) in the flash flood warning. Results show that (1) IMERG-F presents acceptable accuracy over the study area, with a relatively high hourly correlation coefficient of 0.46 and relative bias of 23.33% on the grid, which performs better than IMERG-E; and (2) when the RTI model is calibrated with the gauge data, the IMERG-F results matched well with the gauge data, indicating that it is viable to use MERG-F in flash flood warnings. However, as the flash flood occurrence increases, both gauge and IMERG-F data capture fewer flash flood events, and IMERG-F overestimates actual precipitation. Nevertheless, IMERG-F can capture more flood events than IMERG-E and can contribute to improving the accuracy of the flash flood warnings in Yunnan Province and other flood-prone areas.

A New Flash Flood Warning Scheme Based on Hydrodynamic Modelling

Flash flooding is one of the most severe natural hazards and commonly occurs in mountainous and hilly areas. Due to the rapid onset of flash floods, early warnings are critical for disaster mitigation and adaptation. In this paper, a flash flood warning scheme is proposed based on hydrodynamic modelling and critical rainfall. Hydrodynamic modelling considers different rainfall and initial soil moisture conditions. The critical rainfall is calculated from the critical hazard, which is based on the flood flow depth and velocity. After the critical rainfall is calculated for each cell in the catchment, a critical rainfall database is built for flash flood warning. Finally, a case study is presented to show the operating procedure of the new flash flood warning scheme.