A Real-time Flood Monitoring Index Based on Daily Effective Precipitation and its Application to Brisbane and Lockyer Valley Flood Events

An objective index for flood monitoring is pragmatic tool for flood early warning systems. This study investigates a novel Flood Index (I _F ) based on Effective Precipitation (P _E ) for quantifying floods in Brisbane and Lockyer Valley. Using daily precipitation (P) data as an input, the I _F was determined by calculating P _E using exponentially-decaying time-reduction function considering gradual depletion of water resources over the passage of time and comparing and normalizing the P _E per day with the means and standard deviations of yearly maximums in the hydrological period. Start of flood was identified for I _F ≥0, severity (I _F ^acc ) assessed by running-sum on consecutively positive I _F , duration (D _F) as number of days with positive I _F and peak danger (I _F ^max ) as maximum I _F . The ability of I _F for flood warning was verified with river height and discharge rates. The most severe flood was recoded in January 1974 in Brisbane (I _F ^acc =118, I _F ^max =4.4, D _F = 104 days) with return period (T) =106.2 years. Next was the December 2010–January 2011 event (I _F ^acc =61.8, I _F ^max =2.6, D _F = 89 days) with T = 53 years. For Lockyer Valley, December 2010–January 2011 was the most severe (T = 104.4 years). Consequently, we advocate the practicality of the daily I _F for flood risk assessments where severity, peak danger, duration or return periods are to be considered.