Development of synoptic analogue model for quantitative precipitation forecast in the sub-basins of river Krishna

Abstract

Average areal precipitation (aap) data during south west monsoon season (2012 to 2022) in 10 sub-basins of Krishna river basin were computed and synoptic systems inducing rainfall in the sub-basins were collected. Five synoptic systems-depression/deep depression, low/well marked low (WML) pressure area, Upper air cyclonic circulations (UAC), off-shore trough (OST)/OST with embedded cyclonic circulations, east-west shear zone are considered in the study. Rainfall (AAP) occurrence in the range of 11-25 mm, 26-50 mm, 51-100 mm and > 100 mm due to these systems are considered. OST/OST with embedded cyclonic circulation leads to highest frequency of rainfall in all the sub-basins. Occurrence heavy rainfall (AAP from 26-50 mm) culminating flood in the river basins is mainly due to Off-shore trough/OST with embedded cyclonic circulation at different locations around the river basin. Frequency of 26-50 mm range is more than 51-100 mm in different sub-basins. Shear zone and upper air cyclonic circulations are also contributed significantly to heavy rainfall. Off-shore troughs, upper air cyclonic circulations and East-West shear zone resulted >51-100 mm rainfall in Ghataprabha, Bannehalla, Upper Krishna, Upper Tungabadra and Lower Bhima. Off-shore trough resulted >100mm rainfall in Upper Krishna and Upper Tungabhadra. Upper air cyclonic circulations resulted  >100 mm rainfall in Upper Tungabhadra sub-basin. Heavy rainfall >100 mm in maximum number of occasions are due to off-shore trough from Gujarat to Kerala and Karnataka. Number of days for which these synoptic systems contributed rainfall under each range was computed. The rainfall range with highest frequency for the particular system is considered as synoptic analogue model. Validation of synoptic analogue model indicates better performance of the models in different sub-basins and it can be used to improve the accuracy of operational Quantitative precipitation forecast (QPF) issued for flood forecasting.