Analyzing the impact of bias correction of ensemble rainfall forecasts
on streamflow prediction skill of a hydrodynamic model
Abstract
Use of ensemble rainfall forecasts has gained popularity in providing
detailed uncertainty information and improving hydrologic prediction
skill. India Meteorological Department (IMD) provides medium-range
multi-model ensemble (MME) forecasts for all over India with 1- to 5-day
lead time. In this study, we bias correct the IMD MME rainfall forecasts
using a modified version of Kohonen Self-Organizing Maps (KSOM) and
analyse the effect of bias correction on the streamflow prediction skill
of MIKE 11 Hydrodynamic (HD) model for the years 2012-2014. We have
selected the upper region of the Mahanadi River basin as the test bed.
The results indicate improvement of rainfall forecasts after bias
correction. Subsequently, use of bias corrected rainfall forecasts as
input forcing to the MIKE 11 HD model provides better streamflow
forecasts at all the lead times (Nash Sutcliffe Efficiency, NSE ranging
from 0.89 to 0.41) compared to the use of raw forecasts (NSE ranging
from 0.89 to -0.51). To further improve the streamflow forecasts, we
have applied the recently developed robust wavelet-based non-linear
autoregressive with exogenous inputs dynamic neural network model,
WNARX. This post-processing operation tends to improve the streamflow
forecast quality to an acceptable range (NSE = 0.92-0.71). The results
encourage us to conclude that the IMD MME forecasts has great potential
to improve streamflow prediction skill of a hydrodynamic model.