Abstract. This paper presents an analysis of the effects of biased
extended streamflow prediction (ESP) forecasts on three deterministic
optimization techniques implemented in a simulated operational context with
a rolling horizon test bed for managing a cascade of hydroelectric reservoirs
and generating stations in Québec, Canada. The observed weather data were
fed to the hydrological model, and the synthetic streamflow subsequently generated
was considered to be a proxy for the observed inflow. A traditional,
climatology-based ESP forecast approach was used to generate ensemble
streamflow scenarios, which were used by three reservoir management
optimization approaches. Both positive and negative biases were then forced
into the ensembles by multiplying the streamflow values by constant factors.
The optimization method's response to those biases was measured through the
evaluation of the average annual energy generation in a forward-rolling
simulation test bed in which the entire system is precisely and accurately
modelled. The ensemble climate data forecasts, the hydrological modelling and
ESP forecast generation, optimization model, and decision-making process are
all integrated, as is the simulation model that updates reservoir levels and
computes generation at each time step. The study focussed on one hydropower
system both with and without minimum baseload constraints. This study finds
that the tested deterministic optimization algorithms lack the capacity to
compensate for uncertainty in future inflows and therefore place the
reservoir levels at greater risk to maximize short-term profit. It is shown
that for this particular system, an increase in ESP forecast inflows of
approximately 5 % allows managing the reservoirs at optimal levels and
producing the most energy on average, effectively negating the deterministic
model's tendency to underestimate the risk of spilling. Finally, it is shown
that implementing minimum load constraints serves as a de facto control on
deterministic bias by forcing the system to draw more water from the
reservoirs than what the models consider to be optimal trajectories.