Title: Linking flood frequency to long-term water balance: Incorporating effects of seasonality Authored by: Sivapalan, M., Blöschl, G., Merz, R. and Gutknecht, D. Abstract:
Derived flood frequency models can be used to study climate and land use change
effects on the flood frequency curve. Intra-annual (i.e., within year) climate variability
strongly impacts upon the flood frequency characteristics in two ways: in a direct way
through the seasonal variability of storm characteristics and indirectly through the
seasonality of rainfall and evapotranspiration which then affect the antecedent catchment
conditions for individual storm events. In this paper we propose a quasi-analytical derived
flood frequency model that is able to account for both types of seasonalities. The
model treats individual events separately. It consists of a rainfall model with seasonally
varying parameters. Increased flood peaks, as compared to block rainfall, due to random
within-storm rainfall time patterns are represented by a factor that is a function of the
ratio of storm duration and catchment response time. Event runoff coefficients are allowed
to vary seasonally and include a random component. Their statistical characteristics are
derived from long-term water balance simulations. The components of the derived
flood frequency model are integrated in probability space to derive monthly flood
frequency curves. These are then combined into annual flood frequency curves.
Comparisons with Monte Carlo simulations using parameters that are typical of Austrian
catchments indicate that the approximations used here are appropriate. We perform
sensitivity analyses to explore the effects of the interaction of rainfall and antecedent soil
moisture seasonalities on the flood frequency curve. When the two seasonalities are in
phase, there is resonance, which increases the flood frequency curve dramatically. We are
also able to isolate the contributions of individual months to the annual flood frequency
curve. Monthly flood frequency curves cross over for the parameters chosen here, as
extreme floods tend to mainly occur in summer while less extreme floods may occur
throughout the year.
Reference: Sivapalan, M., Blöschl, G., Merz, R. and Gutknecht, D., 2005, Linking flood frequency to long-term water balance: Incorporating effects of seasonality, Water Resources Research, 41, W06012, doi:10.1029/2004WR003439 | 
