The role of hydrological model complexity and uncertainty in climate change impact assessment

Abstract

Abstract. Little quantitative knowledge is as yet available about the role of hydrological model complexity for climate change impact assessment. This study investigates and compares the varieties of different model response of three hydrological models (PROMET, Hydrotel, HSAMI), each representing a different model complexity in terms of process description, parameter space and spatial and temporal scale. The study is performed in the Ammer watershed, a 709 km 2 catchment in the Bavarian alpine forelands, Germany. All models are driven and validated by a 30-year time-series of observation data. It is expressed by objective functions, that all models, HSAMI and Hydrotel due to calibration, perform almost equally well for runoff simulation over the validation period. Some systematic deviances in the hydrographs and the spatial patterns of hydrologic variables are however quite distinct and thus further discussed.Virtual future climate (2071-2100) is generated by the Canadian Regional Climate Model (vers 3.7.1), driven by the Coupled Global Climate Model (vers. 2) based on an A2 emission scenario (IPCC 2007). The hydrological model performance is evaluated by flow indicators, such as flood frequency, annual 7-day and 30-day low flow and maximum seasonal flows. The modified climatic boundary conditions cause dramatic deviances in hydrologic model response. HSAMI shows tremendous overestimation of evapotranspiration, while Hydrotel and PROMET behave in comparable range. Still, their significant differences, like spatially explicit patterns of summerly water shortage or spring flood intensity, highlight the necessity to extend and quantify Correspondence to: R. Ludwig (r.ludwig@lmu.de) the uncertainty discussion in climate change impact analysis towards the remarkable effect of hydrological model complexity. It is obvious that for specific application purposes, water resources managers need to be made aware of this effect and have to take its implications into account for decision making. The paper concludes with an outlook and a proposal for future research necessities.

An ensemble approach to assess hydrological models' contribution to uncertainties in the analysis of climate change impact on water resources

“…Jones et al (2006) suggest that conceptual and physical based models have a different role in impact assessment, where the former can be used to rapidly assess the impact of different climate scenarios, while the latter can assess the joint impacts of land-use and climate change. Nowadays, the most used approach is to calibrate a hydrological model on current day data and then use the calibrated model to predict the response under changed conditions (e.g., Ludwig et al, 2009;Poulin et al, 2011). However, for example, Mauser and Bach (2009) have pointed out that any calibration of a model on present conditions may become invalid for the evaluation of climate change impacts.…”

“…However, larger differences between model results occur when comparing the simulated hydrological impact of climate change. Ludwig et al (2009) investigated the response of three hydrological models to change in climate forcing: the distributed model PROMET, the semi-distributed model Hydrotel and the lumped model HSAMI over one alpine catchment in Bavaria in southern Germany. Climate data was generated by one RCM run.…”

Climate change impacts on the hydrologic regime of a Canadian river: comparing uncertainties arising from climate natural variability and lumped hydrological model structures

“…Intercomparison studies offer a simple way of unravelling uncertainties associated with the many hydrological structures and concepts. As an example, Ludwig et al (2009) focused on uncertainties emanating from hydrological modelling, comparing structures of different complexity. They confirmed the importance of the climatic projection uncertainty (i.e.…”

“…Vicuna et al, 2007;Minville et al, 2008;Kay et al, 2009;Boyer et al, 2010;Görgen et al, 2010;Teng et al, 2012;Jung et al, 2012) while others focused on specific ones (e.g. Ludwig et al, 2009;Gardner, 2009;Poulin et al, 2011;Bae et al, 2011;Teng et al, 2012;Velázquez et al, 2013). However, all these works are based on ensemble intercomparison and advocate the necessity of assessing uncertainties before, for example, comparing river discharges over reference (REF) and future (FUT) periods.…”

Intercomparison of different uncertainty sources in hydrological climate change projections for an alpine catchment (upper Clutha River, New Zealand)

“…high-flow events) hydrological models can be associated with a comparable uncertainty range to the driving climate projections (e.g. Ludwig et al, 2009;Muerth et al, 2012).…”