Dionysia Panagoulia

Sensitivity of flood events to global climate change

Abstract The sensitivity of Acheloos river flood events at the outfall of the mountainous Mesochora catchment in Central Greece was analysed under various scenarios of global climate change. The climate change pattern was simulated through a set of hypothetical and monthly GISS (Goddard Institute for Space Studies) scenarios of temperature increase coupled with precipitation changes. The daily outflow of the catchment, which is dominated by spring snowmelt runoff, was simulated by the coupling of snowmelt and soil moisture accounting models of the US National Weather Service River Forecast System. Two threshold levels were used to define a flood day—the double and triple long-term mean daily streamflow—and the flood parameters (occurrences, duration, magnitude, etc.) for these cases were determined. Despite the complicated response of flood events to temperature increase and threshold, both hypothetical and monthly GISS representations of climate change resulted in more and longer flood events for climates with increased precipitation. All climates yielded larger flood volumes and greater mean values of flood peaks with respect to precipitation increase. The lower threshold resulted in more and longer flood occurrences, as well as smaller flood volumes and peaks than those of the upper one. The combination of higher and frequent flood events could lead to greater risks of inudation and possible damage to structures. Furthermore, the winter swelling of the streamflow could increase erosion of the river bed and banks and hence modify the river profile.

Impacts of GISS-modelled climate changes on catchment hydrology

Abstract The hydrological regime of a mountainous catchment, in this instance the Mesochora catchment in Central Greece, was simulated for altered climates resulting when using the Goddard Institute for Space Studies (GISS) model for carbon dioxide doubling. The catchment snow water equivalent was predicted on the basis of the snow accumulation and ablation model of the US National Weather Service River Forecast System (NWSRFS), while the catchment runoff, as well as actual evapotranspiration and soil moisture storages, were simulated through application of the soil moisture accounting model of NWSRFS. Two scenarios of monthly climate change were drawn from the GISS model, one associated with temperature and precipitation changes, while the other referred to temperature changes alone. A third hypothetical scenario with temperature and precipitation changes similar to those corresponding to the mean monthly GISS scenarios was used to test the sensitivity of the monthly climate change of the hypothetical ca...

Artificial neural networks and high and low flows in various climate regimes

Abstract An algorithm coupling linear least squares and simplex optimization (LLSSIM) is used to examine the ability of a three-layer feedforward artificial neural network (ANN) to simulate the high and low flows in various climate regimes over a mountainous catchment (the Mesochora catchment in central Greece). The plot of the long-term annual catchment pseudo-precipitation (rain plus snowmelt) simulated by the snow accumulation and ablation model (SAA) of the US National Weather Service (US NWS) showed trends of three climatically distinct periods, described by clearly descending, rising and moderately descending segments in pseudo-precipitation. The ANN model was calibrated for each of the three climate types and each was validated against the others. A set of statistical measures and graphs adapted for high and low flows showed the robustness of the ANN model under various climates and transient conditions. The ANN model proved capable of simulating well the daily high and low flows when it is calibrated for increasing pseudo-precipitation and validated for moderately decreasing pseudo-precipitation. For the entire period, the ANN model provided a better simulation of high and low flows than the conceptual soil moisture accounting (SMA) model of the US NWS, which was also employed in this study. Because the ANN is not a physically-based model, it is by no means a substitute for the SMA model. However, it is concluded that the ANN approach is an effective alternative for daily high- and low-flow simulation and forecasting in climatically varied regimes, particularly in cases where the internal dynamics of the catchment do not require an explicit representation.

Sensitivities of groundwater-streamflow interaction to global climate change

Abstract The sensitivities of groundwater-streamflow interaction to global climate change over the medium-sized mountainous Mesochora catchment in central Greece have been analysed. The global climate change was simulated through a set of hypothetical and monthly GISS (Goddard Institute for Space Studies) scenarios of temperature increases coupled with precipitation changes. The catchment hydrological regime, which is dominated by spring snowmelt runoff, was simulated by the coupling of the snowmelt and soil moisture accounting models of the US National Weather Service River Forecast System (US NWSRFS). The groundwater was represented through a lower zone one-tension water storage and two free water storages parameterized by the soil moisture model, while the streamflow was the sum of direct runoff, surface runoff and interflow from the upper zone free water, plus the primary and secondary baseflows yielded by the model. The interaction between groundwater and streamflow was expressed by the ratio of the ...

Assessment of daily catchment precipitation in mountainous regions for climate change interpretation

Many recent researchers have ventured a physical modelling of mean areal precipitation with a view to ensuring an appropriate analysis of climate change. Preliminary results of a simple, practical and dynamic integration method of incomplete daily precipitation data for a mountainous catchment are presented here. This is a combinatorial technique of the Thiessen method and precipitation gauge availability. The estimated catchment precipitation is corrected for elevation variations. This double technique preserves, to a large extent, the physical structure of precipitation information which is vital for climate change interpretation. Furthermore, the proposed method can handle successfully any change in the gauge network, the greatest limitation of the inflexible Thiessen method.

Catchment Hydrological Sensitivities to Climate Changes

While climate changes over periods of thousands of years are well documented, hydrologists were rather reluctant to agree for as long as a decade (1960 to 1970) as to whether changes (signals) within typical water resources systems design periods (100 years or less) can indeed be distinguished from random variations (noise) in a physical hydrological time series (US. National Academy of Sciences, 1977). The advent of general circulation models (GCMs) over the last decade and consensus about the direction of future global climate change threw abundant light on the controversial theme, thus making acceptable the aspect that climate change does exist.