N. Mamassis

On the credibility of climate predictions

Abstract Geographically distributed predictions of future climate, obtained through climate models, are widely used in hydrology and many other disciplines, typically without assessing their reliability. Here we compare the output of various models to temperature and precipitation observations from eight stations with long (over 100 years) records from around the globe. The results show that models perform poorly, even at a climatic (30-year) scale. Thus local model projections cannot be credible, whereas a common argument that models can perform better at larger spatial scales is unsupported.

A comparison of local and aggregated climate model outputs with observed data

Abstract We compare the output of various climate models to temperature and precipitation observations at 55 points around the globe. We also spatially aggregate model output and observations over the contiguous USA using data from 70 stations, and we perform comparison at several temporal scales, including a climatic (30-year) scale. Besides confirming the findings of a previous assessment study that model projections at point scale are poor, results show that the spatially integrated projections are also poor. Citation Anagnostopoulos, G. G., Koutsoyiannis, D., Christofides, A., Efstratiadis, A. & Mamassis, N. (2010) A comparison of local and aggregated climate model outputs with observed data. Hydrol. Sci. J. 55(7), 1094–1110.

A decision support system for the management of the water resource system of Athens

Abstract The main components of a decision support system (DSS) developed to support the management of the water resource system of Athens are presented. The DSS includes information systems that perform data acquisition, management and visualisation, and models that perform simulation and optimisation of the hydrosystem. The models, which are the focus of the present work, are organised into two main modules. The first one is a stochastic hydrological simulator, which, based on the analysis of historical hydrological data, generates simulations and forecasts of the hydrosystem inputs. The second one allows the detailed study of the hydrosystem under alternative management policies implementing the parameterisation–simulation–optimisation methodology. The mathematical framework of this new methodology performs the allocation of the water resources to the different system components, keeping the number of control variables small and thus reducing the computational effort, even for a complex hydrosystem like the one under study. Multiple, competitive targets and constraints with different priorities can be set, which are concerned among others, with the system reliability and risk, the overall average operational cost and the overall guaranteed yield of the system. The DSS is now in the final stage of its development and its results, some of which are summarised in the paper, have been utilised to support the new masterplan of the hydrosystem management.

Scientific dialogue on climate: is it giving black eyes or opening closed eyes? Reply to “A black eye for the Hydrological Sciences Journal” by D. Huard

Citation Koutsoyiannis, D., Christofides, A., Efstratiadis, A., Anagnostopoulos, G.G. and Mamassis, N. (2011) Scientific dialogue on climate: is it giving black eyes or opening closed eyes? Reply to “A black eye for the Hydrological Sciences Journal” by D. Huard, Hydrol. Sci. J. 56(7), 1334–1339.

Comparing environmental flow scenarios from hydrological methods, legislation guidelines, and hydrodynamic habitat models downstream of the Marathon Dam (Attica, Greece): Hydrological & ecosystem-based eflows in the Marathon Reservoir

In their effort to balance anthropogenic water demand and ecosystem conservation within a sustainable water resources management framework, water managers and stakeholders need sound scientific guidance. In this study, we applied a two-dimensional hydrodynamic habitat model using benthic macroinvertebrates as the target aquatic community, and carried out an environmental flow (eflow) assessment downstream of the Marathon Reservoir (Attica, central Greece). Hydrology-based eflow scenarios were additionally developed over an 11-year period, and the lowest acceptable ecosystem-based eflow was compared with the hydrology-based environmental flow predictions. We found that the hydrological methods tend to under-estimate the eflows required to ensure functional aquatic ecosystems. The results showed that (i) the different hydrological methods developed highly variable eflow scenarios, ranging from 0.0006 m/s to 0.18 m/s, (ii) the ecosystem-based environmental flow was up to 183% higher than the hydrology-based ones and 26% to 465% higher than those defined by the national legislation and (iii) the probability of agreement between hydrological and ecological predictions was 12.5%, as only one out of the eight hydrology-based scenarios coincided with the ecosystem-based eflows. We conclude that hydrological methods should be used with caution in the absence of ecological information. Their use as stand-alone tools seems problematic and bears a high risk of producing inappropriate environmental flow scenarios. Integrative frameworks combining hydrological-ecological methods could be useful to provide information on what is ecologically-acceptable and hydrologically-socially feasible, but since the two methods comprise structurally-different, non-interacting concepts, they are inherently insufficient to increase the confidence of predicting and selecting environmental flows. Author’s pre-print version