A. Christofides

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.

openmeteo.org: A Web Service for the Dissemination of Free Meteorological Data

Individuals or organizations managing meteorological or hydrological stations typically need to either collect the data on personal computers or bear the costs required to setup a server. As an alternative, the openmeteo.org database provides users and organizations the option to upload their time series, on condition that their data will be available to the public under a free license (the Open Database License and the Creative Commons Attribution-ShareAlike License, depending on the type of data). Each user has write access to his own data, whereas the public has read access to all the data. Enhydris, the software that powers openmeteo.org, is also free, available under the GNU General Public License v.3, and provides several useful features like time series graphs and plots, display of online data, maps etc. The purpose of openmeteo.org is not only to enable people to manage their data more easily, but also to bring people into a community and encourage a spirit of openness and sharing.

Hydrometeorological network for flood monitoring and modeling

Due to its highly fragmented geomorphology, Greece comprises hundreds of small- to medium-size hydrological basins, in which often the terrain is fairly steep and the streamflow regime ephemeral. These are typically affected by flash floods, occasionally causing severe damages. Yet, the vast majority of them lack flow-gauging infrastructure providing systematic hydrometric data at fine time scales. This has obvious impacts on the quality and reliability of flood studies, which typically use simplistic approaches for ungauged basins that do not consider local peculiarities in sufficient detail. In order to provide a consistent framework for flood design and to ensure realistic predictions of the flood risk –a key issue of the 2007/60/EC Directive– it is essential to improve the monitoring infrastructures by taking advantage of modern technologies for remote control and data management. In this context and in the research project DEUCALION, we have recently installed and are operating, in four pilot river basins, a telemetry-based hydro-meteorological network that comprises automatic stations and is linked to and supported by relevant software. The hydrometric stations measure stage, using 50-kHz ultrasonic pulses or piezometric sensors, or both stage (piezometric) and velocity via acoustic Doppler radar; all measurements are being temperature-corrected. The meteorological stations record air temperature, pressure, relative humidity, wind speed and direction, and precipitation. Data transfer is made via GPRS or mobile telephony modems. The monitoring network is supported by a web-based application for storage, visualization and management of geographical and hydro-meteorological data (ENHYDRIS), a software tool for data analysis and processing (HYDROGNOMON), as well as an advanced model for flood simulation (HYDROGEIOS). The recorded hydro-meteorological observations are accessible over the Internet through the www-application. The system is operational and its functionality has been implemented as open-source software for use in a wide range of applications in the field of water resources monitoring and management, such as the demonstration case study outlined in this work.