Lampros Vasiliades

Potential climate change impacts on flood producing mechanisms in southern British Columbia, Canada using the CGCMA1 simulation results

Abstract The potential impacts of the future climate change on the causes of flood flows were investigated for two mountainous watersheds located in two different climatic regions of British Columbia. The Canadian Centre for Climate Modeling Analysis General Circulation Model (CGCMa1) has been used to estimate changes in the precipitation and temperature. The UBC Watershed Model (Version 4.0) was used to simulate the discharge of the two study watersheds and to identify the causes of peak flows. In the simulations, apart from changes in precipitation and temperature, changes in the spatial distribution of precipitation with elevation, cloud cover, glacier extension, vegetation distribution, vegetation biomass production, and plant physiology were considered. The results showed that the future climate for the two study watersheds would be wetter and warmer than the present climate. The majority of the flood events in the coastal rainfed watershed of Upper Campbell are and would be generated by fall rainfall events and winter rain-on-snow events, whereas in the interior snowcovered Illecillewaet basin the floods are and would be produced by spring rain and snowmelt events and summer events. The analysis indicated that the overall flood magnitude and frequency of occurrence in the Upper Campbell watershed would increase. On the other hand, the number and the magnitude of the flood flows would decrease under the future climatic conditions in the Illecillewaet basin. Based on these findings, different management practices should be applied in the two watersheds to overcome the effects of the future climate change.

Severity-duration-frequency analysis of droughts and wet periods in Greece

Abstract There is an escalation in the frequency and severity of extreme events due to a number of environmental and/or anthropogenic factors. Droughts and exceptionally wet periods are regional phenomena, which are considered as major environmental extremes, especially in semiarid regions of the world, such as Greece. The development of severity-duration-frequency (SDF) relationships of droughts and wet periods over Greece is important in contemporary hydroclimatic and agroclimatic design and planning in the country. The Palmer Drought Severity Index (PDSI) is used for a quantitative description of droughts and wet periods. Statistical tests and visual inspection indicate that the EV1 (Gumbel) frequency distribution fits satisfactorily all the identified durations of droughts and wet periods, respectively. Moreover, the SDF curves show that decreasing frequencies (i.e. increasing recurrence intervals) correspond to increasing severities of droughts and wet periods, respectively. The developed SDF relationships are used to produce tables and isoseverity maps of Greece for each identified duration and all the selected return periods or frequencies, which constitute an essential aid for design purposes. The results of the study indicate that there is a decreasing pattern of the severities of droughts and wet periods from west to east and that, for similar durations and return periods, the wet spells are, in general, more extreme than droughts in Greece.

Multi-Criteria Analysis Framework for Potential Flood Prone Areas Mapping

A fundamental component of the European natural disaster management policy is the detection of potential flood-prone areas, which is directly connected to the European Directive (2007/60). This study presents a framework for mapping potential flooding areas incorporating geographic information systems (GIS), fuzzy logic and clustering techniques, and multi-criteria evaluation methods. Factors are divided in different groups which do not have the same level of trade off. These groups are related to geophysical, morphological, climatological/meteorological and hydrological characteristics of the basin as well as to anthropogenic land use. GIS and numerical simulation are used for geographic data acquisition and processing. The selected factor maps are considered in order to estimate the spatial distribution of the potential flood prone areas. Using these maps, the study area is classified into five categories of flood vulnerable areas. The Multi-Criteria Analysis (MCA) techniques consist of the crisp and fuzzy analytical hierarchy processes (AHP) and are enhanced with different standardization methods. The classification is based on different clustering techniques and it is applied in two approaches. In the first approach, all criteria are normalized before the MCA process and then, the clustering techniques are applied to derive the final flood prone area maps. In the second approach, the criteria are clustered before and after the MCA process for the potential flood prone area mapping. The methodology is demonstrated in Xerias River watershed, Thessaly region, Greece. Xerias River floodplain was repeatedly flooded in the last few years. These floods had major impacts on agricultural areas, transportation networks and infrastructure. Historical flood inundation data has been used for the validation of the methodology. Results show that multiple MCA techniques should be taken into account in initial low-cost detection surveys of flood-prone areas and/or in preliminary analysis of flood hazard mapping.

Flood producing mechanisms identification in southern British Columbia, Canada

Abstract The causes of peak flows in two climatically different mountainous-forested basins of British Columbia have been identified. The U.B.C. watershed model was used to identify the causes of peak flows, since this model separately calculates the runoff components, i.e. rainfall, snowmelt and glacier runoff. The results showed that the flood flows in the maritime basin of Upper Campbell are mainly generated by rainfall during the fall months and winter rain-on-snow events. Rainfall runoff constitutes the largest percentage of peak flow for all types of events. On the other hand, the flood flows in the inland basin of Illecillewaet are mainly produced by spring rain and snowmelt events, snowmelt events alone and summer events when runoff from the glacier melt contributes to peak discharge. However, snowmelt runoff is the dominant component of peak flows. Based on these findings, flood frequency analysis showed that considering the flow component frequency distributions marginally improves the probability distribution flows in the two examined watersheds.

Nonstationary Frequency Analysis of Annual Maximum Rainfall Using Climate Covariates

The perception that hydrometeorological processes are non stationary on timescales that are applicable to extreme value analysis is recently well documented due to natural climate variability or human intervention. In this study the generalized extreme value (GEV) distribution is used to assess nonstationarity in annual maximum daily rainfall time series for selected meteorological stations in Greece and Cyprus. The GEV distribution parameters are specified as functions of time-varying covariates and estimated using the conditional density network (CDN) as proposed by Cannon (2010). The CDN is a probabilistic extension of the multilayer perceptron neural network. If one of the covariates is dependent on time, then the GEV-CDN model could perform non stationary extreme value analysis. Model parameters are estimated via the generalized maximum likelihood (GML) approach using the quasi-Newton BFGS optimization algorithm, and the appropriate GEV-CDN model architecture for a selected meteorological station is selected by fitting increasingly complicated models and choosing the one that minimizes the Akaike information criterion with small sample size correction or the Bayesian information criterion. For each meteorological station in Greece and Cyprus different formulations are tested with combinational cases of stationary and non stationary parameters of the GEV distribution, linear and nonlinear architecture of the CDN and combinations of the input climatic covariates. Climatic covariates examined in this study are the Southern Oscillation Index (SOI), which describes atmospheric circulation in the eastern tropical Pacific related to El Niño Southern Oscillation (ENSO), the Pacific Decadal Oscillation (PDO) index that varies on an interdecadal rather than inter annual time scale and atmospheric circulation patterns as expressed by the Mediterranean Oscillation Index (MOI) and North Atlantic Oscillation (NAO) indices.

Rainfall-frequency mapping for Greece

Abstract For the design of hydrotechnical projects in ungauged watersheds, the flood flow is estimated by various methods, which demand the estimation of rainfall of particular critical duration and return period. For medium-sized and large basins, the storms causing flood flows have usually duration larger than 24 hours. In this study daily rainfall data from 24 meteorological stations for the period 1950 to 1981 were used. These stations are evenly distributed over Greece. From these data, the rainfall depths for various durations were computed, i.e. 1 to 7 days. The Extreme Value I (Gumbel) theoretical distribution had the best fit to the data from other theoretical distributions and it was fitted to the maximum annual rainfall depths for various durations. As a result, the Depth-Duration_Frequency relationships for each station were estimated and mapped for Greece. Moreover, the analysis showed that the rainfall of various durations and return periods represents a certain percentage of the mean annual precipitation for hydrologicaly homogeneous areas of Greece. The homogeneous areas were identified through factor analysis of monthly precipitation data from 37 meteorological stations. The results of this study can be used for the estimation of rainfall at ungauged sites in medium and large watersheds but they should be applied with caution in mountainous areas. For the estimation of rainfall in these areas the climatic conditions of the region and the orographic enhancement of rainfall should be considered.

Evaluation of Water Resources Management Strategies to Overturn Climate Change Impacts on Lake Karla Watershed

The effects of climate change on meteorology, hydrology and ecology have become a priority area for research and for water management. It is crucial to identify, simulate, evaluate and, finally, adopt water resources management strategies to overturn the impacts of climate change. This paper is dealing with the assessment of climate change impacts on the availability of water resources and the water demands and the evaluation of water resources management strategies in the Lake Karla watershed, central Greece and it is a contribution to the “HYDROMENTOR” research project. The outputs of the Canadian Centre for Climate Modelling Analysis Global Circulation Model CGCM3 were downscaled using a statistical hybrid method to estimate monthly precipitation and temperature time series for present and future climate periods. The analysis was conducted for two future periods 2030–2050 and 2080–2100 and three SRES scenarios (A2, A1B and B1). The surface water and groundwater have been simulated for present and future climate periods using a modelling system, which includes coupled hydrologic models. Two operational strategies of hydro-technical project development are coupled with three water demand strategies. Overall, eight water management strategies are evaluated for present climate conditions and twenty four water management strategies for future climate conditions have been evaluated. The results show that, under the existing water resources management, the water deficit of Lake Karla watershed is large and it is expected to become critical in the future, even though the impact of climate change on the meteorological parameters is very moderate.

Estimation of crop water requirements using remote sensing for operational water resources management

An integrated modeling system, developed in the framework of “Hydromentor” research project, is applied to evaluate crop water requirements for operational water resources management at Lake Karla watershed, Greece. The framework includes coupled components for operation of hydrotechnical projects (reservoir operation and irrigation works) and estimation of agricultural water demands at several spatial scales using remote sensing. The study area was sub-divided into irrigation zones based on land use maps derived from Landsat 5 TM images for the year 2007. Satellite-based energy balance for mapping evapotranspiration with internalized calibration (METRIC) was used to derive actual evapotranspiration (ET) and crop coefficient (ETrF) values from Landsat TM imagery. Agricultural water needs were estimated using the FAO method for each zone and each control node of the system for a number of water resources management strategies. Two operational strategies of hydro-technical project development (present situation without operation of the reservoir and future situation with the operation of the reservoir) are coupled with three water demand strategies. In total, eight (8) water management strategies are evaluated and compared. The results show that, under the existing operational water resources management strategies, the crop water requirements are quite large. However, the operation of the proposed hydro-technical projects in Lake Karla watershed coupled with water demand management measures, like improvement of existing water distribution systems, change of irrigation methods, and changes of crop cultivation could alleviate the problem and lead to sustainable and ecological use of water resources in the study area.

A hybrid downscaling approach for the estimation of climate change effects on droughts using a geo-information tool. Case study: Thessaly, Central Greece

Abstract Multiple linear regression is used to downscale large-scale outputs from CGCM2 (second generation CGCM of Canadian centre for climate monitoring and analysis) and ECHAM5 (developed at the Max Planck Institute for Meteorology), statistically to regional precipitation over the Thessaly region, Greece. Mean monthly precipitation data for the historical period Oct.1960-Sep.2002 derived from 79 rain gauges were spatially interpolated using a geostatistical approach over the region of Thessaly, which was divided into 128 grid cells of 10 km × 10 km. The methodology is based on multiple regression of large scale GCM predictant variables with observed precipitation and the application of a stochastic time series model for precipitation residuals simulation (white noise). The methodology was developed for historical period (Oct.1960–Sep.1990) and validated against observed monthly precipitation for period (Oct.1990–Sep.2002). The downscaled proposed methodology was used to calculate the standardized precipitation index (SPI) at various timescales (3-month, 6-month, 9-month, 12-month, 24-month) in order to estimate climate change effects on droughts. Various evaluation statistics were calculated in order to validate the process and the results showed that the method is efficient in SPI reproduction but the level of uncertainty is quite high due to its stochastic component.

Water balance of forested mountainous watersheds using satellite-derived actual evapotranspiration

The use of actual evapotranspiration derived by satellite data at watershed scale in water balance modelling of forested mountainous watersheds is studied. Mean monthly maximum composites of the Normalized Difference Vegetation Index (NDVI), derived from the National Oceanic and Atmospheric Administration’s (NOAA) / Advanced Very High Resolution Radiometer (AVHRR) were correlated with monthly actual evapotranspiration rates estimated by a water balance model. The water balance model was applied to three mountainous and forested watersheds of Central Thessaly in Greece and the actual basin-wide evapotranspiration was estimated using two methods for the estimation of basin wide precipitation and two methods of potential evapotranspiration. The derived values of actual evapotranspiration were then correlated to NDVI data, and the developed equations were validated temporally and spatially. The actual evapotranspiration estimates, derived from NDVI and used in the water balance model, resulted in equally accurate simulations of monthly runoff when compared with the simulations acquired from the classical application of water balance model.