Ioannis K. Tsanis

Hydroinformatics in evapotranspiration estimation

Abstract The design, development, and application of a hydroinformatic system for estimating evapotranspiration is presented. Reference evapotranspiration is calculated via the Penman-Monteith approach as well as the Class A pan evaporation records. Station- and grid-based methods for estimating reference evapotranspiration are developed and coupled to GIS technology. The station-based method provides the user with evapotranspiration estimates at point locations, corresponding to meteorological stations within the study area. The grid-based method is developed in order to provide an improved understanding of the spatial variation in evapotranspiration. A graphical interface provides model execution and functionality for use in the management phase of the analysis. The island of Crete is used as a case study to illustrate the applicability of the system.

The threat of soil salinity : A European scale review

Soil salinisation is one of the major soil degradation threats occurring in Europe. The effects of salinisation can be observed in numerous vital ecological and non-ecological soil functions. Drivers of salinisation can be detected both in the natural and man-made environment, with climate and the foreseen climate change also playing an important role. This review outlines the state of the art concerning drivers and pressures, key indicators as well as monitoring, modeling and mapping methods for soil salinity. Furthermore, an overview of the effect of salinisation on soil functions and the respective mechanism is presented. Finally, the state of salinisation in Europe is presented according to the most recent literature and a synthesis of consistent datasets. We conclude that future research in the field of soil salinisation should be focused on among others carbon dynamics of saline soil, further exploration of remote sensing of soil properties and the harmonization and enrichment of soil salinity maps across Europe within a general context of a soil threat monitoring system to support policies and strategies for the protection of European soils.

The effect of spatially distributed meteorological parameters on irrigation water demand assessment

Abstract Geographic information systems technology was used to utilize meteorological data and crop distributions in order to estimate irrigation requirements. The irrigation requirements were estimated as the difference between crop evapotranspiration and effective rainfall. Crop evapotranspiration was evaluated as the product of reference evapotranspiration and the crop coefficient, while the reference evapotranspiration was calculated via the FAO Penman–Monteith method. Monthly effective rainfall was estimated from total monthly rainfall according to the method developed by the USDA Soil Conservation Service. For the purpose of this paper, the island of Crete in Greece was used as a case study. Based on individual meteorological stations as representative stations for the whole island the irrigation water demand was estimated at 362±135 Mm3 for the year 1991. The large variation is caused by the location and number of representative meteorological stations. A combination of up to 10 meteorological stations, chosen for geographical reasons as representatives of different regions of the island, resulted in a significant reduction of this variation. The irrigation water demand for the year 1991 was estimated, based on 10 stations, at 359 Mm3. The station of Lefkogia can be considered the representative station for the island. An increase in irrigation water requirements is projected to be 8–10 Mm3/year for Crete. These analyses should assist in the strategic planning of water use for irrigation, particularly in cases where the number of stations is inadequate, by identifying representative stations for different regions and projecting further irrigation water demand. The accurate estimation of irrigation water demand is also essential for developing a rational policy for sustainable water resources.

A GIS precipitation method for analysis of storm kinematics

Abstract This paper describes a program developed within Arc-Info GIS as a set of Arc-macros that can be used to identify storm characteristics from a set of rainfall gages through visualization. Three different interpolation techniques, spline, inverse distance weighted and kriging are used to visualize the spatial distribution of rainfall. An automated process using Mpeg technology that displays the storms in a movie sequence was developed to analyze the storm characteristics, i.e. speed and direction. The functionality of this method is illustrated through a case study on Hamilton–Wentworth Region in Ontario, Canada.

A Three-Dimensional Nested Hydrodynamic/Pollutant Transport Simulation Model for the Nearshore Areas of Lake Ontario

Abstract A three-dimensional hydrodynamic/pollutant transport quality simulation model was developed to simulate the currents and pollutant transport in Lake Ontario and its nearshore areas. The computational efficiency of the model was improved by using an implicit scheme to compute barotropic pressures. The model was applied to Lake Ontario using a 4-km-square grid to simulate wind-induced circulation under isothermal and stratified conditions. A nested model approach was used to study the currents and pollutant transport in the nearshore area along the Metropolitan Toronto waterfront and the mouth of Mimico Creek. In this approach, three models were nested using the following spatial discretization: a 2-km grid for Lake Ontario, a 500-meter grid for the Metropolitan Toronto waterfront, and a 100-meter grid near the mouth of Mimico Creek. An interpolation scheme applied at the open boundaries minimized truncation errors generated by using different grid sizes. Two cases which consisted of lake stratified and isothermal conditions were selected for model calibration. Predictions of lake circulation patterns and conductivity were in good agreement with field measured time series data.

A GIS pre-processor for pollutant transport modelling

Abstract A GIS pre-processor was developed to produce bathymetric grids and shorelines for open and closed boundary as input to a three-dimensional hydrodynamic/pollutant transport model to simulate the currents and pollutant transport in lakes and coastal areas. The pre-processor operates within ArcView GIS and can read hydrographic files in different formats. The use of this GIS module facilitates the implementation of different pollutant transport scenarios, which in turn can significantly contribute to the decision-making process concerning one of the most contemporary environmental problems. The applicability of the pre-processor is illustrated through a case study on Suda Bay, located in Crete, Greece.

Spatiotemporal Characteristics of Meteorological Drought for the Island of Crete

Abstract A modified drought index, named the spatially normalized–standardized precipitation index (SN-SPI), has been developed for assessing meteorological droughts. The SN–SPI is a variant index to the standardized precipitation index and is based on the probability of precipitation at different time scales, but it is spatially normalized for improved assessment of drought severity. Results of this index incorporate the spatial distribution of precipitation and produce improved drought warnings. This index is applied in the island of Crete, Greece, and the drought results are compared to the ones of SPI. A 30-year-long average monthly precipitation dataset from 130 watersheds of the island is used by the above indices for drought classification in terms of its duration and intensity. Bias-adjusted monthly precipitation estimates from an ensemble of 10 regional climate models were used to quantify the influence of global warming to drought conditions over the period 2010–2100. Results based on both indic...

Evaluation of precipitation and temperature simulation performance of the CMIP3 and CMIP5 historical experiments

Abstract The fifth phase of the Coupled Model Intercomparison Project (CMIP5) is the most recent coordinated experiment of global climate modeling. Compared to its predecessor CMIP3, the fifth phase of the homonymous experiment—CMIP5 involves a greater number of GCMs, run at higher resolutions with more complex components. Here we use daily GCM data from both projects to test their efficiency in representing precipitation and temperature parameters with the use of a state of the art high resolution gridded global dataset for land areas and for the period 1960–2005. Two simple metrics, a comprehensive histogram similarity metric based on the match of simulated and observed empirical pdfs and a metric for the representation of the annual cycle were employed as performance indicators. The metrics were used to assess the skill of each GCM at the entire spectrum of precipitation and temperature pdfs but also for the upper and lower tails of it. Results are presented globally and regionally for 26 land regions that represent different climatic regimes, covering the total earth’s land surface except for Antarctica. Compared to CMIP3, CMIP5 models perform better in simulating precipitation including relatively intense events and the fraction of wet days. For temperature the improvement is not as clear except for the upper and lower hot and cold events of the distribution. The agreement of model simulations is also considerably increased in CMIP5. Substantial improvement in intense precipitation is observed over North Europe, Central and Eastern North America and North East Europe. Nevertheless, in both ensembles some models clearly perform better than others from a histogram similarity point of view. The derived skill score metrics provide essential information for impact studies based on global or regional land area multi-model ensembles.

Apparatus for Atmospheric Surface Layer Measurements over Waves

Abstract This paper describes an apparatus developed for simultaneously measuring water elevation and static and dynamic pressure, momentum, and heat fluxes above waves close to the interface. The apparatus was used successfully at the Lake Ontario wave research tower of the Canada Centre for Inland Waters. The principle and purpose of the various sensors used, calibration procedures, and data-gathering processes are described. Simultaneous measurements of the atmospheric surface layer’s physical quantities are presented. All the quantities necessary to close the kinetic energy budget in the atmospheric surface layer have been measured.

Tree crown detection on multispectral VHR satellite imagery.

A new method called Arbor Crown Enumerator (ACE) was developed for tree crown detection from multispectral Very High-resolution (VHR) satellite imagery. ACE uses a combination of the Red band and Normalized Difference Vegetation Index (NDVI) thresholding, and the Laplacian of the Gaussian (LOG) blob detection method. This method minimizes the detection shortcomings of its individual components and provides a more accurate estimation of the number of tree crowns captured in an image sample. The ACE was applied successfully to sample images taken from a four-band QuickBird (0.7m 0.7m) scene of Keritis watershed, in the Island of Crete. The method performs very well for different tree types, sizes and densities that may include non vegetation features such as roads and houses. Statistical analysis on the tree crown detection results from the sample images supports the agreement between the measurements and the simulations. The new method reduces considerably the effort of manual tree counting and can be used for environmental applications of fruit orchard, plantation and open forest population monitoring.