Bojana Horvat

Interest in Natural Water Retention Measures (NWRMs) for large river basins is growing rapidly as a result of a wide range of benefits, including improved water retention capacity and regulation of ecosystem services. However, suitable site-specific NWRMs in small ungauged basins prone to flash floods and erosion, such as the Vrutci Reservoir Basin in Serbia, have yet to be evaluated and applied, primarily because of a lack of necessary data. The aim of this study was to design an easy-to-implement approach to evaluating the effects of NWRMs on peak discharge, tailored specifically to small basins with significant data gaps. The approach involves developing and analyzing a synthetic unit hydrograph (SUH) based on the available landscape geospatial data and evaluating the effects of NWRMs on the SUH before and after implementation of site-specific NWRMs. This methodological framework allows for quantification of the NWRMs’ effects on the basin and evaluates the proposed measures’ impact to secure better acceptance among stakeholders and informed decision-makers regarding their location in the basin. The results underscore a peak discharge rate reduction from 5% to 33% and hence indicate a positive impact on basin water retention potential. These results highlight the need for support for improved regulating ecosystem services in integrated water management.

Various factors influence wildfire probability, including land use/land cover (LULC), fuel types, and their moisture content, meteorological conditions, and terrain characteristics. The Adriatic Sea coastal area in Croatia has a long record of devastating wildfires that have caused severe ecological and economic damages as well as the loss of human lives. Assessing the conditions favorable for wildfires and the possible damages are crucial in fire risk management. Adriatic settlements and ecosystems are highly vulnerable, especially during summer, when the pressure from tourist migration is the highest. However, available fire risk models designed to fit the macro-scale level of assessment cannot provide information detailed enough to meet the decision-making conditions at the local level. This paper describes a model designed to assess wildfire risks at the meso-scale, focusing on environmental and anthropogenic descriptors derived from moderate- to high-resolution remote sensing data (Sentinel-2), Copernicus Land Monitoring Service datasets, and other open sources. Risk indices were integrated using the multi-criteria decision analysis method, the analytic hierarchy process (AHP), in a GIS environment. The model was tested in three coastal catchments, each having recently experienced severe fire events. The approach successfully identified zones at risk and the level of risk, depending on the various environmental and anthropogenic conditions.

Flood risk assessment at the mesoscale requires data that are spatially and thematically detailed enough to provide reliable estimates at the catchment level. However, data availability and suitability are often contradictory: available data are rarely suitable at the required level of detail. To overcome this problem, numerous disaggregation methods have been proposed in recent decades, often based on somewhat generalised imperviousness characteristics derived from the available urban land use/land cover (LULC) nomenclature. To reduce generalisation, we propose a new disaggregation approach using a spatially distributed imperviousness density (IMD) layer at a very detailed spatial resolution of 10 m as ancillary data to improve the thematic detail of the urban classes of the available LULC datasets (Coastal Zones, Natura 2000) and the dasymetric mapping of the census data. The nomenclature of the urban classes and the impervious density thresholds were taken from the detailed Urban Atlas dataset. The disaggregation of the census data is then built on the resulting geometry of thematically improved residential classes. Assuming that IMD values indicate a built-up density, the proposed weighting scheme is IMD-dependent: it accounts for variability in the built-up density and, hence, variability in population. The approach was tested in three catchments in Croatia, each with a different degree of urbanisation. The resulting statistics (mean square error and percentage error) indicate that residential areas and population density depend on IMD. Using IMD as additional data therefore greatly improves the assessment of elements that are exposed to flooding and, consequently, the damage and flood risk assessment.

Since the beginning of the 21st Century, Europe has been affected by destructive floods. European Union Member States have an obligation to develop flood hazard and flood risk maps as support to the Flood Risk Management Plan (FRMP). The main objective of this study is to propose a methodological framework for hazard and risk assessment of pluvial flash floods in Croatia at the catchment level, which can be integrated into the FRMP. Therefore, a methodology based on the source–pathway–consequence approach for flood risk assessment is presented, which complies with the EU Floods Directive. This integrated and comprehensive methodology is based on high-resolution open data available for EU Member States. Three scenarios are defined for a low, medium, and high probability, defined by design storms of different durations. The proposed methodology consists of flood hazard analysis, vulnerability assessment, and risk analysis. Pluvial flash flood hazards are analyzed using a 2D hydrologic–hydraulic model. The flood vulnerability assessment consists of a GIS analysis to identify receptors potentially at risk of flooding and an assessment of susceptibility to potential flood damage using depth–damage curves. Flood risk is assessed both qualitatively in terms of risk levels and quantitatively in terms of direct damages expressed in monetary terms. The developed methodology was applied and tested in a case study in the Gospić catchment in Croatia, which surrounds a small rural town frequently affected by pluvial flash floods.

U radu je provedena ocjena pogodnosti područja za izgradnju solarnih parkova primjenom višekriterijske analize, i to metode analitičkog hijerarhijskog procesa (AHP) u GIS okruženju. U prvoj fazi analize pogodnosti izuzeta su područja nepogodna za izgradnju solarnih parkova, dok su u drugoj fazi klasificirane razine pogodnosti preostalih područja primjenom AHP metode.

U radu su, na primjeru poplave koja je u svibnju 2014. godine zadesila istočnu Hrvatsku, uspoređene tri metode kartiranja i procjene opsega poplavljenog područja: metoda analize refleksije s površine u blisko infracrvenom (IC) dijelu spektra (jednokanalna metoda) te metode vegetacijskog indeksa NDVI (Normalized Difference Vegetation Index) i vodenog indeksa NDWI (Normalized Difference Water Index). Metode kao ulazne podatke koriste snimke snimljene pasivnim senzorom ugrađenim na satelitsku platformu Landsat 8. Analizirane su četiri snimke; snimljene su prije (jedna snimka), tijekom (jedna snimka) i nakon poplave (dvije snimke). Procjena temeljena na jednokanalnoj metodi rezultirala je površinom manjom od površina procijenjenih primjenom višekanalnim metodama. Rezultati se mogu objasniti kompleksnošću spektralnog potpisa plitkih poplavnih voda s visokim udjelom suspendiranog nanosa koji će utjecati na refleksiju takvih površina u blisko IC dijelu spektra i klasificirati ih kao nevodene površine. S druge strane, kombiniranjem različitih spektralnih kanala u višekanalnim metodama kompenzira se utjecaj suspendiranog nanosa na refleksiju takvih voda te je klasifikacija na vodene i nevodene površine preciznija.

One of the most prominent tourist destinations in the Adriatic coast, the city of Opatija, is facing a problem concerning seasonal drinking water shortages. The existing water resources are no longer sufficient, and attention is being given to alternative resources such as the underlying karstic aquifer and several coastal springs in the city itself. However, the water potential of the area still cannot be estimated due to the insufficient hydrological data. The goal of this research was to evaluate the use of thermal infrared (TIR) remote sensing as the source of valuable information that will improve our understanding of the groundwater discharge dynamics. Ten Landsat ETM+ (enhanced thematic mapper plus) and two Landsat TM (thematic mapper) images of the north Adriatic, recorded during 1999–2004 at the same time as the field discharge measurements, were used to derive sea surface temperature (SST) and to analyze freshwater outflows seen as the thermal anomaly in the TIR images. The approach is based on finding the functional relationship between the size of the freshwater thermal signatures and the measured discharge data, and to estimate the water potential of the underlying aquifer. It also involved analyzing the possible connection between the adjusted size of the spring’s thermal signatures and groundwater level fluctuations in the deeper karst hinterland. The proposed methodology resulted in realistic discharge estimates, as well as a good fit between thermal anomalies with measured discharges and the groundwater level. It should be emphasized that the results are site specific and based on a limited data set. However, they confirm that the proposed method can provide additional information on groundwater outflow dynamics and coastal springs’ freshwater quantification.

Oborine su izrazito varijabilna komponenta bilance voda, koja ovisi o nizu faktora, kao što su geografski položaj, udaljenost od mora i nadmorska visina, a ključne su u razumijevanju hidroloških procesa nekog područja. Mjerenja oborina provode se na diskretnim lokacijama meteoroloških postaja (osim u slučaju radarskih opažanja oborina) te su saznanja o njihovoj varijabilnosti u prostoru rezultat primjene različitih metoda interpolacije izmjerenih vrijednosti u točki na analiziranom prostoru. U GIS okruženju, oborina može biti prikazana u formi diskretnog ili kontinuiranog polja pa će o tome ovisiti i odabir metode interpolacije. U radu su, na primjeru srednjih godišnjih količina oborina za razdoblje 1961. – 1990. na području Istre, prikazane i uspoređene tri najčešće primjenjivane metode prostorne interpolacije: Thiessenovi poligoni, TIN (Triangular Irregular Network) te VLR (metoda višestruke linearne regresije). Prve dvije metode ne uzimaju u obzir faktore koji utječu na količinu palih oborina, već su procijenjene vrijednosti u funkciji udaljenosti promatrane točke od oborinskih postaja. Za razliku od njih, metoda višestruke linearne regresije omogućuje određivanje vrijednosti oborina u prostoru u ovisnosti o drugim čimbenicima; u ovome slučaju to su geografski položaj, udaljenost od mora te nadmorska visina.

Evapotranspiration (ET) is the most significant water balance component and is also a very complex component to evaluate in spatio–temporal scales. Remotely-sensed data greatly increases the accuracy of basin wide ET estimation but only in periods with available satellite images. This paper describes an attempt to estimate daily ET regardless of the availability of the satellite images. The method is based on application of the interpolated evaporative fraction (Λ) from “historical” satellite images to periods with no satellite data available. Basin wide daily ET is obtained by combining interpolated Λ and standard PET methods on meteorological stations. The reliability of such approach was evaluated by comparing the obtained daily ET to the SEBAL ET estimates through the analysis of residuals (Δ), standard deviations of residuals (σ) and the Nash–Sutcliffe coefficient (NSE) over the basin. The SEBAL ET estimates were validated with the data from two lysimeters. The discrepancy of obtained ET versus the SEBAL ET estimates (Δ = 0.13 mm day⁻¹, σ = 0.64 mm day⁻¹, NSE = 0.07) indicated that the proposed concept has relatively high accuracy, which is notably higher than the Penman–Monteith interpolated ET estimates (Δ = 1.94 mm day⁻¹, σ = 1.03 mm day⁻¹, NSE = −4.71). It was shown that a total of five images can provide a reliable estimate of interpolated Λ and thus represent specific characteristics of a basin. As the presented concept requires minimum remote sensing data and ground based inputs, it could be applied to estimate basin wide daily ET in data scarce regions and in periods with no satellite images available.

An approach to the global estimation of water balance elements and their spatial distribution using GIS is presented. It is primarily related to the catchments where measured data are scarce and the spatial differentiation of the hydrological characteristics is not possible without climatological data. Emphasis is placed on estimating the water balance of transboundary karstic aquifers, where problems concerning the hydrometeorological data, catchment boundaries and determination of water balance elements in general are far more complex. The runoff estimation was done using the Turc and Langbein methods, which are the most frequently applied in this region. The years 1961–1990 were used as the reference period. Based on comparison of the results, the applicability of the methods is discussed. The approach proposed is suitable for estimation of water balance in the study area and may also be applied in a wider region. Résumé Une approche de l'évaluation globale des termes du bilan hydrologique et de leur distribution spatiale sous SIG est présentée. Elle concerne notamment les bassins versants où les données mesurées sont rares et où la différentiation spatiale des caractéristiques hydrologiques n'est pas possible sans données climatologiques. L'accent est mis sur l'estimation du bilan hydrologique d'aquifères karstiques transfrontaliers, où les problèmes liés aux données hydro-météorologiques, aux limites des bassins versants et à la détermination des termes du bilan sont en général beaucoup plus complexes. L'estimation de l'écoulement a été réalisée en utilisant les méthodes de Turc et de Langbein, les deux méthodes le plus souvent utilisées dans cette région. Les années 1961–1990 ont été utilisées comme période de référence. L'applicabilité des méthodes est discutée, sur la base de la comparaison des résultats. L'approche proposée est appropriée pour l'estimation du bilan hydrologique dans la zone étudiée, et peut é...