8.  Nikolova, N., Nejedlik, P. and Lapin, M.: Temporal variability and spatial distribution of drought events in the lowlands of Slovakia.

Atmospheric drought in lowlands in Slovakia is analyzed on the bases of Standardised Precipitation Index (SPI) and Standardised Precipitation Evaporation Index (SPEI). This paper gives information about the dynamic, intensity, seasonal and territorial differences in occurrence of drought with various intensity: mild (near to normal), moderate, severe and extreme for the period 1961-2011. Future changes in occurrence of drought are determined on the basis of model data (regional circulation models KNMI and MPI) for temperature and precipitation for two periods: 2001-2050 and 2051-2100.

The results show that temperature has an important role for occurrence of moderate and severe drought at monthly level and precipitation is the main factor for occurrence of extreme drought. There are an increasing number of cases with severe or extreme drought in summer for most of the investigated stations. Future projection of drought shows general tendency to increasing frequency of severe dry events in 2001-2050 and 2051-2100 while there will be a little decreasing of extremely dry months in comparison to 1961-2010.

Keywords: drought, lowland, Slovakia, Standardized Precipitation Index (SPI), Standardized Precipitation Evapotranspiration Index (SPEI)

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9.  Genc, O., Ozgur Kisi, O. and Ardiclioglu, M.: Modeling shear stress distribution in natural small streams by soft computing methods.

Artificial intelligence (AI) systems have opened a new horizon to analyze water engineering and environmental problems in recent decades. In this study performances of ordinary kriging (OK) as a linear geostatistical estimator and two intelligent methods including artificial neural networks (ANN) and adaptive neuro-fuzzy inference system (ANFIS) are investigated. For this purpose, geographical coordinates of 120 observation wells that located in Tabriz plain, north-west of Iran, were defined as inputs and groundwater electrical conductivities (EC) were set as output of models. Eighty percent of data were randomly selected to train and develop mentioned models and twenty percent of data used for testing and validating. Finally, the outputs of models were compared with the corresponding measured values in observation wells. Results indicated that ANFIS model provided the best accuracy among models with the root mean squared error (RMSE) value of 1.69 dS.m-1 and correlation coefficient (R) of 0.84. The RMSE values in ANN and OK were calculated 1.97 and 2.14 dS.m-1 and the R values were determined 0.79 and 0.76, respectively. According to the results, the ANFIS method predicted EC precisely and can be advised for modeling groundwater salinity.

Keywords: ANN, ANFIS, linear regression, shear stress, stream, turbulent flow

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10.  Jeričević, A., Džaja Grgičin, V., Telišman Prtenjak, M., Vidič, S. and Bloemen, H.: Analyses of urban and rural particulate matter mass concentrations in Croatia in the period 2006-2014.

Air pollution due to particulate matter with an aerodynamic diameter ≤ 10 µm (PM10) and diameter ≤ 2.5 µm (PM2.5) was investigated using available measurements in Croatia. Hourly and daily PM10 and PM2.5 mass concentrations were analysed for urban and rural background stations. Urban and industrial PM10 measurements from 2006 to 2014 and rural background PM10 and PM2.5 measurements from 2011 to 2014 were used to determine the main characteristics of regional and local air pollution related to particles and to assess the level of air pollution according to the defined limit values (CAFÉ Directive 2008/50/EC). Significant difference between coastal and continental urban and rural PM10 levels was found with high PM10 concentrations in continental areas and considerably lower PM10 values at the coast. Substantially different spatial distribution of rural background PM concentrations with relatively high annual average concentration ~ 30 µg/m3 at e.g. continental station Kopački rit, to only ~ 5 µg/m3 at Hum located on the island of Vis was found. Strong spatial PM gradients from the continent towards the coast are resulting from the distinct differences in climatological characteristics between Croatia's inlands and the coastline and different physical processes affecting the PM concentrations in the two regions (e.g. sea breeze, deposition, wet removal, resuspension). Furthermore, distinct complex chemical mechanisms that depend on emission rate and PM composition and on meteorological parameters (sun radiation, humidity etc.) have different influence on the formation of secondary organic aerosol in marine and continental boundary layer. Ratio between rural PM2.5 and PM10 mass concentrations (PM2.5 / PM10) for all sites was investigated and compared to the results obtained in other European studies. Rural site-specific PM2.5 / PM10 ratios ranged from 0.6 to 0.9 during the warmer part of the year while during the colder part of the year ratios were higher and ranged from 0.85 to 0.98. The spatial gradient of rural PM2.5 / PM10 values is orientated from the coast to the continent implying that at the coast the PM concentrations are mainly composed of fine particles. Observed hourly temperature, relative humidity and wind values in the period from 2006 to 2014 are analysed together with the corresponding PM concentrations and an initial source identification was conducted based on bivariate polar plots.

Keywords: urban and rural air quality, spatial distribution of PM mass concentration, PM2.5 / PM10 ratio, source identification, Croatia

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11.  Dragčević, D., Pavasović, M. and Bašić, T.: Accuracy validation of Croatian official geoid solutions over the area of City of Zagreb.

Height (altitude) determination in geodesy is faced with problems that are directly attributed to the method of measurements and used geoid solutions. Due to the reliability of CROPOS as well as growing progress in geoid determination (increase of their external and internal accuracy), GNSS observations using CROPOS_VRS_HTRS96 VPPS service became most commonly used method of height determination in Croatian every day geodetic practice. This paper describes establishment of 33 GNSS/levelling points using CROPOS_VRS_HTRS96 VPPS service and geometric levelling at the area of the City of Zagreb. It also gives the analysis of the quality of performed GNSS observations, analysis and comparison of the geoid undulations from official geoid solutions of the Republic of Croatia, HRG2000 and HRG2009 with undulations obtained by GNSS/levelling for established GNSS/levelling points and brief overview of current state of vertical network of the City of Zagreb.

Keywords : height (altitude) determination, CROPOS, GNSS/levelling, City of Zagreb, HRG2000, HRG2009, vertical network

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