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Precipitation is the main water resource for agronomy. The frequency is one of the most significant characteristics of precipitation. The objectives of this study are (1) to identify the homogenous regions, (2) to determine the probability distribution that fits precipitation the best for each region, (3) to perform regional precipitation-frequency analysis by using L-moment methods, and (4) to derive the return levels for precipitation. In this study, the precipitation data collected from 24 meteorological stations for the period 1965–2013 over Serbia were analyzed. Three distributions [generalized extreme value (GEV), generalized Pareto (GPD), and generalized logistic (GLO)] based on three parameters (scale, shape, and location) are investigated. The L-moment method is applied to determine the parameters. Three independent precipitation regions (R1, R2, and R3) were studied. The homogeneity test indicates that the identified regions are homogenous. To confirm the goodness-of-fit for the selected three probability distributions, the Z-statistics was applied. Based on the obtained results, the GEV distribution best fits the precipitation data in the regions R1 and R2, while the GPD was selected for the region R3.

In confluence areas, where river flow slowdowns can be substantial, the selection of design flows for the purpose of designing a flood control system directly depends on flood waves at the mainstem and its tributaries. The aim of this paper is twofold: to elaborate a procedure that will define the flood exceedance probability in the analyzed area within a multidimensional probability space and to develop a methodology for defining flood coincidence in the mainstem reach with its main tributaries and thus determine design flows in order to design the flood control system in the confluence area. Mathematical models are based on (1) two-dimensional probability distribution (PROIL model) and (2) the copula function (Archimedean class of copulas), and fitted to a practical application in a two-dimensional probability distribution space. In case of random variables, simultaneous quantitative characteristics of flood wave (water flow) hydrographs for the mainstem and a tributary are considered. The paper discusses the specific reach of the Danube, from the Hungarian-Serbian border to the city of Smederevo, which encompasses three significant tributaries—the Drava, the Tisa, and the Sava.

Precipitation is one of the key components in the water cycle. To analyse the changes in precipitation at a specific location, it is necessary to identify the distribution that best fits the precipitation data. For this purpose, three distributions i.e. generalized extreme value (GEV), generalized Pareto (GPD), and generalized logistic (GLO) were fitted to the annual precipitation data collected from 28 meteorological stations in Serbia for the period 1946–2019 using the method of L-moment. The goodness-of-fit for the selected three distributions was confirmed using the L-diagram and three measures namely relative root mean square error, relative mean absolute error, and probability plot correlation coefficient. From the results of this analysis, the GEV distribution was selected as the best fitting distribution of the annual precipitation data in Serbia. The increasing trends are presented in the western part of Serbia that can cause higher risks of floods than in other parts.

The present study investigated the potential of new ensemble method, Bayesian model averaging (BMA), in modeling monthly solar radiation based on climatic data. Data records covered monthly maximum temperature (Tmax), minimum temperature (Tmin), sunshine hours (Hs), wind speed (Ws), relative humidity (RH), and solar radiation values obtained from two weather stations of Turkey. The BMA estimates were compared with the artificial neural networks (ANN), extreme learning machines (ELM), radial basis function (RBF), and their hybrid versions with wavelet transform technique (wavelet-ANN or WANN, wavelet-ELM or WELM, and wavelet-RBF or WRBF). Three evaluation criteria e.g., root mean square error (RMSE), Nash–Sutcliffe efficiency, and determination coefficient (R2), were applied to measure the accuracy of the employed methods. The results indicated the superior accuracy of the BMA4 models over six machine learning models for estimating monthly solar radiation; improvements in accuracy of ANN4, ELM4, RBF4, WANN4, WELM4, and WRBF4 models comprising Tmax, Tmin, Hs, Ws and RH input variables were about 56–41%, 44–31%, 57–46%, 35–26%, 27–16%, and 43–28% in terms of RMSE reduction in both stations. While the hybrid models (i.e., WANN4, WELM4, and WRBF4) increased the accuracy of the single models about 31–21%, 23–18%, and 26–25% for ANN4, ELM4, and RBF4, respectively.

Reference evapotranspiration (ETo ) is an essential parameter of the hydrologic cycle that plays a key role in the water resources management, especially in arid and semi-arid regions where the tot...

The Penman-Monteith (PM) method for estimation of reference evapotranspiration (ET0) uses numerous data that are often missing in many regions. In such circumstances, temperature-based equations can be used for estimating ET0. The primary objective of this note was to compare the calibrated temperature-based ET0 approaches with the standard PM equation using meteorological data from fifteen CLIMWAT stations located in the Pannonian Basin. The most of these locations are classified as humid. Twelve temperature-based equations were evaluated according to the PM method. The regionally calibrated Hargreaves equation (HT) gave the lowest RMSE at seven sites and the second lowest RMSE at three sites. New regionally calibrated Thornthwaite approach (TT) yielded the lowest RMSE three times and the second lowest RMSE seven times. These approaches resulted in the lowest average RMSE for all fifteen locations (0.28 and 0.30 mm day−1, respectively). The other temperature-based approaches significantly fall behind the HT and TT equations at most stations. The overall results show the advantage of the HT approach except for a few southeast stations where the TT approach is dominant. It can be concluded that the regionally calibrated temperature-based approaches (HT and TT) are the most suitable to estimate ET0 in the Pannonian Basin.

By using GIS tools, it is possible to improve the preview of hydrological processes such as evapotranspiration, precipitation, flood and drought. In order to quantify drought, different type of drought indicators have been developed such as Standardized Precipitation Index (SPI), Reconnaissance Drought Index (RDI), Standardized Precipitation Evapotranspiration Index (SPEI) or Water Surplus Variability Index (WSVI). In this paper the precipitation-based SPI indicator was applied to the monthly precipitation data from Serbia during the period 1948-2012. The data were processed in the QuantumGIS software package. For the purpose of application in the monitoring of drought at the national level, a spatial presentation of meteorological drought was obtained.

The study presents problem of floods management for lowland rivers and provides solution for such complex task. The paper aims to elaborate a methodology for flood management model on large lowland rivers using precision digital terrain models (DTM) and combined 1D/2D unsteady flow model. The river Danube on the territory of Serbia was used with its tributaries for the development of the model. The length of the hydraulic model is 715 km and the achieved accuracy of the model, by comparing the calculated and observed levels on 10 water stations, is below 10 cm. Combined 1D/2D HEC-RAS model is adjusted by making use of the resulting high-resolution input. The ability of the combined 1D/2D model, based mainly on the high-accuracy input data, provides an accurate estimate of flood wave propagation. The result of this paper is a defined methodology providing sufficient accuracy to the hydraulic model of flood wave propagation in case of large lowland rivers, requiring acceptable short calculation time. Also, the methodology to specify relevant flood stage (design flood) which is used to determine levee crest elevation is developed in this paper.

Evapotranspiration is one of the crucial components of hydrological cycle. The Penman-Monteith method (PM) is recommended as the sole standard method for estimating reference evapotranspiration (ET0). The usage of the PM method is limited in many regions due to the lack of required weather data. In such circumstances, simple Thornthwaite equation is often used to estimate ET0. The main objectives of the present study are (i) to estimate reference evapotranspiration using different Thornthwaite approaches, (ii) to develop optimal adjusted equation, and (iii) to consider the spatial variability of the empirical coefficient(s) of adjusted equation for the study area. In this study, six Thornthwaite approaches were compared to the full set PM equation using weather data from Vojvodina region, Serbia. The original Thornthwaite equation was very poor in estimating ET0 and greatly underestimated PM values at all locations. It can be concluded that an adjustment of the Thornthwaite equation is necessary. The obtained results indicate that ET0 could be estimated from the new Th65 approach (effective temperature, k = 0.65), which reproduced statistical characteristics better compared to other Thornthwaite approaches. The spatial variability of the empirical k coefficient showed that k values varied from 0.62 to 0.69 across the study area with deviations of − 5% to 6% compared to a unique k value of 0.65. These results suggested that single regional k value can be successfully used for estimating ET0.

This paper deals with dynamic analysis of rockets launcher on a moving vehicle. Mechanical model of a launch rail system with a rocket is represented as a set of solid bodies and deformable elements with a damped elastic support. These launch rail systems enable to fire rockets of different weights and geometric configurations. Unlike them, today´s multiple rocket launcher systems are located in containers. Movement of this type of mechanical system is described with three defined coordinates: movement of a rocket on a deformable ramp, curvature of the top of a deformable ramp and an angle of rotation of the ramp around its longitudinal axis. Mathematical model of the whole system, including rockets launcher and vehicle, represents a system of five nonlinear, nonhomogeneous differential equations of second order. This system is transformed to a system of 10 differential equations of the first order, suitable for numerical solving through the software package MATLAB. Rocket launcher designers can find the obtained simulation and experimental results, represented in a graphical form which is very useful during the development of a new and modification of existing constructions.

Evapotranspiration is a fundamental component of the hydrological cycle. The standard Penman-Monteith (PM) equation uses a plenty of data to assess reference evapotranspiration (ET0) that are not available at many meteorological locations. In such circumstances, temperature-based ET0 equations are often used. The objectives of this research are as follows: (i) to assess ET0 using several temperature-based approaches and (ii) to evaluate an impact of the estimated wind speed on the temperature-based ET0 approaches. Thornthwaite, Hargreaves, and three PM approaches based on temperature were used to assess ET0 for eight locations in Serbia. Accurate ET0 estimates at all locations are provided by the temperature-based PM equation with local average wind speed. The ET0 estimates are less precise in the case if the regional average (1.3 m s−1) or the global average (2.0 m s−1) is used. The low reliability of the Hargreaves equation decreases additionally by decreasing the wind speed. The reliability of the Thornthwaite equation is also very low independently from the wind speed. This study clearly proposes using local average wind speed in the temperature-based PM equation. Further research should be done in the other regions with a higher average wind speed than in Serbia.

Frequent floods and deterioration of drained water quality are the main problems in rapidly developing urban zones, mostly because urbanization reduces the areas with natural ground that can absorb stormwater and therefore prevent floods and pollution. In order to have a solution which can solve these problems and which could be acceptable for the nature and people, decentralized drainage systems were developed and applied. The primary goal of decentralized systems is to improve infiltration, evapotranspiration, and reuse of stormwater. This study presents the analysis of three variant solutions for the management of atmospheric stormwater. Analyzed solutions are based on the classical sewage system and on low impact development (LID) techniques applied in urban areas (Kucevo, Serbia). The main aim of this analysis was to define the pilot procedure to reduce pollutants and quantity of drained atmospheric water and using stormwater management, because the Pek River is one of the Danube tributaries. After the analysis of all solutions, the third variant solution based only on the LID techniques (vegetative swales, infiltration trenches, rain barrels, and bio-retention cells) gave the best results. According to simulation results, the proposed techniques in the third solution totally remove all pollutants from stormwater and stormwater surplus.

Over the years, the appropriateness of selection and application of drought indices in a particular climate area have been discussed. A number of drought indicators have been defined for each type of drought (meteorological, hydrological, agricultural) based on different measured data. The Standardized Precipitation Index (SPI) and the Streamflow Drought Index (SDI) were used to establish the association between meteorological and hydrological droughts. Based on the availability, type and accuracy of data, SPI and SDI are the simplest indices to obtain. This paper analyzes the different ways of processing drought data for the South Morava basin in a GIS environment. The largest agricultural drought was recorded in 2007 and because of that this year was selected for the drought analysis. The intensity of the SPI index for the year 2007 was calculated based on monthly precipitation data from eight meteorological stations in the South Morava basin. The SDI data for the year 2007 are provided for 16 hydrological stations. The paper compares the results of meteorological and hydrological droughts in the South Morava basin for the year 2007. The data were processed in the Quantum GIS software package and as a result visualisation of spatial data on meteorological and hydrological droughts was obtained in order to be applied in drought monitoring at the regional level.

Effective chemical protection of fruit is a complex task which can enable production of healthy food without chemical residues. As food health is a growing global concern, it is important to automate and optimize the fruit protection process. Different data mining techniques can be used to identify pattern diseases so as to prevent the excessive use of chemicals. However, application of data mining systems in this field is very complex task. Besides that, these systems are often designed for just one specific plant species. One solution for prediction a risk of fruit infection based on data that represent weather (meteorological) conditions and data pathogens is presented in this paper. The research is performed on the data collected at the region of Toplica in Republic of Serbia during five year period. In this paper data mining based tool for early prediction of fruit pathogen infection is performed. The application is based on the open source engine WEKA with GUI created in C#, and uses several data mining algorithms which are evaluated in this paper. Results shown that the prediction accuracy is 89%.

Accurate estimation of reference evapotranspiration (ETo) is a major task in hydrology, water resources management, irrigation scheduling and determining crop water requirement. There are many empirical equations suggested by numerous references in literature for calculating ETo using meteorological data. Some such equations have been developed for specific climatic conditions while some have been applied universally. The potential for usage of these equations depends on the availability of necessary meteorological parameters for calculating ETo in different climate conditions. The focus of the present study was a global cross-comparison of 20 ETo estimation equations using daily meteorological records of 10 weather stations (covering a period of 12 years) in a semi-arid region of Iran. Two data management scenarios, namely local and cross-station scenarios, were adopted for calibrating the applied equations against the standard FAO56-PM model. The obtained results revealed that the cross-station calibration might be a good alternative for local calibration of the ETo models when proper similar stations are used for feeding the calibration matrix.

The following case study is part of a wider research of the impact of rock ramps on river environment. It aims to give a quantitative assessment of the velocity reduction in upstream section of a rock ramp. The alteration of the flow velocities is one of the most considerable factors for the habitat modification. The creation of still water environment in upstream impoundment might affect the physical properties of the habitat. Thus a mutation of the hydrobionts diversity may occur. By means of one - dimensional numerical model ? comparative analysis of velocity fields is executed. Two cases are examined: before and after construction of a rock ramp with step - pools. The model proofs a significant flow velocity reduction in upstream section, which might have a negative environmental impact. Another point of interests of the study is the high flow river capacity. The flooded areas and the water level variation are evaluated at Q50%, Q5% and Q1%. The results can be used for assessment of the structure reliability and for analysis of both: saturation of riparian zone and alteration of floodplain ecology.

Periodic bathymetric surveys are carried out to define quantity of sedimented material in reservoirs, as well as to determine the areas most endangered by the silting process. Such surveys in the Republic of Macedonia were started as an obligatory and regular practice in the seventies of the last century, immediately after the formation of the larger artificial lakes. These were carried out for almost all reservoirs in the country and it can be said that there is already a sufficient amount of data on some of them that can serve as a basis for high quality analyses of the silting trend of the reservoirs and of the extent to which erosion is affecting the basin area. This paper provides a review of the results from the latest field surveys and analyses of changes in the configuration of the Shpilje reservoir bottom, carried out in the period 2014 to 2016.

The aim of this study is to test how effective and physically correct are the mathematical approaches of operational indices used by relevant National Agencies across the globe. To do so, the following indices were analysed Standardized Precipitation Index (SPI) -1, 3, 6, 12 and 24, Standardized Precipitation – Evapotranspiration Index (SPEI) – 1, 3, 6, 12 and 24, Effective Drought Index (EDI) and Index of Drying Efficiency of Air (IDEA). To make regions more comparable to each other and follow the spatial development of drought SPI index was advised by World Meteorological Organisation to be used widely by official meteorological services. The SPI and SPEI are used for Drought Early Warning in the USA, National Drought Mitigation Center and NASA, and in the EU by the European Drought Centre (EDC) and in the Balkan Region by National Meteorological Agencies. The EDI Index has wide application in Asia. In this paper four different issues were investigated: 1) how the mathematical method used in a drought indicator's computation influence drought indices' (DI) comparative analyses; 2) the sensitivity of the DIs on any change of the length of observational period; 3) similarities between the DIs time series; 4) and how accurate DIs are when compared to historical drought records. Results suggest that it is necessary to apply a few crucial changes in the Drought Monitoring and Early Warning Systems: 1) reconsider use of SPI and SPEI family indices as a measure of quality of other indices; and for Drought Early Recognition Programs 2) switch to DIs with a solid physical background, such as EDI; 3) Adopt solid physics for modelling drought processes and define the physical measure of drought, e.g. EDI and IDEA indices; 4) investigate further the IDEA index, which, supported by our study as well, is valuable for simulation of a drought process.

This paper reconsiders the precipitation concentration index (PCI) in Serbia using precipitation measurements such as the mean winter precipitation amount, annual total precipitation, mean summer precipitation amount, mean spring precipitation amount, mean autumn precipitation amount and the mean of precipitation for the vegetation period (April–September). Potentials for further improvement of PCI prediction lie in the improvement of current prediction strategies. One of the options is the introduction of model predictive control. To manage the PCI, it is good to select factors or parameters that are the most important for PCI estimation and prediction, i.e. to conduct variable selection procedure. In the present study, a regression based on the adaptive neuro-fuzzy inference system (ANFIS) is applied for selection of the most influential PCI inputs based on the precipitation measurements. The effectiveness of the proposed strategy is verified according to the simulation results. The results show that the mean autumn precipitation amount is the most influential for PCI prediction and estimation and could be used for the simplification of predictive methods to avoid multiple input variables.

Mathematical modelling of the behavior of the radio propagation at mmWave bands is crucial to the development of transmission and reception algorithms of new 5G systems. In this study we will model 5G propagation in nondeterministic line-of-sight (LOS) conditions, when the random nature of LOS component ratio will be observed as Inverse Gamma (IG) distributed process. Closed-form expressions will be presented for the probability density function (PDF) and cumulative distribution function (CDF) of such random process. Further, closed-form expressions will be provided for important performance measures such as level crossing rate (LCR) and average fade duration (AFD). Capitalizing on proposed expressions, LCR and AFD will be discussed in the function of transmission parameters.

Precipitation is one of the most important meteorological variables which can impact on the occurrence of drought. Analysis of precipitation and drought data provides useful information for planning water resources, agricultural production and land use in the region. Monthly precipitation data from 28 synoptic stations in Serbia over the period 1946–2017 were used to analysed precipitation and drought in Serbia. For this purpose, the rainfall variability index was used. Two years (2000 and 2011) were specially analysed as the driest years when most of Serbia were affected by severe droughts. Spatial distribution of annual mean precipitation in Serbia is presented in this study. The north part of Serbia is the area with the least amount of precipitation. The south and the southeast part of Serbia have the moderate precipitation regime, while the west part is the wettest part. According to the applied analysis, it is evident that the stations in the western part of Serbia have the significant increasing trend in annual precipitation. The significant decreasing trend is not identified.

The objective of this study was to perform a long-term modeling of the sedimentation rate of one of the largest reservoirs in the Republic of Macedonia, i.e., the “Tikvesh” reservoir. The developed mathematical model should serve for detailed analysis of the sedimentation rate in the reservoir over time, and if the obtained results are acceptable, it should be further developed and used in defining practices of sustainable management of the reservoir in future. For this purpose, a widely applied, semi-distributed, and process-based watershed-scale model SWAT was used. Using SWAT, the production of sediments in the watershed as well as their transport through the river network was modeled. Based on the empirically estimated reservoir trap efficiency as well as bulk density of the settled material, volumetric sediment budgeting was done, whereby the temporal distribution of the reservoir sedimentation rate was defined. The obtained results were compared with the information from several bathymetric surveys of the reservoir whereat a satisfactory match was found. The model was generated for the period extending from 1969, when the reservoir was put into operation, to 2016, when the last bathymetric survey was conducted. The period between 1969 and 1985 was used for calibration of the model, while the period from 1986 to 1991 was used for its validation. Forecast referring to the change of the deposited quantities of sediments in the reservoir was made for the period from 1992 to 2016. In the absence of reliable data from measurements done in this period, climate data generation and consequently watershed sedimentation yield estimation by using the WXGEN—weather generator—were conducted. The obtained results point to variable sedimentation rate of the reservoir in different periods, depending on the variability of the weather conditions within the watershed. The average sedimentation rate of the reservoir in the analyzed period 1969–2016 at an annual level is 0.02–1.28% of the initial volume, which is around the estimated world average amounting to 0.5–1%.

The objective of this research was to determine the probability of road overtopping occurrence for a road culvert caused by surface runoff from the upstream catchment. A hydrological–hydraulic model was used for the development of an algorithm for road culvert maintenance based on the overtopping occurrence probability (CMOOP algorithm) for small mountain catchments. The hydrological model defines the regression dependence between the runoff hydrograph peak values and the probability of occurrences, whereas the hydraulic model calculates the culvert flow capacity by including in the calculation the level of sediment that culvert is filled with. The relationship between occurrences of overtopping and peak runoff value was defined using the runoff hydrograph transformation model in the accumulation on the upstream side of the road. In addition to the calculation of overtopping occurrence probability for the existing culvert condition, the CMOOP algorithm was used to analyze the impact of rehabilitation and reconstruction works from the perspective of legally based safety criterion for road overtopping occurrence probability (SCROOP). The CMOOP algorithm was appled to 67 concrete culverts located in a mountain road section in the Republic of Serbia. The results show that the application of rehabilitation works on selected culverts will increase the percentage of culverts that satisfy SCROOP from 49.25% to 89.55%, which confirms that the accumulated stone sediment is the main reason for the SCROOP unfulfillment.

The monthly precipitation data from 29 stations in Serbia during the period of 1946–2012 were considered. Precipitation trends were calculated using linear regression method. Three CLINO periods (1961–1990, 1971–2000, and 1981–2010) in three subregions were analysed. The CLINO 1981–2010 period had a significant increasing trend. Spatial pattern of the precipitation concentration index (PCI) was presented. For the purpose of PCI prediction, three Support Vector Machine (SVM) models, namely, SVM coupled with the discrete wavelet transform (SVM-Wavelet), the firefly algorithm (SVM-FFA), and using the radial basis function (SVM-RBF), were developed and used. The estimation and prediction results of these models were compared with each other using three statistical indicators, that is, root mean square error, coefficient of determination, and coefficient of efficiency. The experimental results showed that an improvement in predictive accuracy and capability of generalization can be achieved by the SVM-Wavelet approach. Moreover, the results indicated the proposed SVM-Wavelet model can adequately predict the PCI.

The crop evapotranspiration has the great effect on defining and planning of water resources. The estimation of evapotranspiration depends on various climatic parameters. In this study, the analysis of the effect of solar radiation (Rs) on daily reference evapotranspiration (ET0) was conducted. The FAO-56 Penman-Monteith method (FAO-56 PM) was used for the estimation of ET0 in Serbia at eight meteorological stations for the period 1980-2010. The Rs was estimated using the ten one-parameter global solar radiation models. The ET0 with Almorox and Hontoria model 1 had the smallest deviation related to the ET0 with Angstr?m-Prescott (AP) model, and ET0 with To?rul et al. model 2 and Rietveld model had the greatest deviation from ET0 with AP model.

Accurate estimation of the reference evapotranspiration (ET0) is important for the water resource planning and scheduling of irrigation systems. For this purpose, the radial basis function network with particle swarm optimization (RBFN-PSO) and radial basis function network with back propagation (RBFN-BP) were used in this investigation. The FAO-56 Penman–Monteith equation was used as reference equation to estimate ET0 for Serbia during the period of 1980–2010. The obtained simulation results confirmed the proposed models and were analyzed using the root mean-square error (RMSE), the mean absolute error (MAE), and the coefficient of determination (R 2). The analysis showed that the RBFN-PSO had better statistical characteristics than RBFN-BP and can be helpful for the ET0 estimation.

The monthly ET0 data were obtained by the Penman-Monteith method.ANFIS was applied for selection of the most influential ET0 parameters.Tmin, ea and sunshine hours are the most influential for ET0 estimation.Variables selection with ANFIS improves ET0 predictive accuracies.The ANFIS model can be used for ET0 estimation with high reliability. The adaptive neuro-fuzzy inference system (ANFIS) is applied for selection of the most influential reference evapotranspiration (ET0) parameters. This procedure is typically called variable selection. It is identical to finding a subset of the full set of recorded variables that illustrates good predictive abilities. The full weather datasets for seven meteorological parameters were obtained from twelve weather stations in Serbia during the period 1980-2010. The monthly ET0 data are obtained by the Penman-Monteith method, which is proposed by Food and Agriculture Organization of the United Nations as the standard method for the estimation of ET0. As the performance evaluation criteria of the ANFIS models the following statistical indicators were used: the root mean squared error (RMSE), Pearson correlation coefficient (r) and coefficient of determination (R2). Sunshine hours are the most influential single parameter for ET0 estimation (RMSE=0.4398mm/day). The obtained results indicate that among the input variables sunshine hours, actual vapor pressure and minimum air temperature, are the most influential for ET0 estimation. The maximum relative humidity and maximum air temperature are the most influential optimal combination of two parameters (RMSE=0.2583mm/day).

Extreme climatic events are the most important elements of climate changes, which directly affect the nature and society. In the recent years, the plethora of extreme climatic indices have been developed for the different parameters, in order to analyze and monitor the extreme climate changes. This paper presents the analysis of maximum and minimum air temperatures (T max , T min ) and precipitation using the eight extreme climatic indices in the city of Nis and Belgrade (Serbia) for the period 1974-2003. The selected indices are: frost days (FD), summer days (SU), ice days (ID), max TX (TXx), max TN (TNx), max 1-day precipitation (Rx1day), consecutive dry days (CDD) and consecutive wet days (CWD). The results show that there are no significant changes in the FD and ID indices, and there are also no changes in the indices CDD and CWD in Nis. The SU, Rx1day, TXx and TNx were increased in each of the observed cities. CDD and CWD were slight decreased in Belgrade.