AN ALGORITHM FOR IDENTIFICATION OF HYDROLOGIC HOMOGENEOUS REGION FOR UNGAUGED BASIN Borislava Blagojevic Faculty of Civil Engineering and Architecture, University of Nis Aleksandra Medvedeva 14, Nis/Serbia b.blagojevic@eunet.rs Aleksandra Ilic Institute for the Development of Water Resources ‘Jaroslav Cerni’ Belgrade Jaroslava Cernog 80, Pinosava/Serbia ilicsaleksandra@gmail.com Abstract One of the crucial steps of ungauged basins prediction is identification of hydrologic homogeneous region. This region consists of basins which, in hydrologic terms, behave similarly. Consequently, temporal and spatial interpolation of hydrologic information can be performed to an ungauged basin when hydrologic homogeneous region is defined. The underlying methodology of multiple nonlinear regression is based on standardization methods for normalization of correlation. Synthetic runoff series generation at ungauged basin is based on spatial correlation function. Both theoretical and empirical spatial correlation functions are involved. While empirical correlation function is estimated according to correlation coefficients of runoff series at gauged basins and their mutual distance, its pair - theoretical correlation function is merely a shift of empirical correlation function. This shift is made to achieve correlation coefficient of one for zero distance. However, this shift is acceptable only if performed in homogeneous region. This paper explains the procedure for stepwise rejection of basins from initial hydrologic region until hydrologic homogeneous region is identified. An algorithm for homogeneous region identification is suggested with three levels of criteria for rejection of basins that violate region homogeneity. Keywords - Ungauged basins, homogeneous region identification, mean monthly runoff. 1 INTRODUCTION Hydrologic regionalization involves application of different methods and procedures to delineate homogeneous regions which comprise of the basins with similar physical, climatic and/or hydrological characteristics in order to transfer the information and models to areas (basins) in which there are no measurements.