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13 Refrences - Akhtari, R., Mahdian, M.H., Morid. S., Assessment of spatial analysis of SPI and EDI drought indices in Tehran province J. Iran- Water Resources Research, 2, Apaydin, H., Sonmez, K., Yildirim, E., Spatial interpolation techniques for climate data in the GAP region in Turkey. J. Climate Research, 28, Banejad, H., Zare Abyaneh, H., Nazarifar, M. H., Sabziparvar, A., Application of standard precipitation index (SPI) with Geostatistic Method for analyzing meteorological drought in Hamedan province. J. Agricultural Reserch Water, Soil & Plant in Agricultural, 6, Bodagh jamali, J. Javanmard, S., Shirmohammadi, R., Monitoring drought status of Khorasan province by using standard precipitation index. J. Geographical Research. 21, Bonaccorso, B., Cancelliere, A., Rossi, G., Network design for drought monitoring by geostatistical techniques. J. European Water, 3, Diodato, N., The influence of topographic co-variable on the spatial variability of precipitation over small regions of complex Terrain. J. climatology, 25, Goovaerts, P., Geostatistical apaches for incorporating elevation into the spatial interpolation of rainfall. J. Hydrology, 228, Hong, W., Hayes, J., An evaluation of the standardized precipitation index, The China- Z Index and the statistical Z-Score Int. J. Climatol, 21, Issaks. E. H., Srivastava, R. M., Applied geostatistics, Newyork, Oxford University Press, 561 p. - Johnston, K., Ver Hoef, J. M., Krivoruchko, K., Lucas, N., Using arcgis geostatistical analyst. ESRI, Redlands, CA. - Machlica, A., Stojkovova, M., Groundwater drought in different geological conditions. XXIVth Conference of the Danubian Countries, McKee, T. B., Doesken, N. J., Kleist, J., The relation of drought frequency and duration to time scales. Preprints, 8 th Conference on Applied Climatology, January, Misagi, F., Mohammadi, K., Monitoring precipitation by using deterministic methods and geostatistic and comparison with artificial neural networks, Scientific Journal of Agricultural, 29, Moried, S., Moghaddasi, M., Paemozd, SH., Ghaemi, H., Designing drought monitoring system of Tehran province, applied research report ministry Energy, 253P - Mosaedi, A., Sharifan, H., Shahabi, M Risk Management by identification of microclimates in Golestan province, Applied research report, Iran Meteorological Organization, 171P. - Quiring, S. M., Papakryiakou, T. N., An evaluation of agricultural drought indices for the Canadian parairies. J. Agricultural and Forest Meteorology, 118, Richard, R., Heim, H., A review of twentieth century drought indices used in the United States. J. American Meteorological Society, Rusoo, F., Napolitano, F., Gorgueei, E., Rainfall monitoring system over an urban area: The city of Rom. Hydrological processes, 19, Tallakesen, L. M., van Lanen, H. A. J., Hydrological drought, Processes and estimation methods for streamflow and groundwater, Development in water science 48, 579p. - Tonkaz, T., Spatio-temporal assessment of historical drought using SPI with GIS in GAP region, Turkey, J. Applied Sciences, 6,

14 Journal of Range and Watershed Management, Iranian Journal of Natural Resources, Vol. 64, No. 1, pp Monitoring and Spatial Analysis of Meteorological Drought in Golestan Province using Geostatistical Methods M. Eivazi 1 and A. Mosaedi *2 1 MSc. Graduate, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, I.R. Iran 2 Associate Prof., Faculty of Natural Resources and Environment, Ferdowsi University of Mashhad, Mashhad, I.R. Iran (Received: 10 March 2010, Accepted: 09 March 2011) Abstract Region drought monitoring is one of the important subjects in drought risk management. For this reason, relevant rain gauge stations in Golestan province in which data had been recorded until the end of water year , after sufficient statistical test, were selected. Drought conditions for each station was investigated in nine different periods (including eight monthly and one annual periods) using Standardized Prediction Index (SPI) in order to determine the best interpolation method for drought monitoring in the region. Some deterministic interpolation methods such as RBF, GPI, IDW and a geostatistical method were considered. After determining the best interpolation method, according to the error factors and extending point drought information to regional one, the severity maps of this phenomena over 25 years, was plotted. Then, spatial distribution of drought conditions over the statistical period in Golestan province was plotted using ArcGIS ver9.2. According to the results, kriging and RBF methods have shown the best response as interpolation methods in monitoring of drought severity at different time periods. Keyword: Drought, Standardized Precipitation Index, Geostatistics, Interpolation, Golestan *Corresponding author: Tel: , Fax: , mosaedi@yahoo.com