]1] Ceballos, A., Martınez-Fernandez, J. and Luengo-Ugidos, M. A. (2004). Analysis of rainfall trends and dry periods on a pluviometric gradient representative of Mediterranean climate in the Duero Basin, Spain, Journal of Arid Environments, 58,214-232.
 Dolling, K., Pao-Shin, Ch. and Fujioka, F. (2003). The validity of Keetch/Bayram drought index in the Hawaiian Islands, Second International Wild land Fire Ecology and Fire Management Congress, Orlando, USA.
 Ehsani, A. (2007). Determination of the vegetative index to estimation of the longer term production in semi-arid regions of Iran, PhD. Thesis in Rangeland management, University of Tehran (In Persian).
 Fazeli, F., Ghorbanli, M. and Niknam, V. (2007). Effect of drought on biomass, protein content, lipid per oxidation and antioxidant enzymes in two sesame cultivars, Biologia Plantrum, 51(1), 98-103.
 King, J.R., Scott, J.M. and Boschma, S.P. (2006). Forage and Grassland Management. Session 22, Forage persistence under extremes of cold and drought, 403-410.
 Narasimhan, B., Srinivasan, R. (2005). Development and evaluation of soil moisture deficit index (SMDI) and evapotranspiration deficit index (ETDI) for agricultural drought monitoring, Agricultural and forest meteorology, 133, 69-88.
 Ogallo, A.L. (1993). Post-impact syndromes and drought response strategies in sub –Saharan Africa, International Journal of Climatology, 9, 145-167.
 Prasad, A.K., Sarkar, S., Singh, R.P. and Kafatos, M. (2007). Inter-annual variability of vegetation cover and rainfall over India, Advances in space research, 39(1), 79-87.
 Quiring, S.M., and Papakryakou, T.N. (2003). An evaluation of agricultural drought indices for the Canadian prairies, Agricultural and forest meteorology, 118, 49-62.
 Rahimzadeh Bajgiran, P., Darvishsefat, A.A., Khalili, A., Makhdoum, M.F. (2008). Using AVHRR-based vegetation indices for drought monitoring in the northwest of Iran, Journal of Arid Environments, 72, 1086-1096.
 Rangeland and forest research institute of Iran (2005). The research project of rangeland assessment in different climatologically regions of Iran (In Persian).
 Smart, A.J., Gates, R., and Dunn, B.H. (2005). Drought and stocking rate effects on forage yield from western South Dakota rangelands, Animal and rangeland sciences, 1-3.
 Stampfli, A. and Zeiter, M. (2004). Plant regeneration directs changes in grassland composition after extreme drought: a13- year study in southern Switzerland, Journal of Ecology, 92, 568-576.
 Tsugihiro, W. and Kanber, R. (2006). Innovation cross-disciplinary approach to impact assessment of climate change on agricultural production system in arid areas, Eighth International Conference on Dry land Development, Beijing, China.
 Turner, N.C. (2004). Sustainable production of crops and pastures under drought in a Mediterranean environment, Annals of Applied Biology, 144(2), 139-147.
 Weiss, J.L., Gutzler, D.S., Allred Coonrod, J.E. and Dahm, C.N. (2004). Seasonal and inter annual relationships between vegetation and climate in central New Mexico, USA, Journal of Arid Environments, 57, 507-534.
 White, D.H., Howden, S.M., Walcott, J.J. and Cannon, R.M. (1998). A framework for estimating the extent and severity of drought, based on a grazing system in sought-eastern Australia, Agricultural systems, 57(3), 259-270.