Assessing the impacts of meteorological drought on yield of rainfed wheat and barley (Case study: Khorasan Razavi province)

The drought causes severe damages to agricultural sector especially rainfed crops production. In this study, the impacts of meteorological drought, in terms of some common indices, on rainfed wheat and barley were assessed. 19 years (1995-2013) weather data including rainfall, temperature, sundial, evaporation and relative humidity of meteorological stations in Khorasan Razavi province, north east of Iran, were collected and examined. Several drought indices namely, The Standardized Z index, Standardized Precipitation Index, Percentage of normal and Deciles were worked out. The statistical relation of both crops' yield with meteorological data was determined. During the cropping year 2000-2001, Mashhad, Sarakhs, Sabzevar, Gonabad, Kashmar, Nishapur and Golmakan stations, had the lowest amount of rainfall which led to severe and extreme drought. The minimum amount of the crops yield was recorded at the same year. For the rest of stations, i.e. Torbatjam, Ghoochan and Torbat Heydarieh stations, the driest year was 2007-2008 followed by an intense to extreme drought but the lowest yield was not observed in the same year. The most significant variables affecting the yield were found to be rainfall and relative humidity. The relations between yield and meteorological variables were significant in most of the cases. In general, the agricultural and meteorological droughts occurred almost simultaneously, except for the regions with very low rainfall.