Evaluation of drought impacts on irrigated and rainfed wheat yields in Bojnourd region

Drought is a slow-onset and creeping phenomenon that imposes many irreparable natural hazards and affects all climates. One of the important climatic consequences for agriculture is consecutive droughts that occur every few years and reduce the production yield, in particular under rainfed farming conditions. Therefore, this study was conducted to monitor droughts and the impact of agricultural drought on the strategic wheat crop under rainfed and irrigated cultivation conditions in the Bojnourd region. In this regard, to calculate the standardized drought indices i.e. Standardized Precipitation Index (SPI), Percent of Normal Index (PN), and Z-score Index (ZSI), rainfall statistics, and information of Bojnourd meteorological station during the period 2005 to 2019 were used. Likewise, to relate droughts to agricultural products, statistics and information on the area under cultivation, production, and yield of rainfed and irrigated wheat were used during the statistical period of 1983 to 2019. The results of pearson correlation between drought indices and area under cultivation, production, and crop yield of rainfed and irrigated wheat indicated that the lowest (r = 0.23) and the highest (r = 0.73) correlation levels belonged to the ZSI index with irrigated yield and rainfed production with the PN index, respectively. Temporal changes in the area under cultivation of irrigated and rainfed wheat in Bojnourd region showed that the area under irrigated wheat crop cultivation decreased sharply over time (a negative slope for the trend line of the equation), which is mainly due to the decline in precipitations and droughts in the region causing irreparable damage to farmers. The results of variations in the SPI index on the harvest level from rainfed and irrigated fields indicated that the harvest level from rainfed and irrigated fields increased during the wet year while it decreased during droughts. However for irrigated cultivation, the reduction of irrigated crop yield was less severe over drought years probably due to the use of other methods of water supply for cultivation, including drilling illegal wells and deepening agricultural wells.