A Review of the Effects of Drought on the Grain Yield in the Vays, Mollasani, and Salamat Regions of the Khuzestan Province

Abstract

The issue of drought and its effect on crops especially wheat, which is considered to be a strategic crop is of the utmost importance. In this research, the effects of drought on the yield of irrigated wheat in the Northeast irrigation network of the Khuzestan province (i.e., the Vays, Mollasani, and Salamat regions) over the years spanning 2006–2010 has been taken into account. To carry out the research, an SPI index (Standardized Precipitation Index) using the rainfall collection data of nine metrological stations for the specified drought years was used. To check the validity of the results obtained from the above index mentioned, the data was cross-referenced with ETM+ multispectral images obtained from the Landsat 7 satellite. One of the main difficulties associated with the research was the blurred ETM+ images, which is due to an SLC-off error during the period under study. However, using additional images (images taken before or after the main image) and the application of a mathematical algorithm using an attached module to the software ENVI (gap fill) to modify the band gaps in the blurred image. This resulted in recovering most of the information in the images after which the NDVI Index (Normalized Difference Vegetation Index) was applied. The images during the study period have determined the crop concentration in the area. Since the yield of irrigated wheat was the objective, another problem faced by the researchers was the fact that the low resolution of the multispectral images of the Landsat satellite (with a resolution of 30 m) did not allow for determining the boundary between the various plots or types of crops. To rectify the problem, agricultural cadastral images and descriptive information (such as ownership documents) of the region were used. By superimposing the data related to the boundaries of the farmland and the images related to the Normalized Difference Vegetation Index with the information related to the plots of land where wheat was cultivated during the study period, the amount of wheat yield during the drought years was determined. The obtained results were compared with the analyzed data obtained from GIS imagery and its juxtaposition using SPI indices showed a correlation between the occurrence of drought in the study period and a decrease in the amount of irrigated wheat yield. With due consideration to the repetition and duration of the drought in the future, it is necessary that drought preventive management strategies be applied in the agricultural sector and in addition to the optimal use of water in the irrigation network, modern irrigation techniques be applied in the farms. What more, it is proposed that existing agricultural patterns be changed and that a sturdier and more resistant variety be used during low water periods.