Spatial and Temporal Monitoring of Agricultural Drought in the Wheat Cultivated Area using Standard Precipitation Index (Case Study: West of Golestan Province)

Drought is not a characteristic of a region and may occur in any weather regime. Therefore, reasonable management is required to deal with this natural disaster which can be creating a management system and providing accurate information at different time scales. Meteorological, agricultural, hydrological and socioeconomic drought are defined based on lack of rainfall, lack of soil moisture, shortage of rivers stream and the shortage of some commodities affected by the drought trend. One of the effective methods for analyzing various kinds of drought is the evaluation of drought indices, which aims to provide a simple and quantitative assessment of drought characteristics. The purpose of this research is to investigate the Spatial and temporal monitoring of agricultural drought in the Wheat cultivated area using standard precipitation index in west of Golestan province.

In this research, in order to monitor the spatial and temporal distribution of drought in the years of 2000 to 2016 in AQ-Qala, Ali Abad, Gorgan, Bandar-e- Gaz, Bandar-e- Torkaman and Kordkouy counties, 15 meteorological stations with common statistical database (1984 to 2016) were used to estimate the rainfall. After calculating the standard precipitation index (hereafter SPI) and more reliable correlation of May’s three-month SPI index (hereafter SPI3) with the mean wheat yield, this index was zoned with ordinary Kriging interpolation method and then drought was assessed. In order to prepare a drought risk map, SPI3 rasters were reclassified as binary (BOOLEAN) for a time span of 17 years (2000 to 2016). Then, a map of the drought frequency was provided by the overlaying of Boolean maps. Using drought frequency maps of the SPI index, a final agricultural drought risk map was generated.

In 2000, 88% of the total area were affected by moderate drought and another 12% (the majority of which was in Aliabad) was affected by moderate classes of drought. But in 2007 and 2016 there was no drought in the investigated counties. In this research, by studying the drought severity and drought risk maps, it was clarified that the SPI index was an effective index in evaluating the drought patterns in different temporal and spatial scales and during drought periods. Also, the results showed that six studied counties in Golestan Province were classified into two risky drought areas (including severe and extreme classes). Risk map showed that in the applied statistical time period (2000 to 2016), an extensive part of the study area (about 98%) is at extreme risk class. Also, a small northern part of the Bandar-e-Torkaman (about 2% of the total area) has experienced an extreme drought. In fact, the magnitude of the drought range in this region is greater due to coexistence with the Turkmen desert and its dry and semiarid weather conditions, which leads to a potential for drought sensitivity.  

The results revealed a positive correlation between wheat yield and SPI3 in AQ-Qala, Ali Abad, Gorgan, Bandar-e- Gaz, and Kordkouy counties. The effect of meteorological drought on the crop production can be a concern (especially in drought-prone areas) and suggests that SPI3 can be helpful for predicting drought-induced yield loss. These results indicate that the western region of Golestan province is one of the areas where droughts will increase in the future. Therefore, rain-fed cropping systems will be in danger in the future, and some of the agroecosystems currently dedicated to the cultivation of rain-fed products will be excluded from the production process. rainfall reduction in recent years, has been led to retreat the Caspian Sea in Bandar-e-Torkaman area, as well as the eliminating of many crops in recent years, which reveals that the consequences of these droughts have been emerged.  Therefore, agricultural policy makers need to consider the replacement of crops with high efficient water usage instead of current ones in cropping patterns in the coming years, as well as be concerned more about land salinization.