Analysis of temporal-spatial changes of water deficit index in Khuzestan province in the last decade

Extended Abstract
Introduction
Drought as a long-term stage of water scarcity is a challenging issue in water resources management and a very widespread natural disaster. Being aware of the drought situation can significantly reduce the risk of losses caused by this phenomenon through predicting and zoning the severity of the drought. One method of determining drought is the Standardized Precipitation Index (SPI), which was proposed by (McKay et al., 1993), for drought monitoring in the Colorado area. The SPI index is one of the appropriate indices to be used due to its advantages in the regional analysis of drought and the temporal relationship between events.
 
Materials and methods
First, TWSI data were downloaded from GRACE-CSR satellite. The TWSI data obtained from GRACE satellite were received using coding in Google Earth engine in EXCEL format and were provided for the entire province of Khuzestan. Since the TSDI index provides a comprehensive picture of drought, TSDI values had to be calculated after reviewing the TWSA data from Google Earth Engine. To calculate this index, TSD and cumulative TSD values were calculated first. Then, the total water shortage was calculated cumulatively. In addition, the 15-year SPI index (2002-2006) was used to study drought in Khuzestan province in this study. To do this, from the stations that had better conditions in terms of data, 11 stations were selected and SPI-6-12-24 was obtained through DIP software for each of the selected stations on a monthly and annual basis.
 
Results and Discussion
Drought study of SPI-12-24 in Khuzestan province showed that the onset of drought in this province started in 2008 or 2009 and continued until 2013 or 2016. Among all the stations, 2009 and 2012 were the most severe years in terms of drought and in most of the stations in SPI-12-24 these two years were the driest years in the drought periods, and they were in drought conditions in all these stations during these two years. In terms of drought severity, Safi Abad, Omidiyeh, Ahvaz and Abadan stations were all ranked first to fourth with very severe drought. With regard to time, November and January in SPI-12 with frequency of 4 and May, July, August and September in SPI-24 were the most affected by standard precipitation drought. The TWSA values for Khuzestan province from 2002 to 2016 showed that according to this figure, the value of TWSA in this area found a negative trend from April 2008 to December 2016. in Khuzestan province from 2008 to 2016, three dry periods were observed, which are from April 2008 to January 2010, April 2010 to January 2014 and May 2014 to December 2016. The lowest TWSI values in each period were -11.27, -13.03, and -10.58 mm.
 
Conclusion
In this study, spatial-temporal changes of TSDI water deficit index in Khuzestan province were investigated. To do this, first the monthly index SPI-12-24 was calculated using the monthly rainfall values of 11 meteorological stations for the whole region in the period 2002 to 2016 using the DIP software. Then, to calculate the TSDI index, the data of total water storage anomalies obtained from GRACE-CSR satellite were used. Drought survey of SPI-12-24 in Khuzestan province showed that drought in this province started in 2008 or 2009 and continued until 2013 or 2016. Among all the stations, 2009 and 2012 were the most severe years in terms of drought, and in most stations in SPI-12-24 were the driest years in the drought periods. In terms of severe drought, Safiabad, Omidieh, Ahvaz and Abadan stations all ranked first to fourth with very severe drought. November and January in SPI-12 and August and September in SPI-24 were mostly affected by standard rainfall drought, with 2% of the area in normal condition, 27% in moderate drought condition, 68% in severe drought condition and 3% in a very severe drought situation, meaning that most of Khuzestan province was covered by severe and very severe drought. The study of water shortage in Khuzestan province showed that in Khuzestan province, August, January, and April were the most affected by water shortage and August with -6/89, the driest month in the whole statistical period was studied, which according to the classification The TSDI index is in a very strong category. In terms of seasonality in winter, due to the fact that the amount of groundwater was strengthened in this season, its amount changes sinusoidally and sometimes it was in a moderate position and sometimes in a very severe category. Among the seasons, autumn had the least changes compared to the other seasons and was located in the middle to upper class.