فهرست مطالب علی اکبر مهران

The effective and timely monitoring of drought can help to develop drought systems and optimal management of water resources. Therefore, in this research, the drought situation in the synoptic stations of Fars province (Abadeh, Shiraz, Fasa and Lar) was investigated in different time scales (3, 6, 9 and 12 months) using precipitation-evaporation and transpiration (SPEI) and Multivariate standardized precipitation (MSPI) indices. The Mann-Kendall test was used in order to check the trend of the investigated indicators. Based on the results, the frequency of dry and wet periods is high in short-term time scales. But with the increase of time scales, the frequency of dry and wet periods decreases and their duration increases. In terms of the SPEI index, in the 3-month time scale, the most severe drought is at Abadeh station (-5.20) and the most severe drought is at Shiraz station (5.21). In the time scale of 6 months, the most severe drought and drought were observed in Abadeh (-3.45) and Shiraz (3.10) stations, respectively. In the time scale of 9 months, the most severe drought and drought are in Lar station with values of -3.63 and 2.48, respectively. Also, on a 12-month scale, the most severe drought is in Shiraz station (-3.37) and the most severe drought is in Abadeh station (2.37). Principal component analysis of SPI time series showed that the first principal component (PC1) can account for a large percentage of changes in the original SPI time series in all regions studied in this research. Also, the results showed that MSPIs follow the fluctuations of the SPI time series, especially in long-term dry and wet periods. So, partial wet and dry periods in severe and prolonged dry or wet periods may be excluded by MSPI.

Effective and timely drought monitoring can contribute to the development of drought systems and the optimal management of water resources using these systems in turn can minimize the costs of drought. The purpose of this study is to investigate the drought using Landsat satellite data and meteorological and agricultural drought indices in three regions with different climatic conditions (Birjand, Shiraz and Rasht). For this purpose, drought indices based on satellite data including Normalized Difference Vegetation Index (NDVI), Soil Adjustment Vegetation Index (SAVI) and Simple Ratio (SR) were extracted from Landsat images for the period 2002, 2014 to 2020. Then the results of these indices were compared with the values of standard precipitation index (SPI) and Reconnaissance Drought Index (RDI). The study of indicators shows that the amount of indicators is high in all studied years in Rasht region. In Shiraz region, a significant decrease in the average value of indicators occurred in August and September from 2015 to 2020. Also, this decrease was seen in the average value of indicators in Birjand region from September 2002 to 2020. On the other hand, among the studied months, September 2015 in Rasht and Shiraz regions and 2014 (September) Birjand had the most drought in terms of remote sensing indicators. The results showed that in all three regions, remote sensing indices including NDVI and SAVI have a high correlation with SPI and RDI indices. The RDI index is superior to the SPI index for drought monitoring and prediction. As a result, the RDI index takes into account evapotranspiration in addition to rainfall and is more sensitive especially in dry areas such as Shiraz and Birjand where evapotranspiration is higher than rainfall.