Investigating the characteristics of meteorological drought and groundwater drought and its relationship with meteorological teleconnection patterns (Sefiddasht and Faradonbeh plains, Chaharmahal and Bakhtiari province)

Drought is a natural phenomenon that occurs as a result of a decrease in the amount of precipitation in a period of time, compared to the normal or expected amount in the same period of time. Irregularity of meteorological variables, including the precipitation with a long periodicity, is affected by the phenomena that occur all over the earth with different periodicity and are known as meteorological signals. Teleconnections are a category of meteorological signals. Teleconnection refers to two regions on the surface of the earth that have a high correlation with each other in terms of climate. In addition, some low-frequency events (with long periodicity) in tropical regions also affect atmospheric patterns in higher latitudes. Since the amount of precipitation has a direct effect on recharging the aquifers, the prolongation of the drought period due to teleconnection patterns can also affect the groundwater level. Investigating the effects of the teleconnection patterns and predicting them, especially during drought periods, will be a great help for more accurate planning and management of the watershed. Since teleconnection patterns are in the category of large-scale phenomena, it is expected that the areas affected by them will be very vast. In most of the conducted studies, the relationship between drought indices and these phenomena has been done at station points. Considering the effect of local factors on the phenomenon of precipitation, point analysis can increase the uncertainty in the results. In this study, the regional average of precipitation in Chaharmahal and Bakhtiari provinces was used to calculate the drought index and to investigate its relationship with the groundwater level. Also, in order to study the role of teleconnection phenomena in creating meteorological and hydrological (groundwater) droughts in Faradonbeh and Sefiddasht plains, the relationship between the indicators of several well-known teleconnection patterns and meteorological and hydrological (groundwater) droughts has been investigated.Methods:In order to study the meteorological drought, the monthly precipitation data of the synoptic stations of Chaharmahal and Bakhtiari province from 2000 to 2020 were used. Also, the water level measured at 19 observation wells were used to investigate the groundwater drought of the Faradonbeh and Sefiddasht plains. The Standardized Precipitation Index (SPI) and the Groundwater Resource Index (GRI) were applied to monitor the meteorological and groundwater droughts of the Faradonbeh and Sefiddasht plains, respectively. Since the stations in the study area do not have the same distribution and each station has a different effect area, the average precipitation of the Chaharmahal and Bakhtiari province was calculated by weighted average method (based on area and distance) and the regional monthly precipitation time series was used to calculate the SPI index. Also, the values of teleconnection indicators including Madden-Julian Oscillation (MJO), El Nino-Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) for the period of 1991-2021 were downloaded from the website of The National Center for Atmospheric Research and the National Center for Environmental Prediction (NCEP/NCAR). Since teleconnection phenomena have two positive and negative phases, to investigate the relationship between meteorological and groundwater drought indices with these phenomena, the correlation between SPI and GRI with teleconnection indicators has been done in several cases: Simultaneous correlation of data (correlation between all data), correlation in positive and negative phases of each teleconnection pattern (only positive phases or negative phase of teleconnection indicators were considered), calculation of correlation in each season (based on the solar calendar) separately, removing 5 dry months of the year (June to October) and calculating the correlation with a delay of one month.Results:The results showed that the NAO and IOD indices have the highest correlation with precipitation and SPI index, and have had the greatest impact on precipitation and drought in the study area. Also, the IOD and ENSO indices have a negative and inverse correlation with the GRI index. In general, it can be concluded that the difference in the response time of meteorological and groundwater droughts has a direct role in the extent of its influence from teleconnection events. So that the NAO phenomenon, which has a shorter periodicity than El Nino and IOD, is more significantly related to meteorological drought, which has a shorter response time, and hydrological drought, which has a longer response time, is more affected by El Nino teleconnection, which has a longer periodicity. The MJO phenomenon, which has the shortest periodicity among the studied teleconnection phenomena, had no significant relationship with the droughts of these plains.