كليدواژه :
SPI , افت سطح آبخوان , تحليل سر زماني , خشكسالي , ميان يابي , PSI
چكيده لاتين :
Introduction Natural and anthropogenic factors in recent decades caused water crisis and the drop in groundwater levels in most regions of the country, including Khorasan Razavi province.The Standard Precipitation Index (SPI) has the ability to assess meteorological drought and its impact on groundwater drought can be evaluated through the appropriate indices, e.g. Groundwater Resource Index (GRI) and Piezometric State Index (PSI). Their capability has been proven in many studies around the world (Memarian, Balasundram, Talib, Sood, Abbaspour, 2012; Verdi Pourazad, Azarakhshi, Mosaedi, Farzadmehr, 2014; Rezvanian, Assadi, Goudarzei, 2013; Yasamani, Mohamadzadeh, Mosaedi, 2012; Imani, Talebi Esfandarani, 2011; Shakiba , Mirbagheri, Kheiri, 2010; Shahid &Hazarika, 2009, 1989-2006; Mendicino &Senatore, 2008; Khan ).The main objective of this study is to evaluate the effects of drought on the changes of groundwater resources by using statistical time series analysis of meteorological drought and groundwater drought indices, temporally and spatially. 2. Materials and Methods In this study for evaluating the effects of meteorological drought on groundwater table, the indices SPI and PSI during a 30-year period (1984-2014) were calculated and analyzed using the Mann-Kendall time series analysis and Pettit test.IDW (Inverse Distance Weighted) interpolation approach and Hot Spot Analysis were employed in spatial analysis of groundwater drought and its relation to meteorological drought was evaluated through the Pierson’s correlation coefficient. 3. Results and Discussion Interpolated maps of SPI index showed that during the period 1999-2000, 2000-2001, 2005-2006, 2007-2008, 2010-2011 and 2013-2014 watershed area mainlyisclassified into dry and very dry classes. However, the results of time series analysis of SPI in all stations except Androkh station in the period 1984-2014 shows that the gradual changes of SPI is not significant at the level of 0.05.As a result, it can be stated that the Chenaran-Mashhad watershed has not experienced a gradual change in rainfall and meteorological drought in most of stations in the last threedecades. The gradual changes of PSI time series at all observation wells were significant and decreasing except GhasemAbad, Kalat Nader, Meskaran, Noumhan and Hashem Abad observation wells.PSI index had a decreasing trend in all observation wells except in Television Boulevard.Abrupt changes of PSI in most of observation wells were significant and reducing. This time, mostlywas correspondedto the years 1997-1998 and 1998-1999.Zoning maps also show that the PSI index on the plain from 1984-1985 to 1999-2000 was situated in normal conditions, whereas from1999-2000 up to now was classified in dangerous situations and historical minimum categories. During the years 2011-2012, 2012-2013 and 2013-2014 historical minimum condition of PSI is clearly visible.Correlation analysis between the two indices SPI and PSI showed that in most cases and years there are poor relationships between groundwater drought and meteorological drought. By analyzing the moderate to high correlations between the SPI, and PSI indices, it can be established that in most cases the relationship is in the reverse form. According to the analysis of annual water flow records of the main recharging rivers, it can be revealed that the gradual change time series is not significant at the level of 0.05. Again, it confirms that there is no strong relationship between hydrological drought and groundwater drought in the study region. 4. Conclusion The groundwater level of Mashhad plain from 1985 to 2014 has been experienced more than 25 meters of drop that mostly occurred between1999 to2003. During this period, the number of drilled wells is 1054. The measurement results of the groundwater level during ten years (1996-1997 to 2006-2007) show that the drop in groundwater levels of the Mashhad-Chenaran’s aquifer is in accordance with the exploitation magnitude by wells and aquifer recharge. In fact, uncontrolled exploitation of groundwater resources can be considered as a major factor of drop in groundwater level, which caused subsidence and leading salty water into fresh water in Mashhad plain
