Department of watershed Management, Faculty of Natural Resources, Natural Resources and Agricultural Science University, Sari, Iran
Drought as a natural phenomenon characterized by a significant decrease of water availability during a period of time and over a large area. In recent years, droughts and its frequent in arid and semi-arid regions like Iran on the one hand, and water demand has been rising on the other hand and, as a result, their impacts are being aggravated. Therefore, the meteorological and hydrological droughts are receiving much more attention. This research focused on the Standardized Precipitation Index (SPI), Streamflow Drought Index (SDI) and Groundwater Resources Index (GRI) to investigate the correlation between these indices and overlapping periods of 3 to 48-months in the centeral Iran over the period of 1970–1971 to 2014–2015. Furthermore, the driest year based on the SPI were 2007–2008 and 2011-2012, while they were detected to be 1999–2000 and 2003-2004 based on the SDI and GRI, respectively. The decreasing time series trends using Spearman’s rho and Kendall’s tau tests were more evident for the all three indices at most of the years. SPI on time scales of 18, 24 and 48-months, with SDI and GRI showed a significant relationship in 0.01 and 0.05 percent levels that it can be confirmed directly affected by a groundwater drought in the plains. The Spearman correlation analysis indicated a strong correlation between SPI on time intervals of 18, 24 and 48-months, with SDI and GRI that showed a significant relationship in 0.01 and 0.05 percent levels that it can be confirmed directly affected by a groundwater drought in the plain. In general, the results showed that the study area suffered from the meteorological drought more than the other two types of droughts. Moreover, the results revealed that the study area has become drier over the last three decades.