The Evaluation of Discharge Regime Impressibility of Karstic Springs from Drought Occurrence (Case Study: Karstic Springs of Alvand River Basin)

Introduction Drought occurrence as an anomaly of the atmosphere rooted in change of climate lead to the imbalance between supply and demand for water, as well as social, economic and environmental consequences (Zhang et al, 2012: 482). The lack of rainfall in one area for a long period of time is known as meteorological drought and this lack of water in the hydrological cycle causes different types of drought (Fiorillo and Guadagno, 2010: 1868). Karstic systems respond to drought is controlled by the rate of the development of karstic systems. Sarabgarm, Vardanaw and Marab springs with a total discharge of more than 80 million liters of cubic meters supply water needed for drinking and agriculture for the societies around them and have a fundamental role in sustaining the human life in the area. Thus, understanding the influence of drought on these springs is essential for the management of karstic water resources in the region. The purpose of this study is to evaluate the impressibility of discharge regime of karstic springs of Sarabgarm, Marab, and Vardanaw from drought occurrence.
Methodology According to the purpose of the study, the three springs of Sarabgarm, Vardanaw and Marab having the same climatic conditions were selected. To identify the drought occurrence in the area SPI index was used. To assess the influence of the springs’ Discharge of fluctuations in rainfall and drought occurrence, comparing of standard annual precipitation and annual standard Discharge was used. Analysis of springs’ Discharge and the precipitation were done by the statistical method, RAPS. Also to evaluate the impact of rainfall on the discharge regime of springs the standardized average annual precipitation rate was calculated first, and then using equation (6) the impressibility of the discharge regime of springs was clarified by drought occurrence. By comparing the rate of annual average standard SPI index at different time scales of 12, 24 and 48 months, the impact of meteorological drought on hydrological drought occurrence in the springs was evaluated.
Discussion Comparing the annual rainfall and the standard rate shows that discharge of three springs is sensitive to reduced rainfall, but time reaction to rainfall fluctuations in all three springs are not the same.
Evaluation of time series of RAPS, Piran rain gauge station and springs under investigation indicates a generally increasing trend from 1983 to 1997 and a decreasing trend from 1998 to 2010. This trend is a result of occurrence of long-term periods of decreasing rainfall in the region.
In the short-term fluctuations in rainfall, impressibility of discharge of Marab and Vardanaw is more than Sarabgarm, and in the long-term precipitation fluctuations, due to the influence of aquifer aquifer memory, Sarabgarm reacts to the occurrence of precipitation fluctuations in the previous years with much delay, while the other two springs have less time delays.
The reflect of meteorological drought on hydrological drought in karstic systems of Alvand River basin is mostly a gentle and long-term drought and gentle and the reaction of Marab and Vardanaw is different from the reaction of Sarabgarm. The differences in response to meteorological drought depend on the effect of the memory of karstic aquifers.
Conclusion Drought occurrence as an anomaly of the atmosphere rooted in change of climate lead to the imbalance between supply and demand for water, as well as social, economic and environmental consequences (Zhang et al, 2012: 482). The lack of rainfall in one area for a long period of time is known as meteorological drought and this lack of water in the hydrological cycle causes different types of drought (Fiorillo and Guadagno, 2010: 1868). Karstic systems respond to drought is controlled by the rate of the development of karstic systems. Sarabgarm, Vardanaw and Marab springs with a total discharge of more than 80 million liters of cubic meters supply water needed for drinking and agriculture for the societies around them and have a fundamental role in sustaining the human life in the area. Thus, understanding the influence of drought on these springs is essential for the management of karstic water resources in the region. The purpose of this study is to evaluate the impressibility of discharge regime of karstic springs of Sarabgarm, Marab, and Vardanaw from drought occurrence. According to the purpose of the study, the three springs of Sarabgarm, Vardanaw and Marab having the same climatic conditions were selected. To identify the drought occurrence in the area SPI index was used. The results of the study showed that Karstic springs under the study were influenced by fluctuations in rainfall and from 1998 they are in a downward discharge trend. Due to memory effect of aquifer, meteorological drought occurrence and its impact on hydrological drought in the springs are not equal and impressibility of Sarabgarm has been less than the two other springs. Impressibility of these springs from fluctuations in rainfall depends on development of Karstic systems, memory effect of aquifer and the duration of precipitation fluctuations and severity of the occurrence. The occurrence of severe dry periods (1997-1998 to 2000-2001 and 2005-2006 to 2009-2010) largely modifies the memory effect of aquifer and cause the predominance of mild hydrological drought in the period of 1999 to 2010.