عنوان مقاله [English]
Karst aquifers act as large natural reservoirs of rainfall, and spring discharges reflect periods of poor or abundant rainfall, as well as long term climate change. The annual discharge of karst springs depends on climate, geology and karst. The karst springs Discharge in a 42-year period in China shows that the discharge of Shentou Springs responds remarkably to precipitation change (Ma & et al.; 2004, 274). The determinations of large karst systems discharge have been analysis by the investigation of precipitation and supplement reduction periods. Data show that hydrologic year depended to last year precipitation. In Mediterranean climate and regional condition the annual peak hydrograph occurs during spring season. Also, Insufficient recharge due to poor annual rainfall affected the peak discharge in hydrograph; this hydrograph reveal drought which effected by reduction in discharge during the following year as well (Fiorillo; 2009, 290).
Study area consist of Kermanshah, Ravansar and Eslamabad_Gharb Township in west of Iran. SarabBiabr and SarabVarmenjeh spring located in North and SarabNilofar spring in south of Kermanshah plain. Weather station of Kermanshah located in longitude 47°, 9¢ E. and latitude 34°, 21¢ N. Weather station of Ravansar located in longitude 46°, 39¢ E. and latitude 34°, 43¢ N. Weather station of Eslamabad_Gharb located in longitude 46°, 28¢ E. and latitude 34°, 7¢ N.
Materials and methods
In order to study the long-time series of hydrological, Karst spring discharge and precipitation, we used from Standard Precipitation Index (SPI) and nonparametric Man_Kendall test. Also, the relationship between precipitation-discharge and lag time in short and long-term analyzed by Pearson correlation. In this study, we used monthly and annual data from discharge stations of SarabBiabr, SarabVarmanjeh, and SarabNilofar spring, and precipitation data of Kermanshah, Ravansar, and Eslamabad_Gharb Weather Stations for the period 1989-2010.
In the Man _ Kendall test, out of 95 significant level, indicated significant changes in the time series and determine real data behavior during the time series the ascent or descent of the series.
Also, was used from Markov Chain Model for the possibility of repeated periods of dry or wet and its effect on Dubai karst springs.
Result and discussion
Maximum amount of discharge are in SarabNilofar and SarabVarmanjeh spring. Since the beginning of the study period to 2010, Karst spring discharge decreases, the greatest loss is occurring in SarabNilofar spring. In this spring amount discharge from 1241 liter/sec has decreased to less than 100 liter/sec for year 2010. Karst aquifer is the main water source which influenced by fluctuations in the short and long term precipitation.
The present study was investigated on the effects of drought on rate of discharge and relation between discharges with precipitation. Also, effect of precipitation lag time on fluctuations discharge was studied. The result shown the most correlation was between discharge of SarabVarmanjeh spring (about of 0.639) and SarabBiabr spring (about of 0.642) with precipitation meteorology station of the Eslamabad_Gharb. So, SarabNilofar spring discharge (about of 0.484) had most correlation with Kermanshah precipitation meteorology station. In this paper, the authors obtained the lag time for the discharge values response to the precipitation factor, six months for long time and two months for short time. The reason of the difference between the two times is precipitation factors (such as monthly distribution, intensity and state of solid or liquid).
The reason of this difference is precipitation characteristics such as solid state, distribution, and intensity. The results of the Man – Kendall test showed that were increase in precipitation (1989-98) and then decreased (1999-2010). Also, SarabBiabr spring discharge shows the same trend. The most decreases fluctuations was in SarabBiabr spring discharge and the most decreases fluctuations in precipitation was during 2003. The SarabVarmanjeh spring discharge decreases from 1996 year. Precipitations on Kermanshah station had decreases during 1999–2010 years and observe this condition during 1999-2010 in SarabNilofar spring discharge and from 2009 year have changed. The results of the Markov test showed that Probability occurrence condition dry to dry in stations more than others conditions, this is in Eslamabad_Gharb 0.892, in Ravansar 0.89 and in Kermanshah 0.886. It should be noted that this represents the future trend of decreasing rainfall and consequently reduced rate of Karst spring discharge. Computation annual SPI showed which in droughts SPI precipitation is a very similar trend with spring discharge. Overall, the results of Markov Chain Model indicated an increased risk of drought in weather stations that will affect the future on Karst spring discharge declining in study area. Prediction of drought periods and that effect on Karst spring discharge could help us to planning for best use of Karst aquifer sources.