Introduction

In the recent decades, earth has become warmer, and water shortage has been an issue, almost all over the world, because of changes in climate (Bostrom et al. 1994; Abbasnia et al. 2019b). The increase in average global temperature and sea level (Hasan et al. 2014; Yousefi et al. 2017), amplifies coastal erosion, generates greenhouse effect (Ali 1999; Khamutian et al. 2015), melts ice caps and glaciers (Karamia et al. 2019), creates imbalance of levels of precipitation and evaporation (Kumar 2012), decreases the groundwater level (Döll 2009), and especially heightens the drought (Mizyed 2018); these are already the most common consequents of climate change (Green et al. 2011). Consequently, these changes can directly or indirectly influence the hydrological processes and mainly groundwater aquifers (Kumar 2012; Qasemi et al. 2019; Yousefi et al. 2018).

Groundwater aquifers are the second most abundant reservoir for freshwater in the world, after glaciers (Saito et al. 2016; Abbasnia et al. 2018; Cancelliere et al. 2007; Mirzaei et al. 2015). In Iran, groundwater supplies a significant part of water demand for irrigation, drinking, and industrial purposes (Abbasnia et al. 2019a; Jalili et al. 2018). Irrigation sector, which consumes the highest amount of water in Iran (Qasemi et al. 2019) with more than 80% of exploitation of groundwater resources (Qasemi et al. 2018), plays a critical role in qualitative and quantitative changes in aquifers (Alizadeh and Keshavarz 2005; Radfard et al. 2019; Rezaei et al. 2019; Dehghani et al. 2019). Unfortunately, within the last decades, withdrawal of these resources for expanding irrigation and other purposes, together with climate changes and global warming, has caused prolonged drought in many regions of Iran.

Drought is a condition of reduction in rainfall and increases in temperature that can occur during long or short periods (such as a season or a year) in all types of climate (Bloomfield et al. 2019). This catastrophic environmental phenomenon leads to a change in hydrological regimes and consequently makes a significant decrease in the chemical quality of water resources (Ranjpisheh et al. 2018; Yousefi et al. 2018). Therefore, protection and proper management of groundwater resources as vital water reservoirs also undertake a qualitative and hydrologic assessment during the drought, and the global water crisis should be a necessary and undeniable response (Mirzaei et al. 2015).

In order to evaluate the effects of climate change and drought on the quality of groundwater, research has been carried out (Karamia et al. 2019; Soleimani et al. 2018b; Radfard et al. 2018; Ali 1999; Bloomfield et al. 2019; Hasan et al. 2014; Green et al. 2011). Accordingly, several indices used for forecasting the drought include Palmer drought severity index (PDSI) (Palmer 1968), soil moisture drought index (SMDI) (Hollinger et al. 1993), reconnaissance drought index (RDI) (Zarei et al. 2019), and Standardized Precipitation Index (SPI) (Mckee et al. 1993). Also, a comprehensive review of drought concepts has been carried out by Mishra and Singh (2010). Besides, there are various methods to analyze water quality, such as the Schoeller and Wilcox diagrams (Choramin et al. 2015).

Schoeller’s diagram is one of the most common methods to assess water quality for drinking purposes that presents the possibility of water samples at a specified point in an area, but the spatial variability of groundwater quality cannot be evaluated by this method (Afzali et al. 2014). Also, the Wilcox diagram is commonly used for agricultural water classification in hydrological studies. It was suggested by Wilcox in 1948 and completed by Torn in 1951. The studied indices and methods present a clear picture of drought and water quality (Choramin et al. 2015; Afzali et al. 2014; Shams et al. 2014). Since major parts of Iran have an arid and semi-arid climate with average annual precipitation of less than one-third of the international standard (Alizadeh and Keshavarz 2005), it is necessary to evaluate drought conditions and water quality changes to proper management of water resources.

The study area of the present investigation (Saveh) is the largest industrial-tourism city in Markazi province with a warm arid climate that is the hub of agricultural production. Wells play a significant role in the potable water of Saveh, but their qualitative and quantitative features have been lowered in the recent drought period (Mohammadi et al. 2012). Thus, this study sheds new light on the effects of drought and decline in precipitation on water chemical quality of wells in various regions of Saveh for 12 years, from 2004 to 2015. For this aim, physicochemical parameters of 29 wells in the studied area have been analyzed by the Standard Precipitation Index (SPI) and were compared with national and international standards. Also, the Wilcox and Schoeller diagrams were used to evaluate the water quality of wells in terms of irrigation and drinking purposes, respectively. Finally, the GIS software was applied for the zoning of the groundwater quality parameters.

Materials and methods

Description of the study area

Saveh is the largest city of the Markazi province, with a population of about 220,762 and an area of approximately 4748 km2. This city is located at the height of 960–1110 m above sea level, with 50.20° E and 35.3° W geographical longitudes and latitudes, respectively. It has a semi-arid climate with warm summers and slightly cold winters. Its average temperature and average annual precipitation are 18.2 °C and 202.2 mm, respectively.

In the present investigation, to run a more exhaustive survey of water chemical quality of Saveh wells during the study period, the wells were grouped into five areas as follows:

  1. 1.

    Sayyed Gholi area with fifteen wells

  2. 2.

    Yahyaabad area with seven wells

  3. 3.

    Surkan area with two wells

  4. 4.

    Shahrak area with two wells

  5. 5.

    Alavi area with three wells

Figure 1 presents the location of the study area in Markazi province.

Fig. 1
figure 1

Location of Saveh County and sampling points in the Markazi province

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Sampling procedure and data analysis

This descriptive cross-sectional study intends to assess the impacts of drought and decline in precipitation on water chemical quality of wells in various regions of Saveh for 12 years, from 2004 to 2015. Twenty-nine groundwater samples were collected from active wells of five parts of Saveh County (Fig. 1). Before sampling, all dug wells were pumped for about 4 mins to remove the impacts of stagnant water, and all sample containers (polyethylene containers with 1-L capacity) were rinsed three times by deionized water. Then, the samples were labeled, stored at 4 °C, and transported to the laboratory for chemical analysis of essential parameters. All specific analysis was performed according to the Standard Methods for Examination of Water and Wastewater (Federation and Association 2005).

In order to investigate the changes of water quality during the study period, various parameters such as total dissolved solids (TDS), electrical conductivity (EC), total hardness (TH), level of cations such as Ca+2, Na+, Mg+2, and K+ as well as anions such as Cl− and So42− were analyzed (Table 1). These parameters are effective in the determination of the best water quality in drinking and irrigation purposes in the index years of drought based on the Wilcox and Schoeller diagrams (Mir et al. 2017). Also, the precipitation level was surveyed through the SPI by the application of the DIC™ program. The Schoeller and Wilcox diagrams were plotted by the CAD™ package. Finally, data were mapped by Arc Map GIS 10.3 software.

Table 1 SPI classification, according to Abba (2015)
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Standardized precipitation index

Generally, the drought process is analyzed monthly and annually. Although an annual period is long, it is used to collect and interpret regional data. Severity and duration of drought, as well as its spatial orientation, are among the commonly employed criteria to study the drought process. Some indices such as Palmer drought severity index (PDSI) (Palmer 1968), surface water supply index (SWSI) (Jang et al. 2017), rainfall anomaly index (RAI) (Rangarajan et al. 2019), and reconnaissance drought index (RDI) (Zarei et al. 2019) are among the most well-known criteria to investigate drought. In the present research, which is the well-documented one, Standardized Precipitation Index (SPI) was primarily developed for determining and assessing the drought. This index is based on the probability of hydrologic rainfall variable for multiple time scales (Eq. 1) (Gandhi and Parekh 2017; Cancelliere et al. 2007). A striking feature of SPI is its applicability for several spatial series, including year and month. Taking its advantage, we can use the index to assess all kinds of long-period (surface and groundwater resources) and short-period (existent moisture in agriculture soil) water resources (Gandhi and Parekh 2017).

$$ SPI=\left({X}_{ik}-\hbox{---} {X}_i\right)/{\sigma}_i $$
(1)

where

Xik:

precipitation level of the ith station and kth observation

Xi:

the mean of long-term precipitation for the ith station

σi:

standard deviation of the ith station

Table 1 shows the classification of climate according to the SPI.

The SPI can be calculated by Drought Indices Calculator (DIC) software, in which 12 years of data of annual average precipitation from Saveh rain gauge and weather stations were applied as input data (Chaussard et al. 2017).

Wilcox diagram

Excessive sodium in water resources produces the undesirable influence of altering soil characteristics and decreasing soil permeability. Also, high concentrations of this metal lead to higher alkaline levels in soil. A Wilcox diagram can be used to determine the suitability of water for agriculture purposes (Shams et al. 2014). Wilcox plot is evaluated by two main parameters of EC and SAR (Table 2), where C and S refer to the EC and SAR classification, respectively. According to the values of these two parameters, the water classification for agricultural purposes in the Wilcox diagram has four categories (Table 3). This diagram is a simple scatter plot of the sodium adsorption ratio (SAR) on the Y-axis and salinity hazard (conductivity (μS/cm)) on the X-axis. SAR is measured by the following equation (Eq. 2), where all the ions (Ca+2, Na+, Mg+2) are expressed in milliequivalents per liter unit (meq/L). (Shammi et al. 2016).

$$ \mathrm{SAR}=\frac{Na^{+}}{\sqrt{\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$2$}\right.\left( Ca+ Mg\right)}} $$
(2)
Table 2 Classification of irrigation water based on SAR and EC values (Richards 1954)
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Table 3 Water classification for agriculture purposes based on the Wilcox plot (Shams et al. 2014)
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According to the Wilcox classification, which is based on electrical conductivity (EC) and sodium absorption (SAR), water is grouped into four main grades, including excellent, good, average, and unsuitable (Table 2).

Table 3 illustrates water classification for agriculture purposes based on the Wilcox plot (Shams et al. 2014).

Schoeller diagram

The Schoeller diagram is a semi-logarithmic diagram that portrays the relative concentrations of cations and anions and is typically expressed in milligrams per liter. If ions are plotted in a Schoeller diagram, it is suggested to use the milliequivalents per liter unit since it allows the comparison of the ion ratios directly (Abba 2015). Generally, this diagram is drawn and analyzed in order to classify potable water in the hydrologic reports. In this diagram, water samples are divided into six types, including good, acceptable, average, inappropriate, generally unpleasant, and non-drinkable (Table 4) (Choramin et al. 2015).

Table 4 Standardized classification of drinking water based on the Schoeller diagram (Choramin et al. 2015)
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Result and discussion

Average precipitation and SPI

Average annual precipitation in Iran is 250 mm per year that is less than one-third of the world’s average (Madani et al. 2016). Primary reasons for low average annual precipitation of Saveh County (that is estimated to be 176 mm per year) can be related to regular drought in recent decades in Iran, as well as the climatic condition (Tahrudi et al. 2016). The amount of average annual precipitation of this area was 288 and 126.3 mm in 2004 and 2015, respectively. Figure 2 indicates the annual average rainfall of Saveh during the studied period.

Fig. 2
figure 2

Annual average precipitation in Saveh from 2004 to 2015

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The Standardized Precipitation Index (SPI) is a universally accepted index to characterize meteorological drought on a range of timescales. In short deadlines, this index is almost related to soil moisture, while at longer timescales, the SPI can be related to groundwater resources and reservoir storage (Bordi et al. 2001; Bonte et al. 2013). Figure 3 shows that during the studied period (2004–2015), the catchment area of Saveh has faced such a severe drought that SPI had been varied from 1.25 (moderately wet class) in 2004 to − 2.79 (extreme drought) and − 1.88 (severe drought) in 2014 and 2015, respectively (Table 1).

Fig. 3
figure 3

The amounts of standardized precipitation index of Saveh from 2004 to 2015

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The results show a negative trend of SPI for study years. At the beginning of the study period (2004), the SPI was moderately wet, but continuous drought during 12 years, severe drought in 2014 (SPI = −2.79), and overuse of groundwater resources in recent years could have caused changes in qualitative and quantitative features of water reservoirs (Jang et al. 2017). According to previous investigations, drought plays a critical role in diminishing well’s water and consequently, a significant drop in groundwater (Rangarajan et al. 2019; Cancelliere et al. 2007; Abba 2015; Chaussard et al. 2017; Gandhi and Parekh 2017). Moreover, previous studies suggested a meaningful and robust link between SPI and decline in groundwater resources (Shammi et al. 2016).

Effects of drought on the chemical quality of wells based on Wilcox classification

Chemical quality is among the main parameters of water resources management and sustainable development and should be considered in terms of human and ecosystem health (Shams et al. 2014; Choramin et al. 2015). Figure 4 indicates a qualitative change of the studied wells in terms of salinity and sodium absorption ratio for agricultural purposes in 2004 and 2015.

Fig. 4
figure 4

Classification of studied wells according to the Wilcox diagram (2004–2015)

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According to Fig. 4, the water quality of 13.8, 20.7, 37.9, 3.4, 3.5, and 17.2% of studied wells are grouped as C2S1, C3S1, C3S2, C3S4, C4S4, and C4S3, respectively, in 2004 (Table 3). Also, the results of the study in 2015 show that water quality of 37.9, 34.5, and 27.6% of wells were in C4S2, C4S3, and C4S4 classes, respectively, which means that the water quality was in the very salty—harmful for agriculture class (Table 3) (Shammi et al. 2016).

Water with a high level of Sodium is not acceptable for agriculture purposes, because the high level of salt leads to lower soil aggregation, osmosis potential of agriculture products, and soil permeability (Yidana et al. 2010; Tweed et al. 2009).

Chemical quality changes based on Wilcox and Schoeller diagrams

As discussed earlier, the studied area was grouped into five regions in order to conduct a more detailed study (“Description of the study area”) and changes in chemical quality of water were studied by the Schoeller and Wilcox diagrams. First, the primary chemical qualitative parameters of studied wells were examined. TDS, EC, and levels of sodium, magnesium, calcium, chlorine, sulfate ions, and pH were examined in order to check water quality for agricultural and drinking purposes, and then they were analyzed by the Schoeller and Wilcox diagrams for drinking and agriculture purposes, respectively. Table 5 shows the results of the annual average of qualitative parameters in 2004.

Table 5 Annual average results obtained from analyzing qualitative parameters of the studied wells in 2004
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Changes in water chemical quality of Sayyed Gholi’s wells

Figure 5 represents changes in water quality of fifteen wells in the Sayyed Gholi region. The figure was plotted by obtained data of TDS, TH, levels of Ca+2, Mg+2, Na+1, Cl−, SO4−2, and HCO3− based on the Schoeller diagram (Alavi et al. 2016). The diagrams showed that although water quality of most of the wells in the region was normal in 2004, their quality was unacceptable for drinking purposes in 2015.

Fig. 5
figure 5

The Schoeller diagram—comparison of water quality of wells located in the Sayyed Gholi region in 2004 and 2015

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Moreover, Fig. 6 represents levels of well qualitative changes in terms of salinity and sodium absorption from 2004 to 2015. According to the diagram, each well is classified into four groups regarding both salinity and sodium adsorption. The Wilcox classification suggests qualitative changes in water quality for agriculture purposes. The diagram suggests that, in 2004, although most of the wells in the studied region were grouped as C3S1 and C3S2 (Table 3); they gradually changed into C4S2, C4S3, and C4S4 over the study period (Alavi et al. 2016; Mishra and Singh 2011).

Fig. 6
figure 6

The Wilcox diagram compares the water quality of wells located in the Sayyed Gholi region for drinking purposes in 2004 and 2015 (S:Sayyed Gholi)

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Changes in water chemical quality of wells located in the Yahyaabad region

Figure 7 represents changes in the water quality of seven wells in the Yahyaabad region. The figure was plotted by using obtained data of TDS, TH, levels of Ca+2, Mg+2, Na+, Cl−, SO42−, and HCO3− based on the Schoeller diagram. The diagrams showed that although water quality of most wells in the region was acceptable in 2004, their quality was normal for drinking purposes in 2015.

Fig. 7
figure 7

The Schoeller diagram—comparison of water quality of wells located in Yahyaabad region in 2004 and 2015

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Moreover, Fig. 8 represents qualitative changes in wells in terms of salinity and sodium absorption from 2004 to 2015. According to Wilcox classification, changes in water quality of wells for agricultural purposes in 2004 for the most wells in the studied region was C2S1, C3S1, and C3S2, but they gradually changed into C3S2 and C3S3 (Raju 2007).

Fig. 8
figure 8

The Wilcox diagram compares the water quality of wells located in the Yahyaabad region for agricultural purposes in 2004 and 2015 (Y: Yahyaabad)

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Changes in chemical quality of wells in the other areas

Figures S.1, S.2, S.3, S.4, S.5, and S.6 represent changes in water quality of other seven studied wells located in Surkan, Shahrak, and Alavi regions. These diagrams were plotted using obtained data of TDS, TH, Ca+2, Mg+2, Na+, Cl−, SO4−2, and HCO3− based on the Schoeller and Wilcox diagrams (Raju 2007).

About Surkan area, the diagrams showed that although water quality of most of the wells was acceptable in 2004, their quality was inappropriate in 2015 (Fig. S.1).

Moreover, although the water quality of most of the wells in the Shahrak region was average in 2004, it was generally unpleasant in 2015 (Fig. S.3). Also, the water quality of three wells of the Alavi region was unacceptable in 2004, and they changed to generally unpleasant in 2015 (Fig. S.3).

Regarding salinity and sodium adsorption, surveying of water in all Surkan, Alavi, and Shahrak regions showed that water quality in these wells was C4S3, C3S4, and C4S3 in 2004, respectively, but it changed to C4S4 in 2015 (Table 2) (Figure S.1).

Effect of drought on the study parameters during the study period

As discussed earlier, for this research to run a more exhaustive survey of water chemical quality, the wells were grouped into five areas and different parameters including pH, TDS, TH, Ca+2, Mg+2, Na+, Cl−, and SO4−2 were surveyed regarding the changes during the study period and these changes were finally mapped by GIS.

Effect on pH levels

The Schoeller diagram is a tool used to evaluate the quality of water for drinking purposes (Tahrudi et al. 2016; Bordi et al. 2001). Based on the Iranian National Standard, the pH level of potable waters ranges from 6.5 to 8.5 (Bonte et al. 2013). The results of the Schoeller diagram showed that the water pH of 72.4% of wells was acceptable for drinking purposes in 2004, and these amounts did not change much in 2015. The pH of wells in the studied period meets the Iranian National Standard (Fig. 9) (Yidana et al. 2010).

Fig. 9
figure 9

Spatial distribution of well water pH of the study area (2004–2015)

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Effect on TDS levels

According to the Iranian National Standard, the TDS level of potable water is 1000 mg/L (Madani et al. 2016). The Schoeller graph showed that the chemical quality of 17.2% and 72.5% of wells was unacceptable for drinking purposes in 2004 and 2015, respectively. Findings showed that the TDS level of 46.1% of wells located in Sayyed Gholi, Surkan, Shahrak, and Alavi regions was above standard levels of Iran in 2004. However, the TDS of all wells was higher than the Iran National Standard in 2015 (Fig. 10). Thus, the quality of these wells is unacceptable for drinking purposes. Total dissolved solids in drinking water sources originate from factors such as natural resources, industrial wastewater, sewage, urban runoff, and chemical materials used in the water treatment plant (Bonte et al. 2013). Potable water with a high level of TDS is the primary cause of digestive difficulties. Our findings are consistent with previous results (Madani et al. 2016; Bordi et al. 2001).

Fig. 10
figure 10

Spatial distribution of well water TDS of the study area (2004–2015)

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Effect on TH levels

Soluble minerals are among the causes of water hardness. Generally, hard water is high in dissolved mineral content, mainly calcium and magnesium (Tweed et al. 2009), and it is an essential parameter in the study of water resources for drinking purposes. According to the Iranian national standard, and the WHO guidelines, the permissible limit of drinking water hardness is 200 mg/L (Bonte et al. 2013; Alavi et al. 2016). The Schoeller diagram illustrated that 62% of wells were in the range of acceptable for drinking in 2004, whereas, at the end of the study period, 13.8% and 4.4% of wells were in the category of acceptable and inappropriate quality for drinking purposes, respectively (Table 4).

Furthermore, the spatial variation maps of TH in 2004 showed that whereas the total water of wells in the Shahrak area, 50% of the wells in Surkan and 40% in Alavi regions, were higher than the standard limits, TH level of all wells were not compatible with the standard level, in 2015 (Fig. 11). Drinking water with excessive hardness can damage the urethra, kidneys, bladder, blood vessels, and stomach (Sharma et al. 2017).

Fig. 11
figure 11

Spatial distribution of well water TH of the study area (2004–2015)

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Effect on Ca+2 levels

Calcium can be naturally found in water. The natural occurrence in the earth’s crust, as well as high solubility of Ca2+, has led to its presence in groundwater (WHO 2011). According to WHO and Iranian National Standard guidelines, the acceptable limit of this element in potable waters is 200 mg/L (Alavi et al. 2016). The spatial variation maps of Ca2+ showed that during the study period, all wells had acceptable quality for drinking purposes, and the levels of the calcium ion gradually became standard from 2004 to 2015 (Fig. 12) (Raju 2007).

Fig. 12
figure 12

Spatial distribution of well water Ca2+ of the study area (2004–2015)

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Effect on Mg+2 levels

The notable feature of magnesium cations is forming the water-soluble salts. The Iranian National Standard and WHO guidelines suggest that the standard level of the magnesium in potable waters needs to be 30 and 50 mg/L, respectively (WHO 2011). The Schoeller diagram suggests that the water quality of all wells was unacceptable in the year 2015. The level of magnesium ion during the studied period changed significantly. Findings indicated that although the concentration of the Mg2+ ion in the wells of Yahyaabad and Surkan regions met the Iranian National Standard in 2004, it was above the standard in 2015 (Fig. 13) (Soleimani et al. 2018a).

Fig. 13
figure 13

Spatial distribution of well water Mg2+ of the study area (2004–2015)

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Effect on Na+ levels

Sodium cations make the water salty and the sodium level is affected by the cations exchange mechanism (WHO 2011). According to the Iranian National Standard, the maximum standard concentration of the sodium ion in potable waters needs to be 200 mg/L (Bonte et al. 2013). Results of the Schoeller diagram in 2004 suggest that although 27.6% of wells had high levels of sodium ion and the water quality was unacceptable for drinking purposes, it was 65.5% in 2015 which indicates a marked increase in the level of the sodium (Fig. 14) and consequently salinity.

Fig. 14
figure 14

Spatial distribution of well water Na+ of the study area (2004–2015)

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Although the level of the sodium ion was above standard only in wells of regions 3–5 (“Description of the study area”) in 2004, there has been a general increase in all wells of the county in 2015 (Fig. 15). Results suggested that there has been a significant decline in water quality of the wells due to a general shortage of precipitation and, consequently, drought in the area.

Fig. 15
figure 15

Spatial distribution of well water Cl− of the study area (2004–2015)

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Findings also indicated that the water quality of the wells was unacceptable for drinking and agriculture purposes from 2004 to 2015. In a study, Saito et al. investigated how global warming affects the static level and quality of groundwater resources of thirty-four wells in Japan. The present study was carried out in 27 months, and significant changes in the static level of underground waters and levels of ammonium, sodium, potassium, and magnesium ions were observed. Observed changes in temperature were around 7 °C (Saito et al. 2016). Generally, it can be said that drought, decline in precipitation, and changes in temperature during the study period are among the main causes of changes in the water quality of Saveh wells.

Effect on Cl− levels

Levels of Cl− anion play a pivotal role in the taste of water (Soleimani et al. 2018a). The standardized level of the ion in potable waters is 250 mg/L (Tweed et al. 2009). According to Schoeller diagram, 3.4 and 44.9% of the water wells were in the category of inappropriate for drinking purposes in 2004 and 2015, respectively (Table 5). Figure 15 shows the spatial distribution of Cl− changes during the studied period.

There has been a general increase in the level of Cl− during the studied period, to the extent that at the beginning of the period, the level of Cl− in most of the wells was lower than the standard, but in 2015, it was higher than the Iranian National Standard level (Fig. 15). Some natural phenomena such as high rates of vaporization, passing water through salty parts of the soil, and pumping urban or industrial sewage into the groundwater cause to raise levels of Cl− (Bordi et al. 2001). High levels of Cl− in potable water cause some diseases such as high blood pressure, kidney stone, asthma, and osteoporosis (Soleimani et al. 2018a).

Effect on SO4 2− levels

High levels of sulfate and magnesium ions may cause laxative effects (Abbasnia et al. 2019b). The Schoeller diagram suggests that levels of SO42− in 20.7 and 69% of wells were in the category of inappropriate in 2004 and 2015, respectively. According to the Iranian National Standard, the maximum amount of SO42− in potable water needs to be 250 mg/L (WHO 2011). Although there has been an increase in SO4−2 levels only in some wells in 2004, it was above standard limits in all wells in 2015 (Fig. 16).

Fig. 16
figure 16

Spatial distribution of well water SO4−2 of the study area (2004–2015)

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Even though previous works found that drought has only increased levels of Cl− in groundwater resources of Yazd desert in the center of Iran during 2000–2004, in the present study, we found that there has been a general increase in levels of both SO42− and Cl−1 anions during 2004–2015 (Soleimani et al. 2018a). Rapid population growth around wells, higher cost of living, and overuse of valuable water resources are among the common causes of the decline in the quality of groundwater in dry climates. Overuse of groundwater not only decreases the water level and its quality but also leads to subsidence (Akbari et al. 2018).

Conclusions

To investigate the causes of decline in quality and quantity of groundwater resources, the focus has always been on climate change and the prolonged drought, among which changes in the amount of precipitation directly affect soil humidity, surface flow, and variation in water resources. The shortage of rainfall in Saveh during the studied period has led to a significant decline in the chemical quality of groundwater and reusing water plays a vital role in preserving the resources and supplying water. The decline in factors such as TDS, TH, Na+, Mg2+, Cl−, and SO42− was marked. It is clear that supplying drinking water requires setting an apparatus to make a reduction in the level of water salinity and hardness or use alternative resources, if possible.