Document Type : Research Paper
Authors
1 M.Sc. Student of Water Resource Management, Department of Irrigation & Reclamation Eng, College of Agriculture & Natural Resources, University of Tehran, Karaj, Iran.
2 Professor, Irrigation & Reclamation Eng, Dept., College of Agriculture & Natural Resources, University of Tehran, Karaj, Iran.
3 Assistant Professor, Soil Conservation and Watershed Management Research Institute (SCWMRI), ARREO, Tehran, Iran.
Abstract
Keywords
Main Subjects
In recent years, the indiscriminate extraction of groundwater and poor management of water resources has resulted in a significant decline in groundwater levels many regions of the country. As a result, effective groundwater monitoring is essential. However, designing and implementing a comprehensive groundwater level monitoring network is both costly and time-consuming. In this context, remote sensing technology offers a promising solution for monitoring fluctuations in groundwater levels.the study aims to evaluate the accuracy and precision of remote sensing data in estimating changes in groundwater levels compared to the measurements collected from observation wells.
The groundwater level has been monitored for 20 years using 173 observation wells the Qazvin aquifer . The hydrograph indicates that, on average, the groundwater level has dropped by nearly 20 meters during this period.
Data from 173 groundwater observation wells in the Qazvin Plain were used to calculate the monthly and annual Groundwater Resources Index (GRI) from 2002 to 2022. This index shows the behavior and the trend of groundwater decrease/increase during the several years in the study area. This index was calculated monthly for the whole study area from 2002 to 2022. The time series of GRI is presented in Figure 4.
(GRACE) satellite can detect fluctuations in groundwater. Monthly groundwater fluctuation data is available from (NASA) at three centers (JPL, GFZ, CSR) from 2002 to the present. These data were extracted for the study area. The time series of groundwater fluctuation presented at Figure 7.
Statistical tools such as (R2, R, …) are used for validation and accuracy of The GRACE (JPL, CSR) satellite dat and Index (GRI) over the period from 2002 to 2022.
In this research, GRACE (JPL, CSR) satellite data and Index (GRI) were utilized to compare groundwater level fluctuations in the Qazvin Plain over a 20-year period.
The hydrograph of groundwater observation wells reveals a sharp decline in groundwater levels . also shows groundwater level dropping sharply by about 15 meters during the last 3 years of the study period. the maximum and minimum drops in groundwater levels observed in the wells are 10.99 meters and 0.77 meters, respectively, occurring in mid-spring and mid-fall.
The GRI results indicate a trend of decreasing groundwater levels over the 20-year period, with the eastern and central regions of the plain being more significantly affected. Furthermore, the GRI demonstrates that the first eight years correspond to a wet period, while the final three years reflect a dry period.
The JPL and CSR products of the GRACE satellite both exhibit a downward trend from 2002 to 2022, indicating a decline in groundwater levels. the JPL product presents slower fluctuations compared to the CSR product. Additionally, from 2018 to the end of the period, both products demonstrated greater fluctuations than in the earlier years.
Both the GRACE data and the GRI index displayed similar decreasing trends in groundwater levels. To assess accuracy and validity, the following statistical indicators were employed: determination coefficient (R²), correlation coefficient (R), mean absolute error (MAE), and Nash-Sutcliffe coefficient (NSE). According to the results (Table 2), all four statistical indicators yielded favorable values, underscoring the high accuracy of the GRACE satellite data. The CSR product demonstrated a high correlation coefficient of R = 0.91 indicating very high accuracy. The JPL product achieved a Nash-Sutcliffe coefficient of NSE = 0.72, reflecting good model efficiency.
The statistical indicators demonstrated the high accuracy of the GRACE satellite data, which exhibited a similar decreasing trend, with the CSR model identified as the most suitable for monitoring these fluctuations. Moiwo et al. (2012) conducted similar research in China, and their findings indicated a lower correlation compared to the results of this study. Additionally, Famiglietti et al. (2011) reported a significant decreasing trend in groundwater levels in their research. Both the JPL and CSR products of the GRACE satellite effectively represent observed groundwater data, validating their application for monitoring groundwater levels.
Given the GRACE satellite's capabilities for rapid estimation, access to real-time data, and cost-effective monitoring of groundwater fluctuations, this data can play a crucial role in groundwater management, decision-making, drought and wetness estimation, and forecasting aquifer levels in the region. Therefore, this research recommends the use of both GRACE (CSR and JPL) satellite products, which effectively represent observed groundwater data and validate their application for monitoring groundwater levels.
“Conceptualization, methodology, validation, Abdeh Kolahchi, A.; software, formal analysis, Ranjbar, S.; and Abdeh Kolahchi, A.; investigation, resources, data curation, Abdeh Kolahchi, A. and Ranjbar, S.; writing—original draft preparation, writing—review and editing, visualization, supervision, project administration, funding acquisition, Kholgi, M., Ranjbar, S. and Abdeh Kolahchi, A. .
All authors have read and agreed to the published version of the manuscript.”
Data available on request from the authors.
The authors would like to thank all participants of the present study.
The authors avoided data fabrication, falsification, plagiarism, and misconduct.
The author declares no conflict of interest.
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