ارزیابی نوسانات سطح آب زیرزمینی دشت جیرفت با استفاده از تصاویر ماهواره‌ای grace

در چند دهه ‌ی اخیر، استفاده ی بی‌رویه از منابع آب زیرزمینی به افت سطح این آب در بسیاری از دشت‌های ایران منجر شده‌ است. با توجه به ضرورت موضوع، در این پژوهش با استفاده از تصاویر ماهواره‌ای گریس به بررسی روند تغییرات سطح آب زیرزمینی در دشت جیرفت در دوره ی 2016 2003 پرداخته شد. در این راستا، ابتدا داده‌ها در سامانه ‌ی شبکه ‌ی موتور گوگل ارث انجین با سه الگوریتم jpl، gfz و csr پردازش و نتایج آنها با داده‌های مشاهداتی (پیزومتری) 2003 تا 2016 مقایسه شد. این مقایسه، با بررسی همبستگی خطی بین تغییرات به دست آمده از الگوریتم‌ های سنجنده ‌ی grace و داده‌های مشاهداتی صورت گرفت و نتایج، همبستگی بالایی را بین الگوریتم‌ها و داده‌های مشاهداتی نشان داد. بر طبق نتایج، مدل jpl با 64 درصد همبستگی، مناسب ‌ترین مدل برای پایش سطح آب‌های زیرزمینی دشت جیرفت بود. همچنین پهنه‌بندی مکانی سطح آب زیرزمینی، با نرم افزار arcgis و روش کریجینگ صورت گرفت. نتایج پهنه‌بندی در طی 2003 تا 2016 نشان داد که افت سطح آب زیرزمینی در قسمت مرکزی، غربی و جنوب غربی دشت جیرفت بیش از سایر نقاط آبخوان است که علت آن، وجود تعداد زیاد چاه‌های بهره‌برداری و گسترش فعالیت‌های کشاورزی در این قسمت‌ها است. همچنین بررسی آماری روند نوسانات سطح این آب نیز نشان داد که هم داده‌های مشاهداتی و هم الگوریتم‌های jpl، csr و gfz، روندی کاهشی و معنی‌دار در سطح 5 درصد دارند. یکسان بودن روند داده‌‌های مشاهداتی و الگوریتم‌ها نیز از صحت نسبتاً بالای تصاویر grace در بررسی نوسانات سطح آب زیرزمینی حکایت دارد.

Evaluation of groundwater level fluctuations in Jiroft plain using GRACE satellite images

Extended Abstract1IntroductionIn recent decades, the excessive use of groundwater resources has led to a drop in groundwater levels in most plains of Iran. To this end, the use of remote sensing techniques has recently expanded to study the fluctuations of groundwater levels. GRACE satellite data is a valuable new tool for groundwater monitoring and is currently the only remote sensing satellite which is capable of monitoring groundwater level changes. Hence, considering the special and critical conditions of Jiroft plain from the point of view of water resources, the study on the identification of the change of groundwater resources (as the main water resource in the region) have special importance. Therefore, the purpose of this study is to investigate and analyze the fluctuations of groundwater levels in Jiroft plain using GRACE satellite images from 2003 to 20162MethodologyThis study investigates the trend of groundwater level changes in Jiroft plain using GRACE satellite images during 20032016. In this regard, the data was firstly processed in Google Earth Engine based on three algorithms, including JPL, GFZ, and CSR, and their results were compared with observational data (piezometric) from 2003 to 2016. This comparison was performed by examining the linear correlation between the changes obtained based on the GRACE satellite algorithms and the observational data. Also, for temporal and spatial analysis, the aquifer water level was mapped using Kriging method in ARCGIS software.3 ResultsThe results showed a good correlation between algorithms and observational data. According to the results, JPL algorithm with 64% correlation was the most suitable model for monitoring the quantity of groundwater in Jiroft plain. The results of groundwater mapping from 2003 to 2016 indicated the most drop of groundwater level in the central, western and southwestern parts of Jiroft plain, due to more wells and the expansion of agricultural activities in these regions. The examination of groundwater change trend showed that both observational data and JPL, CSR, and GFZ algorithms had a significant decreasing trend at the level of 5%. The similarity trend of observational data and algorithms also indicated the relatively good accuracy of GRACE images to investigate the groundwater level fluctuations.4Discussion and conclusionThe recent droughts and increasing the number of exploitation wells have led to the decrease in groundwater levels. Therefore, the assessment of groundwater level fluctuations of Jiroft plain is necessary. In this study, GRACE satellite data were used to evaluate groundwater level fluctuations in Jiroft plain. The results of groundwater mapping from 2003 to 2016 indicated the most drop of groundwater was related to regions with more wells and more agricultural activities that are in line with Hao et al., 2019. The study of linear correlation between the results of the three algorithms of GFZ, CSR, JPL, and piezometers, showed a good correlation between the algorithms and the observational data. According to the results of JPL model with 64% correlation, it was the most suitable model for monitoring the groundwater level in Jiroft plain. Considering the appropriate correlation obtained, it can be concluded that researchers and organizations can apply GRACE data as a lowcost and easy method to monitor and analyze groundwater level fluctuations that are compatible with the findings of Farokhnia and Morid (2014); Faraji et al., (2017) and Nabavi et al., (2020). Investigating the change trend of groundwater showed that both observational data and JPL, CSR, and GFZ algorithms have a significant decreasing trend at the level of 5%. The similarity trend of observational data and algorithms also indicated the relatively good accuracy of GRACE images to investigate the groundwater level fluctuations. The findings of Farokhnia et al., (2014) also showed the similarity of changes trend of the total water balance of the basin by the Grace satellite and the observational data.