پايش و تحليل تطبيقي نقش خشكسالي هواشناسي بر تغييرات سطح ايستابي چاه هاي پيزومتري دشت مرند

Monitoring and comparative analysis of meteorological drought on the groundwater level changes Marand plain

در اين پژوهش، دوره هاي متوالي خشكسالي هواشناسي و ژئوهيدرولوژيكي با استفاده از شاخص خشكسالي SPI و SWI در 6 بازه زماني (6، 9، 12، 18، 24 و 48 ماهه) در دشت مرند واقع در استان آذربايجان شرقي، بررسي شد. براي اين منظور، از داده هاي هواشناسي (متوسط بارش ماهانه) 7 ايستگاه باران سنجي در دوره آماري (91-1359) و داده هاي ماهانه سطح آب 23 چاه پيزومتري در دوره آماري (90-1380) استفاده شد. نقشه هاي مربوطه با استفاده از نرم افزار Arc Gis و با روش كريجينگ تهيه و ترسيم شدند كه پهنه هاي درگير خشكسالي در منطقه را نمايان ساخت. همچنين شديدترين خشكسالي و فراواني نسبي خشكسالي هاي هواشناسي و آب زيرزميني در طول دوره آماري به دست آمد. نتايج بررسي مقادير SPI نشان داد كه خشكسالي هواشناسي از نظر مكاني داراي روند مشخصي نمي باشد در حالي كه خشكسالي آب هاي زيرزميني به طور تصادفي در منطقه رخ نداده و تمركز آن در غرب آبخوان بيش از شرق آن بوده است. جهت بررسي اثرات خشكسالي بر افت سطح ايستابي، بهترين همبستگي بين آن ها، 0/720- با تاخير زماني 5 ماهه به دست آمد كه در سطح 1 درصد معني دار بوده و تاثيرپذيري منابع آب زيرزميني را با يك تاخير 5 ماهه نمايان مي سازد. همچنين نتايج بررسي داده هاي ماهانه سطح آب دشت مرند در دوره آماري (90-1380) نشان داد كه تراز آب زيرزميني دشت داراي روند منفي بوده كه با افت حدود 2 متر مواجه بوده است.

Introduction: Drought is a natural occurrence that occurs repeatedly or alternately and is likely to occur in almost every kind of climatic event. Also، the distinction between this phenomenon and other natural disasters is that unlike other disasters، this phenomenon gradually over a relatively long period of time to act and its effects may be delayed after a few years and more than any other natural disaster appears. Several indicators have been presented to decide the characteristics of hydrological and meteorological drought. These indicators are generally based on one or more climatic elements. The SPI and SWI indicators are similar in terms of ease in calculations and results، and use monthly precipitation data and monthly spatial data rates. The simultaneous effect of meteorological droughts on groundwater levels rarely happens. Therefore، the present study investigates the effect of meteorological droughts on the groundwater level of Marand plain and calculates the time delay of drought on groundwater level. Materials and Methods: The study area in this study is Marand Plain in East Azarbaijan Province. In this research، we used meteorological data (average monthly rainfall) of 7 rain gauge stations during the statistical period (1980-2012)، and the monthly water level data of 23 piezometric wells during the statistical period (2001-2011). The correlation between stations and piezometric wells and linear regression method was used to reconstruct the statistical defects، then SPI and SWI indices were used to study the rainfall and groundwater changes process and the analysis of drought conditions in the meteorological and underground watersheds. The SPI index is basically calculated for periods of 3، 6، 9، 12، 18، 24، and 48 months. Also، the standardized water level indicator (SWI) has been used as a criterion for assessing occur drought and wet years in the Marand plain. The purpose of the SWI index is to allow zoning of groundwater level fluctuations at the study area. Extraction of drought and wet year intensities in different scales and basin zonation for drought maps in Marand plain was first calculated by entering the monthly values in DIP software، SPI values for 12-month time series. SWI values were calculated from monthly data of piezometric stationary level surfaces، such as SPI values، with the help of DIP، Minitab and Excel software. Geostatistical Analyst was also used to decide the weather drought and groundwater drought periods for the ArcGIS software. Conclusion and Discussion: The results of the SPI values showed that meteorological drought is not of a definite local place، while groundwater droughts have not occurred randomly in the area and its concentration in the west of the aquifer is more than the east. Considering the increase in the area under cultivation، to compensate for the water needs of agricultural lands، an increase in the harvesting of underground water table has occurred in order to compensate for the need for water، indicating a tangible relationship between the rainfall and the level fluctuation in the Marand plain. Therefore، considering the increase in the area under cultivation during the years of drought in the region، the best correlation between them was -0.720 with a delay of 5 months، in order to investigate the effects of drought on the surface of the station، which was significant at 1% level It illustrates the impact of groundwater resources with a 5-month delay. Also، the results of the survey of monthly data of Marand plain surface during the statistical period (2001-2011) showed that the groundwater level of the plain had a negative trend that fell by about 2 meters. Conclusion: The SPI and SWI indices make it possible to calculate the start and end times of meteorological and groundwater droughts in a steady period of information computed by these indicators، as well as the severity، duration and frequency of droughts. Drought zoning maps using SPI and SWI values in the Arc Gis environment showed that meteorological droughts، due to the characteristics of droughts، do not have a definite spatial location، while droughts Underground water does not occur accidentally in the area and their concentration has been created at specific points in the aquifer، which have tropical and human stresses (in terms of excessive and permissible withdrawal). Although the weather factor has had the greatest impact on the level of stagnation in the Marand Plain in recent years، this crisis is the result of a set of factors، including free radicals، which is itself due to meteorological droughts; therefore، due to the trend of change The level of the stand is consistent with drought changes، it can be concluded that the drop in the surface of the Marand Plain is mainly affected by drought. According to the results of this study، it seems that continuous monitoring of drought situation and strong monitoring of harvesting، especially in severe and prolonged droughts، is very necessary to prevent a significant drop in groundwater level in the Marand plain.