ارزیابی تغییرات زمانی-مکانی رطوبت خاک در عراق (مقاله علمی وزارت علوم)
درجه علمی: نشریه علمی (وزارت علوم)
آرشیو
چکیده
تغییرات محیطی ناشی از تغییرات طبیعی و فعالیت های انسانی می تواند در میزان رطوبت خاک تأثیر بگذارد و زمینه کاهش آب خاک را فراهم آورد؛ از این رو در پژوهش حاضر برای ارزیابی تغییرات زمانی و مکانی رطوبت سطحی (2 تا 5 سانتی متری) خاک در عراق داده های رطوبت حجمی خاک با تفکیک 25/0 درجه ای و بازه زمانی روزانه در یک دوره سی ساله (1991-2020) از پایگاه داده های اقلیمی کوپرنیکوس برداشت شد. در این مطالعه برای ارزیابی روندهای زمانی و مکانی از آزمون های روند رگرسیون خطی و مان-کندال استفاده شد. بررسی ها نشان داد که رطوبت حجمی خاک در ماه های گرم کاهش و در ماه های سرد افزایش یافته است؛ به طوری که مقدار های رطوبت خاک در ماه های سرد بیش از دو برابر ماه های گرم است. ارزیابی روند سری زمانی ماهانه رطوبت حجمی خاک در عراق نشان داد که ماه های دوره سرد روند کاهشی داشته است. میانگین مکانی سالانه رطوبت حجمی خاک در عراق 164/0m3/m-3 برآورد شد. کمترین مقدار رطوبت حجمی خاک در جنوب عراق در مرز کویت (093/0m3/m-3) و بیشترین رطوبت حجمی خاک در منطقه پایکوهی شمال شرق عراق (24/0m3/m-3) است. مقدار رطوبت خاک در عراق از شمال به جنوب کاسته می شود. بررسی نقشه های روند نشان داد که بیشترین روندهای کاهشی به ترتیب در ماه های دی، بهمن و اسفند بوده است که در ماه های دوره گرم سال از وسعت پهنه های با روند کاهشی کاسته می شود. گستره جغرافیایی روندهای کاهشی روند شمال غرب–جنوب شرق داشته است و بیشتر در امتداد رودهای دجله و فرات و در اطراف دریاچه الرزازه و الثرثار مشاهده می شود. استان دیالی، میسان و به ویژه استان واسط در بیشتر ماه ها در معرض روندهای کاهشی رطوبت خاک قرار داشتند که این حکایت از در معرض خطر قرار داشتن این مناطق دارد. مناطقی که در معرض کاهش رطوبت خاک قرار داشته اند، بیشتر در معرض خطر تبدیل شدن به کانون های تولید گرد و غبار هستند. در پایان پژوهش به پژوهشگران پیشنهاد می شود که اقدام های حفاظتی مانند کاشت درختان خشکی پسند (نیاز آبی اندکی دارند) انجام شود تا از کاهش بیشتر رطوبت خاک جلوگیری شود.Examining Temporal and Spatial Variations of Soil Moisture in Iraq
This study aimed to evaluate the temporal and spatial variations in surface soil moisture in Iraq, taking into account the influence of both natural fluctuations and human activities on environmental changes. Volumetric soil moisture data with a resolution of 0.25 degrees and daily intervals covering a thirty-year period (1991-2020) were obtained from the Copernicus climate database. Trend analysis was conducted to examine temporal and spatial trends in soil moisture levels. The results indicated a decrease in volumetric soil moisture during warm months and an increase during cold months, with the latter period exhibiting soil moisture values more than twice as high as the former. Furthermore, a declining trend in volumetric soil moisture during the cold months in Iraq was observed based on the evaluation of monthly time series. The average annual volumetric soil moisture in the country was estimated to be 0.164 m3/m3. The lowest soil moisture value was found in southern Iraq near the border with Kuwait (0.093 m3/m3), while the highest value was recorded in the northeastern mountainous region of Iraq (0.240 m3/m3). Notably, there was a gradual decrease in soil moisture from north to south in Iraq. The analysis of maps revealed that the most substantial decreasing trends occurred in January, February, and March, progressively diminishing as the warm season approached. These decreasing trends were predominantly observed along the rivers of Tigris and Euphrates, as well as around the Razazah Lake and the Tharthar Lake extending from northwest to southeast. The provinces of Diyala, Maysan, and Wasit, particularly Wasit, consistently exhibited decreasing trends in soil moisture in most months, indicating their vulnerability to soil moisture reduction. Keywords: Volumetric Soil Moisture, Trend Tests, Copernicus Climate Database, Iraq Introduction:Soil surface moisture is a crucial variable in hydrological processes that influence water and energy exchanges at the Earth's surface and in the atmosphere. Accurate estimation of temporal and spatial variations in soil moisture is vital for various environmental studies. In recent years, remote sensing techniques combined with satellite observations have enabled the measurement of soil surface moisture, providing valuable global-scale information for monitoring and drought prediction (Wang & Qu, 2009). Despite its relatively small quantity, soil moisture plays a significant role in the global water cycle (McColl et al., 2017). The land of Iraq with its ancient civilization owes its existence to the life-giving rivers of Tigris and Euphrates. Despite being located in an arid belt, these rivers have mitigated the adverse effects of the high-pressure desert climate, transforming the otherwise dry and arid land into a lush and vibrant region. However, human interventions in the environment, such as dam construction on the tributaries of the rivers, as well as the impacts of global warming leading to increased temperature and irregular rainfall patterns, have resulted in changes in soil moisture in Iraq. Consequently, extensive areas of the country, particularly along the rivers of Tigris and Euphrates, have experienced a significant decrease in soil moisture. Materials & Methods:In this study, soil moisture data obtained from the Copernicus database were utilized. The dataset covered the period from 1991 to 2020 and provided daily temporal resolution and a spatial resolution of 0.25 x 0.25 degrees of latitude and longitude. The soil moisture data used in this research represented the volumetric soil moisture content measured in cubic meters of water per cubic meter of soil (m3/m3). To analyze the trend in the time series of soil moisture data, the Kendall test, a non-parametric method, was employed. The Mann-Kendall method initially introduced by Mann (1945) and further developed by Kendall (1970) was used as well. The null hypothesis of the Mann-Kendall test assumes randomness and the absence of a trend in the data series, while the alternative hypothesis (rejecting the null hypothesis) indicates the presence of a trend. A positive Z statistic indicates an upward trend in the data series, while a negative value indicates a downward trend. One notable advantage of this test is that it does not require the data to follow a normal distribution, making it robust in analyzing non-normal data. Research Findings:The average annual volumetric soil moisture in Iraq was 0.164 m3/m-3 with significant spatial variation ranging from 0.068 to 0.286 m3/m-3, indicating an uneven distribution across the country. The spatial variability coefficient was relatively high at approximately 23.6%. The southern regions of Iraq bordering Kuwait exhibited the lowest levels of volumetric soil moisture, while the highest levels were observed in Baghdad Province, gradually decreasing towards the surrounding areas. Overall, there was a northeast-southwest trend in volumetric soil moisture in Iraq with values decreasing from the northeast to the southwest. This pattern was influenced by the topography and geographical location of the rivers of Tigris and Euphrates. In the northeastern mountainous region of Iraq, the volumetric soil moisture was approximately 0.18 m3/m-3. Conversely, in the foothill region encompassing Sulaymaniyah, Kirkuk, Erbil, Dohuk, and the northern half of Nineveh Province, the moisture content exceeded 0.2 m3/m-3 and occasionally reached beyond 0.26 m3/m-3. Analyzing the monthly variations in soil moisture revealed distinct patterns. For example, in January, about 54% of Iraq experienced a decreasing trend in soil moisture. This trend extended in a northwest-southeast direction along the rivers of Tigris and Euphrates, covering provinces, such as Diyala, Wasit, Maysan, Qadsiyeh, Babol, Dhi Qar, Basra, and Mushani. In February, a decreasing trend was observed in approximately 42% of the area of Iraq. The February trend map showed similarities to the pattern observed in January, albeit with lower intensity. The spatial extent of decreasing trends widened in a northwest-southeast direction along the rivers of Tigris and Euphrates. In March, declining trends covered around 24% of the area of Iraq, particularly along the northwest-southeast direction along the Tigris River in the provinces of Diyala, Wasit, and Misan, exhibiting increased density and intensity. In April, around 12% of the area of Iraq experienced a decreasing trend. These declining trends followed a specific geographic pattern, mostly occurring along the Tigris River and including provinces, such as Diyala, Wasit, Misan, and parts of Basra. In May, a similar geographic pattern was observed, with approximately 12% of the area of Iraq exhibiting declining trends. These trends were primarily noticed along the Tigris River in Wasit, Maysan, Dhi Qar, and parts of Basra, as well as around the Al-Razzah Lake and the Al-Tharsar Lake, along with a portion of Kirkuk Province. The extent of decreasing trends decreased in June, while the extent of increasing trends expanded. In July, the extent of increasing trends surpassed that of decreasing trends. Decreasing trends covered 7.4% of the area of Iraq primarily observed around the Al-Razzah Lake and the Al-Tharsar Lake, as well as in parts of the provinces of Wasit, Maysan, and Babol. In August, decreasing trends encompassed 6% of the area of Iraq mainly witnessed around the Al-Tharsar Lake, the Al-Razzah Lake, southern Dhi Qar Province, and northern Mothni Province. The trend pattern in September mirrored that of August with declining trends covering 8% of the area of Iraq predominantly observed around the Al-Razzah Lake and the Al-Tharsar Lake and along the Euphrates River in Qadsiyeh Province, north of Mothni Province, and the center of Dhi-Qar. In October, decreasing trends affected 12% of the area of Iraq primarily noticed around the Al-Razzah Lake and the Al-Tharsar Lake, as well as along the Tigris River in the provinces of Diyala and Wasit and parts of the provinces of Qadisiyah and Dhi Qar. The trend map for November highlighted the smallest range of decreasing and increasing trends compared to other months. In this month, 97% of the area of Iraq exhibited no discernible trend. In December, a trend pattern resembling that of April was observed with 11.5% of the area of Iraq experiencing a decrease. This decrease was mainly noticed along the rivers of Tigris and Euphrates, surrounding Al-Razzazeh Lake, below Al-Hadithah Lake, and in the provinces of Diyala, Wasit, and Misan. Discussion of Results & Conclusion:For this research, we utilized soil moisture data from the Copernicus Climate Base. The data had a spatial resolution of 0.25 degrees and covered the period from 1991 to 2020 collected on a daily basis. Within the geographical extent of Iraq, we identified a total of 688 cells for analysis. To assess temporal and spatial trends, we employed linear regression trend tests and Mann-Kendall tests. In the temporal analysis, we initially explored the annual changes in soil moisture. Our findings revealed that the average volumetric soil moisture in Iraq from 1991 to 2020 was 0.1646 m3/m-3. The highest recorded soil moisture during this period was 0.1782 in 1993, while the lowest was 0.1514 in 2017. Examining the annual time series of soil moisture indicated an overall decline. Furthermore, our monthly analyses highlighted significant decreasing trends in January, February, and March with a subsequent reduction in the extent of areas exhibiting declining trends as the warmer months approached. Conversely, the increasing trends in soil moisture were more modest during the colder months but exceeded 20% during the warmer months of the year. Geographically, the decreasing trends extended from the northwest to the southeast, primarily along the rivers of Tigris and Euphrates. It is worth noting that the decrease in river flow attributed to the construction of dams in Turkey, particularly Ilisu Dam at the source of the Tigris River, might have contributed to this phenomenon. In conclusion, our research indicated an overall decline in soil moisture in Iraq over the studied period. The decreasing trends were most pronounced during the colder months, while increasing trends were more prominent in the warmer months. The geographical distribution of these trends suggested a strong influence from the rivers of Tigris and Euphrates potentially impacted by upstream dam construction. These findings provide valuable insights into the patterns of soil moisture in Iraq and can contribute to better understanding and managing water resources in the region.
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