واکاوی سامانه بارشی‌ مولد سیلاب تیرماه 1394 شهرستان سقز در استان کردستان

واکاوی سامانه‌های بارشی امکان شناسایی الگوهای جوی منجر به سیل و پیش‌بینی آن را فراهم می‌کند. بنابراین در این پژوهش، بارش سنگین و سیل‌زای 27 تیرماه 1394 شهرستان سقز در استان کردستان مورد واکاوی همدیدی قرار گرفت. بدین منظور از نقشه‌های متوسط فشار سطح دریا و ارتفاع ژئوپتانسیل سطوح 700، 850، 500 و 300 هکتوپاسکال و همچنین نقشه‌های امگا، آب قابل‌بارش و رطوبت نسبی استفاده شد. تحلیل این نقشه‌ها برای دو روز قبل و یک روز بعد از وقوع سیل صورت گرفت. بررسی‌های آماری نشان داد که در سامانه بارشی مورد مطالعه در کمتر از 45 دقیقه ایستگاه همدید سقز و ایستگاه باران‌سنجی کسنزان به‌ترتیب 7/29 و 64 میلی‌متر بارش دریافت کرده‌اند. واکاوی همدیدی نیز نشان داد سامانه پرفشار مهاجر اروپایی و زبانه کم‌فشار عربستانی باعث بارش‌های شدید در این روز شده است که دریای مدیترانه، دریای سیاه و دریای سرخ نیز در تقویت رطوبت این سامانه‌ نقش داشته‌اند. در روز قبل از شروع بارش در سطح زمین سامانه پرفشار اروپایی از سمت شمال‌‌غرب و زبانه کم‌فشار عربستانی از طرف جنوب‌‌غرب به کشور نزدیک شده‌اند و در روز وقوع سیل ادغام این دو سامانه باعث بارش سنگین شده است. در سطوح بالایی جو نیز در روز قبل از شروع بارش محور ناوه در امتداد ترکیه، عراق و خلیج‌فارس واقع شده است. با جابه‌جایی موج کوتاه و تغییر موقعیت محور آن به‌طرف شرق و نزدیک‌تر شدن آن به منطقه، مراکز فشار در سطح زمین نیز به‌طور هم‌زمان پیشروی کرده است. در این حالت، تمام منطقه غرب کشور، در زیر شرق محور ناوه موج کوتاه قرار گرفته و باعث تشدید ناپایداری و صعود هوای مرطوب شده است و شرایط را برای ریزش بارش‌های سیل‌آسا در منطقه فراهم نموده است. لذا مدیریت جامع حوزه‌های آبخیز به‌عنوان یکی از راهکارهای مناسب برای سازگاری و تاب‌آوری در برابر سیلاب ضرورت می‌یابد.

analysis of rainfall system, leading to floods in july 2015 in saghez city in kurdistan province

floods are among inevitable hazards but its frequencies and volumes can be varied due to climate change. a comprehensive analysis of synoptic status can be useful for predicting similar events in the future. it is therefore very important for a good environmental management. flash flood of july 2015 in saghez was a catastrophe and did severe damage. in order to analyze the catastrophic precipitation, sea level pressure, 300 hpa, 500 hpa, 700 hpa, 850 hpa maps along with omega, perceptible water map and humidity maps were investigated and analyzed, starting two days before the rainfall until the end of rainfall and even a day after. results show that immigrant european high-pressure system along with arabian low-pressure tongue have caused intense rainfall during the day. mediterranean sea, black sea and red sea have been effective in enhancing the system too. a day before the rainfall, at surface level, a high-pressure european system from the north west and the low-pressure tongue from the south west were approaching the country and the combination of these two systems have caused intense rainfall on the region. ag the higher level, trough axis was over turkey, iraq and persian gulf. short waves displacements along with change in axis positioning eastward caused pressure centers in the surface level to get closer. at this time, all the western part was located under the eastern axis short wave trough, causing intensifying instabilities along with uplifting humid weather and finally a catastrophic intense rainfall on saghez and its surroundings on july 18 2015. it is important to pay attention to comprehensive watershed management as one of the major strategies for adaptation and resilience in flood-prone areas.extended abstract1. introductionenvironmental hazards have always changed and threatened various aspects of life throughout the history of human life. flood is one of the most harmful risks, which is always associated with economic damage and in some cases with human casualties. with the highest relative incidence of natural disasters in the world (about 40%), a flood has not only caused great damage but also made many people homeless and immigrate to other countries. precipitation is one of the most important atmospheric and effective parameters in floods that plays a vital role in the natural environment. however, its abnormal and irregular behavior can cause great damage to the natural and human environment. one of the most important consequences of global warming is the increase in the frequency of large and rare precipitation events due to rising atmospheric humidity and the activity of large-scale storms and tropical storms that occur every year around the world, with floods killing a number of people and rendering thousands of cubic meters of fresh water and thousands of tons of valuable soil inaccessible. therefore, the analysis of these precipitation systems is very important to know the mechanism and predict them.2. materials and methodsthis study is based on the method of environmental analysis to focus on atmospheric circulation, so that based on the occurrence of floods, synoptic patterns of this phenomenon have been identified. in order to accurately study the flood that occurred on july 18, 2015, the precipitation data of saghez station were synchronized and the synoptic maps of different atmospheric levels from 10 to 70 degrees north latitude and zero to 70 degrees east longitude taken from noaa from 48 hours before the flood up to one day after its occurrence were studied. so the synoptic patterns of the mentioned flooding system were analyzed at different levels of the atmosphere for four consecutive days. the geographical area was selected to include all atmospheric systems affecting the study area.3. resultsthe results showed that the high-pressure system of european immigrants and the low pressure of saudi arabia caused heavy rainfalls on this day. furthermore, the mediterranean sea, black sea and the red sea also played a role in strengthening the humidity of these systems. the day before the rainfall, the european high-pressure system from the northwest and low-pressure saudi arabia from the southwest approached iran, and on the day of the flood, the merging of the two systems caused heavy rainfall in the region. at the upper levels of the atmosphere, the day before the onset of rainfall, the trough axis was located along with turkey, iraq and the persian gulf, and west of the region’s borders. by moving the short wave and shifting its axis to the east and getting closer to the region, the pressure centers on the ground have also advanced simultaneously. in this case, the whole western region of the country was located below the east axis of the shortwave and has intensified instability and rising humid air and has provided the conditions for heavy rains in the region.4. discussionthe mechanism of the studied heavy rainfall system showed that these rainfalls are due to high-pressure european migratory systems and low-pressure saudi arabia, which absorb a lot of moisture by passing through water zones and colliding with these two cold systems. and hot, the conditions for the formation of the front and instability are provided and lead to heavy rainfall in the west of the iran. dustan and mirdrikvand (2013) in the study of heavy and pervasive rainfall in western iran showed that low-pressure southern currents and the placement of a high-pressure pattern on the arabian sea are effective factors in rainfall in this region. examination of humidity and perceptible water maps showed that the mediterranean sea, black sea and red sea have an important role in providing rainfall moisture of this system, which is consistent with the studies of arvin et al. (2013) and ahmadi and jafari (2015).5. conclusionflood event july 18, 2015; it is one of the unprecedented and destructive floods in the western half of the iran. in this regard, the synoptic maps of the earth’s surface and the upper atmosphere were analyzed. the results showed that in the period under study, first a cold air mass after passing over europe and the northern mediterranean sea and the black sea and finally turkey and iraq entered the western and northwestern regions of iran. also, the warm air mass entered western iran by forming in northeastern africa and saudi arabia, crossing the red sea, absorbing moisture from this sea and moving to the north of saudi arabia and iraq. the approximate coexistence of these two warm and cold air masses and also the continuation of warm air mass during rainy days can be the main cause of the mentioned heavy rainfall in the west of the iran.