Investigation of Rainfall Variation of Sudan Low during the Historical Process in Southwestern Iran

Document Type : Full length article


1 PhD Candidate in Climatology, Shahid Beheshti University, Tehran, Iran

2 Associate Professor of Climatology, Shahid Beheshti University, Tehran, Iran


Rain is one of the most important elements of the atmosphere. In addition to supplying water of the natural ecosystems, the rainfall plays an irrefutable role in the atmosphere and thermodynamics. The purpose of this research is to study the behavior of the southwestern region of Iran as one of the important agricultural and industrial poles in the country. Therefore, understanding changes in rainfall from the past to now, and the readiness for the changes, should be one of the most important goals of the administration.
Material and methods 
At first, daily precipitation data of 22 stations were obtained from the Meteorological Organization of Iran. The rainfall data were used from 1957 to 2017 for a period of 8 months (October to May). In order to determine the prevalence of rainfall, the rainfall criterion is considered to be above 5 mm. In the next step, by determining 3 priorities, the frequency of the system was obtained with a continuity pattern per day. The first priority is to see the daily rainfall occurrence over 5 mm in common at all synoptic stations. The second priority is that the rain above 5 mm has occurred at least in 50% of the selected stations. If the two top priorities are not observed, in the third priority, and the precipitation is above 5 mm for at least one third of the stations (7 stations), it is acceptable as a result of atmospheric pressure on that day. The purpose of this research is to investigate the historical trend of Sudan's low pressure system in terms of durability and intensity. Thus, for selecting rainwater systems due to Sudan's low pressure, we have used surface-level maps (slp) and pressure levels of 1000 hP from database of the National Center for Atmospheric Research (NCEP / NCAR), with spatial resolution 2.5 * 2.5 degrees, for all continuity patterns. Using the optical analysis method and using the results of the Lashkari (2013) and Alfandi (1950) based on the determination of the spatial displacement of the Sudan low pressure system during the cold period; we investigated logging of the systems into the southwest region of Iran. 
Result and discussion  
There are a total of 227 days or a one-day billing system. The highest number of overnight days is in January with 53 records. The lowest number of day offs was in October and May, with 2 records. Precipitation frequency with continuity of 2 days with 306 repetitions over the course of eight months from the past to today has been superior to the prevalence of precipitation occurrence with one to several days. In other words, from October to May, the share of precipitation with duration of 2 days during the historical process is rising relative to the share of other precipitation with different lengths. Meanwhile, the maximum amount of monthly rainfall with a 2 day continuation in January is 68 with a minimum share in October and May. The precipitation with the duration of one day and the most frequent repetition occurred in January and the lowest in October. However, with the increase in the duration of the precipitation, the share of January will be lower in these rainfalls. With the exception of May, the prevalence of rainfall distribution is approximately the same for all three months. These conditions can be counted with less frequency for 4 days persistence, with the difference that they have a very small contribution to the 4-day rainfall in April and May. Rainfall with duration of five days in March and February was the most frequent with 4 and 3 occurrences, respectively. Precipitation is not formed for six days only in November and April. The precipitation of seven days is just one case in January. Here is the question that how the flow pattern of the Southwest region in the historic process has been dominated, which is increasing with two days' persistence over other rainfall. To understand the reasons for these changes, other studies are required to investigate changes in air masses and circulation patterns in the southwestern region of Iran.  
Compared with other months of the cold season, January has had the most rainfall in most stations (about 17 stations). This month can be important for agriculture and cultivation in the southwestern region of Iran. At all stations, from October to January, the slope of the high rainfall variations shows a rising pattern. Since February, except for the Yasuj station, in all other stations the frequency of precipitation is reduced at the same station. In fact, a general overview of the monthly rainfall variations in Khuzestan province shows that this area is much weaker than in other provinces from February to the end of the cold season. Certainly, this disrupted changes in the availability of atmospheric precipitation in the production, industry, agriculture and even supply of drinking water in the area. Precipitation survey in the pattern of continuity in the day showed that during the historical process from the past to the present day, the frequency and severity of precipitation with duration of 2 days was more than the precipitation occurred with duration of one or more. As the frequency of precipitation systems varied from one to five days or more, there is an increasing trend in Sudanese systems entrance into the South West region. Therefore, it can be concluded that the contribution of Sudanese low pressure precipitation is increasing in the region.


Main Subjects

پرک، ف.؛ روشنی، ا. و علیجانی، ب. (1394). واکاوی همدیدی سامانة کم‏فشار سودانی در رخداد ترسالی و خشک‏سالی‏های نیمة جنوبی کشور، مجلة جغرافیا و مخاطرات محیطی، 15: 75-90.
خلیلی، ع. (1370). شناخت اقلیمی ایران و بررسی‏های اساسی بارندگی، برنامة جامع آب کشور، وزارت نیرو، بخش‏های یک و دو.
خلیلی، ع. و بذرافشان، ج. (1383). تحلیل روند تغییرات بارندگی‏های سالانه، فصلی، و ماهانة پنج ایستگاه قدیمی ایران در یکصد و شانزده سال گذشته، مجلة بیابان، 1: 25-33.
زرین‏کمر مجد، ش. و کتیرایی بروجردی، پ.‏س. (1395). بررسی تغییرات فصل‏پذیری و ناهنجاری‏های بارش فصلی در ایران طی دورة 1977 تا 2006، مجلة پژوهش علوم و فنون دریایی، 3: 1-15.
علیجانی، ب. (1378). نوسانات زمانی و مکانی ارتفاع سطح 500 هکتوپاسکال در مدیترانه و اثر آن بر اقلیم ایران در ماه فوریه، دومین کنفرانس منطقه‏ای تغییر اقلیم، سازمان هواشناسی کشور، 13 و 14 آبان‏ماه.
غیاث‏آبادی فراهانی، ف.؛ خوش‏اخلاق، ف.؛ شمسی‏پور، ع.‏ا.؛ عزیزی، ق. و فتاحی، ا. (1397). بررسی و تحلیل تغییرات درون‏دهه‏ای روند و الگوی فضایی بارش‏های سالانه و فصلی (مطالعة موردی: نیمة غربی ایران)، نشریة تحقیقات کاربردی علوم جغرافیایی، 48: 59-79.
کتیرایی بروجردی، پ.س.؛ حجام، پ. و ایران‏نژاد، س. (1386). سهم تغییرات فراوانی و شدت بارش روزانه در روند بارش ایران طی دورة 1960 تا 2001، مجلة فیزیک زمین و فضا، 33: 67-83.
فرجی، ا. (1360). بررسی مسیر سیستم‏های فشار کم باران‏زا بر روی ایران و ارائة الگوهایی از موقعیت و چگونگی حرکت آن‏ها، پایان‏نامة کارشناسی ارشد هواشناسی، مؤسسة ژئوفیزیک دانشگاه تهران.
قائمی، ه.؛ عساکره، ح. و رضایی، ش. (1395). تحلیل طیفی میانگین سالانة کم‏فشار دریای سرخ طی دورة 1330-1389، مجلة ‏اندیشة جغرافیایی، 15: 103-111.
لشکری، ح. (1375). الگوی سینوپتیکی بارش‏های شدید جنوب و جنوب غرب ایران، رسالة دکتری، دانشگاه تربیت مدرس.
لشکری، ح. (1381). مسیریابی سامانة‏ کم‏فشار سودانی ورودی به ایران، برنامه‏ریزی و آمایش فضا، 6(2): 133-157.
لشکری، ح. (1382). مکانیسم تکوین، تقویت و توسعة مرکز کم‏فشار سودان و نقش آن بر روی بارش‏های جنوب و جنوب غرب ایران، مجلة پژوهش‏های جغرافیایی، 46: 1-18.
لشکری، ح.؛ قائمی، ه. و پرک، ف. (1391). تحلیل رژیم بارندگی منطقة جنوب و جنوب غرب ایران، مجلة اطلاعات جغرافیای سپهر، 22(85): 57-63.
لشکری، ح.؛ متکان، ع.‏ا.؛ آزادی، م. و محمدی، ز. (1395). تحلیل همدید نقش پُرفشار عربستان و رودباد جنب‏حاره‏ای در کوتاه‏ترین طول دورة بارشی جنوب و جنوب غرب ایران، فصل‏نامة علوم محیطی، 4(4): 59-74.
لشکری، ح.؛ متکان، ع.ا. و محمدی، ز. (1397). تحلیل الگوهای همدیدی منجر به بارش‏های زودرس جنوب و جنوب غرب ایران طی دورة آماری (1979-2015)، جغرافیا و برنامه‏ریزی، 64: 247-266.
محمدی، ب. (1390). تحلیل روند بارش سالانة ایران، مجلة جغرافیا و برنامه‏ریزی محیطی، 43: 95-106.
محمدی، ح.؛ اکبری، م.؛ فتاحی، ا. و شمسی‏پور، ع.‏ا. (1391). تحلیل دینامیکی سامانه‏های سودانی و رخداد بارش‏های سنگین در جنوب غرب ایران، تحقیقات کاربردی علوم جغرافیایی، 24: 7-23.
مفیدی، ع. (1378). کم‏فشار سودانی مکانیسم بارش‏زا در جنوب و جنوب‏ غرب ایران، نشریة جغرافیا، 1، آموزش و پرورش منطقة 17: 47-55.
مفیدی، ع. و زرین، آ. (1384). تحلیل سینوپتیک سامانه‏های کم‏فشار سودانی (مطالعة موردی طوفان دسامبر 2001)، فصل‏نامة جغرافیایی سرزمین، 6: 24-48.
مفیدی، ع. و زرین، آ. (1385). بررسی سینوپتیکی تأثیر سامانه‏های کم‏فشار سودانی در وقوع بارش‏های سیل‏زا در ایران، فصل‏نامة تحقیقات جغرافیایی، 77: 1-24.
مفیدی، ع. و زرین، آ. (1385 الف). تحلیلی بر ماهیت و ساختار مراکز پُرفشار و کم‏فشار (قسمت اول)، مجلة رشد آموزش زمین‏شناسی، 46: 53-61.
مفیدی، ع. و زرین، آ. (1385ب). تحلیلی بر ماهیت و ساختار مراکز پُرفشار و کم‏فشار (قسمت دوم)، مجلة رشد آموزش زمین‏شناسی، 47: 54-58.
Alijani, B. (1999). The temporal and temporal fluctuations of the surface level of 500 hectares in the Mediterranean and its effect on the climate of Iran in February, the 2nd Regional Climate Change Conference, Iran's Meteorological Organization, 13th and 14th of November.
Akinremi, O.; Mcginn S.M. and Cutforth, H. (2001). Seasonal and Spatial Patterns ofRainfall Trends on the Canadian Prairies, Notes and Correspondence, 2177.
Angel, J.R. and Huff, F.A. (1997). Changes inheavy rainfall in Midwestern United States, Journal of water Resources planning andmanagement, July/August. 246-249.
Brunrtti, M.; Maugeri, M. and Nanni, T. (2000). Variation of Temperature and precipitation in Itly from 1866 to 1995, Theor.Apl.Climatol., 65.
De Luis, M.; Raventos, J.; Gonzalez-Hidalgo, J.C.; Sanchez, J.R. and Cortina, J. (2000). Spatial analysis of rainfall trends: a cause of study in Valencia region (Spain), International journal of climatology, 20: 1451-1469.
De Luis, M.; Gonzalez-Hidalgo, J.C.; Longares, L.A. and Martín-Vide, J. (2010). Changes in seasonal precipitation in the Iberian Peninsula during 1946–2005, Global and Planetary Change, 74(1): 27-33.
Diop, L.; Bodian A. and Diallo, D. (2016). Spatiotemporal trend analysis of the mean annual rainfall in Senegal, European scientific journal, 12(12): 231-245.
Elfandy, M.G. (1950a). Effects to topography and other Factors on the Movement of lows in the Middle Eastand Sudan,  Bull.Amr. Met. Soc., 31: 375-381.
Faraji, I. (1981). Investigating the Paths of Low-Pressure Systems on Iran and Providing Patterns of Position and How to Move them, MSc Thesis of Meteorology. Institute of Geophysics, University of Tehran.
Ghyasabadi, F.; Khoshakhlagh, F.; Shamsipour, A.K.; Azizi, GH. And Fatahi, E. (2018). Analysis of inter-decade changes in trends and spatial patterns of annual and seasonal precipitation, case study: West of Iran, Researches in Geographical Sciences, 18(48): 59-78.
Ghaemi, H.; Asakreh, H. and Rezaei, SH. (2016). Spectral analysis of the annual average low pressure of the Red Sea during the period 1330-2009, Journal of Geospatial, 15: 103-111.
Gitau, M.) 2016(. Long term seasonality of rainfall in the southwest Florida Gulf coastal zone, Climate Research, 69: 93-105.
Hidalgo G.J.C.; De Luı´s, M.; Ravento´ s, J. and Sa´nchez, J.R. )2003(. Daily rainfall trend inthe Valencia Region of Spain, Theor. Appl.Climatol. 75, 117–130.
Haigh, M.J. (2014). Sustainable management of head water resources: the Nairobi headwater declaration (2002) and beyond, Asian J. Water, Environ. Pollut., 1(1-2): 17-28.
Karl, T.R. and Knight, R. )1998(. Secular trends of precipitation amount, frequency, and intensity in the United States, Bulletin of the AMS, 79: 231-241.
Katiraei Brojerdi, P.S.; Hejam, P. and Iran Nezhad, S. (2007). The Contribution of Frequency and Intensity of Daily Precipitation to the Precipitation Process of Iran During 1960 to 2001, Journal of the Earth and Space Physics, 33: 67-83.
Khalili, A. (1991). Climatic recognition of Iran and fundamental surveys of rainfall, comprehensive water plan of the country, Ministry of Energy, Sections one and two.
Khalili, A. and Bazrafshan, J. (2004). An Analysis of the Changes in Annual, Seasonal, and Monthly Rainings in Five Iranian Old Stations in 116 Years, Journal of desert, 1: 25-33.
Langat, P.K.; Kumar, L. and Koech, R. (2017). Temporal Variability and Trends of Rainfall and Streamflow in Tana River Basin, Kenya. Sustainability, 9, 1963.
Lashkari, H. (1996). Synoptic Pattern of Severe Precipitation of Southwest Iran, Ph.D. Thesis, Tehran, Tarbiat Modarres University.
Lashkari, H. (2002). Route of Sudanese Systems Entry into Iran, Journal of Modares, 2: 133-160.
Lashkari, H. (2003). Genesis Mechanism, Strengthening and Developing Sudan's Low Pressure Center and its Role in South and Southwest Iran, Journal of Geographical Research, 46: 1-18.
Lashkari, H.; Ghaemi, H. and Parak, F. (2012). Analysis of the rainfall regime in the south and southwest of the Iran, Journal of Sepehr Geography Information, 22(85): 57-63.
Lashkari, H.A.; Matkan, A.K. and Mohammadi, Z. (2018). Analysis of patterns of consistency led to premature precipitation in south and southwest of Iran during the statistical period (1979-2015), Journal of Geography and Planning, 64: 247-266.
Lashkari, H.; Metcanan, A.K.; Azadi, M. and Mohammadi, Z. (2016). The analysis of the role of Saudi high pressure and tropical rainbow in the shortest period of the southern and southeast of Iran, Quarterly Journal of Environmental Science, 4: 59-74.
Liebmann, B.; Vera, C.S.; Leila Carvalho, M.V.; Camilloni, I.S.A.; Hoerling, M.P.; Allured, D.; Barros, V.R.; Ba´ Ez, J.N. and Bidegain, M. )2004(. An Observed Trend in Central South American Precipitation, Journal of Climate, 17: 4357-4367.
Mohammadi, H.; Akbari, M.; Fatahi, I. and Shamsipour, A.A. (2012). Dynamic Dynamic Analysis of Sudan Systems and Heavy Rainfall Events in Southwest of Iran. Journal of Applied Geosciences Research, 24: 7-24.
Mohammadi, B. (2011). Annual Iran rainfall analysis, Journal of Geography and Environmental Planning, 43: 106-95.
Mofidi, A. (1999). Sudan Low Pressure Precipitation Mechanism in South and Southwest Iran, Journal of Geography, 1: 47-55.
Mofidi, A. and Zarrin, A. (2005). Synoptic Analysis of Low Pressure Systems (Thousand Case Study of December 2001, Journal of Geographic Land Code, 6: 24-48.
Mofidi, A. and Zarrin, A. (2006). An Analysis of the Nature and Structure of High Pressure and Low Pressure Centers (Part I), Journal of the Growth of Geological Education, 46: 53-61.
Mofidi, A. and Zarrin, A. (2006). An Analysis of the Nature and Structure of High Pressure and Low Pressure Centers (Part II), Journal of the Development of Geological Education, 47: 54-58.
Mercy, I. C. (2015). Trend analysis of rainfall pattern in Enugu state, Nigeria, European Journal of Statistics and Probability, 3(3): 12-18.
Merabtene T.; Siddique M. and Abdallah, SH. (2016) Assessment of Seasonal and Annual Rainfall Trends and Variability in Sharjah City, UAE, Advances in Meteorology, vol., Article ID 6206238, 13 pages.
Parak, F.; Roshani, A. and Alijani, B. (2015). An Analysis of the Sudan Low Pressure System in the Southern Hemisphere and Southern Drought, Journal of Geography and environmental hazards, 15: 75-90.
Serrano, A.; Mateos, V.L. and Garcia, J.A. (1999). Trend Analysis of Monthly Precipitation Over the Iberian Peninsula for the Period 1921-1995 phys, Chem. EARTH (B), 24: 85-90.
Tabari, H.; Taye, M.T. and Willems, P. (2015) Statistical assessment of precipitation trends in the upper Blue Nile River basin Stoch Environ Res Risk Assess, DOI 10.1007/s00477- 015-1046-0.
Taxak A.K.; Murumkar A.R. and Arya, D.S. (2014) Long term spatial and temporal and homogeneity analysis in Wainganga basin, Weather and Climate Extremes, 4: 50-61.
Turkes, M. (1996). Spatial and temporal analysis of annual rainfall variations in turkey, I. Journal of Climatology, 16: 1057-1076.
Turkes, M. (1999). Vulnerability of Turkey to desertification with respect to precipitation and aridity condition, Turkish Journal of Engineering and Environmental Science, 23: 363-380.
Zarrinkamar Majd, SH. and Katiraei Brojerdi, P.S. (2016). Changes in Seasonality and Seasonal Rainfall Abnormalities in Iran during 1977-2006, Journal of Marine science and technology research, 3: 1-15.
Volume 51, Issue 2
July 2019
Pages 373-387
  • Receive Date: 30 December 2018
  • Revise Date: 30 April 2019
  • Accept Date: 30 April 2019
  • First Publish Date: 22 June 2019