در این پژوهش، روند نوسانهای زمانی عنصر بارش در طیفهای ارتفاعی سراسر ایرانزمین موردبررسیقرارگرفت. بدینمنظورازدادههای122 ایستگاههواشناسیکشوردردوره (2012-1992) استفاده شده است. ابتدا تمام این 122 ایستگاه در طیفهای ارتفاعی کمتر از 500 متر، 500 تا 1000، 1000 تا 1500 و بیش از 1500 متر تقسیم شدندو در ادامهبابه کارگیریآزمونغیرپارامتریمن-کندال،وجود روندمعنیداربرایسریهایزمانیماهانه وسالانه درسطوحمعنیداری95 و99 درصدموردارزیابیقرارگرفت. با توجه به نتایج بهدستآمده در این پژوهش در ارتفاعات زیر 500 متر بیشترین کاهش بارش در ماه مارس مشاهدهشده است و در مقیاس سالانه همه ایستگاهها دارای روند منفی میباشند. در ارتفاعات 500 تا 1000 متر بیشترین کاهش بارش در ماههای مارس، می و اکتبر مشاهده شده است و در مقیاس سالانه همه ایستگاهها دارای روند منفی بارندگی میباشند. در ارتفاعات 1000 تا 1500 متر بیشترین کاهش بارش در ماه فوریه و ژوئن مشاهده شده است و در مقیاس سالانه همه ایستگاهها دارای روند منفی بارندگی میباشند که این روند منفی در ایستگاههای مراغه، ارومیه، مهاباد، ماکو و بیرجند منفی معنیدار است. علاوه بر این نتایج نشان داد که در ارتفاعات بیش از 1500 متر تقریباً روند بارش در مقیاس ماهانه و سالانه در ایستگاههای بیشتری ثابت بوده و روند بارش در طیف ارتفاعی زیر 1000 متر نسبت به طیف ارتفاعی بیش از 1000 متر، تعداد ایستگاه بیشتری دارای روند منفی معنیدار هستند که این نشاندهنده این است که تغییرات بیشتر بارش در این طیف ارتفاعی میباشد. در نهایت با توجه به روند منفی بارش در تمام ایستگاه، میتوان گفت که در منطقه تغییر اقلیم رخداده است.
عنوان مقاله [English]
Study of Iran’s monthly and annual Rainfall variations in different classes
Global warming and climate change are terms for the observed century-scale rise in the average temperature of the Earth's climate system and its related effects. Multiple lines of scientific evidence show that the climate system is warming. Many of the observed changes since the 1950s are unprecedented over tens to thousands of years. In 2014, the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report concluded that "It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century. The largest human influence has been emission of greenhouse gases such as carbon dioxide, methane and nitrous oxide. Human activities have led to carbon dioxide concentrations above levels not seen in hundreds of thousands of years. Climate model projections summarized in the report indicated that during the 21st century, the global surface temperature is likely to rise a further 0.3 to 1.7 °C (0.5 to 3.1 °F) for the lowest emissions scenario and 2.6 to 4.8 °C (4.7 to 8.6 °F) in the highest emissions scenario. These findings have been recognized by the national science academies of the major industrialized nations and are not disputed by any scientific body of national or international standing.
Climate change is one of the main challenges that human being has faced since the 19th century. Anthropogenic changes in climate which leads to global warming and various side effects occurred and affected human life. The global warming leads to some significant changes in environmental, ecological and economic conditions. The spatiotemporal dynamics of vegetation colony and various biodiversity dynamics are also related to global warming. One of the main signal of global warming is the significant trends and changes in some climatic factors such as monthly, daily and annual temperature and rainfall. The spatial dynamics of climatic factors such as temperature and rainfall could also be related to global warming. In this study, we aimed to investigate the rainfall variations in different altitude ranges in Iran.
Precipitation varies from year to year and over decades, and changes in amount, intensity, frequency, and type (e.g. snow vs. rain) affect the environment and society. Steady moderate rains soak into the soil and benefit plants, while the same amounts of rainfall in a short period of time may cause local flooding and runoff, leaving soils much drier at the end of the day. Snow may remain on the ground for some months before it melts and runs off. Even with identical amounts, the climate can be very different if the frequency and intensity of precipitation differ, as illustrated, and in general the climate is changing from being more like that at Station (Stn) to that at Stn A. These examples highlight the fact that the characteristics of precipitation are just as vital as the amount, in terms of the effects on the soil moisture and stream flow. Hydrological extreme events are typically defined as floods and droughts. Floods are associated with extremes in rainfall (from tropical storms, thunderstorms, orographic rainfall, widespread extra-tropical cyclones, etc.), while droughts are associated with a lack of precipitation and often extremely high temperatures that contribute to drying. Floods are often fairly local and develop on short time scales, while droughts are extensive and develop over months or years. Both can be mitigated; floods by good drainage systems and drought by irrigation, for instance. Nonetheless, daily newspaper headlines of floods and droughts reflect the critical importance of the water cycle, in particular precipitation, in human affairs. World flood damage estimates are in the billions of U.S. dollars annually, with 1000s of lives lost; while drought costs are of similar magnitude and often lead to devastating wildfires and heat waves. The loss of life and property from extreme hydrological events has therefore caused society to focus on the causes and predictability of these events. Tropical cyclones typically have the highest property damage loss of any extreme event, and are therefore of great interest to state and local disaster preparedness organizations, as well as to the insurance industry.
Materials & Methods
The data of annual rainfall of 22 synoptic stations has been investigated during 1992 to 2012. First, we sorted these stations based on the altitude ranges into 4 classes, namely: Less than 500 meter, 500 to 1000 meters, 1000 to 1500 and more than 1500 meter above sea level. We used Man-Kendal’s nonparametric trend analysis test to detect any significant trend at 95 and 99 confidence levels (P value= 0.05 and 0.01, respectively).
Discussion and Results
The results indicated that the highest rainfall decrease was observed at the elevations below 500 meters, especially in March and in the annual scale. The highest precipitation at the elevations of 500 to 1000 meters was observed in the months of March, May and October, with the highest drop in rainfall at 1000 to 1500 meters in February and June. On the annual scale, all stations showed a negative trend in rainfall. Many stations, including Maragheh, Maku, Mahabad, Urmia and Birjand, showed a significant decrease in annual scale. The results of this study showed that elevations above 1000 meters have a higher relative stability in rainfall, while rainfall at stations below 500 meter elevations have a more time variability.
Based on the findings of this research, it can be concluded that the monthly and annual rainfall of stations located at elevations below 1000 meters have had greater and more significant changes than the rest of the stations. Thus, it can be said that the climate change has been more noticeable in the stations of this class.