نوع مقاله : مقاله پژوهشی

نویسندگان

1 آب و هوا شناسی، دانشکده علوم زمین، دانشگاه شهید بهشتی

2 آب و هوا شناسی شهری، دانشکده علوم زمین، دانشگاه شهید بهشتی

چکیده

هدف این پژوهش پایش خشکسالی دریاچه نئور طی دوره­های آب و هوایی دیرینه، فعلی و آینده با رهیافتی آماری-مدل­سازی است. برای دستیابی به این هدف از شاخص استانداردشده بارش-تبخیر و تعرق (SPEI) با کاربست داده­های پیمونگاهی، مدل کلان­مقیاس فیزیکی آب و هوایی (MCM) و دینامیک سیالات ژئوفیزیکی (GFDL) استفاده شد. سنجه‌های RMSE و R2 نیز برای اعتبارسنجی مدل­سازی­ها بکار برده شد. نتایج صحت‌سنجی‌های بارش و دما در مقیاس فصلی نشان داده است که مدل­سازی­­های دیرینه و پیش­نگری شده از کارایی قابل قبولی برخوردار هستند. به نظر می­رسد در شرایط دیرینه باوجود فراوانی بیشتر دوره­های خشک در فصل تابستان نسبت به زمستان؛ شدت دوره­های خشکسالی همانند توالی آن در زمستان بیشینه بوده است. افزایش شدت دوره­های خشکسالی در فصول سرد سال نشان داده است که دوره­های سرد منطقه موردمطالعه در حال گرم­تر شدن هستند و با کاهش بارش و افزایش دمای هوا به‌صورت محلی، تبخیر-تعرق در منطقه افزایش داشته است. مقایسه شاخص خشکسالی دیرینه، فعلی و آینده نشان می‌دهد که هرچند وضعیت دریاچه نئور در فصول گرم سال نسبت به دوره دیرینه با کاهش دوره­های خشک و افزایش دوره­های تر همراه است اما در شرایط آینده، فصول گرم با کاهش دوره­های تر و افزایش چشمگیر دوره­های خشک همراه خواهد بود.

کلیدواژه‌ها

موضوعات

عنوان مقاله [English]

Modeling Climate Change in order to Detect Drought Cycles at Lake Neor based on Past and Future Pridiction Approaches

نویسندگان [English]

  • Tayebeh Akbari Azirani 1
  • Mahmoud Ahmadi 1
  • Abbas Ali Dadashi Roudbari 2

1 Meteorology, Faculty of Earth Sciences, Shahid Beheshti University

2 Urban Meteorology, Faculty of Earth Sciences, Shahid Beheshti University

چکیده [English]

Extended Abstract
Introduction
The ecology of paleo-environments can provide researchers with valuable information about climate events such as cycles of drought and periods of more mesic conditions. The results of such investigations can be a significant contribution to investigation of future environmental conditions.
Materials and Methods
This research was initially conducted with the aim of monitoring current drought conditions, and revealing long-term and future droughts of northwestern Iran by calculating and modeling the standardized precipitation evapotranspiration index (SPEI). In order to assess paleoclimate conditions, the Macrophysical Climatic Model (MCM) based upon current conditions, data from synoptic, climatologic, and rain gauge stations during 1950-2016, and future climate conditions derived from the Geophysical Fluid Dynamics Model (GFDL, CM2.1) were used. To verify the reconstructed data of the past 15,000 years and modeled future data for next 83 years, two statistics, the determination coefficient (R2) and root mean square error (RMSE) were used, and eventually the standardized precipitation-evapotranspiration (SPEI) index for Drought monitoring was applied for long, current and future periods.
Results and Discussion
 
Verification of reconstructed paleoclimate temperature and precipitation and future seasonal rainfall data at Lake Neor using root mean square and error coefficients and the determination coefficient, showed that the modeled data results had significant accuracy. Initially for this study, past climatic conditions and the long-standing weather conditions of the Neor Lake in the northwest of Iran for a period of 15000 years B.P. were reconstructed using the Macrophysical Climate Model (MCM). Then present drought conditions were investigated using the observed data of the past 67 years (1960-2016). Then future weather conditions for the period 2018 to 2100 under the A1B emission scenario, which is based on the model of the GFDL, CM2.1 dynamic model, was reconstructed. Then future climatic conditions were illustrated using current data (1950-2016) from synoptic stations, climatology and rain gauges. Finally, the droughts and wet seasons of Neor Lake past, current and the future were calculated using the standardized precipitation-evapotranspiration (SPEI) index.
Reconstructed paleo precipitation data showed that the Lake Neor had a completely different rainfall pattern in spring compared to winter, fall, and summer. Spring rainfall was greater than that of winter between 15000-12000, and from 8700 to 4000 years B.P., overall precipitation was declining. Thereafter, unlike other seasons, spring rainfall at Lake Neor shows a relative increase up to the present. With increasing spring precipitation, increased vegetation cover has occurred in the Neor region since the mid-Holocene, while the trend of spring droughts appears to be due to increasing temperatures.
Other results of this study indicate that the paleo-rainfall regime of about 15,000 years B.P. in the Neor region is not fully consistent with the results those of multiproxy data extracted from sediment cores, although the occurrence of events such as Younger Drays is in agreement with existing studies.
The survey of the SPEI index of Lake Neor led to the identification of seven water phases. During the first three hydrologic phases, which lasted from 15000 to 12000 years B.P., the average rainfall (573.09 mm) of Lake Neor was higher than the long-term average of the region during past 15000 years B.P. This period probably corresponds to the recent glacial period at Lake Neor. Since 12,000 years B.P., despite considerable fluctuation in the modeled rainfall, the average precipitation of each hydrologic phase has declined relative to the long-term average.
By analyzing the temperature regenerated for the hydrologic phases of Lake Neor, we  can see evidence of the long-term increase in  temperature. In the first four hydrologic phases, from 15,000 to 11,000 years B.P., there is a  steady decrease in temperature compared to the long-term average of 8.38 ° C. Since the fifth hydrologic phase 11,000 years B.P., it has been rising, and in the sixth and seventh hydrologic phases, after 8700 years B.P., the average temperature has been higher than the long-term average.
Conclusions
The results of the current investigation has shown that the long-term climate of the Lake Neor region, although the frequency of dry cycles in the summer is more than in the winter, the intensity of winter droughts (SPEI drought Index) was greater. Demonstrating the increasing intensity of drought periods in the cold season as an important result of this study. It shows that cold periods in the study area are getting warmer and with decreasing rainfall and increasing temperature, evapotranspiration in the area has increased as well. This may have some relationship to the increased frequency of dust events.
Comparison of the long-term, current and future drought index shows that although Lake Neor experienced decreasing dry periods and an increase in longer wet periods during warm seasons in the past, in the future, the warm season of the year shows the dramatic rise in dry periods and a decrease in the wet episodes. This will be a critical factor for the survival and growth of plants, such as oak trees, that need moisture in the warm season.

کلیدواژه‌ها [English]

  • Climate Reconstruction
  • MCM Model
  • GFDL Model
  • SPEI Index
  • NW of Iran
  • Lake Neor