پیش‌نگری دوره‌های خشک و مرطوب متوالی در ایران مبتنی‌بر برونداد همادی مدل‌های تصحیح شده اریبی cmip6

تغییر اقلیم می‌‌‌تواند شدت و فراوانی رخدادهای فرین اقلیمی مرتبط با بارش را در آینده تغییر داده و فشار بیشتری بر دسترسی به منابع آب ایجاد کند. این مطالعه به پیش نگری بلند‌‌مدت روزهای خشک (cdd) و مرطوب (cwd) متوالی ایران پرداخته است. برای این منظور از داده های بارش 41 ایستگاه همدید کشور و برونداد بارش پنج مدل منتخبcmip6  شامل gfdlesm4, ipslcm6alr, mpiesm12hr, mriesm20, ukesm10ll در دوره تاریخی (2014–1975) و دو دوره آینده (20602021 و 21002061) تحت سناریوهای مبتنی‌بر مسیرهای اجتماعی و اقتصادی (ssps) استفاده شد. برای درستی‌‌سنجی برونداد بارش مدل‌های منتخب از سنجه های آماری r، rmse، mbe و جدول توافقی مهارتی (roc) استفاده شد؛ سپس روزهای خشک و مرطوب متوالی با استفاده از شاخص های cdd و cwd کارگروه etccdi محاسبه شد. نتایج درستی‌‌سنجی مدل های منفرد نشان داد از بین پنج مدل cmip6، مدل ipslcm6alr دارای بیشینه کم‌برآوردی و ukesm10ll بیشینه بیش برآوردی برای بارش ایران است. پس از بررسی مهارت فردی مدل ها یک مدل همادی با به‌کارگیری روش میانگین وزنی مستقل (iwm) ارائه شد. امتیاز مهارتی پس از ایجاد مدل همادی چندگانه (mme) بهبود قابل‌ملاحظه ای یافت. نتایج این مطالعه شواهدی را ارائه می دهد که بی هنجاری دوره های خشک متوالی به‌عنوان یک نمایه استاندارد برای خشکسالی های کوتاه‌مدت تحت شرایط تغییر اقلیم در ایران افزایشی است. بیشترین افزایش روزهای خشک متوالی در ایران با حداکثر 4/26 روز تحت سناریوی ssp58.5 در دوره 21002061 در حوضه های آبخیز دریای خزر و دریاچه ارومیه خواهد بود.

Projected consecutive dry and wet days in Iran based on CMIP6 bias‐corrected multi‐model ensemble

Climate change with changes in precipitation patterns around the world can cause significant changes in the frequency, intensity and duration of precipitation events. In the context of climate change and with the increase of extreme climate events, irreparable consequences are imposed on the environment and the economy. Therefore, it is necessary to have an appropriate understanding of the frequency, intensity and spatial distribution of these extreme events in order to take a fundamental step in preventing damage caused by them. The purpose of this study is to analyze the characteristics of consecutive dry/wet days during 19752014 and 20212100 based on the output of CMIP6 models. In this regard, the evaluation of CMIP6 models against gauge precipitation data has been done in Iran.In this study, historical precipitation (19752014) and scenariosbased output of CMIP6 models under shared socioeconomic pathways (SSPs) in the two future periods (20212060 and 20612100) were used. Basic statistics of r, RMSE, MBE and receiver operating characteristic (ROC) were used to validate the precipitation output of selected models (GFDLESM4, IPSLCM6ALR, MPIESM12HR, MRIESM20, UKESM10LL). Then, consecutive dry and wet days were calculated using the CDD and CWD indices of the Expert team on climate change detection and indices (ETCCDI). After examining each individual model, an ensemble model is applied with independent weighted mean (IWM) method.The results showed that among the five CMIP6 models, the IPSLCM6ALR model has the most underestimation and the UKESM10LL has the most overestimation for Iran precipitation. The average amount of precipitation bias in the whole country for GFDLESM4 (2.56), IPSLCM6ALR (2.29), MPIESM12HR (2.89), MRIESM20 (2.18), and UKESM10LL (2.53) mm were calculated. The skill score is improved significantly by applying the multi model ensemble (MME). Consecutive dry days in Iran will increase by a maximum of 26.4 days under the SSP58.5 scenario in the period 20612100 for the Caspian Sea and Lake Urmia basins. In contrast, consecutive wet days will decrease in these two basins.Validation results for the period of 19752014 showed that (compared to observations), CMIP6 models have a high performance in estimating precipitation in Iran. However, despite the uncertainties in precipitation change, the CMIP6 results provide evidence that the anomaly of consecutive dry and wet periods is an indicator for shortterm droughts under increasing climate change conditions. Consecutive dry days will increase significantly in the north and northwest of Iran in the future.The maximum changes related to CDD and CWD indices are observed under SSP5–8.5 scenario, while the lowest frequency for both indices is under SSP1–2.6 scenario. Examination of CDD and CWD anomalies showed that even in the optimistic scenario (SSP12.6), drought responses to climate change are significant. Consecutive dry periods are increasing in most of the northern, northwestern and northeastern regions of Iran. It is urgent to consider these changes in the hydrological cycle as a tool to improve water management, especially in the northern and northwestern regions of Iran. Also, in some areas, such as the southeast and the coasts of the Persian Gulf, there is a significant decrease in consecutive dry periods, which indicates an increase in precipitation on a seasonal and interannual scale in the future.