پايش خشكسالي بر مبناي شاخص بارش- تبخير و تعرق استاندارد شده (SPEI) تحت تأثير تغيير اقليم

آب و خاک  

دوره 29 - شماره 2

نوع مقاله: Original Article
چكيده: ويژگي‌هاي خشكسالي به عنوان يكي از وقايع محيطي، در دوره‌هاي آتي ممكن است تحت تأثير تغييرات اقليمي تغيير نمايد. در اين تحقيق با بررسي شاخص‌هاي بارش- تبخير و تعرق استاندارد شده (SPEI)، شناسائي خشكسالي (RDI) و بارش استاندارد شده (SPI)، از شاخص SPEI براي پايش وضعيت خشكسالي ايستگاه سينوپتيك همدان تحت تأثير تغيير اقليم در دهه‌هاي آتي استفاده شده‌است. بدين منظور دورة۲۰۱۰-۱۹۸۱ به عنوان دورة پايه انتخاب و شبيه‌ سازي شرايط اقليم آتي بر مبناي سناريوهاي انتشار A۱B، A۲ و B۱ و اجراي گروهي داده‌هاي ۵ مدل گردش عمومي جو با استفاده از مدل LARS-WG۵ در دوره آماري ۲۰۴۰-۲۰۱۱ انجام شد. با شبيه‌سازي مقادير بارش و دما، شاخص‌هاي SPEI، RDI و SPI در مقياس‌هاي زماني سالانه و هم‌چنين ۱ و ۳ و ۶ ماهه (كوتاه‌مدت) و ۱۲، ۱۸ و ۲۴ ماهه (بلندمدت) براي دوره‌هاي پايه و آتي محاسبه و ارتباط بين آن‌ها بررسي گرديد. در ادامه، با پايش وضعيت‌هاي رطوبتي از طريق شاخص SPEI، ويژگي‌هاي دوره‌هاي خشك و مرطوب بر مبناي تئوري ران استخراج و براي دوره‌هاي پايه و آتي با هم مقايسه شدند. نتايج شبيه‌سازي اجراي گروهي مدل‌ها نشان‌داد طي سه دهة آينده بر اساس نتايج سناريوي محتمل A۲، دماي متوسط و بارش نسبت به دورة پايه به ترتيب 0.82 درجه سانتي‌گراد و2.5درصد افزايش مي‌يابند. پايش وضعيت رطوبتي بر مبناي شاخص SPEI نيز نشان‌دهندة تغييرات زياد شرايط رطوبتي در دهة اول پيش‌بيني، نسبت به دهه‌هاي دوم و سوم مي‌باشد. هم‌چنين انتظار مي‌رود در مقياس‌هاي بلندمدت تعداد دوره‌هاي خشك كاهش و تداوم طولاني‌ترين دوره خشك و متعاقب آن حجم كمبودها نسبت به دورة پايه افزايش يابند. علاوه بر اين انتظار مي‌رود مجموع حجم مازادها در دوره‌هاي مرطوب نسبت به دوره پايه كاهش يابد كه مي‌تواند بيانگر افزايش كمبود رطوبتي در دهه‌هاي آتي باشد.
Drought Monitoring Based on Standardized Precipitation Evaoptranspiration Index (SPEI) Under the Effect of Climate Change
Article Type: Original Article
Abstract: Introduction: Drought is a natural and recurrent feature of climate. The characterizations of it may change under the effect of climate change in future periods. During the last few decades a number of different indices have been developed to quantify drought probabilities. Droughts are caused by disruptions to an expected precipitation pattern and can be intensified by unusually high temperature values. Precipitation-based drought indices, including the Standardized precipitation index (SPI), cannot identify the role of temperature increase in drought condition and in addressing the consequences of climate change. Recently, two new standardized drought indices have been proposed for drought variability analysis on multiple time scales, the Reconnaissance Drought Index (RDI, Tsakiris et al., 2007) and the Standardized Precipitation Evapotranspiration Index (SPEI, Vicente-Serrano et al., 2010). The objective of this study is to evaluate the characterization of wet and dry periods under the effect of climate change according to SPEI index in synoptic station of Hamedan for the next thirty years (2011-2040).
Materials and Methods: In this study, the indices of SPEI, SPI and RDI were investigated and the SPEI index as a multiscalar and suitable index was used to detect, monitor, and explore the consequences of global warming on drought conditions in synoptic station of Hamedan (airport). For this purpose, the period of 1981- 2010 was chosen as the base period and the simulation of the future climate variables were done based on A1B, A2 and B2 emissions scenarios and performance of multi model ensemble via LARS-WG5 model for the period of 2011-2040. The performance of the multi model ensemble was done by using five global climate models including IPCM4, MPEH5, HADCM3, GFCM21, and NCCCS in the IPCC Fourth Assessment Report (Semenov and Stratonovitch, 2010). By simulating the values of precipitation ,and the values of temperature and the values of estimated evapotranspiration , the values of SPEI, RDI and SPI indices were calculated annually and 1, 3 and 6 months (short- term period) and 12, 18 and 24 months (long- term period) time scales for the base period and the three next decades. Then, the relation among them was computed and investigated via correlation coefficient. Then, by monitoring the humidity condition via SPEI index, the characterization of wet and dry periods including period numbers, longest period, total deficit or surplus, and maximum deficit or surplus were derived based on Run theory and were comprised for the base period and three future decades.
Results and Discussion: Evaluation of LARS-WG5 model for base period showed that the model was able to simulate minimum and maximum temperatures and precipitation data with high accuracy based on statistic error and can be used to generate data for future years according to emission scenario. According to the simulated results of performance of multi model ensemble, the average values of mean temperature and precipitation will increase by 0.820 C and 2.5 % for A2 scenario, respectively. In addition, the minimum and maximum temperatures have increased in all of the months according to the three scenarios in comparison with the base period. The correlation results between the investigated indices showed that the maximum and minimum of correlation can be observed between SPI & RDI and SPEI & SPI indices in the base period and future decade for each scenario, respectively. Drought assessment based on the SPEI index in the base period shows that the main drought episodes occurred in the 1999 to 2001 that were consistent with FAO report (2006). Comparison of wet and dry periods in relation to the base period showed that the number of dry periods will increase in time scales of 1 and 3 months and will decrease in other long-term time scales.
Conclusion: Climate change and its effects are among the main challenges of water resources management in the present century. In this study, the effects of this phenomenon on drought monitoring and change of characterizations were investigated. For this purposes, we used daily meteorological variables during thirty years (1981-2010) from Hamedan Synoptic station. The results of drought monitoring were based on SPEI index, and it revealed the high variability of humidity condition in the first decade of simulation in comparison with the second and third decades. This issue indicated that this decade requires more attention and management measurements. Also, according to the results of the derived characterization via Run theory, the number of dry periods will decrease and persistence of the longest dry period and consequently the volume of deficit will increase in the next three decades. In addition, the total volume surplus of wet periods will decrease in relation to the base period that can be interpreted as the increasing of moisture deficit in future decades The SPEI is based on precipitation and temperature data, and it has the advantage of combining multiscalar character with the capacity to include the effects of temperature variability on drought assessment. Thus, we recommend SPEI, as a suitable index for studying and identifying the effect of climate change on drought conditions.
قیمت : 20,000 ريال