تحلیل آماری بلندمدت روند خشکسالی هواشناسی استان اصفهان

خشکسالی هواشناسی یکی از بزرگ‌ترین بلاهای طبیعی است که وجود یک سیستم نظارت موثر برای تحلیل روند خشکسالی و کاهش اثرات آن نیاز ضروری است تا بتوان به‌کمک آن اقدام موثری برای مدیریت این بحران انجام داد. هدف از این پژوهش، تحلیل روند خشکسالی استان اصفهان با استفاده از داده‌های بارش ماهانه 10 ایستگاه همدیدی با طول دورۀ آماری 30 ساله (19902020)، شاخص معیار استاندارد (zsi) در مقیاس‌های زمانی متفاوت و آزمون‌های ناپارامتری منکندال، پتیت و سن می‌باشد. درمجموع نتایج آماری برای مقیاس‌های زمانی متفاوت شاخص zsi نشان داد که در سطح 5% روند خشکسالی براساس آزمون من-کندال در 58% از ایستگاه‌ها، بر اساس آزمون پتیت در 81% از ایستگاه‌ها و بر اساس آزمون سن در 56% از ایستگاه‌ها روند معنی‌دار نزولی دارد. بارش ماهانه در هیچ ایستگاهی روند معنی‌دار ندارد. از تحلیل سری‌های زمانی در مقیاس‌های مختلف مشخص شد که سری زمانی‌های بلندمدت روند تغییرات خشکسالی را بهتر آشکار می‌کنند. بنابراین با توجه به نتایج روندیابی خشکسالی در استان اصفهان مشخص شد خشکسالی در استان با روند نزولی مواجه است. به نظر می‌رسد افزایش فراوانی خشکسالی و بروز خشکسالی‌های شدید بر اکوسیستم منطقۀ مطالعاتی و در نتیجۀ آن برخورداری از خدمات اکوسیستم‌ها تاثیر نامطلوب داشته باشد. در نتیجه، نیاز به سازگاری برای نفی تاثیرات دوره‌های خشک شدید مکرر در استان وجود دارد.

Long-Term Statistical Analysis of Meteorological Drought Trends in Isfahan Province

Introduction: As one of the greatest natural disasters, meteorological drought has traditionally affected human life. Considering the fact that the consequences of drought and its socioeconomic damages increase with increasing population, it is necessary to have an effective monitoring system to analyze the drought process and reduce its adverse effects, thereby taking effective measures to manage the crisis. Materials and methodsThe study area and data: This study was conducted in Isfahan province, located at latitudes of 30 ° 43 #39; to 34 ° 27 #39;N and longitudes of 49 ° 38 #39; to 55 ° 32 #39; E with an area of ​​107145 km2 (equivalent to 3.6 percent of the total area of ​​Iran), whose annual precipitation rate is 130 mm which is less than half the country #39;s average rainfall rate and one sixth of the average global rate. This study used 30year precipitation data collected from 10 meteorological stations and neighboring areas with appropriate statistical quality to investigate the drought indices of the Isfahan province.Case Study Indicators: Trend analysis of precipitation and drought data plays a significant role in the future development and management of water resources. Therefore, this study sought to analyze the trends of meteorological droughts and monthly precipitation rate for the period of 19902020 extracted from 10 synoptic stations in Isfahan province, including Ardestan, East Isfahan, Golpaygan, Isfahan, KabootarAbad, Kashan, Khorobianbanak, Naein, Natanz, Shahreza. Moreover, to investigate the variability of the ZScore Index (ZSI) for different time intervals, the ZSI values of all these stations were calculated at multiple scales of 1, 3, 6, 9, 12, 24 and 48 monthly scales, whose trends were analyzed for all stations by applying the nonparametric Mann -Kendall at 5% significance level. The magnitudes of the trends were also computed and tested using the Sen rsquo;s slope estimator method.Results and discussion: It should be noted that the purpose of the MannKendall test is to statistically assess the existence of monotonic upward or downward trend of the intended variable over time. A monotonic upward (downward) trend means that while the variable consistently increases (decreases) over time, the trend may be eighter linear or nonlinear.To identify a linear trend, the slope is usually estimated by computing the least squares estimates using linear regression. However, this is only valid when there is no serial correlation. Moreover, the least squares method is very sensitive to outliers. Therefore, as a robust method against those two least square assumptions, nonparametric Sen rsquo;s slope estimator was used to analyze ZSI Indices and detect the possible trend. Further trend analysis was also applied to detect possible single changepoint using Pettitt rsquo;s test, which helped investigate significant abrupt changes in the level of time series at 5% significance level for all stations and different ZSI monthly scales. All statistical analyses were carried out via R statistical software and the facilities of its packages.Discussion and Conclusion: The results of applying Mann -Kendall and Sen rsquo;s slope tests based on ZSI Index for 9, 12, 18, 24, and 48month scales indicated that the drought trend was significantly increasing for all stations out of Esfahan and Shahreza stations. In Isfahan station, the drought trend was significantly decreasing in the 48month scale, and in Shahreza station, the drought trend was significantly increasing in all time periods. Moreover, the results of Mann -Kendall and Sen rsquo;s slope tests for a onemonth period revealed a is significantly increasing trend in terms of ZSI Index in Naein and KabootarAbad stations only. Furthermore, applying Mann -Kendall test on monthly precipitation rates of all stations showed an insignificant downward trend.Finally, the results of the Pettitt rsquo;s change point test for 9, 12, 18, 24, and 48month scales indicated the existence of a significant change point in terms of the ZSI Index. However, no change point was observed for all stations #39; monthly precipitation rates throughout the same periods.In short, considering the ZSI drought index, it could be said about 58% of all stations showed significant downward trend according to the results of the MannKendall test, 56% of all stations showed a significant slope trend according to the Sen #39;s slope test, and 81% of all stations showed a significant change point according to the results of the Pettitt #39;s test. In general, it could be argued that drought trends are better analyzed and displayed in terms of the ZSI index for over sixmonth periods, and that under sixmonth scale are unable to produce significant results. Considering what discussed above, it should be reiterated that Isfahan province is facing a water crisis, requiring very urgent water demand management.