پديد آورندگان :
زارع ﭘﻮر، ﻫﺎدي داﻧﺸﮕﺎه ﮐﺎﺷﺎن - داﻧﺸﮑﺪه ﻣﻨﺎﺑﻊ ﻃﺒﯿﻌﯽ و ﻋﻠﻮم زﻣﯿﻦ , وﻟﯽ، ﻋﺒﺎﺳﻌﻠﯽ داﻧﺸﮕﺎه ﮐﺎﺷﺎن - داﻧﺸﮑﺪه ﻣﻨﺎﺑﻊ ﻃﺒﯿﻌﯽ و ﻋﻠﻮم زﻣﯿﻦ , ﻗﺮﺑﺎﻧﯽ، ﺣﻤﯿﺪ داﻧﺸﮕﺎه ﮐﺎﺷﺎن - داﻧﺸﮑﺪه ﻋﻠﻮم رﯾﺎﺿﯽ , ﺳﺎداﺗﯽ ﻧﮋاد، ﺟﻮاد داﻧﺸﮕﺎه ﺗﻬﺮان - داﻧﺸﮑﺪه ﻋﻠﻮم و ﻓﻨﻮن ﻧﻮﯾﻦ , ﻋﻠﻮي ﻧﯿﺎ، ﺣﺴﻦ داﻧﺸﮕﺎه ﮐﺎﺷﺎن - داﻧﺸﮑﺪه ﻣﻨﺎﺑﻊ ﻃﺒﯿﻌﯽ و ﻋﻠﻮم زﻣﯿﻦ
كليدواژه :
اﺳﺘﺎن اﺻﻔﻬﺎن , آزﻣﻮن ﭘﺘﯿﺖ و آزﻣﻮن ﺳﻦ , آزﻣﻮن ﻣﻦ-ﮐﻨﺪال , ﺗﺤﻠﯿﻞ روﻧﺪ , ﺧﺸﮑﺴﺎﻟﯽ , ﺷﺎﺧﺺ ZSI
چكيده لاتين :
As one of the greatest natural disasters, meteorological drought has traditionally affected human
life. Considering the fact that the consequences of drought and its socio-economic 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 methods
The study area and data: This study was conducted in Isfahan province, located at latitudes of 30° 43' to 34°
27'N and longitudes of 49° 38' to 55° 32' 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's average rainfall rate
and one sixth of the average global rate. This study used 30-year 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 1990-2020 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 Z-Score 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 non-parametric Mann–
Kendall at 5% significance level. The magnitudes of the trends were also computed and tested using the Sen’s
slope estimator method.
Results and discussion: It should be noted that the purpose of the Mann-Kendall 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 non-linear.
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, non parametric Sen’s slope estimator was used to analyze ZSI Indices and detect the possible trend.
Further trend analysis was also applied to detect possible single change-point using Pettitt’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’s slope tests based on ZSI Index
for 9, 12, 18, 24, and 48-month 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 48-
month scale, and in Shahreza station, the drought trend was significantly increasing in all time periods.
Moreover, the results of Mann–Kendall and Sen’s slope tests for a one-month 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’s change point test for 9, 12, 18, 24, and 48-month scales indicated the
existence of a significant change point in terms of the ZSI Index. However, no change point was observed for all
stations' 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 Mann-Kendall test, 56% of all stations showed a significant slope
trend according to the Sen's slope test, and 81% of all stations showed a significant change point according to the
results of the Pettitt's test. In general, it could be argued that drought trends are better analyzed and displayed in
terms of the ZSI index for over six-month periods, and that under six-month 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.
