Projection of Changes in Precipitation Index of the Southern Coast of the Caspian Sea in Order to Hazards Reduction in the Periods of 2021-2050

Document Type : Applied Article


1 PhD Student of Agro Climatology, Dept. of Physical Geography, Faculty of Geography, University of Tehran, Iran

2 Professor of Climatology., Dept. of Physical Geography, Faculty of Geography, University of Tehran, Iran

3 Associate Professor of Climatology., Dept. of Physical Geography, Faculty of Geography, University of Tehran, Iran

4 Assistant Professors of Agricultural Meteorology., Dept. of Physical Geography, Faculty of Geography, University of Tehran, Iran

5 Assistant Professors of Climatology., Dept. of Physical Geography, Faculty of Geography, University of Tehran, Iran

6 Assistant Professors of the Department of Agro ecology, Environmental Sciences Research Institute, Shahid Beheshti University, G.C., Tehran, Iran


Precipitation is the most important climatic variable, and an important component of the hydrological cycle, which its fluctuations can have significant impacts on human society and the natural environment. Over the past few decades, the frequency and severity of extreme precipitation events have increased, especially under the influence of global warming. Based on previous researches, precipitation patterns have changed in most parts of the world in recent decades so that the occurrence of extreme precipitation has increased in most parts of the world such as China, USA, and Australia. The purpose of this study was to investigate the changes in annual, seasonal, and monthly precipitation amounts and extreme precipitation events in Guilan and Mazandaran provinces, using CanECM2 climate model data. Evaluating such changes can help policymakers and planners in regulation effective strategies to adapt to the potential risks of climate change.
Data and Method
To study and monitor the precipitation of Guilan and Mazandaran provinces on the Caspian coast and north of Alborz mountain range, 7 synoptic weather stations, including Astara, Rasht, Bandar Anzali, Ramsar, Gharakhil, Noshahr, and Babolsar with appropriate statistical length and geographical distribution were used. SDSM version 3.5 was used to simulate precipitation changes over the future period (2021-2050) and compared to the base period (1986-2015). In addition, daily precipitation data of Astara, Rasht, Bandar Anzali, Ramsar, Gharakhil, Noshahr, and Babolsar synoptic stations for base period (1986-2015), the large scale predictors of atmospheric re-analyzed data (NCEP), and data for CanECM2 model under three scenarios RCP2.6, RCP4.5 and RCP8.5 as large-scale predictors were used. After examining the quality control of precipitation data, the large-scale predictors of atmospheric re-analyzed data (NCEP) using stepwise modeling with respect to Pearson correlation coefficients, partial correlation coefficients and percentage of partial correlation reduction were selected. In order to ensure the efficiency of the model, 15-year period (1986-2000) for model calibration and the 15-year period 2001-2015 for model validation selected. In this step, Wilcoxon non-parametric test, Coefficient of Residual Mass, and Root Mean Square Error (RMSE) as well as index of agreement (d-indices) were used to evaluate the model efficiency. After doing model calibration and validation, the downscaling of precipitation data was performed using CanECM2 data under three emission scenarios for the future period (2021-2050) and changes in simulated precipitation values in different scenarios was investigated in comparison to base (1986-2015). Moreover, nine extreme indices introduced by CCL / CLVAR were used to investigate the intensity, duration and frequency of precipitation in the base and future periods. In addition, the frequency of days above a certain threshold of two extreme indices R10, R20, precipitation intensity from PRCPTOT, Rx5day, Rx1day, R99 and R95, and duration and durability of two CDD and CWD were used. The calculation of these extreme indices performed by the RClimDex1.0 software.
Discussion and Results
Based on the skewness and Kurtosis values and the results of the Kolmogorov-Smirnov and Shapiro-Wilk tests, it was found that the distribution of precipitation data was not normal at Bandar Anzali station. Model validation results showed that difference between observed and simulated values in some of weather stations in some months was positive or negative. In other words, in some months the simulated values were more than observed ones and in others less than observed values. However, based on Wilcoxon test, it was found that P-value was higher than 0.05 at all weather stations and thus, there could be no significant difference between the mean observed and simulated precipitation data on seasonal and annual time series data. Therefore, the efficiency of the model in simulated precipitation was confirmed at the study area. The results revealed that under the RCP2.6, RCP4.5 and RCP8.5 scenarios precipitation will not reduce during 2021-2050 period. It is expected that the average precipitation will increase by approximately 20 to 70 mm during the future period (2020-2021) as compared to base period (1986-2015). Comparison of the mean annual precipitation (PRCPTOT) in the base period with the future period based on RCP2.6, RCP 4.5 and RCP8.5 emission scenarios showed that the annual precipitation of all the weather stations will be increased over the future period (2021-2050). The results also showed that at all weather stations, the number of consecutive dry days reduced during the future period (2021-2050) as compared to the base period (1986-2015). The results also showed that the eastern part of the study area will have higher number of consecutive dry days in the future period as compared to the western part of the study area. The results showed that the number of consecutive wet days during the base and future period indicated that, on average, about one to three days of the number of consecutive wet days in the study area reduced during the 2021-2050 as compared to the base period. Changes in the number of consecutive wet days during the future period also have a similar spatial behavior like the base period. Moreover, the results showed an increase in precipitation of more than 10 mm happened in most of the stations, excluding Babolsar and Gharakhil, in the future 2021-2050 as compared to the base period. For the Gharakhel station, a decrease in precipitation of more than 10 mm for 1 day was observed. The results showed a very slight increase in the number of days with heavy rainfall of 20 mm or more occurred in the future as compared to the base period in the coastal areas of Mazandaran province. Overall, the results showed that the number of days with very heavy rainfall in the study area was similar to the base period in the study area. In addition, based on the results of all emission scenarios, it is expected that the R95p and R99p will decrease in the central part of the study area, including Ramsar and Nowsher stations in the future in comparison with the base period. An increase in the amount of extremely humid days is expected in the future period toward the east and west of the study area, which is much higher in the west coast of the region (Gilan province). The results also showed that, like the R99P, RX1day will decrease toward the western parts of the region, especially in Bandar Anzali Station with maximum daily precipitation of 140, 130 and 141.4 for RCP 2.6 scenarios, RCP4.5 and RCP8.5, respectively, in the future period. The results also showed that in the future period, the maximum daily precipitation increased in the western parts of the study area and decreased in the eastern and central parts relative to the base period.
The results of three scenarios showed that the average annual precipitation in the study area increased, on average, by 20 to 70 mm as compared to base period (1986-2015). In addition, the results of analysis of precipitation indices showed an increase of precipitation with more than one mm in all weather stations and an increase of precipitation with more than 10 mm in most of the weather stations, excluding Babolsar and Gharakhil, in the future period 2021-2050 in comparison with the base period. However, the precipitation more than 20 mm was similar in the future and base period with a little change. The results revealed that a decrease in R95p and R99p indices at Ramsar and Nowshahr stations and an increase in the western and eastern parts will occurred in the future. Moreover, a decrease in the dry period length will happened in the future as compared to the base period. The extreme precipitation values are expected to be high for the region, which will increase the average annual precipitation.


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