Introduction
Drought is one of the most harmful atmospheric phenomena that are likely to occur around the world, but its characteristics vary considerably from region to region. Recorded data suggests that from 1901 to 2012, the surface temperature of lands and oceans increased by an average of 0.89 ° C. This increase in the temperature of the planet, as well as the change in the physical characteristics of the atmosphere, is indicative of climate change; therefore, in order to investigate the future climate change effects on different sectors such as water resources, agriculture, environment, health, industry, economics, etc., climatic variables must first be modeled by greenhouse gas stresses. The most reliable tool to simulate future climate, is using the Atmosphere-Ocean General Circulation Model output. The weaknesses of these models are their inability to model meteorological variables in the point scale of meteorological stations. Therefore, it is necessary the output of models be downscaled at the station scale. The LARS-WG Statistical downscaling model has been used for downscaling the general circulation models to predict climate change and its effects.
Materials and Methods
The purpose of this research is to investigate climate change in Zanjan province during the upcoming period (2011-2050).For simulation and generation of rainfall data, maximum and minimum temperatures as the most effective factors influencing climate change during the upcoming period, four synoptic stations of Zanjan, Khodabandeh, Khoramdareh and Mahneshan were studied. Initially, the normality of the data of these stations was examined and their homogeneity was assessed using Run- Test. Then, using four Coupled Atmospheric–Ocean General Modals (BCM2, HADM3, HADGM-A1 and IPCM4), the meteorological parameters were simulated for the upcoming period. Finally, using the inverse of absolute value of each model’s error, the best model for each station was selected and then, using the SPI and PN index, future droughts were projected.
Discussion and Results
According to the findings of the research at Zanjan station, it can be concluded that the amount of precipitation during the years 2011 to 2050 based on the BCM2 model and the SRAB1 scenario was 2991/3 and the SRB1 scenario was 291.4 mm. This indicates decrease in rainfall over the next 40 years at this station. Based on the SPI index and the SRAB1 scenario, this station will have 5 mild drought years; 4 years of moderate drought and two years of severe drought, respectively. Based on the SRB1 scenario, drought conditions are like the SRAB1 scenario, except one year of severe drought has been reduced. According to the PN index for both scenarios, there is a 5-year mild drought and 2 years of moderate drought. At Khodabandeh station, from 2011 to 2050, the precipitation rate has been reduced by 3.5 mm under the HADGM-A1 model based on the SRA2 scenario and reached 333.1 mm. Based on the SRA1B scenario at Khodabandeh Station, this value was 332/5mm that it has reduced by 4 mm compared to available data. Based on the outputs of both climate scenarios and based on the SPI index for Khodabandeh Station, it has been forecast to drought for 13 years, with the strongest of 2015, 2020 and 2028. According to the PN Drought Index, for the next forty years, only 9 years of precipitation will be less than normal. Based on the HADGM-A1 climatic model, under the two scenarios SRA1B and SRA2, the precipitation for Khoramdareh station was 278.1 and 280.9, respectively, which shows a decrease of 10 and 8 mm based on the output of these two scenarios. The results of the SPI index and SRA1B output indicate that the station will has drought by 14 years between 2011 and 2050.Based on the SRA2 scenario, the number of droughts will be 11 years. Based on the PN Drought Index and output of SRA1B scenario between 2011 and 2050, by 7 years of drought will prevail. According to the SRA2, the number of drought years for the next 40 years will be 8 years. The average rainfall of Mahneshan station is reduced according to the BCM2 model under the SRAB1 and SRB1 scenarios, which indicates a decrease of about 24.3 mm at this station. The SPI index predicts a 9-year drought based on the output of the BCM2 model under the SRAB1 and SRB1 scenarios for the next 40 years. According to the PN index under the SRAB1 scenario, from 2011 to 2050, only six years of dry age will occur. Based on the SRB1 scenario, we will have only one severe and two years of moderate and 3-year weak drought.
Conclusions
In this research, we evaluated the effects of climate change on drought state in Zanjan province during the next 40 years (2011-2050) using SPI and PN. According to the results, LARS-WG model are highly capable to simulate meteorological variables. Investigating the results of changes in climatic parameters of precipitation during 40 years of forecasting in comparison with the base period indicates that the average precipitation is decreasing, so that the lowest for Zanjan Station decreased by 2 mm and the maximum for the Khodabandeh and Mahneshan station decreased by 24 mm they will be. Simulated data indicate that in Zanjan province the drought has a high relative frequency (average of stations is 12 years) most of which are mild and moderate, and only 2 to 3 are severe drought.