M.Sc. Agriculture Engineering-Water Resources Student, University of Tehran, Iram
Associate Professor, Irrigation and Drainage Engineering Department, Faculty of Aboureihan, University of Tehran, Iran
One of the most important impact of climate change is reduction of precipitation in some areas including Iran. Hence, climate change studies are essential in these areas. Besides, according to IPCC, some meteorological stations of Iran, such as Tabriz (capital of East Azerbaijan Province) have showed a downward trend in precipitation. Therefore, East Azerbaijan Province was selected as the study area in this survey. It is one of the north-western provinces with cold dry climate. Firstly, monthly temperature and precipitation observed data over 1981-2012 were gathered from 15 meteorological stations of the region, and they were produced for 0.5-degree cells by interpolation methods and selecting the most appropriate one based on the amount of corresponding errors (RMSE and ME). Thereafter, monthly precipitation and temperature data for 2013-2022 were projected using 16 Atmosphere-Ocean General Circulation Models (AOGCMs) under A2B, A2 and B1 SRES scenarios, and downscaled by Bias Correction/Spatial Downscaling technique at 0.5-degree cells. After applying pattern scaling method on monthly temperature and precipitation data, in order to produce future data under more scenarios, monthly climatic variables were calculated for 10, 25 and 50 percent risk, and risk analysis was done based on the computed parameters. The pattern scaling technique used in this study calculates the variable under a desired scenario, from the base scenario (A2 in this study) with a linear equation in which the global temperature rise was calculated by a model named MAGICC.
Assessing observed climatic variables showed that western parts of the province had lower precipitation and higher temperature, while eastern parts had higher precipitation. However, south-western cells also experienced a better situation. Mean annual temperature over 1981-2012 was between 7.5-13.5 degrees Centigrade, and annual precipitation was 260 to more than 310 millimeters. Moreover, despite precipitation fluctuations over 1981-2012, annual precipitation of the first years is higher than the last years.
After applying pattern scaling method and accessing future monthly precipitation and temperature data under 49 scenarios for 16 AOGCMs, temperature and precipitation boxplots of each month were produced for each month. Results showed that precipitation is right-skewed in all months and all cells. The outliers of March and April are less than others, while August outliers are numerous. Comparing boxplots of temperature and precipitation indicated that outliers of temperature data are much less than precipitation, i.e. uncertainties of AOGCMs and downscaling to project temperature are less than precipitation.
The monthly precipitation and temperature data were calculated for 10, 25 and 50 percent risk and the monthly temperature-risk and precipitation-risk line charts were produced for each cell. The amount of monthly temperature and precipitation with higher and lower risk showed a significant difference. Furthermore, projections with lower risk have less difference and they indicate almost one prediction.
According to the areal interpolated maps of the future mean annual precipitation and temperature, the least temperature will be around Sarab station, and the highest temperature will be near Malekan and Bonab stations. Furthermore, maps showed that the amount of temperature will increase by moving west. Moreover, by moving from high risk to lower risks, the amount of temperature increases about one degree Centigrade. Western regions will experience lower precipitation with all levels of risk, and the maximum annual precipitation will be seen in north-eastern spots.
The difference between the predicted and observed temperature and precipitation with 10, 25 and 50 percent risk for each cell was calculated and their spatial distribution maps were produced by applying different interpolation methods and selecting the best method. It is predicted that temperature will increase 2.9-3.15 degrees Centigrade with 10 percent risk, and the rise amount is bigger in the western areas. Precipitation will decrease about 75 to 150 millimeters. Temperature will increase 2.1-2.25 degree Centigrade with 25 percent risk, and the amount of precipitation in some areas will be lower and in some others will rise even up to 50 millimeters. The temperature with 50 percent risk is projected to increase about 1.2 degree Centigrade, and precipitation will also aggrandize.
In conclusion, the temperature increase in the next decade will be bigger in the southern areas of the province, and precipitation amount of north-western and western areas will experience higher precipitation. The results of this study confirm other research done by others before, indicating the least amount of observed precipitation was in Sarab station. By having these results for future periods the decision makers of this field will have a better vision, ad so they will be able to sufficiently plan for the future.
In addition to this research, some suggestions are proposed as follows to improve and strengthen the results: (i) past and future drought assessment in the area with different drought indexes, (ii) presenting a more logic relationship between temperature and precipitation because of relatively low correlation between temperature and precipitation and so not being linear, or applying models ensemble and comparing the results with this survey, (iii) using daily temperature and precipitation instead of monthly data to improve the results.