نوع مقاله : مقاله پژوهشی
پژوهشکده حفاظت خاک و آبخیزداری
عنوان مقاله [English]
Although climate change is expected to affect many parts of the environment, water is the most critical factor affected by climate change. Iran is always facing limited water resources, and due to the fact that climate change can be considered an aggravating factor in the water crisis, projeting the effect of climate change on the future drought is very important for managing water resources. In this study, the effects of climate change on the meteorological drought of Karkheh basin in the future have been investigated by dynamical model (PECIS) and under A2 and B2 emission scenarios.
In this study, PRECIS dynamic downscaling model was used to estimate precipitation and temperature in the base period (1960 to 2000) and future period from 2070 to 2100 and under two scenarios A2 and B2. For this purpose, the PRECIS model was implemented with a horizontal separation of 0.44 degrees in grids. To use PRECIS model results, it is necessary to evaluate the model first. For this purpose, the model was first run for the 1960 to 1990 years and the projected precipitation and temperature values were compared with the observed values of the stations. The study of climate changes in Karkheh basin showed that under scenario A2, the amount of precipitation will increase by about 11% and the average minimum and maximum temperature will increase by about 5 degrees. For scenario B2, the amount of precipitation will increase by about 7% and the average minimum and maximum temperature will increase by about 3 degrees.
Then, using SPI index drought analysis was performed. The variability of SPI index for 1, 3 and even 6 months is very high compared to the average because any amount of rainfall can change the value of the index quickly in this time scale. This is while the 12-month index can better determine the number of drought events and evaluate their duration and intensity. Therefore, to investigate the meteorological drought in the study area, the 12-month SPI value was used as an annual drought index.
In order to investigate the characteristics of droughts, two selected stations in the region, Khorramabad and Kermanshah stations, which are the closest points to the output grid of the climate model, have been used. The choice of these two stations is due to the fact that in order to compare the drought characteristics of the base period with the drought of the future period, the rainfall data simulated by the climate model which is in the form of a grid (raster) should be used and in order to be able to compare It is necessary that the output grid points of the model match the stations as much as possible in terms of location. Therefore, by adapting the stations on the network of output points of the climate model, two stations, Khorramabad and Kermanshah, which are the closest points to the output grid of the model, were selected. The study of meteorological drought using the SPI index shows that several major droughts occurred in 1966-67, 1970-71, 1973, 1977-78, 1984, 1991, 1995, 1998-2000. The study of drought during the period 2070 to 2100 in Kermanshah and Khoramabad stations shows that under both scenarios, the years 2077, 2081 to 2083, 2087 to 2089, and 2095 to 2096 will experience drought. However, in both scenarios, the intensity and magnitude of the drought will decrease compared to the base period, and this decrease is greater under scenario B2 than A2. The results also show that the number of dry months and the duration of drought will increase in both scenarios. Examining the probability of drought occurrence under different scenarios shows that the probability of drought occurrence for Kermanshah station is equal to 9% under scenario A2 and 15% under scenario B2, which is a decrease compared to the probability of occurrence of drought in the base period of the same station. The probability of drought for Khorramabad station under scenarios A2 and B2 are 12 and 19 percent, respectively, and the same probability is 15 percent for the base period of Khorramabad station. Comparing the probability of occurrence for different scenarios shows that the occurrence of drought under scenario B2 will be associated with a higher probability than scenario A2.
Investigating the effects of climate change on the meteorological drought of the Karkheh basin by dynamic climate model during the period from 2070 to 2100 shows the following results in brief:
The evaluation of scenario A2, during the period from 2070 to 2100, shows that the average rainfall will increase by about 11%. On the other hand, the average minimum and maximum temperature under scenario A2 shows an average increase of 5 degrees in all months. Meanwhile, the projected rainfall under the B2 scenario has shown an average increase of about 7%. Under scenario B2, the average minimum and maximum temperature has increased by about 3 degrees Celsius.
Study of climate change on the meteorological drought of Karkheh Basin shows that the most number of droughts occurred in the stations are 1 to 3 month droughts; Events of 4 to 7 months also show a significant number in stations. The study of meteorological drought during the period from 2070 to 2100 shows that under both scenarios A2 and B2, the severity of droughts will decrease compared to the base period, although the duration of drought and the number of dry months will increase. Examining the probability of drought occurrence under different scenarios shows that the probability of drought occurrence under scenario A2 and B2 will decrease in the region. Comparing the probability of occurrence for different scenarios shows that the occurrence of drought under scenario B2 will be associated with a higher probability than scenario A2.
The results show that to evaluate the drought, the SPI index three and six months shows large variability in most of the stations. Therefore, according to these variabilities and the fact that in order to study drought changes in future periods, the output data of climate models, which are usually less accurate for short-term periods, should be used, to study the meteorological drought from the SPI index 12 months was used.