عنوان مقاله [English]
Climate change due to human activities has the great potential to impact local climate zones. Which will change regional climate zones and reorganize global climate distribution. Under these conditions some zones decrease, some disappear and in some areas, new zones created. In general, two important issues in climate change studies are predicting the intensity and distribution of future climate change and estimating the magnitude and intensity of its potential impacts on Earth's ecosystems. Another important issue is to determine the effect of these changes on existing ecosystems of dryland zones at different spatial scales. Therefore, achieving a classification system that can help detect these changes is one of the challenges in climate change. A look at past studies in this area reveals that the classification scheme that can display both climate and vegetation characteristics in a single format has been used more than other classification schemes in climate change studies. Hence, in this study, the same approach used by researchers around the world as the Koppen–Trewartha classification system is used. Which take into account these two characteristics. This implemented as the most appropriate classification scheme for Iran in climate change and drought management studies in the current and future conditions of the country. In addition, this classification scheme allows for a more accurate representation of climatic ranges and sub-types.
2. Materials and methods
In this research, climatic classification has been done by Koppen–Trewartha method in the Persian Gulf and Oman Sea. In this classification scheme, the global climate is into six major climatic groups. Five groups (A, C, D, E, F), based on temperature criteria, and sixth group (B), or dry group; are based on precipitation criteria.
Climatic classification was by coupon travertine using network data. In order to select the appropriate network size, meteorological stations with 30-year data, which correspond to the normal period of 1961- 1990, selected as validation criteria and their climatic type was based on recorded data, which were calculated by station data. Then the climatic type in the basin mapped based on the network data with different resolutions selected. Based on the geographical coordinates of the stations, their type extracted at each resolution and analyzed with the type obtained from the station data and the best fit was the criterion for the results of both data sources (station and network data). Validation of data with 14 synoptic stations in the study area revealed. The scaled data covers 5 minutes, 74% for the networks, and 87% for the 2.5 minutes and 30 seconds. Finally, in order to perform climatic grouping based on network data, median temperature and 2.5 min spatial resolution data in the 2000 baseline period and 2030s, 2050s and 2080s for the four RCP 2.6, RCP 4.5 scenarios, RCP 6, RCP 8.5 From the climatology centers, the data matrix was created for Iran. Precipitation and temperature ratios of each month calculated from the total annual precipitation for each matrix cell over the time interval under study by ARC MAP software then they extracted based on mean precipitation and mean temperature data generated by programming in Matlab software of their climatic type. Subsequently, the climatic zoning plotted in the mentioned periods in the basin of the Persian Gulf and the Oman Sea.
3. Results and discussion
The results showed 9 climatic zones including warm dry (Bwh), semi-arid (Bsh), semi-arid cold (Bsk), subtropical with dry summer (Csa), warm continental temperate (Dcsa), cold dry temperate (Dcsb), warm dry temperate with winter precipitation (Dcwa), cold dry temperate with summer precipitation (Dcwb) and warm temperate oceanic temperate (Doa) are present in the Persian Gulf basin and Oman sea. The dominant climatic zone in the warm and semi-arid basins is warm. These two zones cover 62 percent of the area, including the east, center and downstream of the western basin. After that, the climate is temperate at 23%. In this climate, the warm temperate oceanic temperate zones accounted for 9 and 7 percent, respectively.
According to the average GCM models, the dry climate type (Bsh) and the semi-arid climate (Bwh) in the most optimistic scenario (RCP 2.6) account for approximately 62% of the Persian Gulf and Oman Sea Basin and in the worst-case scenario, (RCP 8.5) 89% will reach by the end of the 21st century. Simulations also show that temperate climatic types will largely disappear or will be very small and approximately 1% wide and will be scattered across the northwest basins of the study area. The subtropical climate zone also covers about 10% of the area. This zone will be mainly confined to the top of the basins. The results are consistent with research conducted globally such as Rubel et al. (2010), Beck et al. (2018), Tapiador et al. (2018), Barredo et al. (2019), in Algeria, Zeroual et al. (2019). Simulations of research in arid and semiarid regions show that these zones will increase in the future and a significant percentage of temperate zones will decrease.
In this paper, climate classification in the Persian Gulf and Oman Sea basin has been adapted to present and future climate change approaches. In this regard, using the network data, the Koppen–Trewartha classification method has been implemented throughout this basin. Among the existing climate classifications, this method as one of the best methods provides a more accurate representation of climate ranges and its subtypes based on precipitation and temperature boundaries, and more than other classification schemes used in climate change studies. The results show a significant increase in the area of arid and semi-arid climate classes and consequently a decrease in the temperate climate class in the future relative to Basic Climate Period. Accordingly, in this basin, under the RCP 8.5 scenario as the maximum scenario, by the end of the 21st century, nearly 52 percent of the basin will be in arid climate. In addition, the area of temperate warm and cold climate, which covers more than 23% of the basin during the basic climate period, is reduced to 1% by the end of the century under RCP 2.6, RCP 4.5, RCP 6 and RCP 8.5 scenarios. It can be stated that the changes in climate zones are influenced by the interannual fluctuation response of temperature and precipitation elements to climate change and global warming.