عنوان مقاله [English]
Global mean sea level change due to climate change is resulted from changes in the interaction of its associated components in long periods of time. The difference between regional and global predictions of sea level change depends on manifestation of this phenomenon in terms of climatic and hydrological conditions of the regions. Since the rising in sea level in the near future is a serious threat to coastal communities, it is essential to estimate the increase in water level during the coming period. Sea level changes on a large spatial and temporal scale are created by some factors, including thermal expansion, ice melting and etc., resulted from the climate change. Sea level change is affected by two main causes: (1) volume change due to density of sea water, and (2) mass change due to water exchange with atmosphere and land through precipitation, evaporation, river runoff and ice melting. Regional sea level change may differ substantially from a global average. This shows complex spatial patterns resulted from ocean dynamic processes, movements of the sea floor, and changes in gravity due to water mass redistribution (land ice and other terrestrial water storage) in the climate system. In the period 2081–2100 compared with the that of 1986–2005, global mean sea level rise is likely (medium confidence) to be in the 5 to 95% of projections from process-based models. This gives ranges of 0.26 to 0.55 meter, 0.32 to 0.63 meter, 0.33 to 0.63 meter, and 0.45 to 0.82 meter for RCP2.6, RCP4.5, RCP6.0 and RCP8.5, respectively. In this study, an accurate assessment of the sea level changes due to climate change in coastal zones of Persian Gulf and Oman Sea has been estimated in the future, for the first time.
Materials and Method
This study estimates the amount of increase in sea level change using 24 AOGCM models suggested in fifth IPCC report, under the new scenarios of greenhouse gas emissions. In this study, sea level change in Persian Gulf and Oman Sea has been calculated by SIMCLIM model under climate scenarios by 2100 A.D. For this study, the SIMCLIM model has been applied based on different general circulation models, under RCP scenarios for 1995 to 2100. The regional sea level change has been estimated for this case study. In the SIMCLIM model the amount of water level change was estimated for a period based on rising temperatures leading to thermal expansion and polar ice melting. In this model, the spatial resolution is about 2.5° × 2.5° kilometer in global scales, and for regional sea level is about 0.1°.
Results and discussion
To compare the increase in water level in the regional scale to the global mean sea level, the difference in water level is based on AOGCM models. The difference in predictions during 2081-2100 is compared with 2046-2065. This shows that regional sea level change during the same time periods is different from each other. In fact, this is changing with different rates and sea level changes more quickly and will be increased overtime. Predicted values under the RCP 8.5 scenario shows higher difference compared with the mean sea level change, among other RCP scenarios. According to regional predictions of sea level in this case study, the amount of change in the water level is about 11 cm under the RCP 8.5 scenario and about 6 cm under the RCP 2.6 scenario by 2100. To investigate regional sea level changes under different scenarios, the amount of sea level change based on ensembles of AOGCM was considered as the best estimate. The predicted values show that the increase in the water level in the second and third 25 years after 2020 is growing at a faster rate compared with the first 25 years after 2020. The rate of increase in the water level during the 2075 to 2100 is growing at a faster rate than other periods of the time.
The results of this research have indicated that sea level in this region under RCP2.6, RCP4.5, RCP6.0 and RCP8.5 scenarios will be 84.18, 86.62, 89.06 and 181 cm, respectively, by 2100. The values of general sea level change have been predicted about 0.61, 0.71, 0.73 and 0.98 cm per year under RCP scenarios, respectively. Comparison of these values shows the necessity of more accurate coast vulnerability estimation to flooding in the future.