نوع مقاله : مقاله پژوهشی
نویسندگان
1 دپارتمان مهندسی و مدیریت آب، دانشکده کشاورزی، دانشگاه تربیت مدرس، تهران، ایران مدرس
2 دانشکده مهندسی عمران، دانشگاه علم و صنعت ایران، تهران، ایران
چکیده
کلیدواژهها
موضوعات
عنوان مقاله [English]
نویسندگان [English]
Climate change has profound impacts on hydrological processes, with evaporation and wind patterns playing key and determining roles. In this study, using the outputs of 18 climate models from the CMIP6 project under four emission scenarios (SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5), the future changes in evaporation and wind over the Caspian Sea during the period 2021–2100 were investigated. In the first step, the models’ performance was evaluated against observational data for the baseline period (1980–2020), and error analysis was conducted. Subsequently, two models with the best performance, MPI-ESM1-2-HR and MIROC6, were selected for the final analysis. The results indicate that the annual average evaporation will increase in all scenarios compared to the baseline period, with an increase of approximately 11% in SSP1-2.6, 23% in SSP2-4.5, 26% in SSP3-7.0, and 31% in SSP5-8.5. This increase is more pronounced during warm seasons, especially in summer and early autumn, with monthly growth reaching up to 60% relative to the baseline. Moreover, wind patterns exhibit remarkable changes; the average wind speed in the future is projected to vary between 2 and 6 m/s, while in winter, under the influence of the Siberian high-pressure systems, values exceeding 6 m/s are recorded. These changes, by intensifying evaporation through the replacement of saturated air with dry air, will have significant consequences for hydrodynamics, circulation patterns, water balance, and vulnerable ecosystems such as the Gorgan Bay and Kara-Bukaz-Gol. The findings suggest that the combined effects of increased evaporation and altered wind regimes may seriously threaten the water level and ecological stability of the Caspian Sea. Therefore, considering these developments in regional water resource management and policy-making is essential.
کلیدواژهها [English]
Climate change, as a pervasive global challenge, profoundly affects hydrological systems worldwide. The Caspian Sea, due to its landlocked nature and high sensitivity to climatic variability, is particularly vulnerable. Surface water evaporation and wind vector patterns are critical determinants of its water balance and hydrological budget. Changes in either of these factors can result in significant ecological and economic consequences.
This study aims to provide a comprehensive assessment and projection of evaporation rates and wind speed vectors over the Caspian Sea under four Shared Socioeconomic Pathways (SSP1-2.6, SSP2-4.5, SSP3-7.0, SSP5-8.5) from the CMIP6 project. Unlike previous studies that often focused on a single variable, this research analyzes the combined effects of increased evaporation and changes in wind dynamics on the Caspian Sea’s water system stability. The central hypothesis posits that intensified evaporation, coupled with substantial shifts in wind speed and direction, particularly under SSP5-8.5, could lead to a significant water balance deficit and ecological threats.
Using the latest CMIP6 models and a broad ensemble of 18 validated models, this research provides robust long-term projections for 2021–2100, offering a scientific foundation for adaptation strategies and integrated water resource management.
This study employs a quantitative, predictive design using a Multi-Model Ensemble (MME) approach. Data include surface evaporation rates and 10-meter wind vectors extracted from 18 selected GCMs. Analyses were conducted under the four emission scenarios to evaluate near-term (2021–2060) and long-term (2061–2100) projections. Observational data from 1980–2020 (ECMWF-ERA5) were used for model validation with metrics including MAE, Corr, and NSE. The Random Forest method was applied for bias correction and dynamic downscaling. Two models, MPI-ESM1-2-HR and MIROC6, demonstrated the highest accuracy and were selected for ensemble analysis. Periodical mean comparisons were performed across baseline, near-future, and far-future intervals to identify seasonal and long-term trends.
The ensemble projections indicate significant and concerning climatic changes in the Caspian Sea. Annual mean evaporation rates show consistent increases across all SSPs: SSP1-2.6: 11%, SSP2-4.5: 23%, SSP3-7.0: 26%, SSP5-8.5: 31%, with peaks in summer and early autumn reaching 60% above baseline.
Projected wind speeds range from 2–6 m/s, occasionally exceeding 6 m/s in cold seasons due to Siberian high-pressure systems. Interestingly, the near-future period exhibits higher mean wind speeds than the far-future period, reflecting warming-induced weakening of pressure gradients. Wind direction shifts under SSP5-8.5 further amplify evaporation, with northwestern winds increasing up to 40% and southeastern winds up to 34%.
Spatial analysis reveals smaller evaporation patches in the far-future period, linked to the drying of shallow regions, including Gorgan Bay and Ghara-Baghaz Bay. Annual river inflow, notably from the Volga, is projected to decline by 20–30%, exacerbating hydrological stress.
The combined effects of enhanced evaporation and significant wind dynamics changes impose critical hydrological and ecological pressures. In SSP5-8.5, annual evaporation increases by 31%, peaking at 60%, while wind directional shifts (northwest 40%, southeast 34%) intensify these effects. Reduced relative humidity and enhanced dry air advection disrupt surface circulation and contribute to a serious water balance deficit. Concurrent river inflow reductions amplify desiccation in shallow areas.
Theoretical and practical implications are substantial: decreasing water levels, increasing salinity, and irreversible ecological changes threaten sensitive habitats, regional food security, and economic stability. The study underscores the necessity of active adaptation policies, integrated water management, and marine conservation strategies. Future research should focus on high-resolution Atmosphere-Ocean Coupled Models, local wind effects on evaporation, and ecological impacts on key Caspian Sea species to inform sustainable adaptation strategies.
All authors contributed equally to the conceptualization of the article and writing of the original and subsequent drafts.
Statement Data available on request from the authors.
The authors avoided data fabrication, falsification, plagiarism, and misconduct.
The author declares no conflict of interest.
)