Multi-decadal historical regional hydroclimate simulation with two mid 21st century Pseudo-Global Warming futures over Alaska and the Yukon at 4 km resolution

Hydroclimate and terrestrial hydrology greatly influence the local communities, ecosystems, and economies across Alaska and Yukon River Basin. Therefore, we utilized the Regional Arctic Systems Model (RASM) to model the coupled land-atmosphere, and generated a climate and hydrology dataset at 4-km grid spacing to improve our understanding of the regional hydroclimate and terrestrial hydrology. Our model domain encompasses all of the U.S. State of Alaska, the entire Yukon River Basin, part of Western Canada, and the eastern coastal region of Russia. This dataset includes 1) one simulation of the historical climate (Water Years 1991-2021), which serves as a benchmark for climate change studies, and 2) two future simulations (Equivalent Water Years 2035-2065) using the Pseudo-Global Warming method under future greenhouse gas emission scenario SSP2-4.5. The two future scenarios represent median and high changes derived from ensemble means across different Global Climate Models in the Coupled Model Intercomparison Project Phase 6 within SSP2-4.5 respectively. The microphysics schemes in the Weather Research and Forecast (WRF) atmospheric model were manually tuned for optimal model performance. The land component in RASM was replaced using the Community Terrestrial Systems Model (CTSM) given its comprehensive process representations for cold regions. We conducted optimization for uncoupled CTSM to improve its performance in terrestrial hydrologic simulations, especially streamflow and snow (Cheng et al., 2023). In order to maintain the quality for both hydroclimate and terrestrial hydrologic simulation, we implemented a strategy of iterative testing and re-optimization of CTSM. This dataset was then generated using RASM with optimized CTSM parameters and manually tuned WRF microphysics. The historical simulation was evaluated against multiple observational datasets for five key weather variables and hydrologic fluxes, including precipitation, air temperature, snow fraction, evaporation-to-precipitation ratios, and streamflow. The evaluation details can be found in Cheng et al. (2024).

水文气候与陆地水文过程对阿拉斯加及育空河流域的当地社区、生态系统与经济均具有显著影响。因此，本研究采用区域北极系统模型（Regional Arctic Systems Model, RASM）对陆气耦合过程进行模拟，并生成了4公里网格分辨率的气候与水文数据集，以加深对该区域水文气候及陆地水文过程的理解。本模拟的研究区域涵盖美国阿拉斯加州全境、育空河流域全部范围、加拿大西部部分区域以及俄罗斯东部沿海地区。该数据集包含两部分：1）1991-2021年水文年的历史气候模拟结果，可作为气候变化研究的基准数据集；2）基于伪全球变暖（Pseudo-Global Warming）方法、在未来温室气体排放情景SSP2-4.5下开展的2组未来情景模拟（对应等效水文年2035-2065）。上述两组未来模拟分别代表SSP2-4.5情景下，耦合模式比较计划第六阶段（Coupled Model Intercomparison Project Phase 6, CMIP6）中不同全球气候模式集合平均得到的中等变化与强变化情景。研究团队针对天气研究与预报（Weather Research and Forecast, WRF）大气模式的微物理方案进行了手动调试，以实现最优模拟性能。鉴于社区陆地系统模型（Community Terrestrial Systems Model, CTSM）对寒区过程具有全面的表征能力，本研究使用其替换了区域北极系统模型中的陆面分量。本研究还针对非耦合模式下的CTSM开展了优化，以提升其在陆地水文模拟（尤其是径流与积雪模拟）中的表现（Cheng等，2023）。为保障水文气候与陆地水文模拟的质量，研究团队采用了迭代测试与重新优化CTSM参数的策略。最终，本数据集基于搭载了优化后CTSM参数与手动调试微物理方案的区域北极系统模型生成。研究团队针对历史模拟结果，选取降水、气温、积雪占比、蒸发降水比与径流5项关键气象变量及水文通量，与多套观测数据集开展了验证。验证细节可参见Cheng等（2024）。