Climate Change Sensitivity Index for Pacific Salmon Habitat in Southeast Alaska

Global climate change may become one of the most pressing challenges to Pacific Salmon conservation and management for southeast Alaska in the 21st Century. Predicted hydrologic change associated with climate change will likely challenge the ability of specific stocks to adapt to new flow regimes and resulting shifts in spawning and rearing habitats. Current research suggests egg-to-fry survival may be one of the most important freshwater limiting factors in Pacific Salmon's northern range due to more frequent flooding events predicted to scour eggs from mobile spawning substrates. A watershed-scale hydroclimatic sensitivity index was developed to map this hypothesis with an historical stream gauge station dataset and monthly multiple regression-based discharge models. The relative change from present to future watershed conditions predicted for the spawning and incubation period (September to March) was quantified using an ensemble global climate model average (ECHAM5, HadCM3, and CGCM3.1) and three global greenhouse gas emission scenarios (B1, A1B, and A2) projected to the year 2080. The models showed the region's diverse physiography and climatology resulted in a relatively predictable pattern of change: northern mainland and steeper, snow-fed mountainous watersheds exhibited the greatest increases in discharge, an earlier spring melt, and a transition into rain-fed hydrologic patterns. Predicted streamflow increases for all watersheds ranged from approximately 1-fold to 3-fold for the spawning and incubation period, with increased peak flows in the spring and fall. The hydroclimatic sensitivity index was then combined with an index of currently mapped salmon habitat and species diversity to develop a research and conservation priority matrix, highlighting potentially vulnerable to resilient high-value watersheds. The resulting matrix and observed trends are put forth as a framework to prioritize long-term monitoring plans, mitigation experiments, and finer-scale climate impact and adaptation studies.

全球气候变化或成为21世纪阿拉斯加东南部太平洋鲑鱼（Pacific Salmon）保护与管理面临的最紧迫挑战之一。据预测，与气候变化相关的水文变化或将制约特定鲑鱼种群适应全新径流情势的能力，并引发产卵与育幼栖息地的相应变迁。现有研究表明，由于预测洪水事件将愈发频繁，会将鱼卵从移动性产卵基质中冲刷殆尽，因此鱼卵到稚鱼的存活率可能是太平洋鲑鱼北部分布区最为关键的淡水限制因子之一。研究人员构建了流域尺度（watershed-scale）的水文气候敏感性指数（hydroclimatic sensitivity index），结合历史水文站（stream gauge station）数据集与基于多元回归的月度径流模型，对该假说进行了空间制图。利用集合全球气候模式平均值（ensemble global climate model average），涵盖ECHAM5、HadCM3与CGCM3.1三种模式，以及预估至2080年的三种温室气体排放情景（greenhouse gas emission scenarios，分别为B1、A1B与A2），量化了产卵孵化期（spawning and incubation period，即每年9月至次年3月）从当前到未来流域条件的相对变化。模型结果显示，该区域多样的地貌特征与气候背景造就了相对可预测的变化格局：北部大陆地区以及坡度更陡的积雪补给型山地流域（snow-fed mountainous watersheds），径流量（streamflow）增幅最大，春季融雪提前，并向雨水补给型水文模式（rain-fed hydrologic patterns）转变。所有流域在产卵孵化期的预估径流量增幅约为1倍至3倍，春季与秋季的峰值流量亦有所增加。随后，研究人员将水文气候敏感性指数与已绘制的鲑鱼栖息地及物种多样性指数相结合，构建了研究与保护优先级矩阵（conservation priority matrix），以识别易受气候影响与恢复力较强的高价值流域。所得矩阵与观测到的变化趋势可作为框架，用于优先制定长期监测计划、减缓实验（mitigation experiments）以及更精细尺度的气候影响与适应性研究。