Data from: A century of changing flows: forest management changed flow magnitudes and warming advanced the timing of flow in a southwestern US river

The continued provision of water from rivers in the southwestern United States to downstream cities, natural communities and species is at risk due to higher temperatures and drought conditions in recent decades. Snowpack and snowfall levels have declined, snowmelt and peak spring flows are arriving earlier, and summer flows have declined. Concurrent to climate change and variation, a century of fire suppression has resulted in dramatic changes to forest conditions, and yet, few studies have focused on determining the degree to which changing forests have altered flows. In this study, we evaluated changes in flow, climate, and forest conditions in the Salt River in central Arizona from 1914–2012 to compare and evaluate the effects of changing forest conditions and temperatures on flows. After using linear regression models to remove the influence of precipitation and temperature, we estimated that annual flows declined by 8–29% from 1914–1963, coincident with a 2-fold increase in basal area, a 2-3-fold increase in canopy cover, and at least a 10-fold increase in forest density within ponderosa pine forests. Streamflow volumes declined by 37–56% in summer and fall months during this period. Declines in climate-adjusted flows reversed at mid-century when spring and annual flows increased by 10–31% from 1964–2012, perhaps due to more winter rainfall. Additionally, peak spring flows occurred about 12 days earlier in this period than in the previous period, coincident with winter and spring temperatures that increased by 1–2°C. While uncertainties remain, this study adds to the knowledge gained in other regions that forest change has had effects on flow that were on par with climate variability and, in the case of mid-century declines, well before the influence of anthropogenic warming. Current large-scale forest restoration projects hold some promise of recovering seasonal flows.美国西南部河流向下游城市、自然群落及物种持续供水的能力正面临风险，其诱因为近几十年来的气温升高与干旱状况加剧。积雪覆盖率与降雪量均出现下降，融雪与春季峰值径流的出现时间提前，夏季径流量则有所衰减。 与气候变化及气候变异同步发生的是，长达一个世纪的森林防火措施已令森林状况发生显著改变，但目前鲜有研究聚焦于探明森林变化对径流的影响程度。本研究以1914年至2012年间亚利桑那州中部盐河的径流、气候及森林状况变化为研究对象，对比评估森林状况与气温变化对径流的影响。 研究人员通过线性回归模型剔除降水与气温的影响后，估算得出1914年至1963年间年径流量下降了8%至29%，同期美国黄松（ponderosa pine）林的断面积（basal area）增长1倍，冠层覆盖率（canopy cover）提升2至3倍，森林密度至少增加10倍。此时期内夏季与秋季的径流量降幅达37%至56%。 经气候校正后的径流量在20世纪中期出现逆转：1964年至2012年间，春季与年径流量增长了10%至31%，这或许与冬季降雨量增加有关。此外，此时期内春季峰值径流的出现时间较前一时期提前约12天，与冬季及春季气温升高1至2摄氏度的情况相契合。 尽管仍存在不确定性，但本研究补充了其他区域的已有研究成果，证明森林变化对径流的影响可与气候变异相匹敌；而就20世纪中期的径流衰减而言，其影响远早于人为变暖的作用。当前开展的大规模森林恢复项目，对恢复季节性径流量具备一定潜力。