In the Southwest United States, water resources depend heavily on snowpacks, which are temporally and spatially limited in this warm, semiarid region. Snow accumulation and ablation in the Southwest are heavily influenced by forest structure. Therefore, water resource managers urgently need to understand the future impacts of unprecedented forest changes now occurring from drought, insect infestation, and forest management. Here, we present state‐of‐the‐art maps and time series of snow water equivalent (SWE), which account for spatial variability of snow depth and snow density over a large range of forest structure and topographies in the highlands of central Arizona. We show that the degree of forest cover and its geometry largely determine which areas have more/less snow accumulation and faster/slower ablation. Compared with under‐canopy areas, open areas can have 20–30% more accumulation and ablation rates can vary by 15–30% in sunny areas versus shaded areas. Although SWE response to forest cover is widely variable, depending on how much shading the trees provide versus how much snow is intercepted and lost through canopy sublimation, dense forests generally have less SWE than sparser forests. In general, SWE is optimized at intermediate levels of forest cover (~30–50%) on flat and north‐facing slopes. Somewhat counterintuitively, increasing forest cover generally causes a reduction of SWE on south‐facing slopes, where trees are less effective at reducing radiative forcing at the snow surface due to less efficient shading and increased enhancement of longwave radiation from the warm canopy.

中文翻译：

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森林覆盖和地形控制着美国西南半干旱的稀薄暂时性积雪

在美国西南部，水资源严重依赖积雪，积雪在这个温暖的半干旱地区受到时间和空间限制。西南地区的积雪和烧蚀受到森林结构的严重影响。因此，水资源管理人员迫切需要了解干旱，昆虫侵染和森林管理目前正在发生的前所未有的森林变化对未来的影响。在这里，我们介绍了最新的雪水当量（SWE）图和时间序列，这些图和时间序列说明了亚利桑那州中部高地的大范围森林结构和地形上雪深和雪密度的空间变异性。我们表明，森林覆盖的程度及其几何形状在很大程度上决定了哪些地区积雪更多/更少，而烧蚀速度更快/更慢。与树冠下区域相比，在阴暗地区，空旷地区的积聚可增加20％至30％，消融率在晴天区域可变化15％至30％。尽管SWE对森林覆盖的响应变化很大，但取决于树木提供多少遮荫与通过冠层升华截留和损失多少雪，茂密的森林通常比稀疏森林的SWE少。通常，在平坦和北坡的森林覆盖率中等水平（约30-50％）下，SWE进行了优化。有点与直觉相反，森林覆盖率的增加通常会导致南坡的SWE减少，这是由于遮阳效率降低以及温暖的树冠对长波辐射的增强作用增强，树木在降低雪表面的辐射强迫方面效果不佳。