Land cover change plays a critical role in influencing hydrological responses. Change in land cover has impacted runoff across basins with substantial human interference; however, the impacts in basins with minimal human interference have been studied less. In this study, we investigated the impacts of directional land cover changes (forest to/from combined grassland and shrubland) in runoff coefficient (RC; ratio of runoff to precipitation) and runoff volume across 603 low human interference reference basins in the conterminous United States (CONUS). The results indicate basins with significant (p<0.05) increasing trends in runoff and RC were across the northeast and northwest regions of CONUS, and basins with decreasing trends were in the southern CONUS region. A unit percent increase in basin area from grassland and shrubland to forest was associated with a ∼4% decrease in RC across basins with decreasing RC trends. Similarly, a unit percent increase in basin area from forest to a combined grassland and shrubland was associated with a ∼1% increase in RC across increasing RC trend basins. Runoff volume was decreased (increased) by ∼25 × 10⁶ m³ yr⁻¹ (∼9 × 10⁶ m³ yr⁻¹) across basins with decreasing (increasing) trends in runoff and RC. When relating runoff volume with the area of directional land cover changes, each 1 km² increase in area from grassland and shrubland to forest resulted in a decrease of ∼530,000 m³ runoff volume across basins with decreasing trends. In contrast, each 1 km² increase in area from forest to grassland and shrubland increased runoff volume by ∼200,000 m³ across increasing trend basins. Basins in the southern region of CONUS were more impacted by runoff parameters (RC and runoff volume) from directional land cover changes than basins in the northern region. The findings of this study are useful for planning and managing water availability for sustainable and adaptive water resources management at regional scales.

土地覆盖变化在影响水文响应方面起着关键作用。土地覆盖的变化影响了流域间的径流，并受到了大量的人为干扰；然而，对人类干扰最小的盆地的影响研究较少。在这项研究中，我们调查了美国本土 603 个低人为干扰参考流域的定向土地覆盖变化（森林到/从草地和灌木地混合）对径流系数（RC；径流与降水的比率）和径流量的影响（美国）。结果表明流域显着 ( p<0.05) 径流和 RC 的增加趋势在美国大陆的东北和西北部地区，而减少趋势的流域在美国大陆南部地区。从草地和灌木地到森林，流域面积每增加一个百分比，流域间的 RC 下降约 4%，RC 趋势下降。类似地，从森林到草地和灌木地的流域面积每增加一个单位百分比，与 RC 趋势流域的 RC 增加约 1% 相关。径流体积减少（增加）~25 × 10 ⁶ m ³ yr ^-1（~9 × 10 ⁶  m ³  yr ^-1) 跨流域，径流和 RC 呈下降（上升）趋势。当将径流量与定向土地覆盖变化的面积联系起来时，从草地和灌木地到森林的面积每增加1 km ²导致流域间径流量减少约 530,000 m ³并呈下降趋势。相比之下，从森林到草地和灌木地的面积每增加1 km ^{2 会}增加约 200,000 m ^{3 的}径流量跨越上升趋势盆地。CONUS 南部地区的流域比北部地区的流域受定向土地覆盖变化的径流参数（RC 和径流量）的影响更大。这项研究的结果有助于规划和管理区域尺度的可持续和适应性水资源管理的可用水量。