Large sinuous rivers are slowing down in a warming Arctic

Climate warming affects permafrost regions, with strong impacts on the environment such as the greening of river plains. Here the authors use satellite data to show that these changes have stabilized large Arctic sinuous rivers by slowing their lateral migration by about 20% over the past half-century.Arctic regions are disproportionately affected by atmospheric warming, with cascading effects on multiple surface processes. Atmospheric warming is destabilizing permafrost, which could weaken riverbanks and in turn increase the lateral mobility of their channels. Here, using timelapse analysis of satellite imagery, we show that the lateral migration of large Arctic sinuous rivers has decreased by about 20% over the last half-century, at a mean rate of 3.7 parts per thousand per year. Through a comparison with rivers in non-permafrost regions, we hypothesize that the observed migration slowdown is rooted in a series of indirect effects driven by atmospheric warming, such as bank shrubification and decline in overland flow and seepage discharge along channel banks, linked in turn to permafrost thaw. As lower migration rates directly impact the residence timescales of sediment and organic matter in floodplains, these surprising results may lead to important ramifications for watershed-scale carbon budgets and climate feedbacks.

气候变暖影响多年冻土区，对环境产生强烈影响，比如河漫滩的绿化。在此，作者利用卫星数据表明，这些变化在过去半个世纪里使大型北极蜿蜒河流趋于稳定，其侧向迁移速度减缓了约20%。北极地区受大气变暖的影响尤为严重，对多个地表过程产生连锁效应。大气变暖使多年冻土失稳，这可能会削弱河岸，进而增加河道的侧向移动性。在此，通过对卫星图像进行延时分析，我们发现大型北极蜿蜒河流的侧向迁移在过去半个世纪里减少了约20%，平均每年减少3.7‰。通过与非多年冻土区的河流进行比较，我们推测观测到的迁移减缓源于大气变暖驱动的一系列间接影响，比如河岸灌木化以及沿河岸的坡面流和渗流流量的减少，而这些又与多年冻土融化相关。由于较低的迁移率直接影响洪泛区沉积物和有机物的停留时间尺度，这些令人惊讶的结果可能会对流域尺度的碳收支和气候反馈产生重要影响。