At high elevations of ice sheets, melting snow generally percolates and refreezes, so does not contribute to the shrinking of the ice sheet. Here, we systematically map the runoff area of the Greenland ice sheet using surface rivers visible on satellite imagery. Between 1985 and 2020, the maximum runoff elevation rose by 58–329 metres, expanding the runoff area by 29% (–8%/+6%). Excess melt beyond the refreezing capacity of pores in snowfall has created near-impermeable ice slabs that sustain surface runoff even in cooler summers. We show that two surface mass balance models over-estimate the runoff area by 16–30%. Once restricted to our observed areas, they indicate that 5–10% of recent runoff probably comes from the expanded runoff area. Runoff from higher elevations is sensitive to projected warming as further increases in the runoff limit will increase the runoff area disproportionately.

在冰盖的高海拔处，融化的雪通常会渗透并重新冻结，因此不会导致冰盖的缩小。在这里，我们使用卫星图像上可见的地表河流系统地绘制了格陵兰冰盖的径流区域。1985 年至 2020 年间，最大径流海拔上升了 58-329 米，径流面积扩大了 29%（–8%/+6%）。降雪中超出孔隙再冻结能力的过量融化形成了几乎不透水的冰板，即使在凉爽的夏季也能维持地表径流。我们表明，两个地表质量平衡模型将径流面积高估了 16-30%。一旦仅限于我们观察到的区域，它们表明最近径流的 5-10% 可能来自扩大的径流区域。