Seasonal emergence of human-caused expansion of the boreal tropical hydrological cycle

By modifying precipitation and surface wind patterns, the edges of the tropical hydrological cycle set the boundaries between the dry subtropical and wet temperate zones on Earth. By the end of this century, climate models project a poleward shift of the tropical hydrological cycle edge, which will have large climate impacts in arid and semi-arid regions. Over recent decades, anthropogenic emissions have indeed been found to shift the Southern Hemisphere tropical edge poleward, but their role in the Northern Hemisphere is unclear. Here, using sea-level pressure measurements and atmospheric reanalyses, we constrain the poleward shift of the Northern Hemisphere hydrological cycle edge and show that during autumn it exceeded the bounds of internal variability. The emerged poleward shift is found to likely stem from anthropogenic emissions, specifically over the Pacific and Atlantic basins. The human-induced hydrological cycle changes suggest wider consequences for water availability in boreal subtropical regions.