Faster increase in evapotranspiration in permafrost-dominated basins in the warming Pan-Arctic

Land evapotranspiration (ET) is a key factor in the hydrological cycle and is particularly sensitive to climate change. In the past few decades, the Pan-Arctic region has witnessed a strong warming trend, causing substantial changes in ground surface conditions. However, it remains poorly understood how ET varies across such a region. Here, we investigated the spatial-temporal changes in ET over six large Pan-Arctic river basins using corrected ET estimates from GLEAM and ERA5-Land during 1981-2020. The 40-year mean annual ET in the Ob, Yenisei, Lena, Kolyma, Yukon, and Mackenzie River basins were approximately 366 mm.yr(-1), 271 mm.yr(-1), 228 mm.yr(-1), 239 mm.yr(-1), 278 mm.yr(-1), and 295 mm.yr(-1), respectively. Climatologically, permafrost-dominated basins tend to have lower ET than those with less permafrost. Temporally, the annual ET in permafrost-dominated basins has increased faster than that in less permafrost-developed basins over the past four decades. This increase is particularly prominent in the Kolyma River basin (completely covered by permafrost), where the significant trend in ET (7.5 mm.decade(-1), p < 0.001) is the highest among the six basins. Further analyses show that intensified permafrost thawing is likely the key factor contributing to increased ET in permafrost-dominated basins, as seen from the positive relationship between the thickening in the active layer (ALT) and the change in ET. Under an amplified warming background, ET in permafrost-dominated regions is expected to continue to increase. The results reported in this study improve our understanding of the variations in ET and the associated mechanisms in the changing Arctic.

Automated summary

Land evapotranspiration is a key factor in the hydrological cycle and is highly sensitive to climate change. This study investigated the spatial-temporal changes in evapotranspiration in six large Pan-Arctic river basins and found that evapotranspiration in permafrost-dominated regions has been increasing faster than in other regions, with intensified permafrost thawing being the likely key factor contributing to this increase.