Hydrological impacts of near-surface soil warming on the Tibetan Plateau

Climate warming can cause intense changes in regional soil freeze/thaw dynamics and thus exerts strong effects on hydrological processes. Because permafrost conditions vary widely across the Tibetan Plateau (TP), a better understanding the potential influences of permafrost types is helpful to project future hydrological changes. Using multilayer soil temperatures from 45 meteorological stations, this study investigated regional near-surface soil warming on the TP (1981-2015) and related hydrological implications in two typical alpine basins. In cold and warm seasons, near-surface soil temperature gradient (0-5 cm) showed significant increasing trends with average rates of 0.31 +/- 0.13 and 0.19 +/- 0.08 degrees C per decade (p < 0.05), respectively. This implied increasingly more heat transferred downward from the ground surface annually, which also appeared in the deeper layer (5-10 cm) but was relatively weaker. Our results also reflected that increasing warming tended to cause higher baseflow (0.66 m(3) s(-1) a(-1), p < 0.10) and quicker groundwater recession (-0.05 per decade, p < 0.05) in the permafrost-dominated (>60%) basin, but had much weaker hydrological effects in the low-permafrost (<20%) basin. The contrasting responses suggested similar hydrological impacts related to the fraction of permafrost coverage as in the circum-Arctic regions. Our study implies that the warming-induced weakening of freezing process has complicated hydrological impacts in the Tibetan basins dependent on the fraction of permafrost coverage.