Changes of timing and duration of the near-surface soil freeze/thaw cycles on the Tibetan Plateau in the highly wetting period from 1998 to 2005

Abstract

A dual cooling and warming effect of precipitation over the Tibetan Plateau (TP) on permafrost has been reported recently through numerical methods, but predictive relationships among summer rainfall in warm season, snow cover depth in cold season, and thermal regime of frozen ground still have not been well demonstrated, although it will become even more important as precipitation has been projected to increase continuously. Previous studies have confirmed the pivotal wetting period from 1998 to 2005 over the TP. In this study, the anomalies of first date, last date, duration, and actual number of days in the near-surface soil freeze from 1998–2005 were investigated across the TP based on the records of 58 meteorological stations. The results reveal that precipitation plays a primary role on thermal dynamics in arid and semi-arid zones, while in humid and semi-humid zones, the variations in thermal regimes are closely related to air temperature. Thermal response of frozen ground to wetting depends on different precipitation types, which varies seasonally. The combined effects of thinning snow cover depth and increasing rainfall across the TP inhibit the thermal response of permafrost in dry zones to climate warming, while air warming dominated the thermal degradation of seasonal frozen ground in wetter zones.

Dynamics of Freezing/Thawing Indices and Frozen Ground from 1961 to 2010 on the Qinghai-Tibet Plateau

“…Climate warming also benefits the vegetation growth [21][22][23][24], and can induce a earlier start date of frozen through feedbacks to regional climates [25]. Observational analysis further presented that the greening QTP can amplify the warming impact of spring snow cover on surface seasonally frozen ground (SFG), and also can intensify the warming effect of summer rainfall on top permafrost [26]. These studies have shown us the uneven thermal responses of frozen ground to accelerated climate change and the vegetation growth on the QTP served as potential connections.…”