No abstract

Alpine wetlands in the Tibetan Plateau (TP) play a crucial role in the regional hydrological cycle due to their strong influence on surface ecohydrological processes; therefore, understanding how TP wetlands respond to climate change is essential for projecting their future condition and potential vulnerability. We investigated the hydrological responses of a large TP wetland complex to recent climate change, by combining multiple satellite observations and in-situ hydro-meteorological records. We found different responses of runoff production to regional warming trends among three basins with similar climate, topography and vegetation cover but different wetland proportions. The basin with larger wetland proportion (40.1%) had a lower mean runoff coefficient (0.173˘0.006), and also showed increasingly lower runoff level (´3.9% year´1, p = 0.002) than the two adjacent basins. The satellite-based observations showed an increasing trend of annual non-frozen period, especially in the wetland-dominated region (2.64 day¨year´1, p < 0.10), and a strong extension of vegetation growing-season (0.26-0.41 day¨year´1, p < 0.10). Relatively strong increasing trends in evapotranspiration (ET) (~1.00 mm¨year´1, p < 0.01) and the vertical temperature gradient above ground surface (0.043˝C¨year´1, p < 0.05) in wetland-dominant areas were documented from satellite-based ET observations and weather station records. These results indicate recent surface drying and runoff reduction of alpine wetlands, and their potential vulnerability to degradation with continued climate warming.

No abstract

Understanding environmental controls on vegetation spring onset (SO) in the Tibetan Plateau (TP) is crucial to diagnosing regional ecosystem responses to climate change. We investigated environmental controls on the SO of the TP grasslands using satellite vegetation index (VI) from the 3rd Global Inventory Modeling and Mapping Studies (GIMMS3g) product, with in situ air temperature (T a ) and precipitation (Prcp) measurement records from 1982 to 2008. The SO was determined using a dynamic threshold method based on a 25% threshold of seasonal VI amplitude. We find that SO shows overall close associations with spring T a , but is also subject to regulation from spring precipitation. In relatively dry but increasingly wetting (0.50 mm¨year´1, p < 0.10) grasslands (mean spring Prcp = 22.8 mm; T a =´3.27˝C), more precipitation tends to advance SO (´0.146 day¨mm´1, p = 0.150) before the mid-1990s, but delays SO (0.110 day¨mm´1, p = 0.108) over the latter record attributed to lower solar radiation and cooler temperatures associated with Prcp increases in recent years. In contrast, in relatively humid TP grasslands (73.0 mm;´3.51˝C), more precipitation delays SO (0.036 day¨mm´1, p = 0.165) despite regional warming (0.045˝C¨year´1, p < 0.05); the SO also shows a delaying response to a standardized drought index (mean R = 0.266), indicating a low energy constraint to vegetation onset. Our results highlight the importance of surface moisture status in regulating the phenological response of alpine grasslands to climate warming.

No abstract