Frozen soil degradation and its effects on surface hydrology in the northern Tibetan Plateau

Abstract

Frozen soil was simulated at six seasonally frozen and seven permafrost stations over the northern Tibetan Plateau using the Variable Infiltration Capacity (VIC) model for the period of 1962-2009. The VIC model resolved the seasonal cycle and temporal evolution of the observed soil temperatures and liquid soil moisture well. The simulated long-term changes during 1962-2009 indicated mostly positive trends for both soil temperature and soil moisture, and negative trends for soil ice content at annual and monthly time scales, although differences existed among the stations, soil layers, and seasons. Increases in soil temperature were due mainly to increases in daily air temperature maxima and internal soil heat conduction, while decreases in soil ice content were related to the warming of frozen soil. For liquid soil moisture, increases in the cold months can be attributed to increases in soil temperature and enhanced soil ice melt while changes in the warm months were the results of competition between positive precipitation and negative soil temperature effects. Precipitation and liquid soil moisture were strongly correlated with evapotranspiration and runoff but had various degrees of correlations with base flow during May-September. Seasonally frozen stations displayed longer and more active hydrological processes than permafrost stations. Slight enhancement of the surface hydrological processes at the study stations was indicated, due to the combined effects of precipitation changes, which were dominant, and frozen soil degradation.

Change in frozen soils and its effect on regional hydrology, upper Heihe basin, northeastern Qinghai–Tibetan Plateau

“…This study also showed that the thawing of frozen soils increased the liquid soil moisture in the upper Heihe basin, which is consistent with the finding of Subin et al (2013) using the CLM to simulate northern high-latitude permafrost regions, and the findings of Cuo et al (2015) using the VIC model to simulate 13 sites on the QTP. In contrast, Lawrence et al (2015) found that permafrost thawing reduced soil moisture based on CLM simulations of the global permafrost region.…”

“…Subin et al (2013) and Lawrence et al (2015) used the CLM to simulate global changes in permafrost. Cuo et al (2015) used the VIC to simulate frozen soil changes and their hydrological impacts on the plot scale in the headwaters of the Yellow River. The GEOtop model (Endrizzi et al, 2014) simulates three-dimensional water flux and vertical heat transfer in soil, but it is difficult to apply to regional investigations.…”

Simulated annual changes in plant functional types and their responses to climate change on the northern Tibetan Plateau

“…For precipitation, only the amount but not the frequency is changed. These scenarios bear similarity to what has been identified over the NTP in recent decades in general in that S1 plus S2, S3, S4 and S5 represent regional frozen soil degradation, warming, wetting and elevated CO 2 trends, respectively, although the rates of changes and spatial patterns differ (Cuo et al, 2013b(Cuo et al, , 2015. Uniform perturbations are introduced to provide the benchmark for the climate sensitivity comparison across the region and to derive sensitivity spatial pattern.…”

“…Jin et al (2013) found that spatial patterns and temporal trends of phenology were parallel with the corresponding soil physical conditions over the TP, and that 1 • C increase in soil temperature could advance the start of the growing season by 4.6-9.9 days. On the TP where a vast area of seasonally frozen (SFS) and permafrost (PFS) soil exists (Cheng and Jin, 2013), global warming induced frozen soil degradation (Cuo et al, 2015) could potentially affect litter decomposition and plant phenology .…”

“…In particular, the northern TP (NTP;(30)(31)(32)(33)(34)(35)(36)(37)(38)(39)(40)(90)(91)(92)(93)(94)(95)(96)(97)(98)(99)(100)(101)(102)(103)(104)(105) • E) where the Yellow, Yangtze and Mekong Rivers originate, is crucially important in providing water and other ecosystem services to the plateau itself and the downstream regions hosting billions of population. Changes in the composition of different PFTs, and consequently FPCs, could substantially affect surface evapotranspiration, soil water storage and streamflow (Cuo et al, 2009(Cuo et al, , 2013a(Cuo et al, , 2015Weiss et al, 2014;Dahlin et al, 2015), and the partition of net radiation into the sensible and latent heat fluxes, consequently affecting the onset and intensity of south and east Asian monsoon circulations (Wu et al, 2007;Cui et al, 2015). Although there are some studies that connect NDVI (normalized difference vegetation index) and NPP (net primary production) to precipitation, air temperature, and CO 2 concentrations on the TP (Zhong et al, 2010;Chen et al, 2012;Piao et al, 2012), very few studies have examined PFT changes and their relationships with climate for the region (Wang et al, 2011).…”