Soil Hydraulic and Thermal Properties for Land Surface Modelling over the Tibetan Plateau [version 1]

The in situ measurement of soil (hydraulic and thermal) property profiles were taken across the three climate zones (arid, semi-arid & semi-humid) over the Tibetan Plateau. In each climate zone, 1) the soil was sampled (c.a. 200 g) with a plastic bag used to measure gravel content, soil texture and soil organic content; 2) the soil was sampled with standard sample rings (5cm in height, 100 cm3 in volume) for the determination of bulk density, porosity and thermal conductivity; 3) for deriving the Soil Water Retention Curve (SWRC), a dedicated small sample ring (1 cm in height, 20 cm3 in volume) was used; 4) the in situ Ks was measured using the Aardvark permeameter, a fully automated constant-head borehole permeameter. Using these samples, the laboratory analyses were carried out with reference to standard methods. The quality of dataset was evaluated based on quality indicators from World Soil Information Institute and on cross check using values in the literature. This dataset was further used to evaluate the existing soil datasets over the Tibetan Plateau

An Air-to-Soil Transition Model for Discrete Scattering–Emission Modelling of L-Band Radiometry at Maqu site, the Eastern Tibetan Plateau

In situ ELBARA-III radiometer observations of brightness temperature T_B^p (with p = H, V) in Maqu site, the eastern Tibetan Plateau were used for investigations on roughness effects over natural land surface and on coherent and incoherent emission processes in radiative transfer modelling. Aided by in situ soil moisture (SM) and temperature profile measurments and the MCD15A2H - MODIS/Terra+Aqua Leaf Area Index, the study simulated T_B^p and demonstrated a necessity of an air-to-soil transition (AS) model in incorporating roughness effects for understanding seasonal L-band radiometry. Supported by the in situ meteorological observation data in Maqu site, the applicability and uncertainty of AS-based models in T_B^p simulations were discussed. The meteorological data involve precipitation intensity, air temperature, and albedo with ground temperature, which were derived from the in situ four components radiation measurement (i.e., up- and down-welling shortwave and longwave radiations)

HydroThermal Dynamics of Frozen Soils on the Tibetan Plateau during 2015-2016

The hydrothermal dynamics of frozen soil were monitored at a typical meadow ecosystem on the Tibetan Plateau. Soil temperature/moisture profiles were automatically measured at a 30-min. interval by 5TM ECH2O probes (Decagon Devices, Inc., USA) installed at the following depths: 5 cm, 10 cm, 20 cm, 40cm, and 80 cm. The turbulent heat fluxes were measured by an eddy-covariance (EC) system (LI-COR 7500, Campbell Scientific). STEMMUS-FT (Simultaneous Transfer of Energy, Mass and Momentum in Unsaturated Soil with Freeze-Thaw process) model, with two control experiments (Ctrl1 for Van Genuchten hydraulic scheme and Ctrl2 for Clapp and Hornberger hydraulic scheme), was employed to reproduce the simultaneous movement of soil moisture and heat flow in the frozen soil. With the aid of physically based STEMMUS-FT model and in situ measurements, we can investigate the underlying mechanisms of the water and heat transfer in frozen soils

Data underlying the research on Seasonal and interannual variation in evapotranspiration, energy flux, and Bowen ratio over a dry semi-humid cropland in Northwest China

In this dataset, we report on five years of energy flux measurements observed by EC over the Guanzhong Plain cropland. The objectives of this study were to (1) characterize seasonal variation in ET and its components in order to identify the important controlling environmental factors; (2) investigate seasonal variation in energy fluxes and determine the energy budget; and (3) assess the effects of crop growth on ET, Bowen ratio (β), the Priestley-Taylor coefficient (α), and canopy conductance (Gc) and examine the relationships between Gc and other surface parameters

Development of the Hydrus-1D freezing module and its application in simulating the coupled movement of water, vapor, and heat

In cold regions, freeze-thaw cycles play a critical role in many engineering and agricultural applications and cause soil water flow and heat transport studies to be much more complicated due to phase changes involved. A fully coupled numerical module for simulating the simultaneous movement of water, vapor, and heat during freezing-thawing periods was developed and incorporated in the Hydrus-1D software in this study. To avoid numerical instabilities caused by a sudden increase in the apparent heat capacity during a phase change, a new approach based on the available energy concept was adopted to adjust soil temperature when the freezing temperature is reached. The proposed freezing module's performance was then validated using experimental data collected at three field sites with typical seasonal freezing/thawing processes. Results showed that the model could efficiently obtain a convergent solution and that simulated soil moisture and temperature variations captured the observed data well. Driven by soil matric potential and temperature gradients, both liquid water and water vapor flowed towards the freezing front. The isothermal liquid flux was the most significant component of overall flow in most soil depths except in the frozen layer, where it decreased by 1–5 orders of magnitude from values before freezing. Instead, the thermal vapor flux was the dominant moisture transfer mechanism in the frozen layer and contributed about 10% to the ice formation. These results indicate that the model, which considers the coupled movement of water, vapor, and heat, can better describe the physical mechanisms of the hydrological cycle in the vadose zone during the freezing-thawing periods. © 2021 Elsevier B.V

A 10-year (2009-2019) surface soil moisture dataset produced based on in situ measurements collected from the Tibet-Obs

The Tibet-Obs consists of three regional-scale soil moisture (SM) monitoring networks, i.e. the Maqu, Naqu, and Ngari (including Ali and Shiquanhe) networks. This surface SM dataset includes the original 15-min in situ measurements collected at a depth of 5 cm by multiple SM monitoring sites of the three networks, and the spatially upscaled SM records produced for the Maqu and Shiquanhe networks

Supplementary material to the paper: Status of the Tibetan Plateau observatory (Tibet-Obs) and a 10-year (2009-2019) surface soil moisture dataset

The Tibet-Obs consists of three regional-scale soil moisture (SM) monitoring networks, i.e. the Maqu, Naqu, and Ngari (including Ali and Shiquanhe) networks. This surface SM dataset includes the original 15-min in situ measurements collected at a depth of 5 cm by multiple SM monitoring sites of the three networks, and the spatially upscaled SM records produced for the Maqu and Shiquanhe networks