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North China Plain is the largest agricultural production center in China and wheat-maize rotation is a widespread cultivation practice in this area. As gross primary production (GPP) is a proxy of land productivity, research on its spatial-temporal dynamics helps understand the variation of grain production in wheat-maize rotation. Here, Moderate Resolution Imaging Spectroradiometer (MODIS) data and ground observation data were combined to drive Vegetation Photosynthesis Model (VPM) in GPP estimation over wheat-maize rotation area during 2000–2015. Annual GPP has increased by 540.95 g C m−2 year−1 from 2000 to 2015, while total annual GPP has grown ∼150% than that of 2000. Moreover, annual GPP showed an increasing trend in the consecutively wheat-maize rotation area between 2000 and 2015. A strong linear relationship between GPP estimates and grain production demonstrated the potential of using VPM model to evaluate grain production in wheat-maize rotation area of Henan province, China. [ABSTRACT FROM AUTHOR]

There is an urgent need to understand the characteristics of both precipitation and drought in arid regions of China. Different indexes may provide differing results in terms of the detection and estimation of the temporal and spatial extent of droughts. In this study, the temporal and spatial characteristics of rainfall and drought at 53 meteorological stations from 1960 to 2016 across the Xinjiang region of China were analyzed. Four precipitation-related indexes (precipitation concentration degree (PCD), precipitation concentration period (PCP), standardized precipitation index (SPI), and long-cycle drought–flood abrupt alternation index (LDFAI)) were used to investigate the spatial and temporal patterns of drought and flood. In addition, the Bayesian method and Pettitt test were used as detection tools to identify changing points in precipitation time series. The study indicated the following: (1) a wetting tendency was evident in recent years and was supported by the upward trend in SPI and inter-decadal variation in summer precipitation; (2) the spatial patterns and tendencies of PCD, PCP, and SPI were markedly different in southern and northern Xinjiang; (3) compared with the Pettitt test, use of the Bayesian method provided data closer to the real drought events; (4) it is suggested that multiple indices be used for detecting precipitation and drought characteristics as use of the SPI may lead to other indexes related to flood and drought risks being ignored. [ABSTRACT FROM AUTHOR]

Frost heave and thaw settlement of subgrade is the most typical engineering disease in permafrost regions, which seriously threatens the safe construction and operation of transportation infrastructure. On the basis of the Modified Cam Clay model, a thermoelastoplastic constitutive model of unsaturated frozen soil is proposed. This model can effectively describe two key issues of the mechanical behavior of frozen soils, that is, soil hardening caused by temperature reduction and volume compression during thawing. The proposed constitutive model is realized in the established thermo-hydro-mechanical (THM) coupled mathematical model, and the reliability of the coupled model is verified by comparing with the experimental results. In addition, the proposed THM framework is applied to describe the long-term freezing and thawing behavior of typical railway subgrade sections in the permafrost region of western China. The results show that water-heat transfer and deformation frequently occur on the subgrade surface as the seasons change. Moreover, the variation of thaw settlement is greater than that of frost heave, which seriously threatens the operation safety of railways in permafrost regions. • A thermoelastoplastic constitutive model of unsaturated frozen soil is proposed. • A THM framework considering frost heave and thaw settlement is established. • Long-term deformation of a railway subgrade in a permafrost region is simulated. [ABSTRACT FROM AUTHOR]

The long-term drying/wetting (D/W) and freezing/thawing (F/T) cycles damage the structure of the roadbed soil in loess areas, leading to a series of engineering geological disasters, such as roadbed collapse and cracking. In this study, a series of field monitoring was carried out on the Jihe Expressway, which was built on the Loess Plateau in China. It shows that drying/wetting (D/W) and freezing/thawing (F/T) cycles are important factors leading to periodic settlement and heave of loess roadbeds. A new temperature-controlled unsaturated soil triaxial apparatus was developed to explore the deformation mechanism of compacted loess under D/W and F/T cycles. The results of laboratory tests indicate that, in the isotropic stress state, both D/W and F/T cycles can reduce the void ratio and increase the volume deformation of compacted loess. In the D/W cycle, the soil samples show the collapse behavior, but the deformation of heavily over-consolidated samples is relatively less compared with lightly over-consolidated samples. On the other hand, repeated F/T cycles lead to fluctuating changes in the volume of compacted loess. Increasing the dry density can effectively reduce the deformation caused by F/T cycles. Moreover, the combination of the D/W and F/T cycles may further enhance the volume changes of the compacted loess. As the number of D/W and F/T cycles increases, the compressibility and irrecoverable deformation of the compacted loess increases, leading to a deterioration of its engineering properties. • The characteristics and causes of roadbed deformation in loess area were investigated by field monitoring. • A new temperature-controlled unsaturated soil triaxial apparatus was developed. • The mechanism of D/W and F/T cycles on the deformation of compacted loess was discussed. • The coupling of D/W and F/T intensifies the volume changes of the compacted loess. [ABSTRACT FROM AUTHOR]