The climate in Northwest China (NWC) has undergone a warming and wetting trend (WWT) since the 1980s, which has attracted considerable attention from the scientific and policy communities. However, the majority of previous studies have focused on overall effects of WWT, and very few have examined how land surface system responds to climate warming or wetting trend, respectively. For this purpose, this study uses the Community Land Model (CLM5) driven by the Chinese Meteorological Forcing Dataset (CMFD) to conduct four modeling experiments: a control experiment (CTRL) and three sensitivity experiments, in which the annual trend of air temperature (NonWarm), precipitation (NonWet), and both (NonWWT) are removed from the CMFD from 1979 to 2018. Compared to CTRL, the land hydrological variables (i.e. soil moisture, runoff and evapotranspiration) show a visible reduction in magnitude, interannual variability, as well as annual trend in NonWet, while they are enhanced in NonWarm. In both NonWarm and NonWet, the magnitude and trend of both net radiation and sensible heat fluxes increase, with a more pronounced change in NonWWT. Further analysis indicates that the land surface processes are more sensitive to wetting trend than to warming trend. Among all land surface hydrological variables and energy variables, runoff and snow cover fraction are the most susceptible to climate change. Overall, the effects of climate change in Ta and Pr on surface hydrological variables are non-linearly offsetting, while the effects on surface energy budgets are non-linearly superimposed. Compared to warming trend, wetting trend plays a larger impact on the variability of land surface processes in NWC.

Study region: The Northwest inland basins of China (NWC).Study focus: Terrestrial water resources, especially groundwater resources, are the main source of water for human activities and for maintaining the stability of the ecological environment in NWC. Excessive consumption of water resources will seriously affect the sustainable utilization of water resources and ecological security in this region. Therefore, it is urgent to clarify the long-term changes in water storage in this area in order to handle the pressure of future water re-sources and the natural environment. Using GRACE satellite datasets and global hydrological models (GHMs) products, this study analyzed spatiotemporal variations in terrestrial water storage anomalies (TWSA), groundwater storage anomalies (GWSA), soil moisture, snow water equivalent, and canopy interception combined anomalies (SSCA) in NWC through the application of the water balance, trend decomposition, and empirical orthogonal decomposition methods. Furthermore, the driving factors of water storage change and feasible water resource manage-ment strategies were discussed. New hydrological insights for the region: TWSA in the NWC has experienced a continuous decline over the past nearly 40 years, while SSCA has shown a weak increasing trend (0.03 cm yr-1). Since the availability of glacial retreat data (2003-2016), glacial water storage in the NWC has decreased by 0.09 cm per year, while TWSA, SSCA, and GWSA have changed at rates of -0.25, 0.02, and -0.18 cm yr-1, respectively. The North Tianshan Rivers Basin has become one of the areas with the most severe groundwater depletion in China. 2005-2010 was a turning period in the changes of TWSA, followed by widespread water loss across the NWC. Glacier and snow melt are the most important factors for the decline of TWSA in the Tianshan mountains area, and over -exploitation of groundwater by human activities is a secondary factor. For other regions, Groundwater losses remain the most significant contributor to TWSA losses. The massive loss of water storage in the Tianshan Mountains area, especially the accelerated retreat of glaciers, will affect the stable water supply to the middle and lower reaches of the oasis region, perhaps leading to increased groundwater extraction, which will threaten regional water security and sustainable development. Developing a water-saving society and implementing inter-basin water transfer arefeasible ways to alleviate the water resource crisis. Conducting a comprehensive analysis of all inland rivers in China helps to facilitate horizontal comparisons between various basins, thereby providing more comprehensive insights of water storage fluctuations. The data on water storage changes, extending back to 1980, provide a longer-term perspective on water resource changes in the region, which can contribute to enhancing water resource security and ecological environ-mental protection.

Ecological environment in the arid areas of Northwest China is very vulnerable. Ecological vulnerability is considered to be one of the important indicators to measure the status and evolutions of the regional ecological environment and has become a key measure in the study of ecological change. However, studies on the ecological vulnerability in the whole arid areas of Northwest China on the county scale are currently sparse. Here, according to vegetation, land use type, topography, climate and socio-economic data, we present the spatial and temporal evolution of ecological vulnerability in the arid areas of Northwest China over the period 2000-2018 by structuring a pressure (P)-sensitivity (S)-restoration (R) ecological vulnerability evaluation index system and using an ordered weighted average (OWA) model. Our results suggested that the overall ecological vulnerability in the arid areas of Northwest China was dominated by the severe level from 2000 to 2018 with an average multiyear ecological vulnerability index of 0.48, which appeared a slight downward trend with the implementation of ecological restoration measures. Ecological vulnerability exhibited a significant stepped differentiation feature, and the eastern and western regions were markedly lower than that of the central region. Gravity center of the ecological vulnerability index has a significant spatial difference, which developed in the shape of Z direction between Heshuo county and Tuokexun county. Our study revealed the dynamic changes of ecological vulnerability at the county scale and provided decision-making information for the formulation of targeted ecological vulnerability management measures. Under the background of climate change and the new normal of social economy, the dynamic monitoring of ecological vulnerability and effective identification of vulnerability factors still require in-depth research.

The freezing-thawing variation of permafrost active layer increases the complexity of rainfall-runoff processes in alpine river basins, Northwest China. And alpine meadow is the prominent ecosystem in these basins. This study selected a small alpine meadow watershed in the upper reaches of the Shule River Basin, China. We investigated alpine rainfall-runoff processes, as well as impacts of summer thaw depth of active layer, soil temperature and moisture variation on streamflow based on in-situ observations from July 2015 to December 2020. Some hy-drologic parameters or indices were calculated using statistical methods, and impacts of permafrost change on river runoff were assessed using the variable infiltration capacity model (VIC). In the alpine meadow, surface soil (0-10 cm depth) of the active layer starts to freeze in mid-October each year, and begins to thaw in early April. Also, the deeper soil (70-80 cm depth) of the active layer starts to freeze in late October, and begins to thaw in late June. Moisture content in shallow soils fluctuates regularly, whereas deeper soils are more stable, and their response to rainstorms is negligible. During active layer thawing, the moisture content increases with soil depth. In the alpine meadow, vertical infiltration only occurred in soils up to 40 cm deep, and lateral flow occurred in 0-20 and 60-80 cm deep soils at current rainfall intensity. Summer runoff ratios were 0.06-0.31, and runoff floods show lags of 9.5-23.0 h following the rainfall event in the study area. The freeze-thaw process also significantly impacts runoff regression coefficients, which were 0.0088-0.0654 per hour. Recession coefficient decrease negatively correlates with active layer thawing depth in summer and autumn. Alpine river basin permafrost can effectively increase peak discharge and reduce low flow. These findings are highly significant for rainfall-runoff conversion research in alpine areas of inland rivers.

Pollutants, which are usually transported from urban cities to remote glacier basins, and aerosol impurities affect the earth's temperature and climate by altering the radiative properties of the atmosphere. This work focused on the physicochemical properties of atmospheric pollutants across the urban and remote background sites in northwest China. Information on individual particles was obtained using transmission electron microscopy (TEM) and energy dispersive X-ray spectrometry (EDX). Particle size and age-dependent mixing structures of individual particles in clean and polluted air were investigated. Aerosols were classified into eight components: mineral dust, black carbon (soot)/fly ash, sulfates, nitrates, NaCI salt, ammonium, organic matter, and metals. Marked spatial and seasonal changes in individual particle components were observed in the study area. Aerosol particles were generally found to be in the mixing state. For example, salt-coated particles in summer accounted for 31.2-44.8% of the total particles in urban sites and 37.5-74.5% of the total particles in background sites, while in winter, almost all urban sites comprised >50%, which implies a significant effect on the radiative forcing in the study area. We found that in PM2.5 section, the internally mixed black carbon/organic matter particles clearly increased with diameter. Moreover, urban cities were characterized by atmospheric particles sourced from anthropogenic activities, whereas background locations exhibited much lower aerosol concentrations and increased particle density, originating from natural crustal sources (e.g., mineral dust and NaCI salt), which, together with air mass trajectory analysis, indicates a potential spatial transport process and routes of atmospheric transport from urban cities to background locations. Thus, this work is of importance in evaluating atmospheric conditions in northwest China and northeast Tibetan Plateau regions, to discover the transport processes and facilitate improvements in climatic patterns concerning atmospheric impurities. (C) 2018 Elsevier Ltd. All rights reserved.