The rapid growth of the global population and the transformation and upgrading of dietary structures have led to a widening gap in the demand for cropland resources. Research on agricultural land reallocation that seeks to maximize cropland availability and increase grain production while also considering the preservation of natural ecosystems still has gaps. Following the theoretical assumptions of the agricultural land reallocation process, this study constructs a comprehensive framework for integrating scale, structure, and prioritization. Sichuan Province, China's main grain-producing region, is used as an example for a case study. The results demonstrate that the scale of agricultural land reallocation decreased from 56,742.01 to 44,965.52 km2 after correcting the evaluation of ecological conservation importance and crop production suitability under spatial and non-spatial constraints. There are significant differences in crop production suitability for agricultural land reallocation structures. Despite the wide spatial distribution of forest land, its utilization is challenging. Therefore, cropland, garden land, and grassland are prioritized for exploitation and utilization. In the eight priority zones for agricultural land reallocation, the main obstacles are constituted by single or composite factors of utilization convenience, spatial agglomeration, and facility stability. In general, agricultural land reallocation needs to be supported by considering different dimensions of resource availability, structural convertibility, and spatial compatibility. This approach maximizes the availability of resources for grain production while minimizing damage to natural ecosystems.

Rainfall has been recognized as a key factor in triggering landslides. However, it is not entirely clear why many landslides have been triggered by slight-to-moderate rainfall. The Mudui landslide that occurred in Sichuan Province, China, on June 22, 2020, exemplifies the evolution of landslides induced by seasonal rainfall, which can cause substantial damage to infrastructure. This landslide was a deep-seated debris slide with a volume of approximately 0.64 million m3. It occurred in colluvial deposits, which are heterogeneous soil-rock mixtures with high permeability that easily retain water. On the basis of detailed site investigations and various monitoring data-including interferometric synthetic-aperture radar (InSAR), ground-slope and subsurface-slope deformation monitoring, and hydrogeological monitoring-we investigated the landslide-triggering mechanism along with pre- and post-landslide kinematics and assessed the effects of remedial works. The results show that both the soil water content and the slope deformations have significant seasonal characteristics. The soil water content decreases during dry seasons and increases during rainy seasons. Correspondingly, the deformation rates increase with the onset of rainy seasons and decrease with the onset of dry seasons. The landslide area underwent progressive deformations linked to groundwater seepage, inducing a continuous deterioration of the soil body. Finally, prolonged rainfall triggered the landslide of the deteriorated soil mass. The results indicate that the adverse effects of long-term seasonal soil-water-content fluctuations need to be take into account in analyzing slope instabilities in colluvial deposits.

The significant duration is a crucial intensity measure for earthquake-resistant design and seismic hazard assessment (SHA). The Sichuan-Yunnan region is characterized by a high level of seismic activity and possesses the most concentrated network of seismic stations in China. The ground motion prediction equation (GMPE) is the predominant approach to estimating significant durations. The existing prediction equations for the significant duration are not well-suited for the Sichuan-Yunnan region. This study used data from the National Strong Motion Observation Network System (NSMONS) of China in this region to develop prediction equations for significant durations of DS5-75 and DS5-95. The equations took into account variables including moment magnitude (M-w), fault distance (R-rup), average shear wave velocity of 30 m on the soil profile (V-S30), and depth to the top of the rupture (Z(tor)). Our database has a singular instance of the Wenchuan earthquake with M-w > 7. The restricted data complicates the calibration of our model for events with M-w > 7. Therefore, we suggest the equations be valid in the Sichuan-Yunnan region for M-w between 4.2 and 7.0, R-rup from 0 to 300 km, and V-S30 values ranging from 139 to 900 m/s.

Sichuan Basin is encircled by high mountains and plateaus with the heights ranging from 1 km to 3 km, and is one of the most polluted regions in China. However, the dominant chemical species and light absorption properties of aerosol particles is still not clear in rural areas. Chemical composition in PM1 (airborne particulate matter with an aerodynamic diameter less than 1 mu m) and light-absorbing properties were determined in Chengdu (urban) and Sanbacun (rural) in western Sichuan Basin (WSB), Southwest China. Carbonaceous aerosols and secondary inorganic ions (NH4+, NO3- and SO42-) dominate PM1 pollution, contributing more than 85% to PM1 mass at WSB. The mean concentrations of organic and elemental carbon (OC, EC), K+ and Cl- are 19.69 mu g m(-3), 8.00 mu g m(-3), 1.32 mu g m(-3),1.16 mu g m(-3) at the rural site, which are 26.2%, 65.3%, 34.7% and 48.7% higher than those at the urban site, respectively. BrC (brown carbon) light absorption coefficient at 405 nm is 63.90 +/- 27.81 M m(-1) at the rural site, contributing more than half of total absorption, which is about five times higher than that at urban site (10.43 +/- 4.74 M m(-1)). Compared with secondary OC, rural BrC light absorption more depends on primary OC from biomass and coal burning. The rural MAE(Brc) (BrC mass absorption efficiency) at 405 nm ranges from 0.6 to 5.1 m(2) g(-1) with mean value of 3.5 +/- 0.8 m(2) g(-1), which is about three times higher than the urban site. (C) 2021 Elsevier Ltd. All rights reserved.

With Tibetan Plateau higher than 4 km to the west, the location of Sichuan Basin is unique all around the world and provides a good platform to study air pollution in the urban agglomerations over the complex terrain. To fill in the blanks on vertical distributions of PM1 (the particles smaller than 1 mu m) and carbonaceous aerosols within the basin, by means of high topographic relief, PM1 were off-line sampled during 20 January to 2 February 2018 at eight sites with increasing altitudes from the basin to southeastern margins of the Tibetan Plateau. The regional potential sources for each site were revealed by Hybrid-Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model and concentration-weighted trajectory (CWT) method. The lowest carbonaceous aerosol levels occurred at Lixian, while the highest OC (organic carbon) (EC, elemental carbon) was at Hongyuan (the altitude of 3500 m) (Ande, a rural site) due to more primary emissions. The pollutants inside the basin can be transported the altitudes from 2 km to 3 km by vertical dispersion, but they cannot be dispersed to higher altitudes. The vertical stratification of the pollutants was obvious and easily formed high-low-high pattern from Sichuan Basin to southeastern Tibetan Plateau, especially during highly polluted episodes. The regional potential sources significantly varied as the increased altitudes. Regional pollution was significant inside the basin. The sources at the altitudes from 2 km to 3 km originated from southeastern margins of the Plateau and surrounding cities, while those at higher altitudes were transported from southeastern margins of the Plateau. The impact of basic meteorological variables (temperature, wind speed and vapor pressure) on carbonaceous aerosols was opposite between the basin and Plateau sites. This study was essential to understanding formation mechanisms of severe pollution episodes and thus to making control measures for the urban agglomerations inside the mountainous terrain.

Long-term variations in aerosol optical properties, types, and radiative forcing over the Sichuan Basin (SCB) and surrounding regions in Southwest China were investigated based on two-decade data (2001-2020) from the Moderate Resolution Imaging Spectroradiometer, Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation, and the Santa Barbara DISORT Atmospheric Radiative Transfer model. The results showed that the aerosol optical depth (AOD550nm) in the SCB, a major polluted region in Southwest China, experienced an increasing tendency at a rate of +0.052 yr-1 during 2001-2006; thereafter, it decreased speedy up from -0.020 to -0.058 yr-1 over recent years, whereas the interannual variation in angstrom ngstrom exponent (AE470-660nm) presented a persistently increasing trend during 2001-2020, with a rate of +0.014 yr-1. An improved atmospheric environment but an enhanced fine particle contribution to regional aerosols in the SCB was observed. Over the polluted SCB region, the dominant aerosol types were biomass burning/urban industrial and mixedtype aerosols with the proportions of 80.7%-87.5% in regional aerosols, with a higher frequency of clean aerosols in recent years, reflecting an effect of controlling anthropogenic emission in the SCB owing to governmental regulation. By contrast, few changes were observed in the aerosol types and amounts in the eastern Tibetan Plateau (ETP), where clean continental aerosols dominate with high proportion of 93.7% in the clean atmospheric environment. A significant decline in polluted anthropogenic aerosols was observed below 3 km over the SCB, resulting in the regional aerosol extinction coefficients at 532 nm (EC532nm) were declined by -0.22 km-1 from 2013 to 2020. Notably, the decreases in aerosol radiative forcing within the atmosphere were found in

The vertical distributions of BC mass concentration (m(BC)) during a winter pollution period in 2017 over Chengdu, a megacity in the Sichuan Basin, China, were measured by a micro-aethalometer equipped on a tethered balloon. This observation experienced severe air pollution with an averaged ground BC of 11.1 mu g.m(-3), which is higher than two times the annual mean in Chengdu for 2018. The available 68 BC vertical profiles are grouped in to five types: Type A (18%) is the uniform vertical distribution of BC with an unrecognizable mixing layer (ML) height; BC in Type B (26%) is also uniformly distributed in the ML while decreases rapidly above the ML; Type C (7%) is a unimodal distribution with BC peak within the ML when the suspended temperature inversion forms; BC in Type D (29%) is accumulated in the near-ground layer and quickly decreases with height; Type E (20%) is the bimodal or trimodal distribution with BC peaks around the top of ML. Types A and B dominate from noon to afternoon, and Types C-E play critical roles during the evening and night. The different vertical patterns of BC are mainly associated with the evolution of the ML and the local emissions. For all the five types, the calculated radiative forcing of BC (f(BC)) is negative at the surface but positive at the top of profile (TOP), indicating the net absorption of radiation by the atmosphere due to BC. The absolute values of f(BC) at the surface and the TOP are increased with the increase of columnar BC loading, and there is no significant difference in f(BC) at the TOP and the surface among different patterns when the same BC loading is considered. However, the vertical distribution of atmospheric heating rate contributed by BC (h(BC)) is highly related to BC's vertical profile. The uniform distributed BC can result in a positive gradient of h(BC) with altitude, and thus, enhance the stability of the atmosphere. The plateau terrain induced small-scale secondary circulation and relatively lower thermal inversion in the west of the Sichuan basin have an essential effect on the vertical distribution of aerosols and can contribute to an accumulation of aerosols at 0.8-1.4 km above ground level. This study would hopefully have a preliminary understanding of the vertical distribution of BC in the Sichuan Basin, and a vital implication for accurately estimating direct radiative forcing by BC in this region.

The formation mechanism of air pollution events in the Sichuan Basin (SB), which is the fourth most heavily polluted area in China, has not been fully revealed. This study investigated the formation mechanism of a severe air pollution event over the SB using synoptic approaches and model simulations. The results can be summarized as follows: (1) Heavy air pollution in the SB was characterized by low visibility, low atmospheric boundary layer (ABL) height, high temperature, high relative humidity, strong temperature inversion layer, subsidence in the troposphere, high water vapor content between 500 and 900 hPa, southerly winds in the low troposphere, and surface winds with low speed and irregular direction. (2) Air quality in the SB was closely related to the weather system at 700 hPa over the basin. When the 700 hPa weather system affecting the SB was a high-pressure system, the subsidence and stable atmospheric stratification increased the air pollutant concentrations near the ground. When the 700 hPa weather system affecting the SB was a low-pressure system and the basin was in front of this low-pressure system, southwesterly warm and moist airflow and adiabatic subsidence warming formed the thick temperature inversion layer over the basin. As a result, the temperature inversion layer trapped air pollutants in the basin and induced the heavy air pollution event. When the 700 hPa weather system over the SB was a low-pressure system and the basin was behind the low-pressure system, the dry and cold airflow from the north invaded southward to the basin and broke the temperature inversion layer. Consequently, air pollutants dispersed vertically, resulting in decreased concentrations near the ground. (3) Air pollutants from December 17, 2017 to January 4, 2018 were mainly from local emissions. (4) The WRF-Chem model not only reproduced the variations in PM2.5 concentrations, the ABL height, and the height-time cross-sections of temperature, water vapor content, and wind over Chengdu during the air pollution event, but also revealed the formation mechanism of this heavy air pollution event. The results of this study reveal the formation mechanism of winter heavy air pollution events over the SB and help develop effective regional air quality management strategies to reduce the likelihood of local air pollution events and minimize the adverse impacts of air pollution.

The light absorption of brown carbon (BrC) makes a significant contribution to aerosol light absorption (Abs) and affects the radiative forcing. In this study, we analyzed and evaluated the light absorption and radiative forcing of BrC samples collected from December 2016 to January 2017 in Chongqing and Chengdu in the Sichuan Basin of Southwest China. Based on a two-component model, we estimated that BrC light absorption at 405 nm was 19.9 +/- 17.1 Mm(-1) and 19.2 = 12.3 Mm(-1) in Chongqing and Chengdu, contributing 19.0 +/- 5.0% and 17.8 3.7% to Abs respectively. Higher Abs(405,BrC), MAE(405.Br)(C), and AAE(405-980) values were observed during the pollution period over the dean period in both cities. The major sources of BrC were biomass burning (BB) and secondary organic aerosol in Chongqing, and coal combustion (CC) and secondary organic aerosol in Chengdu. During the pollution period, aged BrC formed from anthropogenic precursors via its aqueous reactions with NH4+ and NOx had impacts on BrC absorption in both cities. BB led to higher AbS(405,BrC), MAE(405,BrC), and AAE(405-980) values in Chongqing than Chengdu during the pollution period. The fractional contribution of radiation absorbed by BrC relative to BC in the wavelengths of 405-445 nm was 60.2 +/- 17.0% and 64.2 +/- 11.6% in Chongqing and Chengdu, significantly higher than that in the range 01405-980 nm (262 +/- 6.7% and 27.7 +/- 4.6% respectively) (p 0.001). This study is useful for understanding the characterization, sources, and impacts of BrC in the Sichuan Basin. (C) 2020 Elsevier B.V. All rights reserved.