Remote sensing monitoring of the recent rapid increase in cultivation activities and its effects on desertification in the Mu Us Desert, China

The recent ecological improvement in the Mu Us Desert of China, largely attributed to large-scale afforestation projects, has created new opportunities for cultivation activities. However, the subsequent rapid increase in reclamation on desertification land and its impact on desertification have raised concerns. In this study, we first extracted data on cultivated land and desertification land in 1975,1990, 2000, 2005, 2010, 2015, and 2020 through the human-computer interaction visual interpretation method. By overlaying the cultivated land dynamics and desertification land, we subsequently explored the effect of cultivation activities on desertification in the Mu Us Desert during the six periods from 1975 to 2020(1975–1990, 1990–2000, 2000–2005, 2005–2010, 2010–2015, and 2015–2020). The results showed that cultivated land in the Mu Us Desert showed a fluctuating and increasing trend from 3769.26 km~2 in 1975 to 4865.73 km~2 in 2020, with 2010 as the turning point for the recent rapid increase. The main contributors included the large and regular patches distributed in Yuyang District and Shenmu of Shaanxi Province, and relatively smaller patches concentrated in Inner Mongolia Autonomous Region. The increased cultivated land from the reclamation on desertification land was dominated by moderate and severe desertification lands, and the decreased cultivated land that was transferred into desertification land as abandoned cultivated land was dominated by slight and moderate desertification lands. The effect of cultivation activities on desertification reversal(average area proportion of 10.61% for reversed desertification land) was greater than that of the development of desertification(average area proportion of 5.82% for developed desertification land). Nevertheless, compared to reversed desertification land,both the significant increase of developed desertification land during the periods of 2000–2005 and 2005–2010 and the insignificant decrease during the periods of 2005–2010, 2010–2015, and 2015–2020 implied a potential remobilization risk. Therefore, this study provides a significant theoretical reference for the formulation of ecological restoration projects and regional macroeconomic development policies by considering the influence of cultivation activities, to ensure the overall environmental stability and sustainability in desertification land where reclamation and abandonment activities have taken place.

Modeling potential wetland distributions in China based on geographic big data and machine learning algorithms

Climate change and human activities have reduced the area and degraded the functions and services of wetlands in China.To protect and restore wetlands,it is urgent to predict the spatial distribution of potential wetlands.In this study,the distribution of potential wetlands in China was simulated by integrating the advantages of Google Earth Engine with geographic big data and machine learning algorithms.Based on a potential wetland database with 46,000 samples and an indicator system of 30 hydrologic,soil,vegetation,and topographic factors,a simulation model was constructed by machine learning algorithms.The accuracy of the random forest model for simulating the distribution of potential wetlands in China was good,with an area under the receiver operating characteristic curve value of 0.851.The area of potential wetlands was 332,702 km^(2),with 39.0%of potential wetlands in Northeast China.Geographic features were notable,and potential wetlands were mainly concentrated in areas with 400-600 mm precipitation,semi-hydric and hydric soils,meadow and marsh vegetation,altitude less than 700 m,and slope less than 3°.The results provide an important reference for wetland remote sensing mapping and a scientific basis for wetland management in China.

中国亚热带植被蒸腾驱动力解耦分析

Transpiration(Tc) is a critical component of the global water cycle.Soil moisture(SM) and vapor pressure deficit(VPD) are key regulators of Tc,and exploring their contributions to changes in Tc can deepen our understanding of the mechanisms of water cycling in terrestrial ecosystems.However,the driving roles of VPD and SM in Tc changes remain debated because of the coupling of SM and VPD through land-atmosphere interactions which restrict the quantification of the independent effects of SM and VPD on Tc.By decoupling the correlations between SM and VPD using a novel binning approach,this study analyzed the dominant drivers of vegetation transpiration in subtropical China from 2003 to 2018 based on multi-source data,including meteorological reanalysis,remotely sensed soil moisture,transpiration,and land cover data.The results show that Tc first increased and then remained stable with an increase in SM across the study area but changed slightly with increasing VPD.Overall,the relative contribution of SM to the change in Tc was approximately five times that of VPD.The sensitivities of Tc to SM and VPD differed among vegetation types.Although the sensitivity of Tc to SM was greater than that of VPD for all four vegetation types,the thresholds of Tc in response to SM were different,with the lowest threshold(approximately 35%) for the other forests and the highest threshold(approximately 55%) for short wood vegetation.We infer that this is associated with the differences in ecological strategies.To verify the reliability of our conclusions,we used solar-induced chlorophyll fluorescence(SIF) data as a proxy for Tc based on the tight coupling between photosynthesis and transpiration.Consistent results were obtained by repeating the analyses.The results of this study,in which the impacts of SM and VPD on Tc were decoupled,are beneficial for further understanding the critical processes involved in water cycling in terrestrial ecosystems in response to climate change.

Water storage changes in the North China Plain from 2004 to 2019

In the past few decades,the irrational use of water resources has resulted in many issues such as land subsidence in the North China Plain(NCP),hindering its socio-economic development.An accurate understanding of water resource changes is important for the allocation of water resources in the NCP.In this study,we employed Gravity Recovery and Climate Experiment(GRACE) satellite data to monitor the total water storage(TWS) change in the NCP during 2004–2019.Evapotranspiration,precipitation,and runoff during 2004–2019 were sequentially examined,using the water balance formula(WBF),to retrieve TWS change.Furthermore,the soil moisture,snow water equivalent,and canopy water storage from the Global Land Data Assimilation System were used to calculate the natural component of the TWS variations.A comparison of these results revealed the drivers of the changes in water resources.The results showed that:(1) overall TWS retrieved by GRACE decreased substantially as a consequence of human activity,while TWS obtained by WBF fluctuated periodically around zero under the impact of three natural drivers;(2) TWS in the NCP fell at a remarkable rate of-12.39 mm/y from 2004 to 2019,and the natural part of TWS experienced two significant declines,during 2004–2010 and 2013–2016;(3) variations in runoff,precipitation,and evapotranspiration from 2004 to 2019 were not significant,but human activities contributed more to the decreasing TWS than natural factors.This study provides a reference for water resource management and groundwater exploitation across the NCP under climate change.

Remote Observations in China’s Ramsar Sites: Wetland Dynamics, Anthropogenic Threats, and Implications for Sustainable Development Goals

The Ramsar Convention on Wetlands is an international framework through which countries identify and protect important wetlands.Yet Ramsar wetlands are under substantial anthropogenic pressure worldwide,and tracking ecological change relies on multitemporal data sets.Here,we evaluated the spatial extent,temporal change,and anthropogenic threat to Ramsar wetlands at a national scale across China to determine whether their management is currently sustainable.We analyzed Landsat data to examine wetland dynamics and anthropogenic threats at the 57 Ramsar wetlands in China between 1980 and 2018.Results reveal that Ramsar sites play important roles in preventing wetland loss compared to the dramatic decline of wetlands in the surrounding areas.However,there are declines in wetland area at 18 Ramsar sites.Among those,six lost a wetland area greater than 100 km^(2),primarily caused by agricultural activities.Consistent expansion of anthropogenic land covers occurred within 43(75%)Ramsar sites,and anthropogenic threats from land cover change were particularly notable in eastern China.Aquaculture pond expansion and Spartina alterniflora invasion were prominent threats to coastal Ramsar wetlands.The observations within China’s Ramsar sites,which in management regulations have higher levels of protection than other wetlands,can help track progress towards achieving United Nations Sustainable Development Goals(SDGs).The study findings suggest that further and timely actions are required to control the loss and degradation of wetland ecosystems.