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Small-scale and artisanal mining is widespread in many countries and often causes severe eco-environment problems. The dynamic nature of this extractive activity and its spread in rural and remote areas make its mapping and monitoring very challenging. Therefore, the use of multi-source remote sensing data provides possibilities to monitor landcover changes as well as the destruction and restoration of vegetation in these regions. The study area of this paper is located at the border of El Bagre and Zaragoza, in Bajo Cauca, Colombia, which is greatly affected by small-scale alluvial gold mining. This place has a typical tropical climate with frequent high cloud coverage. Therefore, the multi-source remote sensing images (Sentinel-2, Landsat-8 and Sentinel-1) are selected for this study to detect and map small-scale mining of gold placers. For both Sentinel-2 and Landsat-8 data, clouds are removed according to the information of pixel QA bands through the google earth engine (GEE). Then multiple images within each two months are aggregated after cloud removal. For Sentinle-1 data, post-processing including noise removal, calibration and orthorectification using DEM data is applied with GEE. When cloud-free data is not available within two months, Sentinle-1 data is added to improve the accuracy of the classification. The support vector machine classifier (SVM) is selected as the supervised classification approach. And to avoid possible classification errors, the post-classification based on local geographic information is also applied. Results show the landcover changes of mining areas in recent years and detect the location of mining areas, including mined bare soil and mining ponds and other important land cover. Furthermore, the change of vegetation cover in this area is monitored.

grant entitled "Study on Agricultural Drought Risk Formation Mechanism of the Rain-fed Agricultural Typical Area in China" from the National Science and Technology Foundation 41001059; Climate change is affecting every aspect of human activities, especially the agriculture. In China, extreme drought events caused by climate change have posed a great threat to food safety. In this work we aimed to study the drought risk of maize in the farming-pastoral ecotone in Northern China based on physical vulnerability assessment. The physical vulnerability curve was constructed from the relationship between drought hazard intensity index and yield loss rate. The risk assessment of agricultural drought was conducted from the drought hazard intensity index and physical vulnerability curve. The probability distribution of drought hazard intensity index decreased from south-west to north-east and increased from south-east to north-west along the rainfall isoline. The physical vulnerability curve had a reduction effect in three parts of the farming-pastoral ecotone in Northern China, which helped to reduce drought hazard vulnerability on spring maize. The risk of yield loss ratio calculated based on physical vulnerability curve was lower compared with the drought hazard intensity index, which suggested that the capacity of spring maize to resist and adapt to drought is increasing. In conclusion, the farming-pastoral ecotone in Northern China is greatly sensitive to climate change and has a high probability of severe drought hazard. Risk assessment of physical vulnerability can help better understand the physical vulnerability to agricultural drought and can also promote measurements to adapt to climate change.

Climate change is affecting every aspect of human activities, especially the agriculture. In China, extreme drought events caused by climate change have posed great threaten to food safety. In this work we aimed to study the drought risk of maize in the farming-pastoral ecotone in Northern China based on physical vulnerability assessment. The physical vulnerability curve was constructed from the relationship between drought hazard intensity index and yield loss rate. The risk assessment of agricultural drought was conducted from the drought hazard intensity index and physical vulnerability curve. Results of the drought hazard intensity index showed that the risk of agricultural drought displayed a negative correlation with the precipitation and kept rising from 1966 to 2011. Risk assessments of yield loss ratio shows that physical vulnerability curve has magnify and reduce function to drought hazard. So improving the capacity of maize to resist drought can help them adapt to drought hazard. In conclusion, the farming-pastoral ecotone in Northern China had great sensitivity to climate change and high probability for severe drought hazard. Risk assessment of physical vulnerability can help better understanding the physical vulnerability to agricultural drought and can also promote measurements to adapt to the climate change.

As global surface temperature continues to rise, increasing evidences have shown that social and natural systems are deeply influenced by climate change. The government and farmers' awareness, as well as measures to adapt to these climate-driven changes, are critical for local sustainable development. In this study, we established a conceptual model of the relationship among human adaptation, development demand and environment changes to analyze the mechanism of agricultural drought adaptation based on an empirical research at the famer and government level. These results show that under the impact of climate change, the study area of drought risk has continued to expand. With this condition, the government and farmers have constantly taken measures to control the development demand and adjust to environmental changes in order to adapt to agricultural drought. Interactions among environmental changes, development demand and adaptation measures have kept the regional nature-society-economy compound ecosystem in dynamic balance. In addition, the effect of these adaptation measures always has an inertia that may induce a longer and deeper impact on the region, which is considered when making adaptation strategies. Rainfed areas are considered to be the most sensitive and unstable to environment change. This study reveals the mechanism of adaptation from a macroscopic perspective and may provide some references on measures and strategies for drought adaptation in other rainfed areas.