Spatio-Temporal Variations Of Nighttime Lights In China's Poverty-Stricken Counties

Poverty is one of the most tough and challenging social problems confronted by countries all over the world,especially in developing countries.As the largest developing country in the world,China has made a great contribution to the world poverty reduction,and became the first developing country to achieve the United Nations Sustainable Development goal 1(SDG1: No Poverty).By the end of 2020,China has scored a victory in its fight against poverty.Evaluate the poverty reduction effect is of great importance to build a long-term and effectual mechanism to solve the relative poverty.The key prerequisite for evaluating poverty reduction effect is to identify and measure poverty.In a traditional way,official statistics are the primary data sources to establish one-dimensional or multi-dimensional poverty measurement index.However,official statistics suffer from problems such as data inconsistency,data delay and cost-intensive.Remote sensing of nighttime light emissions offers a unique perspective for investigations into human behaviors and has been shown to be particularly useful for a range of social-economic applications and being more reliable than statistical data.Recently,numerous studies have used the nighttime lights data to establish integrated poverty indices to measure poverty levels in different areas.However,most of existing studies which combine disparate data sources are often limited in singe phase poverty measurement,few of them focused on investigating the poverty reduction effect of poverty-stricken counties from a perspective of spatiotemporal dynamics.In this paper,we constructed an annual nighttime light dataset to measure the poverty reduction effect in China's 831 national-level poverty-stricken counties and14 concentrated contiguous poor areas in the stage of targeted poverty alleviation.The main contents and findings are as follows:(1)By synthesizing an annual dataset of NPP-VIIRS nighttime light(NTL)data from 2014 to2020,we developed a county-level NTL index and a rate of NTL change to investigate the poverty status and reduction effects of 831 national-level poverty-stricken counties in China.The results indicated that the economic level of most poverty-stricken counties in China has been improved significantly during the study period,and the poverty reduction effect is prominent.However,there are still 108 poverty-stricken counties with negative growth trend of NTL intensity,which are mainly located at the junction of concentrated and contiguous poverty-stricken areas in the western region.Besides,the NTL intensity development between the north and south parts of western regions is unbalanced.In terms of time sequence similarity of poverty reduction,poor counties which were large NTL base with a slow growth rate need to guard against falling back into poverty.(2)By using Cluster-Outlier analysis and NTL Gini coefficient(NLGini)analysis,we identified the spatial distribution pattern and balanced development trend of NTL in the14 concentrated contiguous poverty-stricken areas.The results indicated that the concentrated contiguous poverty-stricken areas showed gathering or expanding development,and develop around regions with good economic foundation.Besides,poor counties along the border are vulnerable to marginalization.Four NTL development modes,i.e.,small NTL base with a rapid growth rate(mode I),large NTL base with a rapid growth rate(mode II),large NTL base with a slow growth rate(mode III),and small NTL base with a slow growth rate(mode IV)were identified in the14 concentrated contiguous poverty-stricken areas.In terms of the balance of development,the overall development is uneven,but the imbalance is alleviated to varying degrees due to poverty reduction.(3)Taking several poverty-stricken counties with typical poverty-reduction pathways as case study areas,we analyzed the corresponding nighttime light changes by combining the local policies and poverty measures.The results indicated that significant NTL changes were observed in the poverty-stricken counties with four poverty alleviation paths: infrastructure poverty alleviation,characteristic industry poverty alleviation,asset income poverty alleviation(photovoltaic poverty alleviation),and relocation poverty alleviation.However,the NTL changes in poor counties with poverty reduction models such as ecological compensation poverty alleviation,social security poverty alleviation and agricultural industry poverty alleviation are not obvious.