Recent Vegetation Cover Dynamics and Climatic Parameters Evolution Study in the Great Green Wall of Senegal

The drought recorded in 1970s and 1980s, particularly in the Sahara and Sahel region has greatly affected the population as well as the economies and the eco-systems of this area. In 2007, the African Union launched a Pan-African program, the Great Green Wall for the Sahara, the Sahel Initiative (GGWSSI) to reverse land degradation and desertification by planting a wall of trees stretching from Dakar to Djibouti. The objective is to improve food security, and support local people to adapt to climate change. This paper aims to evaluate the impacts of the reforestation program in Senegal, fifteen years after it was launched. This study uses a time series of satellite-derived vegetation cover and climatic parameters data to analyze the sustainability of these interventions. Change detection approaches were applied to identify and characterize the drives of the eventual changes. A comparative analysis of reforestation on climatic parameters was explored through the temporal analysis of the vegetation index over the periods 2000-2008 and 2009-2020. An increase in vegetation activity was noted through the NDVI at the interannual (+2% to +8%) and seasonal (+1.5% to 7% for the wet season and 1% to 4% for the dry season) scale and a positive and significant evolution is noted on the trace of the GGW. Also, the period 2009-2020 recorded an increase in rainfall of 2% to 8% of the average value 2000-2020 and 4% to 8% of the rainy season. Soil moisture is the climatic parameter that has increased the most, with an increase of 25% to 54% of the 2000-2020 average, i.e. between 20 mm and 70 mm more. This study shows a significant improvement in the relationship between NDVI and climate parameters after the different reforestation actions of the GGW.

Estimation of the Carbon Sequestration Dynamics of Senegal’s Great Green Wall Based on Land Cover over the Past Three Decades

The severe drought observed in the Sahel during 1970s, 1980s and 1990s has deeply affected the population as well as the economies and the eco-systems of this climatic area. The GGW Initiative spearheaded by Africa Union in 2007 proposed to combat the land degradation and desertification by planting a wall of trees stretching from Dakar to Djibouti. A reforestation was then conducted in the Senegal’s GGW since 2006 as part as other areas in the Sahel. This paper aims to evaluate the carbon sequestration dynamics in the sites of the Senegal’s GGW over the last three decades. The method consists firstly of analyzing the evolution of land cover and land use dynamics based on ESA-CCI LC satellite data. There is an improvement of the surface areas of tree and shrub savanna of 11.40% (Tessekere), 8.25% (Syer) and 2.70% (Loughere-Thioly). The regreening of the different localities and a positive dynamic observed is explained by the return to normal rainfall and to reforestation actions, agroforestry practices, better management of natural resources undertaken. However, some non-reforested sites showed an opposite trend despite of the normal rainfall. Secondly, the results on land mapping are used as a proxy for the assessment of carbon stocks. The dynamic observed in vegetation cover since the beginning of the reforestation made it possible to sequester 5.8 million tons of carbon representing respectively 2.31% of African GGW. This gain in stored carbon is equivalent to 21.2 million tons of CO2 captured in the atmosphere. Through this study, it appears that carbon storage becomes significant 8 to 10 years after the start of reforestation. An urbanization without respect for the environmental factors could be a danger for the climate (case of Ballou).

LEAF COLOR SEGMENTATION AND POT VOLUME INFLUENCE ON THE CO_(2) ABSORPTION EFFICIENCY IN TWO COMMON GREEN-WALL PLANTS

Green walls can improve indoor air-quality by reducing concentrations of carbon dioxide(CO_(2))and other air pollutants.Our study focused on the spider plant,Chlorophytum comosum,and devil’s ivy,Epipremnum aureum,both common green-wall plants that have been found to be efficient CO_(2) absorbers.Both species have multiple variants with varying degrees of leaf green-white segmentation.Since pho-tosynthesis depends on the concentration of leaf chlorophylls,we hypothesized that green variants are more efficient carbon absorbers than green-white variants.In addi-tion,we tested the hypothesis that the photosynthetic rate of plants is affected by pot volume,as suggested by previous studies.We used a portable gas exchange system to determine the rate of photosynthesis of the study plants.No evidence was found for better photosynthetic performance in the green vs.green-white variants of each species.In fact,our results suggest the opposite.It was observed that a spider plants assimilated carbon more efficiently when grown in a larger pot volume.In conclusion,our study shows that in terms of carbon assimilation,green-white variants of spider plants are the better choice for indoor green walls.Their efficiency can be improved dramatically by increasing pot volume.

FOOD PRODUCTION ON A LIVING WALL:PILOT STUDY

Living walls and other vertical green infrastructure on building surfaces provide regulating,supporting,and cultural ecosystem services in the built environment.Green walls can also generate food as a provisioning ecosystem service.This article discusses a pilot study monitoring the productivity of a 7.5 m^(2) outdoor living wall system planted with produce crops during the 2015 summer growing season in State College,Pennsylvania,USA.Irradiance,water usage,and soil moisture data were also collected to assess context and performance of the living wall system during the growing season.

Ecological environment quality evaluation of the Sahel region in Africa based on remote sensing ecological index

Long-term monitoring of the ecological environment changes is helpful for the protection of the ecological environment.Based on the ecological environment of the Sahel region in Africa,we established a remote sensing ecological index(RSEI)model for this region by combining dryness,moisture,greenness,and desertification indicators.Using the Moderate-resolution Imaging Spectroradiometer(MODIS)data in Google Earth Engine(GEE)platform,this study analyzed the ecological environment quality of the Sahel region during the period of 2001-2020.We used liner regression and fluctuation analysis methods to study the trend and fluctuation of RSEI,and utilized the stepwise regression approach to analyze the contribution of each indicator to the RSEI.Further,the correlation analysis was used to analyze the correlation between RSEI and precipitation,and Hurst index was applied to evaluate the change trend of RSEI in the future.The results show that RSEI of the Sahel region exhibited spatial heterogeneity.Specifically,it exhibited a decrease in gradient from south to north of the Sahel region.Moreover,RSEI in parts of the Sahel region presented non-zonal features.Different land-cover types demonstrated different RSEI values and changing trends.We found that RSEI and precipitation were positively correlated,suggesting that precipitation is the controlling factor of RSEI.The areas where RSEI values presented an increasing trend were slightly less than the areas where RSEI values presented a decreasing trend.In the Sahel region,the areas with the ecological environment characterized by continuous deterioration and continuous improvement accounted for 44.02%and 28.29%of the total study area,respectively,and the areas in which the ecological environment was changing from improvement to deterioration and from deterioration to improvement accounted for 12.42%and 15.26%of the whole area,respectively.In the face of the current ecological environment and future change trends of RSEI in the Sahel region,the research results provide a reference for the construction of the"Green Great Wall"(GGW)ecological environment project in Africa.

Global Dryland Ecosystem Programme(G-DEP):Africa consultative meeting report

In order to enhance and restore the ecosystems of natural capital in African arid regions,the Global Dryland Ecosystem Programme(G-DEP)consultative meeting was hosted in Dakar,Senegal,from 23 to 25 September 2019.This paper details the first African meeting of the G-DEP.Consultative meeting reviewed preceding dryland ecosystems case studies,identified vulnerable arid and semi-arid regions,and proposed sustainable solutions to problems.It also identified the successes and failures of previous attempts to improve vulnerable ecosystems and ultimately formed an action plan to improve these attempts.Climate,ecosystems,and livelihoods for Sustainable Development Goals(SDGs),Great Green Wall Initiative(GGWI)for Sahara and Sahel,and China-Africa cooperation on science,technology,and innovation are three extra main sections concerned of the meeting.Separately,more specific topics as the complicated relationship between these natural processes and human activity,including pastoralism,soil restoration,and vegetation regenerate techniques,were fully discussed.Consultative meeting also identified the positive effects international collaboration can have on dryland regions,specifically in the capacity of sharing information,technology,and innovation on purpose to develop a joint proposal for long-term research programs in African arid and semi-arid areas.Moreover,meetings that review the progress made on ecosystem management for the sustainable livelihoods in Africa,identification of priority areas,and the development and implementation of ecosystem programs for proper research and collaboration in African arid and semi-arid zones,have been proposed as strategic recommendations to enhance the global partnership for sustainable development.Furthermore,as the outcomes of the workshop,there are three steps proposed to handle African dryland climate changes,several aspects suggested to solve current dilemmas of the GGWI,and a series of actions recommended for G-DEP related activities in Africa.

Analysis of Energy Saving Reconstruction of Existing Campus Dormitories in Chongqing——Taking Dormitory Six on Campus B of Chongqing University as An Example

At present,a large number of historic buildings on campus are lack of energy-saving measures from the design time,especially the dormitories. And the reconstruction mostly focuses on functional reorganization or furniture replacement. However,energy efficiency design has not been paid enough attention,which leads to the high building energy consumption and the harsh physical environment. Based on the analysis of climatic characteristics of Chongqing area,taking Dormitory Six on campus B of Chongqing University as an example,the reconstruction of rooms on the top floor and West end are focused to guarantee the equal benefits of the dormitory environment. Through the simulation analysis of the software, on the basis of energy saving reconstruction of common maintenance structure,this thesis discusses the energy saving reconstruction methods and strategies of the existing campus dormitories,which are more suitable for the existing campus dormitories in Chongqing area.

ENVIRONMENTAL TENDENCIES IN MODULAR GREEN INSTALLATIONS

There are two main approaches when discussing living green walls:an ecological one and an artistic one.Ecological thinking mainly considers environmental aspects,comfort enhancement and energy consumption and oversees human interaction and actual proximity to plants.In opposition,art or architecture installations that involve vegetation,lack technical and ecological aspects,aiming to raise awareness on environmental issues using human interaction either physically(direct)or emotionally(indirect).The present paper aims to analyze methods of combining the two directions,in a functional,ecological,yet aesthetically pleasing composition.In order to further develop previous experiences gathered by the team members,authors of this article,a green installation concept made out of interactive modular systems unites all the knowledge into a new,living,moving,dynamic,interactive structure whose inspiration is taken from nature while using biomimicry as main principle for its development.This new concept responds and is influenced by both external,natural stimuli and by the human factor.Multidisciplinarity is a key element in developing this project,involving architecture,art,interior and landscape design,botany,geometry,mechanical and electrical engineering,leading towards new research directions and innovative approaches in greenery-interior environment connections.

Building a Great Green Wall

China’s forests are being expanded by tree-planting volunteers and national forestry

VERTICAL TURF FOR GREEN FACADES:A VERTICAL GREENERY MODULAR SYSTEM INTEGRATED TO THE BUILDING ENVELOPE

Research has shown the environmental benefits of green envelopes,as well as performance in terms of energy efficiency.To date,there is no analysis of the economic sustainability of these systems,which has allowed the realization of a few,albeit very well known,examples.The research has identified a green modular system integrated into the building envelope,designed to facilitate installation and maintenance,with competitive performance compared to other existing solutions;a system that wants to improve performance and flexibility of vertical applications,experimented on buildings,on the market,and able to adapt,above all,to the needs of the building process.It is important to distinguish architectural aesthetic requirements from those of the building process;the former aim to have an authentic vertical garden,with different kinds of plants where nature dictates the rules,the latter aims to achieve the economic sustainability of vertical greenery systems.This paper provides an analysis of a technique based on the installation of plant bearing modular panels with turf on substructures also provided with a micro-irrigation system,which allows the construction of a modular coating,characterized by reduced thickness,that can also be integrated with other materials;installation is quick and simple,since the panel comes perfectly planted on site.In addition to that it allows,from a botanical point of view,resorting to types of grass selected with a view to climate,exposure,environmental adaptability,color and shape.A comparative analysis of this green façade is also presented compared to other existing case studies,from a constructive and managerial point of view,highlighting both its economic and architectural advantages.

The Great Green Wall

Fierce dust storms have plagued northern China for centuries. Cold, dry winds from Siberia pick up dust from the Gobi Desert, lifting it as high as four miles into the air, reducing visibility to zero in some areas and turning afternoon to night. A long history of human abuse—deforestation, overgrazing, and min-

HiLPD-GEE:high spatial resolution land productivity dynamicscal culation tool using Landsat and MODIS data

Land productivity is one of the sub-indicators for measuring SDG 15.3.1.Land Productivity Dynamics(LPD)is the most popular approach for reporting this indicator at the global scale.A major limitation of existing products of LPD is the coarse spatial resolution caused by remote sensing data input,which cannot meet the requirement offine-scale land degradation assessment.To resolve this problem,this study developed a tool(HiLPD-GEE)to calculate 30 m LPD by fusing Landsat and MODIS data based on Google Earth Engine(GEE).The tool generates high-quality fused Normalized Difference Vegetation Index(NDVI)dataset for LPD calculation through gapfilling and Savitzky–Golayfiltering(GF-SG)and then uses the method recommended by the European Commission Joint Research Centre(JRC)to calculate LPD.The tool can calculate 30 m LPD in any spatial range within any time window after 2013,supporting global land degradation monitoring.To demonstrate the applicability of this tool,the LPD product was produced for African Great Green Wall(GGW)countries.The analysis proves that the 30 m LPD product generated by HiLPD-GEE could reflect the land productivity change effectively and reflect more spatial details.The results also provide an important insight for the GGW initiative.

Combating Desertification and Improving Local Livelihoods through the GGWI in the Sahel Region: The Example of Senegal

The Great Green Wall Initiative（GGWI） has an overall objective of fighting desert encroachment through proven practices of sustainable management of land, and the reinforcement and protection of natural resources and systems of production and transformation, while also ensuring socio-economic development of local communities through multi-purpose activity platforms. The activities described in the present study are designed to accomplish several goals：（1） generate wealth,（2） strengthen access to basic social services,（3） manage the transition to a green economy as a means of creating suitable conditions for the emergence of rural production centers,（4） integrate sustainable development in order to eradicate poverty and food insecurity, and（5） strengthen adaptation and resilience capacities of local populations. The present study was undertaken on the basis of a wide variety of available publications and documentation, including articles and scientific papers, thesis, meeting summaries and reports, concerning the implementation of the Great Green Wall Initiative/GGWI in Senegal.