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Abstract

Effective soil and water management strategies require regional-scale assessment of erosion risk in order to locate prioritized area of intervention. Our study focuses on the Atacora mountain and surrounding areas (covering more than 18% of the total land area of Republic of Benin) which face a serious erosion threat despite their ecological and economic importance. To appraise the level of soil erosion risk of large area, we rely on the Instituto Nacional para la Conservación de la Naturaleza (ICONA) erosion model and use data from geographic information system (GIS). The erosion risk model requires four main inputs, namely, information on slope, lithofacies, land use and vegetation cover. The slope layer computed from ASTER digital elevation model (DEM) and the lithofacies layer inferred from digital pedogeological map are combined to draw soil erodibility map. To build soil protection map, we use land use/land cover layer extracted from LANDSAT 7 ETM + images in addition to vegetation cover layer derived from MODIS NDVI product. The final erosion risk map (with a resolution of 1 arc second) is obtained by overlapping erodibility and soil protection maps. We find that 21.8%, 58.5%, and 19.5% of the study area presents very low to low, medium, and high to very high level of erosion risk, respectively. Moreover, our findings are aggregated at the district-level (administrative unit). We observe that erosion risk is more acute in Boukoumbe district. Kerou, Kobli and Natitingou districts are mildly affected by erosion risk, while Kouande, Materi, Pehunco, Tanguieta and Toucountouna districts face a low risk. Ultimately, the proposed erosion risk map can help researchers and decision makers design and implement effective soil and water management interventions in the study area.

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... Water conservation evaluation was realized by the principle of water balance, which is calculated according to factors such as soil thickness, permeability, terrain, and the flow coefficient. Soil conservation evaluation is mainly calculated by the revised universal soil loss equation (RUSLE) [47,48]. Considering that large-scale human engineering measures cannot be characterized, the factor of soil conservation measures (P) was assigned as 1. ...
... WC is the average annual water conservation (mm); V is the flow coefficient (using the data of model parameter table); D is the terrain index (digital elevation model); K soil is the soil saturated hydraulic conductivity (cm/day); Y is the water production [50] Soil conservation [47,48] Ar is the soil conservation (t/(hm 2 ·a)); Am is the potential soil erosion; A is the actual soil erosion (t/(hm 2 ·a)); R is a factor of rainfall erosion (MJ·mm/(hm 2 ·h·a)) [51]; K is a factor of soil erosion (t·h/(MJ·mm)) [52]; L is a factor of slope length [53,54]; S is the slope degree factor [55]; C is a factor of crop cover and management; P is a factor of soil conservation measures ...
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Facing the demands of biodiversity conservation and ecosystem service improvement, the spatial pattern optimization of nature reserves has always been a research topic of interest. However, there remains a lack of methodological guidance in the planning of nature reserves and the surrounding areas. To promote the landscape sustainability of nature reserves, we constructed ecological security patterns (ESPs) with two scenarios as a case study in Wenchuan, China. In detail, the ecological sources were identified by ecosystem service evaluation, and the resistance surface was characterized by the habitat quality. The ecological corridors were determined based on circuit theory and the minimum cumulative resistance model. The ecological sources were mainly aggregated in the protected areas, with an area of more than 1000 ha; the high-resistance values were mainly in the area with dense roads or high elevation. There were 21 corridors in the scenario of only optimizing the nature reserve, while 31 corridors were identified when considering non-nature reserves, and the landscape connectivity was enhanced accordingly. The result supported constructing the ESPs between nature and non-nature reserves in Wenchuan to further protect pandas, and a methodological contribution was made to understand the differences of ESPs between them, thus supporting a methodological formulation of sustainable landscape patterns.
... The soil conservation capacity was quantified by RUSLE as follows [24,25]: ...
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Against the background of China’s advocating ecological civilisation construction, an urgent task and a major challenge are to identify key places for ecological protection and restoration and then propose optimisation strategies for future land use, especially in the Pearl River Delta (PRD), one of the regions in China that has the highest urbanisation level. In this study, we find the key places by constructing ecological security patterns and proposing optimisation strategies for future land use by analysing land-use status. We also propose a source identification method based on the resistance distance principle. Results show that forty-six sources were mainly distributed in the mountainous areas surrounding PRD but were less distributed along both sides of the Pearl River estuary. The difference in the spatial distribution of sources is remarkable. Eighty-four corridors generally had spider-like shapes. In the central plain of PRD, corridors were relatively long and narrow. Ninety pinch points were concentrated on existing rivers. Three barriers were located in the corridors between adjacent sources. Two artificial corridors were proposed to be established, which can improve the ecological network connectivity. The method for extracting sources based on the resistance distance principle is proven to be advantageous for improving the integrity of source extraction results and making ecological security patterns more reasonable.
... Soil retention is one of the important ESs in the study area. Using the Revised Universal Soil Loss Equation (RUSLE), soil retention was calculated using the following formula (Okou et al., 2016): ...
Article
An in-depth understanding of the complex patterns of ecosystem services (ESs) interactions (i.e., synergies or trade-offs) based on social-ecological conditions is an important prerequisite for achieving sustainable and multifunctional landscapes. This study aimed to explore how ESs interactions are influenced by social-ecological factors. Taking the Sutlej-Beas River Basin as a case study area, where the linkages between ESs interactions and social-ecological processes are poorly understood, ESs interactions were identified through principal component analysis and correlated with a range of social-ecological factors, which were explored spatially based on ES bundles. The results revealed two dominant types of ESs interactions, namely multifunctionality-related synergies and grain production-related trade-offs. Population, nighttime light, precipitation, temperature, and soil clay content were all positively correlated with the two ESs interactions. Contrarily, elevation and soil sand content were negatively correlated with the two ESs interactions. Four main ES bundles were identified, which spatially describe the presence of ESs synergies and/or trade-offs in relation to social-ecological factors. This study provides a feasible way to explore the spatial differentiation and influencing factors impacting the interactions between ESs, which can provide a basis for an integrated watershed-based management of ESs.
... On the other hand, socio-economic factors contribute to the problem and are often responsible for the severity of soil erosion. Among those factors, increased pressure on land resources through population growth is highlighted as a major reason for accelerated soil erosion [4][5][6][7]. ...
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This study presents the calibration and validation of the physically based spatially distributed hydrological and soil erosion model SHETRAN for the Dano catchment, Burkina Faso. A sensitivity analysis of six model parameters was performed to assess the model response and to reduce the number of parameters for calibration. The hydrological component was calibrated and validated using observed discharge data of two years. Statistical quality measures (R², NSE, KGE) ranged from 0.79 to 0.66 during calibration and validation. The calibrated hydrological component was used to feed the erosion modeling. The simulated suspended sediment load (SSL) was compared with turbidity-based measurements of SSL of two years. Achieved quality measures are comparable to other SHETRAN studies. Uncertainties of measured discharge and suspended sediment concentration were determined to assess the propagated uncertainty of SSL. The comparison of measurement uncertainties of discharge and SSL with parameter uncertainty of the corresponding model output showed that simulated discharge and SSL were frequently outside the large measured uncertainty bands. A modified NSE was used to incorporate measurement and parameter uncertainty into the efficiency evaluation of the model. The analyses of simulated erosion sources and spatial patterns showed the importance of river erosion contributing more than 60% to the total simulated sediment loss.
... Not surprisingly, zones located in steep slopes are associated with higher mean values of potential erosion (Trabucchi et al. 2012). Interestingly, even at low levels, with grades just greater than 3%, erosion patterns and ravines begin to form quickly (Shepashenko 1991;Okou et al. 2016). On slopes of medium steepness (up to 15%), the intensity of erosion processes accelerates; here, mining and agricultural land-use activities can cause serious environmental problems . ...
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Exploration and development of oil and gas (O&G) energy resources can create large-scale and permanent landscape effects that are best measured and understood via fieldwork and geospatial technologies. In this article, we examine O&G surface disturbance in the Orenburg steppe region of southwestern Russia for the year 2015. Utilizing field surveys, remote-sensing data and geographic information system (GIS) techniques, we apply a two-pronged approach. First, we map and measure the landscape infrastructure footprint (LIF) to determine the pattern and extent of direct surface disturbance created by O&G facilities and access roads. Second, we conduct a site suitability analysis to identify specific O&G production locations that are most vulnerable to environmental degradation. The approach considers both the particular properties of hydrocarbon production and specific natural features of steppe zones. Suitability patterns represent three indicators: two morphometric parameters (slope and aspect) and one spatial (the remoteness of O&G objects from water bodies). Our findings suggest that O&G production disturbs just over 3% of soil-vegetation cover in our study plot, while more than 13% of O&G objects are located in unsuitable zones based on topographic aspect, and about 11% lie in unsuitable zones regarding distance to water.
... L'envasement des barrages devient alarmant car plus de 75 millions de mètres cubes des capacités des barrages sont perdues chaque année (MATEE, 2007). Le problème d'érosion hydrique au Maroc a fait l'objet de nombreuses études (Rahhou, 1999;Al Karkouri, 2003;Sadiki et al., 2004 ;Faleh, 2004;El Garouani, 2008 ;Abahror, 2009, Tribak et al., 2009Sbai et Kaouass, 2011 ;Elhafid et al., 2012;Markhi et al., 2015, Briak et al., 2016Farris et al., 2016;Iaaich et al., 2016). ...
... Soil erosion by water and wind is a serious environmental problem in Africa [7]. It is mostly caused by physiographic factors such as harsh climatic conditions and the unstable structure of the soil, but also by socio-economic factors such as increased pressure on the land resources [8][9][10]. The harsh climatic conditions refer to the extreme events of abundant rainfall following periods of drought, which affect the soil by lowering its resistance (i.e., soil erodibility) against the impact of splash, therefore favoring higher runoff potential. ...
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Reduction of natural vegetation cover in the savannah of West Africa constitutes a pressing environmental concern that may lead to soil degradation. With the aim to assess the degradation of natural vegetation in the savannah of Burkina Faso, this study combined NDVI trends and fractional Land Use/Cover Change (LULCC). Fractional LULCC maps, derived from the aggregation of a 30 m Landsat LULCC map (1999–2011) to 250 m resolution of MODIS, were used to assess natural vegetation conversions in the small-scale spatial patterns of savannah landscapes. Mann-Kendall's monotonic trend test was applied to 250 m MODIS NDVI time series (2000–2011) to assess modifications of natural vegetation cover. Finally, the Spearman's correlation was employed to determine the relationship of natural vegetation degradation with environmental factors. The study revealed a vast conversion of natural vegetation into agriculture (15.9%) and non-vegetated area (1.8%) between 1999 and 2011. Significant decreasing NDVI trends (p < .05) indicated negative modifications of natural vegetation (2000–2011 period) occurring along the protected areas borders and in fragmented landscapes characterized by disruption of continuity in natural vegetation. Spearman's correlation showed that accessibility, climatic and topographic conditions favored natural vegetation degradation. The results can enable the development of efficient land degradation policies.
... Specifically, soil conservation service was quantified using the Revised Universal Soil Loss Equation (Wischmeier and Smith, 1965;Okou et al., 2016). ...
... Soil erosion by water and wind is a serious environmental problem in Africa [7]. It is mostly caused by physiographic factors such as harsh climatic conditions and the unstable structure of the soil, but also by socio-economic factors such as increased pressure on the land resources [8][9][10]. The harsh climatic conditions refer to the extreme events of abundant rainfall following periods of drought, which affect the soil by lowering its resistance (i.e., soil erodibility) against the impact of splash, therefore favoring higher runoff potential. ...
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Inadequate land management and agricultural activities have largely resulted in land degradation in Burkina Faso. The nationwide governmental and institutional driven implementation and adoption of soil and water conservation measures (SWCM) since the early 1960s, however, is expected to successively slow down the degradation process and to increase the agricultural output. Even though relevant measures have been taken, only a few studies have been conducted to quantify their effect, for instance, on soil erosion and environmental restoration. In addition, a comprehensive summary of initiatives, implementation strategies, and eventually region-specific requirements for adopting different SWCM is missing. The present study therefore aims to review the different SWCM in Burkina Faso and implementation programs, as well as to provide information on their effects on environmental restoration and agricultural productivity. This was achieved by considering over 143 studies focusing on Burkina Faso’s experience and research progress in areas of SWCM and soil erosion. SWCM in Burkina Faso have largely resulted in an increase in agricultural productivity and improvement in food security. Finally, this study aims at supporting the country’s informed decision-making for extending already existing SWCM and for deriving further implementation strategies.
... Due to the amount and intensity of the rainfall, the rainfall erosivity value of Taiwan is many times higher than the global average obtained by Borrelli et al. [2], making water erosion a very serious concern in Taiwan. In fact, not just in Taiwan, the concern of soil erosion has been evident in many published studies in different parts of the world, including Europe [3,4], the US and Mexico [5,6], mainland China [7,8], India [9,10], Africa [11,12], Australia [13,14], etc. A steady increase in the number of studies on soil erosion in the last few years has also prompted a few regional and global studies that provide a bigger picture of the emerging crisis [2,[15][16][17]. ...
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Soil erosion is a global problem that will become worse as a result of climate change. While many parts of the world are speculating about the effect of increased rainfall intensity and frequency on soil erosion, Taiwan’s mountainous areas are already facing the power of rainfall erosivity more than six times the global average. To improve the modeling ability of extreme rainfall conditions on highly rugged terrains, we use two analysis units to simulate soil erosion at the Shihmen reservoir watershed in northern Taiwan. The first one is the grid cell method, which divides the study area into 10 m by 10 m grid cells. The second one is the slope unit method, which divides the study area using natural breaks in landform. We compared the modeling results with field measurements of erosion pins. To our surprise, the grid cell method is much more accurate in predicting soil erosion than the slope unit method, although the slope unit method resembles the real terrains much better than the grid cell method. The average erosion pin measurement is 6.5 mm in the Shihmen reservoir watershed, which is equivalent to 90.6 t ha−1 yr−1 of soil erosion.
... The β of nitrogen or phosphorus are 1.35 and 1.28, respectively, according to the previous literature [48]. Different scholars have assessed soil erosion in a variety of ways, by using the Instituto Nacional para la Conservación de la Naturaleza (ICONA) model [49] and RUSLE model [50][51][52]. Sediment dynamics at the catchment scale depend primarily on climate (especially the rain intensity), soil, and vegetation characteristics, and factitious factors such as agricultural activities or dam construction and operation [53]. ...
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The quantitative estimation of non-point source (NPS) pollution provides the scientific basis for sustainability in ecologically sensitive regions. This study combined the export coefficient model and Revised Universal Soil Loss Equation to estimate the NPS nitrogen (NPS-N) and NPS phosphorus (NPS-P) loads and then evaluated their relationship with Primary Industrial Output Value (PIOV) in the water source area of the middle route of South-to-North Water Diversion Project (SNWDP) for 2000–2015. The estimated results show that: (1) dissolved nitrogen (DN) load increased 0.55%, and dissolved phosphorus (DP) load decreased 4.60% during the 15 years. Annual loads of adsorbed nitrogen (AN) and adsorbed phosphorus (AP) increased significantly before 2005 and then decreased after 2005. Compared with 2000, AN and AP loads in 2015 significantly decreased by 32.72% and 30.81%, respectively. Hanzhong Basin and Ankang Basin are key areas for controlling dissolved pollution, and southern and northern regions are key areas for adsorbed pollution. (2) From 2000 to 2005, NPS pollutants and PIOV showed weak decoupling status. By 2015, NPS pollutants had strong decoupling from PIOV in most counties. (3) Land use has been the main source of NPS-N and NPS-P pollution, accounting for about 75% of NPS-N and 50% of NPS-P based on the average value over the study period. In the future, various measures—such as returning cropland to forest and reducing the number of livestock—could be adopted to reduce the risk of NPS pollution. NPS pollution caused by livestock was grown over the past 15 years and had not yet been effectively controlled, which still needs to be urgently addressed. Collecting ground monitoring data and revising parameters are effective means to improve the accuracy of simulation, which deserve further study. The results will also provide scientific support for sustainable development in similar regions.
... Thus, based on a literature analysis regarding the main drivers of LULCC changes in semi-arid areas (e.g., Brinkmann et al., 2012;Lambin et al., 2001;Teferi et al., 2013) and the availability of data, a set of nine variables was selected that covered three categories (Table 1): (1) natural constraints (slope, toposequence, and type of soil), (2) accessibility (Euclidean distances from roads, rivers, and villages, and traveling time to market), and (3) demography (mean population density for the 2000-2015 period and the change in population density between 2000 and 2015). Among natural constraints, slope is a determinant of soil erosion because it leads to soil fertility loss and chemical soil degradation (e.g., Okou et al., 2016), which, in turn, has an impact on vegetation growth. Slope and toposequence together act as a constraint for land management for cropland expansion in particular, because gentle slopes and low elevations are generally more suitable for agricultural activities (e.g., Teferi et al., 2013;van Asselen and Verburg, 2012). ...
Article
A wide range of environmental and societal issues such as food security policy implementation requires accurate information on biomass productivity and its underlying drivers at both regional and local scales. While many studies in West Africa are conducted with coarse resolution earth observation data, few have tried to relate vegetation trends to explanatory factors, as is generally done in land use and land cover change (LULCC) studies at finer scales. In this study we proposed to make a bridge between vegetation trend analysis and LULCC studies to improve the understanding of the various factors that influence the biomass production changes observed in satellite time series (using integrated Normalized Difference Vegetation Index [NDVI] as a proxy). The study was conducted in two steps. In the first step we analyzed MODIS NDVI linear trends together with TRMM growing season rainfall over the Sahel region from 2000 to 2015. A classification scheme was proposed that enables better specification of the relative role of the main drivers of biomass production dynamics. We found that 16% of the Sahel is re-greening—but found strong evidence that rainfall is not the only important driver of biomass increase. Moreover, a decrease found in 5% of the Sahel can be chiefly attributed to factors other than rainfall (88%). In the second step, we focused on the “Degré Carré de Niamey” site in Niger. Here, the observed biomass trends were analyzed in relation to land cover changes and a set of potential drivers of LULCC using the Random Forest algorithm. We observed negative trends (29% of the Niger site area) mainly in tiger bush areas located on lateritic plateaus, which are particularly prone to pressures from overgrazing and overlogging. The significant role of accessibility factors in biomass production trends was also highlighted. Our methodological framework may be used to highlight changing areas and their major drivers to identify target areas for more detailed studies. Finer-scale assessments of the long-term vulnerability of populations can then be made to substantiate food security management policies.
... The soil conservation module in the InVEST model was used to calculate the importance of water conservation service [31,32] according to the following equation: ...
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The Ecological Protection Redline (EPR) is an innovative measure implemented in China to maintain the structural stability and functional security of the ecosystem. By prohibiting large-scale urban and industrial construction activities, EPR is regarded as the “lifeline” to ensure national ecological security. It is of great practical significance to scientifically evaluate the protection effect of EPR and identify the protection vacancies. However, current research has focused only on the protection effects of the EPR on ecosystem services (ESs), and the protection effect of the EPR on ecological connectivity remains poorly understood. Based on an evaluation of ES importance, the circuit model, and hotspot analysis, this paper identified the ecological security pattern in Guangdong–Hong Kong–Macao Greater Bay Area (GBA), analyzed the role of EPR in maintaining ES and ecological connectivity, and identified protection gaps. The results were as follows: (1) The ecological sources were mainly distributed in mountainous areas of the GBA. The ecological sources and ecological corridors constitute a circular ecological shelter surrounding the urban agglomeration of the GBA. (2) The EPR effectively protected water conservation, soil conservation, and biodiversity maintenance services, but the protection efficiency of carbon sequestration service and ecological connectivity were low. In particularly, EPR failed to continuously protect regional large-scale ecological corridors and some important stepping stones. (3) The protection gaps of carbon sequestration service and ecological connectivity in the study area reached 1099.80 km2 and 2175.77 km2, respectively, mainly distributed in Qingyuan, Yunfu, and Huizhou. In future EPR adjustments, important areas for carbon sequestration service and ecological connectivity maintenance should be included. This study provides a comprehensive understanding of the protection effects of EPR on ecological structure and function, and it has produced significant insights into improvements of the EPR policy. In addition, this paper proposes that the scope of resistance surface should be extended, which would improve the rationality of the ecological corridor simulation.
... Soil retention services were calculated using a modified soil erosion equation (Okou et al., 2016), as shown in Eq. (4): ...
Article
Developed areas are gradually expanding with the acceleration of urbanization. The degree of fragmentation of urban ecological land is increasing, and the risk of reducing the connectivity between important ecological patches is rising. In this context, the municipal governments in China have delineated ‘ecological control lines’ (ECLs) to protect landscape connectivity—however, its effectiveness has not been evaluated. In the study reported here, circuit theory was used to simulate flow among ecological sources, stepping stones carrying ecological flow were identified, and the effectiveness of the ECL, in terms of maintaining landscape connectivity, was evaluated. In this study, we classified the absence of stepping-stone protection based on stepping-stone area, distribution, and potential loss and identified key stepping-stone categories in urgent need of ECL protection, which will be useful for delineating the ecological red line in the future. The results showed that there were 1488 ecological stepping stones in Shenzhen, with an average area of 0.124 km² and a total area of 185.2 km². Under the current ECL protection, five stepping-stone groups were characterized as hotspots lacking protection, and this absence threatened the connectivity between some ecological sources. Through stepping stone classification and analysis, we were also able to show that there were 34 key stepping stones that were not protected effectively by the ECL, and they should be incorporate in the future. Using stepping stone and circuit theory models, our study has provided a reference for policy making that addresses connectivity under landscape fragmentation.
... Soil conservation service was evaluated using the Revised Universal Soil Loss Equation (Okou et al., 2016;Wischmeier and Smith, 1965): ...
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Rapid urbanization would lead to deterioration of the eco-environment and damage the functioning of ecosystem services. Ecological security pattern (ESP) is one of important national strategies in China for coordinating the ecosystem protection and economic development. Previous studies have mainly focused on how to identify ecological sources and extract ecological corridors, but optimization of the identified ecological sources and resistance surfaces are seldom explored. In this study, a new strategy to optimize ecological sources and resistance surfaces was proposed. The optimal diffusion distance of each existing ecological source with poor landscape connectivity was analyzed to meet future needs. The radial effect of resistance in areas with high resistance values were considered in combination with the characteristics of species migration. Hunan is an important province in the Yangtze River Economic Belt (YREB) and the Rise of Central China strategies. Taking a rapidly urbanizing region in Hunan Province as an example, the results showed that the total area of the optimized ecological sources was 9.60% higher than that of the existing area, which expanded the radial range of ecosystem services and enhanced ecosystem internal connectivity. According to the spatial distribution of important ecological landscape elements, the ecological framework of “two axes, four cores, and four belts” was proposed. This study offers a new insight for ESP construction, which can provide a new reference for ecological protection and development planning of rapidly urbanizing regions in central-south China.
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The process of urbanization and urban land use conversion inevitably disturbs the structure and function of ecosystems and their capacity to provide ecosystem services. Integrating ecosystem services into effective policies and planning at the regional scale to achieve sustainable urban development is still a challenge. The goal of this research is to optimize spatial patterns of urban development by assessing and comparing multiple trade-off scenarios between ecological processes and urban expansion, incorporating planning and design into spatially explicit methods, and integrating ecosystem services into decision-making procedures. We develop a conceptual framework for regional urban-ecological sustainability with six steps: pattern recognition, landscape process, problem diagnosis, integrated ecological network, urbanization simulation, and decision-support. We apply this framework to a case in which planning and design have followed the rational-comprehensive approach. Results demonstrate that landscape multi-functionality and regional ecological networks are significantly improved using our integrated approach to planning and design, because it provides vital information for regional planning to cope with the urgent need for ecological protection and urban development. By comparing urban growth under three scenarios, we found that the trade-off scenario based on ecological conservation and restoration (medium security level) resolved conflict more effectively, which restricted urban expansion on land of high ecological importance by constructing regional ecological networks. In addition, using field survey and species distribution model approaches, we design plant community types with complementary tree, shrub, and herb species as part of the decision-making procedure, which can restore zonal vegetation and the hydrological cycle in rugged mountain regions. The research concludes that regional urban-ecological sustainability based on scientific assessment, planning, and design provides a rational basis for sustainable urban development and landscape management.
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Ecological security is premised on ecosystem services (ESs) provided by ecosystems to humans. The construction of ecological security patterns (ESPs) is an effective measure to maintain normal ecosystem function and safeguard ecological security. A static ecosystem services value (ESV) was obtained in the study area in 2000, 2005, and 2010 to calculate the change rate as the priority index. The key indicator of ESs and their quantification to characterize spatial aggregation were used as the richness index. The ESV in 2010 was then dynamically reconstructed. In addition, the ecological sources and corridors of the three security levels were extracted to form the corresponding ESPs by using the source–sink theory of landscape ecology, minimum cumulative resistance model, and geographic information system techniques. The results of this study showed improvements over the traditional method of estimating ESs by using equivalent factors. Using the dynamic, spatial and intuitive values of ESs after reconstruction, a continuous and complete ecosystem security barrier system can be formed by selecting ecological sources with powerful service functions and ecological corridors with good connectivity. This approach provides a reference for urban development and planning of ecological environment layouts in arid inland river basins.
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Vegetation coverage in highly developed areas has been significantly altered in response to multiple disturbances over recent decades. However, the major driving factor of vegetation coverage change in these areas remains unclear, with climate change and anthropogenic factors playing interactive roles under different soil and terrain conditions. Comprehensively understanding the underlying drivers of vegetation change can provide references for regulating environmental management and prevention of vegetation degradation. In this paper, a structural equation modeling (SEM) method was employed to quantify the effects of fundamental natural environment (i.e. the relative stable variables including soil and topography), climate change and human activity change on vegetation coverage change in Jiangsu province, China from 2000 to 2015. Four variables including land use, population density, road impact and night lights were used to indicate human activities. The results showed that the increase of NDVI smaller than 0.10 covered 39.13% of the study area while the decrease of NDVI larger than 0.10 accounted for 20.23%. Areas with NDVI increase mainly distributed in croplands in northern Jiangsu. This could be explained by the increase of crop yield due to the development of modern agriculture. The decrease of NDVI was mainly observed in southern Jiangsu with higher urbanization level and city centers in northern Jiangsu, indicating the effect of rapid urbanization on vegetation degradation. The constructed SEM model suggested that the total effects (influential coefficients) of fundamental natural environment, climate change, and human activity change on NDVI change in Jiangsu were À0.24, 0.17, and À0.74, respectively. Although the fundamental natural environment didn't have a direct effect on NDVI change, but it had an indirect effect through interactions with human activities. We also constructed SEM models for northern and southern Jiangsu separately, due to their different natural environment and changing patterns of climate change. The results indicated the different driving mechanisms of NDVI change in northern and southern Jiangsu. Furthermore, the results suggested night light as the best indicator of human activity change, followed by the road impact index. We concluded that our study offered a framework to better understand and explain the complex interrelationships behind the spatial temporal change of NDVI.
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Dünya nüfusunun artmasıyla arazi üzerindeki baskı artmaktadır. Doğal bir süreç olan erozyon bu artan baskı ile problem haline gelmiştir. Türkiye’de birçok arazi özellikle tarım arazileri erozyon etkisi altında bulunmaktadır. Bu nedenle erozyon etkisini azaltmak için birçok yöntem ve yakla-şımlar geliştirilmiş ve geliştirilmeye devam etmektedir. Bu çalışma ile Bulanık Mantık Analitik Hi-yerarşik Süreç (BAHS) yaklaşımı kullanılarak, 586200 ha alan kaplayan Sinop ili arazilerinin erozyon duyarlılık sınıflarının belirlemesi ve haritalanması amaçlanmıştır. Sinop ili Karadeniz Bölgesi’nde yer almaktadır. İlin kuzeyinde Karadeniz, güneydoğusunda Samsun, güneyinde Çorum, batısında Kastamonu illeri bulunmaktadır. Çalışmada erozyon risk sınıfları belirlenirken hem toplam veri seti (TVS) hem de minimum veri seti (MVS) oluşturulmuş ve sonuçları karşılaştırılmıştır. Erozyon sınıf-ları oluştururken TVS için jeoloji, bitki örtüsü, arazi kullanımı, eğim, derinlik, yağış ve erodobilite parametreleri kullanılmıştır. MVS oluşturulmasında ise temel bileşenler analizi sonucunda, bitki örtüsü, derinlik ve erodobilite parametreleri ele alınmıştır. TVS ve MVS için yapılan sonuç harita-sında doğrusal kombinasyon yöntemi uygulanmış ve bu yöntem uygulanırken ArcGIS coğrafi bilgi sistemi programından yararlanılmıştır. Elde edilen sonuçlara göre, TVS’de çalışma alanının % 33’ü yüksek ve çok yüksek, %36’sı ise düşük düzeyde erozyona duyarlı olduğu belirlenirken, MVS’ye göre ise çalışma alanının % 33’ü yüksek ve çok yüksek ve % 35’i düşük erozyona duyarlı olduğu belirlenmiştir. Böylece TVS ve MVS ile elde edilen sonuçların oldukça birbirine yakın değerler gös-terdiği tespit edilmiştir. TVS ve MVS ile yapılmış her iki erozyon duyarlılık haritası da, özellikle bitki örtüsünün zayıf ve eğimin yüksek olduğu alanlar ile işlemeli tarımın yapıldığı araziler erozyona çok yüksek duyarlı oldukları görülmektedir.
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Soil erosion is a form of land degradation caused by the interactive effects of natural factors and anthropogenic factors (e.g., farmer livelihood behavior). This study investigates the impact of farmer livelihood behavior on soil erosion in erosion controlled (western Fujian Province, WFP) and uncontrolled (northern Guangdong Province, NGP) areas of southern China. A participatory rural appraisal was used to investigate the differences in farmer livelihood behavior and attitudes towards soil erosion in NGP and WFP, and between full-time farmers and part-time farmers. A pressure–state–response (PSR) model was used to analyze the impacts of farmer livelihood behavior on soil erosion. Results were as follows: (1) the PSR value of soil erosion affected by full-time farmers was higher than that of soil erosion affected by part-time farmers; (2) the farmers’ participation in and awareness of soil and water conservation (SWC) were higher in WFP than in NGP, and the influence of the farmer livelihood behavior on soil erosion was considerable; and (3) the impact of full-time farmers’ livelihood behavior on soil erosion in 2016 was higher than that observed in 2012, and the impact of this behavior from part-time farmers was slightly lower in 2012. This study provides a new perspective for farmers’ control and management of soil erosion.
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Soil erosion is a danger that threatens the world today and the basis of the fight against erosion must be sought in the role human. The aim of this study is determine a logical relationship between natural and planted forests conditions with soil erosion risk classes in the kasilian watershed. This basin is located in the Hyrcanian vegetation area on the northern slopes of the Alborz Mountains in northern Iran. In this research, the erosion risk map was prepared using the ICONA model and RS/GIS techniques and it was adapted to the physical realities of the area. The results showed that human interventions and pressures have reduced habitat good species percentage in the downstream areas in the northern part and upstream areas near the forest-rangeland boundary in the southern part. Also, the choice of species was incorrect in some planted forest. Therefore, high erosion risk class is clearly seen in these areas. There is a low erosion risk class (19.3%) in natural forest and a very low erosion risk class (2.73%) in plantation forest. The main reason for the high percentage of very low erosion risk class in planted forests can be due to the presence of 70–80% of canopy, which is a combination of 90% of broadleaf plants with 10% of conifers. These results are consistent with the realities in the study area. The ICONA model and RS/GIS techniques can be used as a reliable framework for erosion risk assessment.
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La dégradation des sols constitue un problème écologique ayant des conséquences néfastes considérables sur la production alimentaire au Niger et dans la région de Tahoua en particulier. L’objectif de cette étude, conduite à Kalfou dans la région de Tahoua au Niger, est d’évaluer les effets des demi-lunes multifonctionnelles sur la production agricole de sorgho. Ainsi l’essai expérimental, installé sur un terrain initialement encrouté et dénudé pendant deux (2) campagnes agricoles successives, est un bloc randomisé complet composé de trois (3) traitements sur (i) un sol aménagé en zaï (Zaï), (ii) un sol aménagé en demi-lunes conventionnelles (DLC) et (iii) un sol aménagé en demi-lunes multifonctionnelles intégrant à la fois les zaï et les tranchés de reboisement (DLM). Les résultats de l’étude ont montré que la croissance des cultures du sorgho est significativement plus élevée dans les ouvrages de demi-lunes multifonctionnelles que dans les ouvrages de zaï et de demi-lunes conventionnelles. En outre, les ouvrages de demi-lunes multifonctionnelles ont permis de produire 639 et 2159 Kg/ha de grains de sorgho respectivement en première et deuxième campagne. Ce rendement en grains est 3 à 4 fois plus élevé dans les ouvrages de demi-lunes multifonctionnelles que dans les ouvrages de zai et des demi-lunes conventionnelles. Ainsi, l’introduction de ces nouveaux ouvrages de demi-lunes multifonctionnelles, adaptés au contexte de la région sahélienne de Tahoua au Niger, permet d’optimiser l’utilisation des éléments nutritifs et des eaux de ruissellement pour la production agricole, ce qui peut renforcer la résilience de la population dans ladite zone. Toutefois, il serait nécessaire d’évaluer les impacts de ces ouvrages sur la production agricole à long terme tout en intégrant également d’autres cultures. Soil degradation is an ecological problem which has considerable negative consequences on food production in Sahel. The objective of this study, undertaken in Kalfou in the Tahoua region in Niger, was to test the effectiveness of multifunctional half-moons (DLM) for agricultural production of sorghum. The experiment design, installed on soil encrusted two (2) successive cropping seasons of sorghum, was a complete randomized block composed of three (3) treatments in three (3) : i) soil with local practice of zai, ii) soil with conventional half-moons (DLC) and iii) soil with multifunctional half-moons (DLM). Results showed that sorghum crop growth was significantly higher in multifunctional half-moons than in zaï and conventional half-moons structures. Besides,, the multifunctional half-moon structures produced 639 and 2159 kg.ha-1 of sorghum grain at the first and second season respectively. This grain yield was three (3) to four (4) times higher in multifunctional half-moon structures than in zai and conventional half-moon structures. Thus, the introduction of these new multifunctional half-moon structures, adapted to the context of Tahoua region allows optimizing the use of nutrients and runoff water for agricultural production, which can improve people’s resilience in the zone. Nevertheless , it would be necessary to evaluate the impacts of these rain water harvesting technologies on agricultural production in the long-term while also integrating other crops.
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In Morocco, hydric erosion is the main factor in soil degradation. It is a dynamic and very complex phenomenon, linked to natural and anthropic factors that are difficult to control in time and space. Land degradation has visible impacts on the environment and hinders economic and social development. The consequences of erosion, both upstream and downstream of watersheds, are costly for the Moroccan economy. The Oued Isly watershed is an elongated mountan basin with an area of 1312km2. It is part of eastern Morocco. It is located in the south of Oujda city. Wadi Isly is characterized by irregular flow. Its flow increases during the winter and early spring. Extreme flows are recorded after exceptional and very intense rain in the Touissit and Guenfouda mountains. The watershed of Wadi Isly knows currently a very active erosive dynamic that affects all the slopes on both banks of the Oued Isly. Several factors contribute to the processes of soil degradation, such as climatic aggression and anthropogenic action. The objective of this study is to estimate soil losses at the Wadi Isly watershed by the application of the universal soil loss equation (USLE) and the use of GIS and Remote sensing. This study also aims to discuss the amplifying factors of the erosive phenomenon in this semi-arid environment. Keywords: Watershed, water erosion, GIS, Isly, Morocco
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Abstract. Soil erosion in Iran due to the destruction of natural resources has intensified in recent years and land use changes have played a significant role in this process. On the other hand, the lack of data in most watersheds to evaluate erosion and sedimentation for finding quick and timely solutions for watershed management has made the use of models inevitable. The purpose of this study was to use the ICONA model and RS and GIS techniques to assess the risk of erosion and to identify areas sensitive to water erosion in the kasilian watershed in northern Iran. The results of this study showed that with very high slope class percentage (20 %–35 %) and sensitivity of shemshak formation to weathering which covers a large part of the watershed, soil erodibility class is high. But there is adequate land cover along with high percentage of natural forest cover, it has mitigated erosion. For this reason, the kasilian watershed is generally classified as low to moderate of erosion risk. Based on the erosion risk map, results show that the moderate class had the highest percentage of erosion risk (26.26 %) at the watershed. On the other hand, the low erosion risk class comprises a significant portion (25.44 %) of the catchment area. Also, 10.92 % of the catchment area contains a very high erosion risk class, with most of it in rangeland and Rock outcrops second. However, the erodibility of the kasilian watershed is currently controlled by appropriate land cover, but the potential susceptibility to erosion is high. If land cover is redused due to inadequate land management, the risk of erosion is easily increased.
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Increased flooding and newly formed rills and gullies were observed in the Cheleleka wetland watershed, over the past three to five years. These events are due to problems related to land use changes and are adversely affecting land productivity. This study was conducted to quantify, analyze and map soil erosion risk areas using the Revised Universal Soil Loss Equation. Only 13.6 percent of the study area has a soil loss value less than 10 ton per hectare per year with the remaining area experiencing a higher soil loss value. A large area, 53.6 percent of the watershed, is under severe to extremely severe soil loss (>45 ton per hectare per year). Another 17.3 percent of the study area has annual soil loss of 20–45 ton per hectare. A significantly large area of the Cheleleka wetland watershed has non-tolerable soil erosion that threatens annual crop production, land productivity, and hydrological functioning of the area. From the conservation perspective, a large proportion of the watershed needs immediate watershed management intervention.
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In this research, the applicability of geographic information system (GIS) and remote sensing (RS) techniques was tested to assess soil erosion risk with the ICONA erosion model. This study was carried out in the Ankara-Beypazari area because of its variety of diverse landforms, land uses and land covers. The erosion risk assessment phase of this model consists of seven steps that mainly use slope, geology. land use and land cover information. A potential erosion risk map (step 3) was obtained from the slope (step 1) and lithofacies layers (step 2) generated using a digital elevation model (DEM) and digital geological maps. As a result of this process, the distribution of the erosion risk classes was 8.0% (very low), 24.7% (low), 23.6% (medium). 23.6% (high), and 20.1% (extreme). Land use (step 4) and land cover (step 5) layers derived from Landsat TM image data classification were combined to produce the soil protection map (step 6). The soil protection map showed that 77.8% of the area was classified as low and very low, and 22.296 of the area was classified as very high, high and moderate in terms of protection class. During the final predictive phase, soil erodibility and soil protection layers were combined to generate the ICONA soil erosion status map (step 7). The final map showed that 45.9% of the area had high and very high erosive status. These areas especially included hilly and mountainous areas, and excluded the forested parts. The rest of the study area had lower (very low, low and appreciable) erosion status. The present study shows that GIS and RS techniques have an important role to play in soil erosion risk studies.
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This study analyzed the ecological factors influencing soil degradation in the Atacora Mountains in northern Benin, which harbor two endemic species,Thunbergia atacorensis and Ipomoea beninensis. Data were collected along line transects from plain to summit within 22 plots of 30 m 330 m. Indicators of physical soil degradation (extent of organic layer, color of topsoil, compactness of soil, presence and extent of rills, and occurrence of sheet erosion) and factors (canopy and ground cover, topography, occurrence of flooding, and slope) were assessed. Cluster analysis identified 4 soil degradation classes: light, moderate, high, and extreme. Discriminant and multivariate variance analyses identified canopy and ground cover as the 2 main ecological drivers of soil degradation. Plant, litter, and stone cover were found to decrease as soil degradation increased. The parts of the Atacora Mountains with high elevation and steep slope were found to be less degraded than areas with low slopes, which are easily accessible for human activities. Policies to mitigate soil degradation should prioritize practices with low impact on vegetation cover and promote soil protection practices such as tree planting and mulching.
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This study on the influence of soil textual properties and land use cover type on soil erosion of a characteristics ultisols. Betem, Cross River State, Nigeria was conducted with the aim of determining the relationship between land use type and soil loss in the context of a characteristics ultisols. Soil samples were manually collected from the respective land use types with the aid of soil auger at the depth of 0-15cm for the laboratory analysis of particle size distribution while data on sediment yield deposit were obtained through the use of sediment traps or dishes placed at the foot of the respective slopes. The result of the textural characteristics revealed that particle size distribution showed large proportion of sand. Thus, sand ranged from 72-78% with a mean of 75.0%, silt ranged from 11-12% with a mean of 11.0% while clay ranged from 12.0% -16% with a mean of 14.0%. The result showed that sand was the dominant particle fraction and any soil that is characterized by huge sand proportion can be vulnerable to erosion perturbation. The various land cover types have revealed their potentials in reducing erosion perturbation. The result of sediment yield obtained under these land use types revealed the following ranges and means: bare land surface ranged from 40-360g with a mean of 182.2g, cassava plot, ranged from 30-238 with a mean of 107.6g, bush fallow ranged from 4-150g with a mean of 30.0g; secondary forest plot ranged from 2-48 with a mean of 15.0 grams while primary forest plot has a range of 1-45 with a mean of 13.4g respectively. The study revealed that it is the unguided use of land that exposes soils to the direct effect of weather elements hence the major cause of soil erosion in the area. The study, therefore suggests an appropriate land or soil management system that can guarantee adequate protection of soil and other variable components of the environment.
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The study presented here makes use of about 300 daily rain gauges covering a 1 700 000 km2 area in order to characterize the rainfall regimes of West Africa at hydrological scales. The rainfall regime is analyzed as a combination of two variables, the average number of events over a given period of time (nT) and the average cumulative rainfall per event (h). These two parameters are a measure of the occurrence rate and magnitude of the convective storms that generate most of the rainfall in this region. They define the average water input to the hydrological systems and the average time available for this water to be redistributed into the continental hydrological cycle before a new input occurs. By analyzing for a period of 40 yr (1951-90), the space and time variations of these two parameters, it is possible to better understand how the intraseasonal to decadal rainfall variability may impact on the hydrological cycle. The analysis is carried out in two steps. First, the annual cycle and migrations of the weather zones characterizing the climate of West Africa are considered. This leads to evidence of a sudden and synchronous rain onset between 9° and 13°N, which does not follow the classic scheme of a progressive migration of the rain zones, north and south with the sun. Second, the differences in the rainfall regimes between the two succeeding subperiods of 20 yr are obtained, the subperiod P1 (1951-70) being wet and the subperiod P2 (1971-90) being dry. The difference-averaged over the 16° by 12° study region-of the mean interannual rainfall between the wet and the dry periods is 180 mm yr1. This difference is relatively evenly distributed in space, with no clear meridional gradient. Between these two periods, the parameter nT displays a systematic decrease, which appears well correlated to the decrease of the mean interannual rainfall. The variations of h are, by contrast, smaller in amplitude and more erratically distributed in space. When looking at the intraseasonal scale, it appears that the rainfall deficit of the dry period is primarily linked to a deficit of the number of events occurring during the core of the rainy season over the Sahel, and during the first rainy season for the region extending south to 9°-10°N. It is also shown that, in the south, the dry period is characterized by a shift in time of the second rainy season. All these characteristics have strong implications in term of agricultural and water resources management. They also raise questions about the traditional scheme used to characterize the dynamics of the West African monsoon.
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. Vegetation phenological phenomena are closely related to seasonal dynamics of the lower atmosphere and are therefore important elements in global models and vegetation monitoring. Normalized difference vegetation index (NDVI) data derived from the National Oceanic and Atmospheric Administration's Advanced Very High Resolution Radiometer (AVHRR) satellite sensor offer a means of efficiently and objectively evaluating phenological characteristics over large areas. Twelve metrics linked to key phenological events were computed based on time-series NDVI data collected from 1989 to 1992 over the conterminous United States. These measures include the onset of greenness, time of peak NDVI, maximum NDVI, rate of greenup, rate of senescence, and integrated NDVI. Measures of central tendency and variability of the measures were computed and analyzed for various land cover types. Results from the analysis showed strong coincidence between the satellite-derived metrics and predicted phenological characteristics. In particular, the metrics identified interannual variability of spring wheat in North Dakota, characterized the phenology of four types of grasslands, and established the phenological consistency of deciduous and coniferous forests. These results have implications for large-area land cover mapping and monitoring. The utility of remotely sensed data as input to vegetation mapping is demonstrated by showing the distinct phenology of several land cover types. More stable information contained in ancillary data should be incorporated into the mapping process, particularly in areas with high phenological variability. In a regional or global monitoring system, an increase in variability in a region may serve as a signal to perform more detailed land cover analysis with higher resolution imagery.
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Understanding the growth and changes in urban environments are the most dynamic system on the earth’s surface is critical for urban planning and sustainable management. This study attempts to present a space-borne satellite-based approach to demonstrate the urban change and its relation with land surface temperature (LST) variation in urban areas of Klang valley, Malaysia. For this purpose an object-based nearest neighbour classifier (S-NN) approach was first applied on SPOT 5 data acquired on 2003 and 2010 and subsequently five land cover categories were extracted. The overall accuracies of the classified maps of 2003 and 2010 were 90.5 % and 91 % respectively. The classified maps were then used as inputs to perform the post classification change detection. The results revealed that the post-classification object-based change detection analysis performed reasonably well with an overall accuracy of 87.5 %, with Kappa statistic of 0.81 %. The changes represented that the urban expanded by 10 % over the period, whereas the urban expansion had caused reduction in soil (1.4 %) and vegetation (11.4 %), and growth in oil palm (2 %), and water (0.7 %). Additionally decision tree method was used to derive the surface heat fluxes from thermal infrared Landsat TM and ETM+bands. Subsequently, a comparison was made with classified result from SPOT 5 images. Results showed high correlation between urban growth and LST.
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The geoindicators of land degradation such as erosion, vegetation change and wetland loss were identified in the Kashmir Himalayan region using a geospatial model. Geomatics techniques were used to generate information on landuse/landcover, NDVI, slope and the lithological formations that form inputs to map the erosion risk. The results of erosion analysis revealed that 48.27 % of the area is under very high erosion risk. The Middle Himalayan watersheds were found to be under high erosion risk compared to the Greater Himalayan watersheds. Pohru and Doodhganga watersheds of the Middle Himalayas were found to be under very high erosion risk. These two watersheds were studied in detail from 1992 to 2001 for vegetation change and wetland loss. In Pohru watershed, significant change was found in the dense forest with 10 % decrease. Wular lake, an important wetland in the Pohru watershed, has shrunk by 2.7 km2 during the last decade. The vegetation change analysis of the Doodhganga watershed revealed that there has been 9.13 % decrease in the forest, 7 % increase in built up and the largest wetland in the Doodhganga, Hokarsar, has reduced by 1.98 km2 from 1992 to 2001. Field studies showed that anthropogenic activities and chemically deficit soil (Karewa) along Pir Panjal ranges are the main factors responsible for high land degradation in the area. The assessment of these geoindicators provided valuable information for identifying causes and consequences of the land degradation and thus outlining potential hazard areas and designing remedial measures.
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Land use/land cover (LULC) classification with high accuracy is necessary, especially in eco-environment research, urban planning, vegetation condition study and soil management. Over the last decade a number of classification algorithms have been developed for the analysis of remotely sensed data. The most notable algorithms are the object-oriented K-Nearest Neighbour (K-NN), Support Vector Machines (SVMs) and the Decision Trees (DTs) amongst many others. In this study, LULC types of Selangor area were analyzed on the basis of the classification results acquired using the pixel-based and object-based image analysis approaches. SPOT 5 satellite images with four spectral bands from 2003 and 2010 were used to carry out the image classification and ground truth data were collected from Google Earth and field trips. In pixel-based image analysis, a supervised classification was performed using the DT classifier using ENVI 4.8 software. On the other hand, object-oriented (K-NN) image analysis was evaluated through Definiens eCognition software using standard nearest neighbour as classifier. Subsequently SVM object-based classification was performed using ENVI software. Five LULC categories of urban area, soil, water bodies, oil palm, and other vegetation were extracted and the results were compared between them. The overall classification accuracies for 2003 and 2010 showed that the object-oriented (K-NN) (90.5% and 91%) performed better results than the pixel-based DT (68.6% and 68.4%) and object-based SVM (80.6% and 78.15%). The advantages that could offer by object-oriented (K-NN) was not provided by other approaches and it was computationally faster and in general, the object-oriented (K-NN) performed better than both DTs and SVMs. The obtained LULC classification maps can be used to improve various applications such as change detection, urban design, environmental management and zooning.
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This article discusses research in which the authors applied the Revised Universal Soil Loss Equation (RUSLE), remote sensing, and geographical information system (GIS) to the maping of soil erosion risk in Brazilian Amazonia. Soil map and soil survey data were used to develop the soil erodibility factor (K), and a digital elevation model image was used to generate the topographic factor (LS). The cover-management factor (C) was developed based on vegetation, shade, and soil fraction images derived from spectral mixture analysis of a Landsat Enhanced Thematic Mapper Plus image. Assuming the same climatic conditions and no support practice in the study area, the rainfall-runoff erosivity (R) and the support practice (P) factors were not used. The majority of the study area has K values of less than 0� 2, LS values of less than 2� 5, and C values of less than 0� 25. A soil erosion risk map with five classes (very low, low, medium, medium-high, and high) was produced based on the simplified RUSLE within the GIS environment, and was linked to land use and land cover (LULC) image to explore relationships between soil erosion risk and LULC distribution. The results indicate that most successional and mature forests are in very low and low erosion risk areas, while agroforestry and pasture are usually associated with medium to high risk areas. This research implies that remote sensing and GIS provide promising tools for evaluating and mapping soil erosion risk in Amazonia. Copyright # 2004 John Wiley & Sons, Ltd.
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Ground-based data on total phytomass were collected in 1998 and 1999 from four sampling domains, each nearly 1000 km2, within the arid shrubland of Western Australia. These data were used in models relating rainfall and landscape characteristics to total phytomass to provide landscape-scale estimates of total phytomass and rainfall-use efficiency for 1992–1999 (referred to as RUEP). These modelled estimates were compared with remotely sensed estimates of total phytomass (I-NDVI) and rainfall-use efficiency (I-NDVI/annual rainfall; referred to as RUEN) using data from NOAA satellites.There was good agreement between ground-based and remotely sensed estimates of total phytomass but less agreement between estimates of rainfall-use efficiency. Partitioning the landscape on the basis of landscape resilience did not improve the amount of variance accounted for in RUEP or RUEN and there were conflicting relationships between landscape-scale indicators of landscape function and RUEN. There was, however, evidence to suggest that temporal change in RUEN may provide a useful broad-scale indicator of landscape degradation or recovery over decadal time intervals. Recommendations are made for broad-scale application of this indicator based on temporal trends in RUEN.
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Soil erosion by water is one of the major causes of land degradation in Lebanon. The problem has not yet been treated in detail although it affects vast areas. This study elaborates a model for mapping soil erosion risk in a representative area of Lebanon at a scale of 1:100,000 using a spatial database and GIS. First, three basic maps were derived: (1) runoff potential obtained from mean annual precipitation, soil-water retention capacity and soil/rock infiltration capacity; (2) landscape sensitivity based on vegetal cover, drainage density and slope; and (3) erodibility of rock and soil. Then two thematic maps were derived: potential sensitivity to erosion obtained from the runoff potential and landscape sensitivity maps, and erosion risk based on the potential erosion and erodibility maps. The risk map corresponds well to field observations on the occurrence of rills and gullies. The model used seems to be applicable to other areas of Lebanon, constituting a tool for soil conservation planning and sustainable management.
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Indicators of land quality (LQIs) are being developed as a means to better coordinate actions on land related issues, such as land degradation. Economic and social indicators are already in regular use to support decision making at global, national and sub-national levels and in some cases for air and water quality, but few such indicators are available to assess, monitor and evaluate changes in the quality of land resources. Land refers not just to soil but to the combined resources of terrain, water, soil and biotic resources that provide the basis for land use. Land quality refers to the condition of land relative to the requirements of land use, including agricultural production, forestry, conservation, and environmental management.The LQI program addresses the dual objectives of environmental monitoring as well as sector performance monitoring for managed ecosystems (agriculture, forestry, conservation and environmental management). The primary research issue in the LQI program is the development of indicators that identify and characterize the impact(s) of human interventions on the landscape for the major agroecological zones of tropical, sub-tropical and temperate environments. Core LQIs identified for immediate development are: nutrient balance, yield gap, land use intensity and diversity, and land cover; LQIs requiring longer term research include: soil quality, land degradation, and agro-biodiversity; LQIs being developed by other authoritative groups include: water quality, forestland quality, rangeland quality, and land contamination/pollution.
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Many spatially distributed environmental models have been developed for small spatial units (e.g. individual plots or fields). Their application at a regional scale (e.g. large drainage basins) was hitherto not very successful since most models are 'scale-specific'. In most cases the lack of input data is a limiting factor for an appropriate model application at a regional scale. The use of simplified models on the other hand, can only be successful if they have the appropriate degree of complexity. This leads to the following paradox: on the one hand a model should be based on process knowledge so that it will react correctly to changes imposed by the modelling system. Including all available process knowledge, however, will lead to an overparametrisation. The error propagation involved in the poor data quality can then deteriorate dramatically the accuracy of the output results. For optimal model predictions at a regional scale the model complexity has to be in balance with the quality of the available input data. The error involved in a model application can be split in two parts: on the one hand the intrinsic model error because of an incomplete description of the processes and on the other hand the input error because of the use of low quality data. The total error is the sum of both parts. A simplification of the modelling structure will lead to an increase of the intrinsic model error and a decrease of the input error. If observed field values are available they can be used to determine which model structure gives the best results, given the available data. In many cases such validation data are not available. However, also in these cases, a model user should be able to select an optimal model structure. In this paper a technique is presented that allows the determination of the optimal degree of model complexity for an application at a regional scale if no observed field data are available. If the uncertainty of a model parameter exceeds a certain threshold, the model structure must be further simplified by replacement of this parameter by an aggregated value or a constant. The use of the technique is illustrated via the application of a soil erosion model.
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Soil erosion by water is recognized to be a critical economic problem in highland Ethiopia. However, nearly all the available information about its severity and economic costs are extrapolated from plot and micro-watershed level studies which are too few in number to represent the diverse environments of the country. Moreover, plot and watershed level studies do not show actual soil losses from cultivated fields, while understanding the magnitude of soil loss at the field scale is important for practical conservation planning. This paper reports results of field-scale soil erosion assessment that employed a survey methodology for rills and was conducted over two wet seasons (the years 2000 and 2001) at two sites, Kechemo and Erene, located in the upstream and downstream reaches of the Chemoga watershed, northwestern highland Ethiopia. The two wet seasons average rill erosion magnitudes were 13.5 Mg ha−1 in the Kechemo and 61 Mg ha−1 in the Erene. Assuming that interrill erosion contributes 30%, actual soil losses were around 18 Mg ha−1 in the Kechemo and 79 Mg ha−1 in the Erene. These estimates, which are well in agreement with results obtained by measurements in a nearby experimental micro-watershed, reveal that soil erosion is a threat to agricultural production in the study area and conservation measures are needed. Soil erosion showed significant spatial (between and within the two sites) and temporal variations. Hence, soil and water conservation (SWC) measures that fit well into local-scale circumstances will be realistic and acceptable to the farmers. Additionally, the problem of soil erosion should be tackled in the watershed context, because there is a strong physical interdependence between upstream and downstream areas. Finally, the study confirms that the rill survey approach gives good semi-quantitative information on soil erosion in real life situations of diverse farming and land use practices in a fast and inexpensive way; and it is commendable for practical conservation-oriented soil erosion assessment purposes.
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This study uses the well-known Universal Soil Loss Equation (USLE) and satellite remote sensing data to assess the long-term soil erosion in a small catchment area and to simulate various soil protection alternatives by assistance of a GIS. -Authors
Article
Data on soil erosion is scarce for the Napahai Catchment in the Qinghai-Tibet Plateau. Specifically, greater information on soil erosion under effects of different plant cover types within this region is required for soil and water conservation as well as to initiate sustainable land use resource practices in Shangri-La County, Yunnan Province, China. This study investigated five representative plant cover types in Napahai Catchment to observe surface runoff and sediment yield. These included barren land, 1-year revegetated plot, three-year revegetated plot, grassland, and pine forestland. They were subsequently analyzed to determine their effects on soil erosion. Results showed that surface runoff and sediment yield were reduced with an increase in plant cover. However, different plant cover types produced significantly different results in surface runoff and sediment yield. Surface runoff volume followed the order barren land > 3-year revegetated plot > pine forestland > 1-year revegetated plot > grassland, whereas sediment yield volume followed the order barren land > 1-year revegetated plot > 3-year revegetated plot > pine forestland > grassland. In addition, soil organic matter and plant cover were closely correlated to surface runoff and soil loss in the Napahai Catchment. Grassland revegetation, in particular, would be a good initial step to take to prevent and control surface runoff and sediment yield during ecological restoration of the Napahai Catchment. This is owing to its natural advantages in soil and water conservation. Field observations could also be helpful to collect much needed information on the region that can subsequently act to prevent and protect against soil erosion, preventing the Napahai Wetland from deteriorating further while simultaneously improving land resources.
Article
In Djebobo Massif (Togo Mountains) harmattan weather is responsible for the development of extreme ecoclimatic conditions which are responsible for the general pattern of vegetation types and for the distribution of many rare montane species. In the course of microclimatological measurements in December 1965 some unusual environmental extremes were recorded: wind velocity 20 m/sec approximately (tree steppe on summit), Piche evaporation per hour 4.4 ml (tree steppe on windward slope), maximum temperature 43.7⚬ C (savanna woodland on lee slope), minimum temperature 12⚬ C (riverain forest in the valley), diurnal range of air temperature 26.8⚬ C (grassy clearing in forest on valley bottom). The mechanical effects of strong harmattan winds play the major role in the summit areas, being responsible for the development of distinct windward and leeward biotopes bearing tree steppe and savanna thicket respectively. The existence of communities of xeromorphic species resembling typical semi-desert forms is due to the intense desiccation caused by the dry, rapid harmattan. The extreme temperatures during the harmattan weather seem to have a selective influence on the distribution of certain herbs and trees.
Article
Ipomoea beninensis Akoègninou, Lisowski & Sinsin and Thunbergia atacorensis Akoègninou & Lisowski, two novelties found in Benin, are described, illustrated and discussed. Despite the relatively dry climate in this part of West Africa (the "Dahomey Gap"), it appeared that undescribed species not only occur in gallery forest but also in low dry forest adjacent to a main road.
Article
Soil erosion in mountainous regions is a key issue in land use planning, and this is particularly true in the Alps where intense anthropogenic influences at low elevations and abandonment in higher regions often coexist to affect soils. Natural hazard and risk assessment are essential given the density of settlements and associated facilities. Soil loss due to water erosion is very common and is becoming more frequent as a consequence of climate change which affects precipitation regimes, frequency of extreme meteorological events, snow melt and vegetation. In this study, we describe the production of a map showing susceptibility to soil erosion in the Aosta Valley (northwest Italian Alps). Most research on slope instability has focused on rock failures, but we investigated upper soil horizons by analysing chemical and physical properties, which could contribute to slope instability. The steps involved in creating the map are explained, and these involved GIS overlay, sampling, soil description, selection of relevant chemical and physical indicators of soil susceptibility to erosion, and overall erosion susceptibility assessment. The resultant indicator values correspond well with field observations to thus validate the methodology and demonstrate its usefulness in land use planning and management in Alpine areas.
Article
plots (6000 kg ha-1) was 35 % of that from non-mulched plots, while runoff threshold values increased from 5.0 to 6.4 mm. (2) Stone rows makes that sorghum water demand (ET:ETc ratio) is satisfied more often than without this WC practice (3) Vegetation barriers, in particular with the perennial grass Andropogon gayanus proved to be very effective in reducing runoff to only 20 % of precipitation. (4) Water conservation tillage (braking the surface crust every 15 days) without an additional increase in external nutrient inputs only had a marginal effect. However, with a complete prevention of runoff (as seems possible with tied ridging) the vegetative period is prolonged and an increase in yield of no less than 40 % seems possible. (5) Termite 'management' reduces runoff significantly. Although WC seems beneficial two important lessens can be drawn from integrative studies. The first is that there is no efficient WC without improved nutrient management. This is proven by the fact that when semi-permeable barriers (stone rows or grass strips) are combined with compost application the synergetic effect is a tripled grain yield. The second lesson is that with WC easily too much water can infiltrate into the soil. In permeable soils this leads to nutrient leaching below the root zone and highering of the groundwater (in some case a much wanted effect). In soils with less impermeable deep layers this leads to saturation of the top soil, causing water logging and risk for saturation overland flow.
Article
Landscape degradation by soil erosion has increased considerably in the Ethiopian Highlands since the deforestation of the natural mountain forests and the cultivation of large areas, resulting in a serious threat to the Ethiopian population. This investigation shows how to integrate remote sensing data into a geographical information system (GIS) for modelling soil loss rates. Stereoimage data of the MOMS-02/D2-sensor, tested during the Second German Spacelab-Mission D-2, served as main database. By application of the Universal Soil Loss Equation (USLE) thematic maps were produced, which emphasize the spatial impact of different soil erosion factors and show the expected dimensions of soil loss. The result shows that the integration of remote sensing data into a GIS offers various applications for resource management in developing countries.
Article
Due to soil erosion processes fertile soils are washed out almost anywhere in the world. Soil erosion protection measures are necessary, especially for food security reasons. This study uses the well-known Universal Soil Loss Equation (USLE) to assess the long-term soil erosion in a small catchment area and to simulate various soil protection alternatives. After completion at this test site the techniques can be applied for larger regions to detect areas that are most afTected by soil erosion and to guide precisely the efficient soil erosion prevention measures that proved to be valuable according to the computer simulation results.This raster-oriented study uses a very accurate multi-temporal land-use classification to determine the land-cover (C-factor). The other input variables have been determined from ancillary data (e.g., digital elevation model and soil data). The compiled data layers of this geographical information system (GIS) allow the calculation of the long-term soil erosion per pixel as well as inquiries about all data layers for every pixel.In addition to the resulting soil erosion risk map it is possible to simulate soil protection measures with the computer. This ensures that only the most effective ones are introduced to the field.
Article
Multitemporal 1 km NOAA/AVHRR Normalized Difference Vegetation Index (NDVI) maximum composite imagery was utilized in combination with rainfall, soil types, and field survey data on dominant rural activities to assess the risk of land degradation in southern Mauritania. Mauritania is one of eight continental West African Sahel countries that stretch from Chad to the northwestern Atlantic coast, and from the southern fringe of the Sahara Desert to the northern limit of the Sudanian climatic zone. The major environmental problem these countries are currently facing is the temporally and spatially erratic character of rainfall, frequently leading to general or local droughts since the late-1960s with subsequent increase of human pressure on the natural resource base and degradation. Image deviation was applied to maximum NDVI composites of the growing season (June to October) for the period 1990–99 to detect temporal and spatial change patterns over the study area. Only pixels whose values were lower than their temporal mean minus 0ċ5 standard deviation were retained as areas under threat. These were combined with soil types and the spatial pattern of deforestation (fuelwood and building material collection areas) grazing, and agricultural land to determine the causes of lowering primary biological productivity. The results show that the below-normal NDVI values generally coincide with the patterns of below-normal rainfall: deforestation, and overgrazing areas, agricultural land, and low primary biological productivity soil types. Thus the observed substantial decrease in biomass production results from the combined impacts of frequent rainfall deficits and uncontrolled resource-base exploitation by the local population. Large chunks of land that show consistent low biomass production are also observed on unproductive soils. Finally, the below-normal rainfall, below-average NDVI values, and human impacts images were cross-classified to produce a three-class (low, moderate, and high) land degradation risk map along with a table containing the area covered by each class. A Boolean mask of the degradation risk map applied to the soils map showed that all soil types in southern Mauritania are at risk of degradation. These products could serve as a strong basis for decision making in regard to planning resource allocation for environmental rehabilitation. Copyright © 2002 John Wiley & Sons, Ltd.
Article
Many landscape models have been developed over the past decades; however, relatively little is known about handling the effects of changing spatial and temporal resolutions. Therefore, resolution effects remain a factor of uncertainty in many hydrological and geomorphological modelling approaches. In this paper we present an experimental multi-scale study of landscape process modelling. Emphasis was laid on quantifying the effect of changing the spatial resolution upon modelling the processes of erosion and sedimentation. A simple single process model was constructed and equal boundary conditions were created. Using artificial digital elevation models (DEMs) eliminated effects of landscape representation. The only variable factors were DEM resolution and the method of flow routing, both steepest descent and multiple flow directions. Our experiments revealed an important dependency of modelled erosion and sedimentation rates on these main variables. The general trend is an increase of erosion predictions with coarser resolutions. An artificial mathematical overestimation of erosion and a realistic natural modelling effect of underestimating resedimentation cause this. Increasing the spatial extent eliminates the artificial effect while at the same time the realistic effect is enhanced. Both effects can be quantified and are expected to increase within natural landscapes. The modelling of landscape processes will benefit from integrating these types of results at different resolutions. Copyright © 2000 John Wiley & Sons, Ltd.
Article
Over the last 30 years, European agricultural policy has influenced agricultural practices. These have led to an increase in numerous environmental issues such as the erosion and runoff risk, which have reached an alarming level in loamy soils of Upper Normandy. To control runoff and erosion at catchment scale, public authorities need tools in order to obtain a better knowledge of present or future pressure on the environment. With such information, it will be easier to act locally on a problem by avoiding negative impacts elsewhere in the area. Numerous models have been developed to assess the impacts of land-use modifications. This paper presents a brief description of the remote sensing version of STREAM, called STREAM-TED, which then is used to estimate and map runoff according to various scenarios of rain event and land-use distribution in a cultivated catchment. Three kinds of scenarios of land-use modifications have been considered: partial or complete reduction of grassland in favour of cash crops, modifications of agricultural practices on arable lands, and insertion of water management on the catchment. Results of 11 management scenarios tested showed the negative effect of a partial or complete ploughing of permanent grassland. Changes on arable land scenarios showed that these modifications reduced runoff in various ways according to rainfall events. The scenario with the most significant impact consists of simulating the introduction of 100% more environmentally friendly production methods on arable lands. With this scenario, runoff is practically eliminated for winter rainfall events and is 0341-8162/$ -see front matter D 2005 Elsevier B.V. All rights reserved.
Article
Information on sediment and nutrient export from catchments and about related erosive processes is required by catchment managers and decision-makers. Many models exist for the consideration of these processes. However, these models differ greatly in terms of their complexity, their inputs and requirements, the processes they represent and the manner in which these processes are represented, the scale of their intended use and the types of output information they provide. This paper reviews several different erosion and sediment and sediment-associated nutrient transport models with regard to these factors. The review of models is limited to those models with explicit considerations of either the sediment generation or transport process.
Article
Field limits, tillage practices and ditch networks constitute man-made hydrological discontinuities in farmed catchments, and are expected to influence hydrological response during flood events. The purpose of this study is to assess the role of human impact, especially the existence of tillage practices and ditch network, on flood events. The study area is the farmed catchment of Roujan (0·91 km2) located in Southern France for which a spatially distributed hydrological model, MHYDAS, was developed and tested. The model considers the catchment as a series of interconnected field parts linked to the ditch network. Descriptions are provided for the main model procedures: computation of Hortonian excess rainfall on fields using the Green and Ampt approach, conversion of excess rainfall to surface runoff, interaction between ditch network and groundwater using a simple Darcian model and flood routing through the ditch network using the diffusive wave model. To analyse the role of both tillage practices and the ditch network, two sets of sensitivity analysis of the model were applied. The first set studied the role of tillage practices by comparing the actual spatial distribution of tillage practices on the catchment with three hypothetical scenarios. The second set studied the role of the ditch network by comparing the actual man-made ditch network with a hypothetical drainage network automatically extracted from a digital elevation model. Results show the importance of the role of tillage and the ditch network on the form of the hydrograph, the lag time, the runoff volume and the peak discharge. This technique could also be applied to study the impact of land use change on the hydrological behaviour of the catchment. Copyright © 2002 John Wiley & Sons, Ltd.
Article
The remarkable large-mammal fauna of the Indonesian island of Sumatra is one of the most endangered on Earth and is threatened by rampant deforestation. We used remote sensing and biological surveys to study the effects of deforestation on populations of endangered large mammals in a Sumatran landscape. We measured forest loss and created a predictive model of deforestation for Bukit Barisan Selatan National Park and an unprotected buffer area based on satellite images between 1985 and 1999. We used automatic cameras to determine the distribution and relative abundance of tigers ( Panthera tigris sumatrae ), elephants ( Elephas maximus ), rhinoceros ( Dicerorhinus sumatrensis ), and tapirs ( Tapir indicus ). Between 1985 and 1999, forest loss within the park averaged 2% per year. A total of 661 km ² of forest disappeared inside the park, and 318 km ² were lost in a 10-km buffer, eliminating forest outside the park. Lowland forest disappeared faster than hill/montane forest ( by a factor of 6 ) and forests on gentle slopes disappeared faster than forests on steep slopes ( by a factor of 16 ). Most forest conversion resulted from agricultural development, leading to predictions that by 2010 70% of the park will be in agriculture and that by 2036 lowland forest habitat will be eliminated. Camera-trap data indicated avoidance of forest boundaries by tigers, rhinoceroses ( up to 2 km ), and elephants ( up to 3 km ). Classification of forest into core and peripheral forest based on mammal distribution suggests that, by 2010, core forest area for tigers and rhinoceros will be fragmented and reduced to 20% of remaining forest. Core forest area for elephants will be reduced to 0.5% of remaining forest. Halting forest loss has proven one of the most difficult and complex problems faced by Indonesia's conservation agencies today and will require a mix of enforcement, wise land-use strategies, increased education, capacity to manage, and new financing mechanisms.
Article
The urban population of the developing countries, which are almost entirely within the tropics and subtropics, increased from 286 to 1,515 million between 1950 and 1990. This figure is expected to reach 4 billion by 2025. Certain major cities (Mexico City, Bombay, So Paulo, etc.) are expected to grow to extremely large sizes. The major physical changes that occur with urbanization can be summarized as changes in hydrology, geomorphology, climate, vegetation, and air and water quality. The intensity and rapidity of such changes require a careful, but urgent assessment of the environmental modification. The tropical environment tends to magnify the environmental impact of urbanization. Geoindicators can be used for the measurement of a number of changes of this nature. This paper presents a selection of geoindicators that could be used to measure such impacts. The geoindicators have been selected according to (1) their effectiveness in measuring environmental impacts and (2) the type of data that is required for their use. Shortage of quantitative information is a common problem for tropical cities. In addition, certain types of geoindicators need to be highlighted for cities in specific types of location such as deltas or coastal plains, steep slopes, or in proximity to convergent or transverse plate margins. The projection, that in another 50 years about half of the population of tropical countries will be urban, adds urgency to this venture.
Article
This paper summarizes the results obtained by land degradation assessment in the Fortaleza Metropolitan Region, in the state of Cear, Brazil. Area assessment was done in a two-phase study: the characterization of the environmental components by field and laboratory work, and a more detailed study in the degraded sites. Environmental geoindicators were used to classify the degradation level for each drainage basin as low, intermediate, or high. Coastal erosion, gravitational mass movements, dune movements, water erosion, sedimentation, water pollution, sanitary landfills in inappropriate sites, caves and abandoned mines of aggregates exploitation and occupation in swamp areas are the main land degradation sources registered in the region. Among the drainage basins for degradation level, 5 were classified as high, 3 as intermediate, and 4 as low. These problems have affected the people living in the region and demanded heavy investments to rehabilitate degraded areas.
Article
Soil erosion is a complex process determined by mutual interaction of numerous factors. The aim of erosion research at regional scales is a general evaluation of the landscape susceptibility to soil erosion by water, taking into account the main factors influencing this process. One of the key factors influencing the susceptibility of a region to soil erosion is land cover. Natural as well as human-induced changes of landscape may result in both the diminishment and acceleration of soil erosion. Recent studies of land-cover changes indicate that during the last decade more than 4.11% of Slovak territory has changed. The objective of this study is to assess the influence of land-cover and crop rotation changes over the 1990–2000 period on the intensity and spatial pattern of soil erosion in Slovakia. The assessment is based on principles defined in the Universal Soil Loss Equation (USLE) modified for application at regional scale and the use of the CORINE land cover (CLC) databases for 1990 and 2000. The C factor for arable land has been refined using statistical data on the mean crop rotation and the acreage of particular agricultural crops in the districts of Slovakia. The L factor has been calculated using sample areas with parcels identified by LANDSAT TM data. The results indicate that the land-cover and crop rotation changes had a significant influence on soil erosion pattern predominately in the hilly and mountainous parts of Slovakia. The pattern of soil erosion changes exhibits high spatial variation with overall slightly decreased soil erosion risks. These changes are associated with ongoing land ownership changes, changing structure of crops, deforestation and afforestation.
Article
Many studies have been concerned with the scale issue in geomorphology and hydrology. Most studies focus on the possibility of data transfer from small to large watersheds. Less attention has been given to the scale problem within very small watersheds where differences in slope length may seriously affect the spatial distribution and extent of runoff-contributing areas to the channel. It is usually assumed that runoff and erosion increase as slope length and angle increase. However, field observations in the Negev Highlands show positive relationships between slope length and deposition rates, regardless of slope angles. Short hillslopes are devoid of colluvial mantle, while thick colluvial deposits, with well-developed soil profiles indicative of long-term stability, are found at the base of long hillslopes. The hypothesis advanced is that temporal variations in effective rainfall control the spatial structures of surface properties that further enhance the effects of temporal variations in rainfall. Long-term monitoring of rainfall and runoff (1982–1998), conducted at spatial scales varying from few hundreds of m2 up to 0.3 km2, show a decrease in runoff at the hillslope scale. The low efficiency of runoff and erosion processes on long hillslopes is because the concentration time required for continuous flow along such slopes is longer than the duration of most effective rain showers prevailing in the area. Field data lead to the notion that runoff and erosion models in which a positive relationship between slope length and angle and runoff and erosion rates is assumed should not be applied to arid and semiarid areas. More attention should be given in latter areas to the complex hydrological relationships between rainfall scales and spatial scales. The implications of data obtained regarding the spatial distribution of areas contributing to channel flow, at a geological time scale and under changing climatic conditions, are discussed.
Article
Landuse changes may dramatically enhance erosion risk. Besides deforestation, also arable landuse may have an important influence on soil loss. We investigated the erosion risk in a 151 km2 subwatershed of the Cuyaguateje watershed (Cuba) using the RUSLE model. It was found that the valleys used for agriculture have the highest erosion risk, with actual erosion surpassing soil loss tolerance. Over the period 1985–2000, about 14 km2 of forest has been converted into arable land. As a result, the area with a very high erosion risk increased with 12%. On arable land it was found that the crop management factor C of a “tobacco/maize” rotation was 0.478, compared to 0.245 for a rotation of various crops (sweet potato, beans, maize, cassava and fallow). When maize in the “tobacco/maize” rotation was intercropped with a leguminous crop (hyacinth bean) the C factor decreased to a value of 0.369. Also contouring may halve soil loss on moderate slopes (< 10%) when high ridges are applied, which is in Cuba generally the case for maize, cassava and sweet potato.
Article
Soil erosion by water is recognized to be a critical economic problem in highland Ethiopia. However, nearly all the available information about its severity and economic costs are extrapolated from plot and micro-watershed level studies which are too few in number to represent the diverse environments of the country. Moreover, plot and watershed level studies do not show actual soil losses from cultivated fields, while understanding the magnitude of soil loss at the field scale is important for practical conservation planning. This paper reports results of field-scale soil erosion assessment that employed a survey methodology for rills and was conducted over two wet seasons (the years 2000 and 2001) at two sites, Kechemo and Erene, located in the upstream and downstream reaches of the Chemoga watershed, northwestern highland Ethiopia. The two wet seasons average rill erosion magnitudes were 13.5 Mg ha−1 in the Kechemo and 61 Mg ha−1 in the Erene. Assuming that interrill erosion contributes 30%, actual soil losses were around 18 Mg ha−1 in the Kechemo and 79 Mg ha−1 in the Erene. These estimates, which are well in agreement with results obtained by measurements in a nearby experimental micro-watershed, reveal that soil erosion is a threat to agricultural production in the study area and conservation measures are needed. Soil erosion showed significant spatial (between and within the two sites) and temporal variations. Hence, soil and water conservation (SWC) measures that fit well into local-scale circumstances will be realistic and acceptable to the farmers. Additionally, the problem of soil erosion should be tackled in the watershed context, because there is a strong physical interdependence between upstream and downstream areas. Finally, the study confirms that the rill survey approach gives good semi-quantitative information on soil erosion in real life situations of diverse farming and land use practices in a fast and inexpensive way; and it is commendable for practical conservation-oriented soil erosion assessment purposes.
Article
In arid and semi-arid grassland, many models hypothesize that desertification leads to the replacement of grassland by shrubland vegetation; however, the theoretical interpretations are open to debate. Therefore, a field study was conducted in the Guinan desertified grassland of the Qinghai-Tibet plateau, North-west China, to test the hypotheses on a regional scale. We used four field sites to represent the four stages of desert development: slight, moderate, severe and very severe. A total of 40 quadrates were investigated in each site. Plant coverage, above-ground biomass, species richness and life-form were recorded; species diversity was calculated using the Simpson index and soil parameters were also measured. Our results indicate that the proportion of silt decreases from 12% in the slight stage to 1% in the very severe stage, clay from 71% to 42% and sand from 17% to 93%. Soil water-holding capacity clearly decreases from the slight to the very severe stage. Soil organic matter (OM) is also reduced with desert development, which leads to destruction of the stability of soil physical structure and nutrient content, such as progressive N, P and K loss in surface and subsoil layers. In response to changes in soil properties, vegetation altered as regards species composition, species diversity, coverage, structure and life-form. Consequently, with desert development, herbaceous species, especially grasses, were lost from the community composition and replaced by xerophytic shrubs or semi-shrubs. Finally, psammophytic annual plants-dominated vegetation composition, while shrub maintained a low coverage. Although our results partially support previous hypotheses at the regional scale, it is considered that, apart from soil texture, soil OM and nutrients are the main factors mediating the dominance balance between shrub and herbaceous species.
Article
Traditionally, assessment of productivity of land took priority over all other aspects of evaluating land use performance. Presently, the effects of land use on the quality of the environment and environmental sustainability of production systems have become the major issues. In hills, the terrain conditions aggravate erosion-induced land degradation. Judicious allocation of available resources for sustainable production requires mapping, monitoring and prioritizing the areas based on their susceptibility to degradation. Remote sensing and Geographic Information Systems are effective tools for inventory, monitoring and management of spatially distributed resources. This paper presents a case study of the 42 km2 Sukhna Lake catchment in the Shiwalik hills conducted for the delineation and prioritization of erosion-prone areas using RS and Geographic Information Systems. Multi-spectral IRS ID-LISS III data acquired in March 1998 was used for the supervised digital classification of the land use/land cover type. The catchment was classified in six land use classes: forest, agriculture, scrub, barren hills, streambed and settlements. These classes were divided into sub-classes based on the cover characteristics. Using the U.S. Soil Conservation Service curve number method, runoff potential of each delineated hydrologic unit was computed in a grid-based analysis using an ARC/INFO GIS. Erosion-prone areas were classified further by integration of a digital elevation model or DEM-derived slope, aspect and flow length. To get an ordered priority of the erosion-prone areas, a cumulative erosion index was computed from the rating given to the three main causative factors, ie, slope, soil erodibility, and land cover, on a scale of 1–7 for each grid. The cumulative index was further classified in four classes for spatial representation of the erosion-prone areas on the catchment map. The study revealed that 32.9 percent of the catchment area is susceptible to high or very high erosion risk and thus has to be managed with appropriate conservation strategies.RésuméTraditionnellement l'évaluation de la productivité des terres a eu la priorité sur tous les aspects d'évaluation de la performance de l'utilisation des terres. Actuellement les effets de l'utilisation des terres sur la qualité de l'environnement et la durabilité environnementale des systèmes de production sont devenus des problèmes majeurs.Dans les collines, les conditions de terrain aggravent encore la dégradation des terres causée par l'érosion. Une allocation judicieuse des ressources disponibles pour une production acceptable exige de cartographier, de suivre l'évolution et de fixer des priorités pour les zones susceptibles de dégradation. Télédétection et Systèmes d'Information Géographique sont des outils effectifs pour l'inventaire, le suivi et la gestion de ressources distribuées dans l'espace. L'article présente une étude de cas du bassin versant du lac Sukhna de 42 km2 dans les collines de Shiwalik pour la délinéation et la détermination de priorités dans les zones à risques d'érosion, en utilisant la télédétection et des Systèmes d'Information Géographique. Des données multispectrales IRS ID-LISS III acquises en mars 98 ont été utilisées pour la classification numérique supervisée des types d'utilisation/d'occupation des sols. Le bassin versant a été classé en six classes d'utilisation des terres, notamment: forêt, broussailles, collines arides, lits des cours d'eau et zones habitées. Ces classes ont été divisées en sous-classes basées sur les caractéristiques de couverture. En utilisant la méthode du nombre de la courbe du SCS (Service de Conservation des Sols, États-Unis 1972) le potentiel d'écoulement de chaque unité hydrologique délinée a été calculée par une analyse à base de mailles à l'aide du SIG d'ARC/INFO. Des zones à risques d'érosion ont été classifiées plus loin par intégration d'un modèle numérique du terrain ou des dérivés de pente, d'orientation, et de longueur des courants. Pour obtenir un ordre de priorité pour les zones susceptibles d'érosion un index cumulatif d'érosion est calculé à partir de l'estimation obtenue par les trois facteurs principaux: pente, érodibilité des sols et occupation des sols à une échelle 1–7 pour chaque maille. L'index cumulatif est de plus classé en quatre classes pour une représentation spatiale des zones susceptibles d'érosion dans la carte des bassins versants. L'étude montre que le bassin versant présente un risque fort ou très fort pour 32.9 pour-cent de la surface et doit être géré avec des stratégies de conservation appropriées.ResumenTradicionalmente, se privilegió la evaluación de la productividad de las tierras por encima de todos aquellos aspectos relacionados con la evaluación del rendimiento del uso de las tierras. Presentemente, se pone énfasis en los impactos del uso de las tierras sobre la calidad del ambiente y la sostenibilidad ambiental del sistema de producción. En áreas de colinas, las condiciones del relieve agravan la degradación de tierras inducida por erosión. Para una juiciosa alocación de los recursos disponibles para produción sostenible es necesario mapear, monitorear y priorizar las áreas de desarrollo en base a su susceptibilidad a la degradación. Teledetección y SIG son instrumentos efectivos para el inventario, seguimiento y manejo de los recursos distribuidos en el espacio geográfico. El artículo presenta un estudio de caso de la cuenca del lago Sukhna con 42 km2 de extensión, ubicada en la zona de colinas de Shiwalik, para la delineación y priorización de áreas expuestas a la erosión mediante el uso de la teledetección y de sistemas de información geográfica. Se usaron datos multi-espectrales IRS ID-LISS III adquiridos en marzo de 1998 para la clasificación digital supervisada de los tipos de cobertura y uso de las tierras. La cuenca fue clasificada en seis clases de uso de las tierras, a saber: bosque, agricultura, matorral, colinas con tierras estériles, cauces de ríos y asentamientos humanos. Estas clases fueron divididas en subclases en base a las caracteristicas de la cobertura. Se calculó el potencial de escurrimiento de cada unidad hidrológica delineada con la aplicación del método de número de curva del SCS (U.S. Soil Conservation Service, 1972), utilizando un análisis de retícula de celdas en ARC/INFO. Adicionalmente, se clasificaron las áreas expuestas a erosión mediante la integración de datos de pendiente, exposición y longitud de flujo derivados de un modelo digital de elevación (MDE). Para obtener el orden de prioridad de las áreas expuestas a erosión, se calculó un índice de erosión acumulativo a partir de la evaluación de los tres factores causales — pendiente, erodabilidad del suelo, y cubertura de las tierras — en una escala de 1 a 7 para cada celda. El índice acumulativo se clasificó en cuatro clases para la representación espacial de las áreas expuestas a erosión en el mapa de la cuenca. El estudio revela que el 32.9% del área de la cuenca tiene una susceptibilidad alta o muy alta al riesgo de erosión y que la cuenca necesita ser manejada con apropiadas estrategias de conservación.
Article
Land degradation, the temporary or permanent reduction of land's productive capacity resulting from poor land management, has gained considerable attention as an environmental and development issue of global importance, in particular in the Earth's drylands. This study presents a global estimate of net primary production (NPP) losses caused by human-induced dryland degradation. Due to the large uncertainties related to international databases on dryland degradation, we compiled a world map of the extent and degree of desertification based on existing regional and global maps. Two distinct approaches were followed in order to estimate NPP losses due to degradation on drylands: in the first approach, we combined these maps with model results on global potential NPP, determined with the LPJ-DGVM, with a set of factors on NPP losses per degradation degree, derived from the literature. In a second approach, we made use of spatially explicit information on potential and current NPP of agricultural areas obtained from a global HANPP assessment [Haberl, H., Erb, K.-H., Krausmann, F., Gaube, V., Bondeau, A., Plutzar, C., Gingrich, S., Lucht, W. and Fischer-Kowalski, M., 2007. Quantifying and mapping the human appropriation of net primary production in earth's terrestrial ecosystems. Proceedings of the National Academy of Sciences of the United States of America, 104: 12942-12947.]. We used the difference between potential and current NPP on croplands situated in drylands in order to quantify the effect of dryland degradation on NPP. NPP losses were found to range between 799 and 1936Â Tg C/yr in the first approach, and to amount to 965Â Tg C/yr in the second approach. Overall, approximately 2% of the global terrestrial NPP are lost each year due to dryland degradation, or between 4% and 10% of the potential NPP in drylands. NPP losses amount to 20-40% of the potential NPP on degraded agricultural areas in the global average and above 55% in some world regions. The results reveal that the contributions of dryland degradation to the total HANPP in drylands is of similar dimension than the overall annual socioeconomic biomass harvest. Accordingly, strategies aimed at reducing dryland degradation could present promising options to sustain future population numbers without putting further pressures on dryland ecosystems.
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Geomorphological research has played an important role in the development and implementation of soil erosion assessment tools. Because policy and management approaches include the use of soil erosion assessment tools, soil erosion research directly affects the public in terms of providing information on natural hazards and human impacts, and also as the basis for regulatory policy on land management. For example, soil loss calculations and geomorphological expertise are used to support soil conservation planning, both through agricultural legislation that defines maximum tolerable soil loss rates, and through federal and local legislation that requires soil erosion controls on many construction sites.
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Sumario: Introduction -- Background and context -- How indicators can influence action (Two case studies. WRI experience) -- Organizing environmental information: indicator types, environmental issues and a proposed conceptual model to guide indicator development -- Pollution emission: illustrative calculations of indicators and of a composite index for the Netherlands -- Resource depletion -- Biodiversity -- Human impact/Exposure indicators -- Approaches to sustainable development indicators -- Implications for action -- Notes -- Appendix I (Valuation methods in natural resource accounting. Country notes) -- Appendix II: Environmental indicator reporting formats