Uncontrolled land use land cover change(LULCC) is impacting watershed hydrology,particularly in tropical watersheds in developing countries. We assessed the extent of LULCC in the southern portion of the Nyong River b...Uncontrolled land use land cover change(LULCC) is impacting watershed hydrology,particularly in tropical watersheds in developing countries. We assessed the extent of LULCC in the southern portion of the Nyong River basin through analysis of three land use maps in 1987, 2000 and2014. LULCC impact on hydrological variables of the Mbalmayo, Olama, Pont So’o, Messam, and Nsimi sub-watersheds of the southern portion of the Nyong River basin were evaluated by using the linear regression modeling and the Mann-Kendall test. This study reveals that dense forest cover decreased by16%, young secondary forest increased by 18%,agricultural/cropland increased by 10%, and built-up area/bare soil increased by 3% from 1987 to 2014.The decrease in dense forest cover at 0.6% per year on average was driven by indiscriminate expansion of subsistence agricultural/cropland through shifting and fallow cultivation farming systems. Nonsignificant trends in total discharge, high flows, and low flows were observed in the large sub-watersheds of Mbalmayo and Olama from 1998 to 2013 with LULCC within the watershed. In contrast, significant decreasing trends in stream discharge(up to-5.1%and-5.9%), and significant increasing trends in high flows(up to 2.1% and 6.3%), respectively, were observed in the small sub-watersheds of Pont So’o and Messam from 1998 to 2013, particularly with increase in agricultural/cropland cover and decrease in dense forest cover. However, we found nonsignificant trends in mean annual discharge and low flows for all and whole watershed with LULCC. The results reveal spatially varying trends of stream discharge, low flows and high flows among the subwatersheds with LULCC within the study watershed.The results suggest that the impacts of LULCC on watershed hydrology are easily detected in small subwatersheds than in large sub-watersheds. Therefore,the magnitude of dense forest cover loss must be significantly greater than 16% to cause significant changes and common trends in the hydrology of the sub-watersheds of the southern portion of the Nyong River basin. The Mann-Kendall and Regression approaches show appreciable potential for modelling the impacts of LULCC on the hydrology of the southern portion of the Nyong River basin and for informing forest management.展开更多
为了探究温室气体(greenhouse gas,GHG)和土地利用/覆盖变化(land use and land cover change,LULCC)对于地面气温日较差(diurnal temperature range,DTR)的影响及相对贡献作用,本文采用耦合地球系统模式(Community Earth System Model...为了探究温室气体(greenhouse gas,GHG)和土地利用/覆盖变化(land use and land cover change,LULCC)对于地面气温日较差(diurnal temperature range,DTR)的影响及相对贡献作用,本文采用耦合地球系统模式(Community Earth System Model)进行了模拟研究。模拟结果表明:GHG浓度的增加导致北半球中高纬度地区年平均DTR显著降低,但GHG引起DTR变化存在显著的季节差异,在暖季和冷季,北美地区和西伯利亚地区呈现出相反的变化特征,GHG增加对于中高纬度地区年平均DTR的降低作用主要是由冷季贡献的。LULCC通过影响叶面积指数和地面反照率显著降低东亚、南亚、欧洲和北美东部地区的DTR。通过创建一种新的分析方式,本文研究了GHG和LULCC对DTR的相对贡献作用,在北半球高纬度地区,GHG在DTR的变化中扮演着主导作用,但在中纬度地区和南亚地区,无论是DTR变化数值的正负符号还是大小,LULCC都起着显著的影响作用。展开更多
This study of vegetation dynamics in the coastal region of Tanzania provides a fundamental basis to better understand the nature of the factors that underlie observed changes.The Tanzanian coast,rich in biodiversity,i...This study of vegetation dynamics in the coastal region of Tanzania provides a fundamental basis to better understand the nature of the factors that underlie observed changes.The Tanzanian coast,rich in biodiversity,is economically and environmentally important although the understanding of the nature and causes of vegetation change is very limited.This paper presents an investigation of the relationship between vegetation dynamics in response to climate variations and human activities using Moderate Resolution Imaging Spectro-radiometer(MODIS),Normalized Difference Vegetation Index(NDVI),meteorological,and Globeland30 Landsat data sets.Spatio-temporal trends and the relationship of NDVI to selected meteorological variables were statistically analyzed for the period 2000-2018 using the Mann-Kendall test and Pearson correlation respectively.The results reveal a significant positive trend in temperature(/?>0,Z=2.87)and a non-significant trend in precipitation(|Z|<1.96).A positive relationship between NDVI and precipitation is observed.Coastal Tanzania has therefore experienced increased temperatures and variable moisture conditions which threaten natural vegetation and ecosystems at large.Classified land cover maps obtained from GlobeLand30 were analyzed to identify the nature and scale of human impact on the land.The analysis of land use and land cover in the region reveals an increase in cultivated land,shrubland,grassland,built-up land and bare land,while forests,wetland and water all decreased between 2000 and 2020.The decrease in forest vegetation is attributable to the fact that most livelihoods in the region are dependent on agriculture and harvesting of forest products(firewood,timber,charcoal).The findings of this study highlight the need for appropriate land-use planning and sustainable utilization of forest resources.展开更多
基金the Observatory for Environment Research (ORE) in the project “Experimental Tropical Watersheds” (SO BVET) funded by IRD, INSU, and OMP for making available the hydrological and climatic data of the Nyong River basin under open access
文摘Uncontrolled land use land cover change(LULCC) is impacting watershed hydrology,particularly in tropical watersheds in developing countries. We assessed the extent of LULCC in the southern portion of the Nyong River basin through analysis of three land use maps in 1987, 2000 and2014. LULCC impact on hydrological variables of the Mbalmayo, Olama, Pont So’o, Messam, and Nsimi sub-watersheds of the southern portion of the Nyong River basin were evaluated by using the linear regression modeling and the Mann-Kendall test. This study reveals that dense forest cover decreased by16%, young secondary forest increased by 18%,agricultural/cropland increased by 10%, and built-up area/bare soil increased by 3% from 1987 to 2014.The decrease in dense forest cover at 0.6% per year on average was driven by indiscriminate expansion of subsistence agricultural/cropland through shifting and fallow cultivation farming systems. Nonsignificant trends in total discharge, high flows, and low flows were observed in the large sub-watersheds of Mbalmayo and Olama from 1998 to 2013 with LULCC within the watershed. In contrast, significant decreasing trends in stream discharge(up to-5.1%and-5.9%), and significant increasing trends in high flows(up to 2.1% and 6.3%), respectively, were observed in the small sub-watersheds of Pont So’o and Messam from 1998 to 2013, particularly with increase in agricultural/cropland cover and decrease in dense forest cover. However, we found nonsignificant trends in mean annual discharge and low flows for all and whole watershed with LULCC. The results reveal spatially varying trends of stream discharge, low flows and high flows among the subwatersheds with LULCC within the study watershed.The results suggest that the impacts of LULCC on watershed hydrology are easily detected in small subwatersheds than in large sub-watersheds. Therefore,the magnitude of dense forest cover loss must be significantly greater than 16% to cause significant changes and common trends in the hydrology of the sub-watersheds of the southern portion of the Nyong River basin. The Mann-Kendall and Regression approaches show appreciable potential for modelling the impacts of LULCC on the hydrology of the southern portion of the Nyong River basin and for informing forest management.
文摘为了探究温室气体(greenhouse gas,GHG)和土地利用/覆盖变化(land use and land cover change,LULCC)对于地面气温日较差(diurnal temperature range,DTR)的影响及相对贡献作用,本文采用耦合地球系统模式(Community Earth System Model)进行了模拟研究。模拟结果表明:GHG浓度的增加导致北半球中高纬度地区年平均DTR显著降低,但GHG引起DTR变化存在显著的季节差异,在暖季和冷季,北美地区和西伯利亚地区呈现出相反的变化特征,GHG增加对于中高纬度地区年平均DTR的降低作用主要是由冷季贡献的。LULCC通过影响叶面积指数和地面反照率显著降低东亚、南亚、欧洲和北美东部地区的DTR。通过创建一种新的分析方式,本文研究了GHG和LULCC对DTR的相对贡献作用,在北半球高纬度地区,GHG在DTR的变化中扮演着主导作用,但在中纬度地区和南亚地区,无论是DTR变化数值的正负符号还是大小,LULCC都起着显著的影响作用。
基金funded by the National Natural Science Foundation of China(Grant No.41476151)“China-Africa Universities 20+20 Cooperation Plan”by the Ministry of Education of China.
文摘This study of vegetation dynamics in the coastal region of Tanzania provides a fundamental basis to better understand the nature of the factors that underlie observed changes.The Tanzanian coast,rich in biodiversity,is economically and environmentally important although the understanding of the nature and causes of vegetation change is very limited.This paper presents an investigation of the relationship between vegetation dynamics in response to climate variations and human activities using Moderate Resolution Imaging Spectro-radiometer(MODIS),Normalized Difference Vegetation Index(NDVI),meteorological,and Globeland30 Landsat data sets.Spatio-temporal trends and the relationship of NDVI to selected meteorological variables were statistically analyzed for the period 2000-2018 using the Mann-Kendall test and Pearson correlation respectively.The results reveal a significant positive trend in temperature(/?>0,Z=2.87)and a non-significant trend in precipitation(|Z|<1.96).A positive relationship between NDVI and precipitation is observed.Coastal Tanzania has therefore experienced increased temperatures and variable moisture conditions which threaten natural vegetation and ecosystems at large.Classified land cover maps obtained from GlobeLand30 were analyzed to identify the nature and scale of human impact on the land.The analysis of land use and land cover in the region reveals an increase in cultivated land,shrubland,grassland,built-up land and bare land,while forests,wetland and water all decreased between 2000 and 2020.The decrease in forest vegetation is attributable to the fact that most livelihoods in the region are dependent on agriculture and harvesting of forest products(firewood,timber,charcoal).The findings of this study highlight the need for appropriate land-use planning and sustainable utilization of forest resources.
