Assessing and Predicting Changes in the Status of Gambari Forest Reserve, Nigeria Using Remote Sensing and GIS Techniques

Rapid population growth and increasing economic activities have resulted in unsustainable exploitation and rapid decline in the spatial extent of forest reserves in Nigeria. Studying land use dynamics of these forest reserves is essential for analysing various ecological and developmental consequences over time. Land use/land cover mapping, change detection and prediction are essential for decision-making and implementing appropriate policy responses relating to land uses. This paper aims at assessing and predicting changes in land use/land cover at Gambari forest reserve, Nigeria using remote sensing and GIS techniques. The study determined the magnitude, rate and dynamics of change in the spatial extent of the forest reserve between 1984 and 2014 using multi-temporal datasets (Landsat TM 1984 and 2000 and OLI/TIRS 2014). The imageries were classified using ArcGIS 10.0 version with support of ground truth data and Land use Change Modeller (LCM) and Markovian processes were employed to analyse the pattern and trend of change. Prediction of 2044 scenario carried out using neural network, which is a built-in module in the Idrisi. The study revealed dramatic decline in the extent of the forest reserve as both the plantation of exotic tree species (Tectona grandis and Gmelina) and the indigenous stands have been logged in several places for timber and to make way for cultivation of crops. In addition, pressures from other land uses like settlements have also led to increased non-forest uses particularly bare grounds. The study concluded that increasing loss of the indigenous forest and plantation would continue thus having implications for biodiversity conservation in the study area. There is the need for participation of different stakeholders and sectors to solve conflicting demands on limited forest resources and ensure ecosystem integrity.

A Forest Fire Risk Assessment Using ASTER Images in Peninsular Malaysia

Based on the physical concept of heat energy of pre-ignition,a new fire susceptibility index (FSI) is used to estimate forest fire risk. This physical basis allows calculation of ignition probabilities and comparisons of fire risk across eco-regions. The computation of the index requires inputs of fuel temperature and fuel moisture content (FMC),both of which can be estimated using remote sensing data. While ASTER data for land surface temperatures (LST) was used as proxys for fuel temperatures,fuel moisture content is estimated by regression technique utilizing the ratio NDVI/LST of ASTER data. FSIs are computed in peninsular Malaysia for nine days before the fires of 2004 and 2005 and validated with fire occurrence data. Results show that the FSI increases as the day approaches the fire day. This trend can be observed clearly about four days before the day of fire. It suggests that FSI can be a good estimator of fire risk. The physical basis provides a more meaningful FSI,allows calculation of ignition probabilities and facilitates the development of a future class of fire risk models. FSI can be used to compare fire risk across different eco-regions and time periods. FSI retains the flexibility to be localized to a vegetation type or eco-regions for improved performance.

Evaluation of deriving fire cycle of forested landscape based on time-since-fire distribution

Estimation of fire cycle has been conducted by using the negative exponential function as an approximation of time-since-fire distribution of a landscape assumed to be homogeneous with respect to fire spread processes. The authors imposed predefined fire cycles on a virtual landscape of 100 cell ×100 cell, and obtained a mosaic composing of patches with different stand ages (i.e. time since fire). Graphical and statistical methods (Van Wagner 1978; Reed et al. 1998) were employed to derive fire cycle from the virtual landscape. By comparing the predefined and the derived fire cycles, the two methods and tested the effects of sample size and hazard of burning (i.e., stand’s susceptibility to fire in relation to its stand age) were evaluated on fire cycle deviation. The simulation results indicated a minimum sample size of 10 times of the annual burnt area would be required for partitioning time-since-fire distribution into homogeneous epochs indicating temporal change in fire cycle. Statistically, there was significant difference among the imposed and the derived fire cycle, regardless of sample sizes with or without consideration of hazard of burning. Both methods underestimated the more recent fire cycle without significant difference between them. The results imply that deviation of fire cycle based on time-since-fire distribution warrants cautious interpretation, especially when a landscape is spatially partitioned into small units and temporal changes in fire cycle are involved.

Does Dust from Arctic Mines Affect Caribou Forage?

This study explores how dust from the Ekati Diamond Mine potentially affects the availability and quality of forage on the seasonal range of the Bathurst caribou herd. Understanding the effects of dust as a source of disturbance is important because the Bathurst caribou population has declined by 93% since the middle 1980s and there are reports that caribou in general may avoid mining projects. There are several challenges for quantifying dust impacts: 1) Natural variations (e.g., topography, natural disturbance, and soil pH) may also impact forage availability and quality for caribou. To minimize their masking effect, we stratified survey sites into seven land cover classes and selected the most populous class (i.e., the dwarf shrub) for assessing the impact. 2) Within class variation (e.g., the proportion of area covered by rocks where vascular plants and lichen do not grow) can further skew the analysis. We eliminated this problem by examining only the area not covered by rocks. 3) Coarse and fine suspended particulates have different spatial coverages, chemical compositions, and pH values. Consequently, their impacts on caribou forage can be different. To distinguish their impacts, we sampled two areas: transects from the Misery Haul Road that has been in active use vs. those from a rarely used spur road outside the Misery Camp. We sampled percent vegetation cover, soil pH, and dust on leaves along these transects during the summers of 2015 and 2016. Our results indicated that the amount of dust on leaves in a zone of ~1000 m from the Misery Haul Road was 3 - 9 times than that of background sites. The zone of reduced lichen percent cover was also about 1000 m. In contrast, these road dust-induced changes in caribou forage were not observed for the dust-free transect from the spur road.

Assessing the Correlation between Forest Degradation and Climate Variability in the Oluwa Forest Reserve, Ondo State, Nigeria

Between 1981 and 1994, Nigeria lost 3.7 million hectares of its forests. It is estimated that less than 4% of Nigeria’s rainforest cover is left. Reckless use and abuse of the forest reserves in Nigeria lead to degradation. However, the relationship between forest degradation and climate variability has not been clearly elucidated. This study assesses the trend of forest degradation between 1986, 2002 and 2014 in the study area and also examines the correlation between forest degradation and climate variability using temperature and rainfall parameters. Classification of Landsat images (TM 1986, ETM+ 2002, and OLI 2014) and change analysis using NDVI values of three-timed period were performed to observe forest degradation in the study area. NDVI values were calculated by combining bands 4 (near infrared) and 3 (visible red) for Landsat TM and ETM+ and bands 5 (near infrared) and 4 (visible red) for Landsat OLI using the spatial analysis extension in ArcGIS environment Linear regression statistical analysis was employed to determine the correlation between forest degradation and climate variability. The results show a fluctuation in the trend of forest degradation, while a positive correlation coefficient of 0.58 shows that there is a relationship between forest degradation and temperature and rainfall variability. The study concludes that though there is a positive correlation between forest degradation and climate variability in the study area, the relationship is weak and not strong enough to make generalizations.

Estimating Ecological Characteristics and Carbon Stock in Uneven-Aged Plantations of Acacia senegal L. in the Savannah Woodlands of Sudan

The aim of this study was to assess Acacia senegal trees’ characteristics as well as evaluate the carbon stock under a variety of ages in the El Demokeya forest in Sudan, where the Gum Arabic belt is located. 12 sample plots, in 2021 were randomly distributed to represent the entire area of the forest prior to the required measurements. The sample was designed as squire plots with one hectare. In each sample plot, all trees were counted, their height (m), and Diameters Breast Height (DBH in cm), respectively. The results showed the highest number of trees per ha at age 20 years old and the lowest number at age 47 years, while the highest values of DBH and volume were found at age 47 years old. As a result, the maximum and minimum values of the aboveground biomass were found in the age 47 years old and 16 years, accounting for 19.87 tons and 1.9 tons respectively. Thus, the amount of carbon stock was 11.92 tons/ha in the 35-years-old and 1.19 tons/ha in the 21-year stands. Furthermore, the average carbon stock in all plots was estimated as 18.70 tons/ha and hence the total carbon stock in the El Demokeya forest is equal to 620.11 tons. Conclusively, the characteristics of trees, amount of aboveground biomass and carbon stock in the El Demokeya forest varied among the uneven-aged plantation groups. The study recommends and encourages the protection of A. senegal in order to increase the carbon sink as well as protect the environment in the era of climatic changes.

中国西部植被水分利用效率的时空特征分析

利用净初级生产力模型C-FIX,陆面过程模型CoLM以及高时空分辨率的遥感数据集,定量估算了2002年西部地区1 km分辨率的水分利用效率（WUE）时空格局分布.模型估算2002年西部地区净初级生产力总量约为0.96 PgC,蒸散发总量约为2 098 km3,整个西部地区平均单位面积上年均WUE约为0.32 gC.mm^-1.西部地区WUE时空分布格局具有显著的异质性：WUE最高值区主要分布在新疆西北部的天山和阿尔泰山区域,年均WUE最高可达4 gC.mm^-1.m^-2;其次为西藏东南隅以及陕西和甘肃南部山区,年均WUE约在1~2 gC.mm^-1.m^-2之间.WUE最低值广泛分布在青藏高原地区和西北沙漠地区,年均WUE基本在0.4 gC.mm^-1.m^-2以下.研究发现,西北干旱区内陆河流域荒漠植被呈现出相对高的WUE水平,反映出适度水分亏缺地区的天然植被生态系统可能具有较水分充足地区植被生态系统更高的水分利用效率功能.通过定量分析比较不同植被生态系统WUE特征及其季节变化廓线,得到西部地区主要植被生态系统的年均WUE大小为山区森林〉荒漠乔灌丛〉灌溉农田〉高寒草地〉寒漠和戈壁.

玉米农田蒸散过程及其对气候变化的响应模拟

应用基于生理生态学过程的EALCO模型,对玉米农田生态系统的蒸散(ET)过程进行了模拟,在模型检验基础上,使用该模型模拟了玉米农田生态系统ET过程对未来气候变化的响应。结果表明,EALCO模型中能量与水过程的动态耦合机制使模型能够较好地模拟农田蒸散过程,基于涡度相关法的观测值与模型模拟值在小时、日尺度上均吻合较好,模型可以解释67%的日蒸散的变化特征。对土壤蒸发与冠层蒸腾的分别模拟显示,生长季土壤蒸发约占ET的36%。温度的升高会引起ET与冠层蒸腾的增加,同时土壤蒸发减少;ET对降水减少的响应较为敏感,主要表现在土壤蒸发的下降。大气CO2浓度升高对冠层蒸腾影响显著,该情景下冠层蒸腾下降幅度最大。研究所假设的2100年气候情景下,该农田生态系统生长季蒸散将减少,然而相对于降水的减少而言,蒸散的减少量较小,即水分支出项相对增加,因此,发生土壤水分匮乏的可能性加大,这可能会加剧该地区的暖干化趋势,给作物产量及生态环境带来威胁。

差分干涉测量技术在四川甲居滑坡监测中应用研究

选择四川省丹巴县甲居滑坡作为监测的示范,检验差分干涉测量(D-InSAR)技术在中国西南山区滑坡监测的有效性。利用差分干涉测量技术,通过EARTHVIEW软件,处理了两期Radarsat-1数据,取到了甲居滑坡的两期位移量。结果表明,甲居滑坡南北两个区域滑动速度有明显的差异,并且北部区域的滑坡边界应后移。甲居滑坡整体滑动有加快的趋势。

干旱／半干旱区MODIS地表温度反演与验证研究

劈窗算法是目前热红外遥感反演地表温度最常用的方法,根据Coll提出的劈窗算法建立基于MODIS适用干旱/半干旱区地表温度反演算法,并用同期的LP DAAC发布的MODIS地表温度产品和相应的53个气象站点的实际观测数据进行验证。通过分析,模型的反演精度与MODIS地表温度产品的反演精度相当,与气象观测数据相一致,反演精度较好,能够较精确地反演干旱/半干旱地区地表温度的时空变化特征。

中亚热带人工针叶林对未来气候变化的响应

利用基于生理生态学过程的EALCO模型,探讨了千烟洲中亚热带人工针叶林生态系统对未来气候变化的响应.结果表明:CO2浓度、温度和降水的变化对该人工林生态系统碳水通量影响的程度不同,其中CO2浓度>温度>降水.CO2浓度是生态系统总光合生产力(GPP)的主要驱动因子,温度与CO2浓度均是控制生态系统呼吸的主要环境因子,温度的升高使植物地上部分呼吸明显增加,而CO2浓度升高则对土壤呼吸影响较大.温度升高使蒸散(ET)增加,而CO2浓度升高则使ET减少.在未来气候变化情景(2100年)下,该人工林生态系统的净初级生产力将增加22%,说明其仍具有较强的固碳潜力.

卫星遥感地面紫外辐射的参数化方法

提出了一个从卫星观测推算地面ＵＶＢ辐射通量密度和红斑生物紫外辐射剂量的 新的参数化方法。该方法基于一个简单的模式：大气辐射传输介质被简化成三个等效层：臭 氧单独构成的吸收层，空气分子、云和气溶胶粒子组成的散射层，以及地面反射层。地面紫 外辐射通量密度和生物紫外辐射剂量可以由臭氧层的等效透过率、散射层和地面的联合反射 率计算。臭氧层的等效透过率可由大气臭氧总量计算。散射层和地面的联合反射率可由不存 在臭氧吸收的紫外或可见光通道的反射辐射强度测量得到。该反演算法形式简单，只包含很 少几个可从卫星测量获得的参数。它通过了一个可靠而相对复杂的基于ＤＩＳＯＲＴ的紫外辐 射传输模式的检验。在广泛的计算条件下，包括晴天、云天、以及混浊大气，用这个简单算 法计算的地面紫外辐射通量密度和红斑生物紫外辐射剂量与精确算法的结果相差无几。另 外，还实际运用这个算法利用卫星观测资料反演地面紫外辐射通量密度，与地面实际观测资 料做了比较，符合较好。

High-resolution Surface Relative Humidity Computation Using MODIS Image in Peninsular Malaysia

Forest fire is a serious disaster all over the world. The Fire Weather Index (FWI) System can be used in ap- plied forestry as a tool to investigate and manage all types of fire. Relative humidity (RH) is a very important parameter to calculate FWI. However, RH interpolated from meteorological data may not be able to provide precise and confident values for areas between far separated stations. The principal objective of this study is to provide high-resolution RH for FWI using MODIS data. The precipitable water vapor (PW) can be retrieved from MODIS using split window tech- niques. Four-year-time-series (2000-2003) of 8-day mean PW and specific humidity (Q) of Peninsular Malaysia were analyzed and the statistic expression between PW and Q was developed. The root-mean-square-error (RMSE) of Q es- timated by PW is generally less than 0.0004 and the correlation coefficient is 0.90. Based on the experiential formula between PW and Q, surface RH can be computed with combination of auxiliary data such as DEM and air temperature (Ta). The mean absolute errors of the estimated RH in Peninsular Malaysia are less than 5% compared to the measured RH and the correlation coefficient is 0.8219. It is proven to be a simple and feasible model to compute high-resolution RH using remote sensing data.

Effect of digital elevation models on monitoring slope displacements in open-pit mine by differential interferometry synthetic aperture radar

Displacement monitoring in open-pit mines is one of the important tasks for safe management of mining processes.Differential interferometric synthetic aperture radar(DInSAR),mounted on an artificial satellite,has the potential to be a cost-effective method for monitoring surface displacements over extensive areas,such as open-pit mines.DInSAR requires the ground surface elevation data in the process of its analysis as a digital elevation model(DEM).However,since the topography of the ground surface in open-pit mines changes largely due to excavations,measurement errors can occur due to insufficient information on the elevation of mining areas.In this paper,effect of different elevation models on the accuracy of the displacement monitoring results by DInSAR is investigated at a limestone quarry.In addition,validity of the DInSAR results using an appropriate DEM is examined by comparing them with the results obtained by global positioning system(GPS)monitoring conducted for three years at the same limestone quarry.It is found that the uncertainty of DEMs induces large errors in the displacement monitoring results if the baseline length of the satellites between the master and the slave data is longer than a few hundred meters.Comparing the monitoring results of DInSAR and GPS,the root mean square error(RMSE)of the discrepancy between the two sets of results is less than 10 mm if an appropriate DEM,considering the excavation processes,is used.It is proven that DInSAR can be applied for monitoring the displacements of mine slopes with centimeter-level accuracy.

Watershed Prioritization of Palar Sub-watershed Based on the Morphometric and Land Use Analysis

Morphometric analysis is an indispensable tool for hydrological investigation that involves the development and management of drainage basin. This study characterizes the micro watersheds in the Palar sub-watershed using morphometric analysis and assesses its risk by land use and land cover features in a particular micro watershed. Palar sub-watershed is divided into 6 micro watersheds for prioritization based on morphometric and land use analysis. Several morphometric parameters(linear, shape and relief)are determined from the drainage map; ranks are assigned based on their capacity to induce erodability and degradation. Final ranking is based on the composite index calculated from the sum of the ranks of each morphometric parameter. Morphometric analysis reveals micro watersheds 5 and 6 as most susceptible and 2 and 3 as low susceptible. Land use is mapped using IRS ID LISS III satellite data. The risk in terms of watershed degradation involved to each micro watershed is based on the ranks of each land use feature, obtained from a similar composite index as that of morphometric analysis. Land use analysis shows that micro watersheds 2 and 4 fall under high priority category while 5 and 6 under low priority category. Integration of the morphometric and land use analysis shows that only micro watershed 1 falls under the same category in both analyses. Control measures are suggested to contain degradation depending on its specific land use pattern and morphometric features. This study can be used to prepare a comprehensive watershed plan for the development or for planning resource conservation strategies, by integrating land use features with the drainage characteristics of the region, in particular for a hill ecosystem as the prioritization is at micro level.

Fire cycle of the Canada's boreal region and its potential response to global change

Interactions of fire cycle and plant species＇ reproductive characteristics could determine vegetation distribution pattern of a landscape. In Canada＇s boreal region, fire cycles before the Little Ice Age （c. 1850s） ranged from 30-130 years and 25-234 years afterwards until the settlement period （c. 1930s） when longer fire cycles occurred in response to climatic change and human interference. Analysis indicated that fire cycles were correlated with growing season （April-October） temperature and precipitation departure from the 1961-1990 normal, varying by regions. Assuming that wildfires will respond to future warming similar to the manner during the past century, an assessment using climatic change scenarios CGCMI, CGCM2 and HadCM2 indicates fire cycles would divert to a range of 80-140 years in the west taiga shield, more than 700 years for the east boreal shield and east taiga shield, and 300-400 years for the boreal plains in 2050.

Modelling Chorabari Lake outburst flood, Kedarnath, India

In this study, the Glacier Lake Outburst Flood(GLOF) that occurred over Kedarnath in June 2013 was modeled using integrated observations from the field and Remote Sensing(RS). The lake breach parameters such as area, depth, breach, and height have been estimated from the field observations and Remote Sensing(RS) data. A number of modelling approaches, including Snow Melt Runoff Model(SRM), Modified Single Flow model(MSF), Watershed Management System(WMS), Simplified Dam Breach Model(SMPDBK) and BREACH were used to model the GLOF. Estimations from SRM produced a runoff of about 22.7 m3 during 16–17, June 2013 over Chorabari Lake. Bathymetry data reported that the lake got filled to its maximum capacity(3822.7 m3) due to excess discharge. Hydrograph obtained from the BREACH model revealed a peak discharge of about 1699 m3/s during an intense water flow episode that lasted for 10–15 minutes on 17 th June 2013. Excess discharge from heavy rainfall and snowmelt into the lake increased its hydrostatic pressure and the lake breached cataclysmically.

孟加拉国砷污染回顾

目前，孟加拉国居民的健康正面临着严重威胁，8，500，000人的饮用水和粮食作物受到了砷污染。孟加拉国的地下水砷污染问题在世界上是最严重的。由于孟加拉国对地表水管理不当，97％居民的饮用水和家庭用水来源于地下水。在孟加拉国，地下水严重受到砷污染引起大量砷中毒事件。砷污染回顾着重于综述近年来砷污染的调查结果和统计数据，尤其是土壤、水和食物的砷污染。世界卫生组织（WHO）规定的饮用水中砷的额定浓度为10μg/L。现有勘查着重于孟加拉国64个地区深水井的地下水中砷的浓度。调查结果显示：59个深水井的地下水中砷的浓度大于10μg／L；43个深水井的地下水中砷的浓度大于50μg／L。受砷污染的地下水常被用于浇灌水稻（居民主要的粮食作物）。这种农业习惯（把受污染的地下水用于灌溉）引起土壤中砷的浓度增加。现有研究显示，稻米和蔬菜中85％-95％的砷是无机砷。在孟加拉国，土壤、地下水和植物中砷的浓度（基于孟加拉国4％的地区）超过报导的最大允许浓度或者正常范围，这（砷浓度大于最大允许浓度）对孟加拉国居民和家畜的健康造成了严重威胁，强调了开展科学研究的必要性，例如，较好地描述自然环境中砷的存在形态以及确定所有潜在的砷污染途径的科学研究。

Numerical simulation and validation of ocean waves measured by an Along-Track Interferometric Synthetic Aperture Radar

A new nonlinear integral transform of ocean wave spectra into Along-Track Interferometric Synthetic Aperture Radar (ATI-SAR) image spectra is described. ATI-SAR phase image spectra are calculated for various sea states and radar configurations based on the nonlinear integral transform. The numerical simulations show that the slant range to velocity ratio (R/V), significant wave height to ocean wavelength ratio (Hs/λ), the baseline (2B) and incident angle (θ) affect ATI-SAR imaging. The ATI-SAR imaging theory is validated by means of Two X-band, HH-polarized ATI-SAR phase images of ocean waves and eight C-band, HH-polarized ATI-SAR phase image spectra of ocean waves. It is shown that ATI-SAR phase image spectra are in agreement with those calculated by forward mapping in situ directional wave spectra collected simultaneously with available ATI-SAR observations. ATI-SAR spectral correlation coefficients between observed and simulated are greater than 0.6 and are not sensitive to the degree of nonlinearity. However, the ATI-SAR phase image spectral turns towards the range direction, even if the real ocean wave direction is 30°. It is also shown that the ATI-SAR imaging mechanism is significantly affected by the degree of velocity bunching nonlinearity, especially for high values of R/V and Hs/λ.