Liem Tran - Academia.edu (original) (raw)

Papers by Liem Tran

Geosciences, 2014

This research examines risk factors for sporadic cryptosporidiosis and Escherichia coli (E. coli)... more This research examines risk factors for sporadic cryptosporidiosis and Escherichia coli (E. coli) O157 infection in East Tennessee, using a case-control approach and spatial logistic regression models. The risk factors examined are animal density, land use, geology, surface water impairment, poverty rate and availability of private water supply. Proximity to karst geology, beef cow population density and a high percentage of both developed land and pasture land are positively associated with both diseases. The availability of private water supply is negatively associated with both diseases. Risk maps generated using the model coefficients show areas of elevated risk to identify the communities where background risk is highest, so that limited public health resources can be targeted to the risk factors and communities most at risk. These results can be used as the framework upon which to develop a comprehensive epidemiological study that focuses on risk factors important at the individual level.

Water Resources Management, 2013

We describe a framework called Regional Hydrologic Modeling for Environmental Evaluation (RHyME 2... more We describe a framework called Regional Hydrologic Modeling for Environmental Evaluation (RHyME 2) for hydrologic modeling across scales. Rooted from hierarchy theory, RHyME 2 acknowledges the rate-based hierarchical structure of hydrological systems. Operationally, hierarchical constraints are accounted for and explicitly described in models put together into RHyME 2. We illustrate RHyME 2 with a two-module model to quantify annual nutrient loads in stream networks and watersheds at regional and subregional levels. High values of R 2 (>0.95) and the Nash-Sutcliffe model efficiency coefficient (>0.85) and a systematic connection between the two modules show that the hierarchy theory-based RHyME 2 framework can be used effectively for developing and connecting hydrologic models to analyze the dynamics of hydrologic systems.

Singapore Journal of Tropical Geography, 2000

Land cover change may impact watershed hydrology and regional climate by altering land‐atmosphere... more Land cover change may impact watershed hydrology and regional climate by altering land‐atmosphere exchanges of energy and water. Conversion of forest to pasture has previously been shown to decrease the rate of evaporation (including transpiration) because of reduced aerodynamic roughness, less canopy rainfall interception and greater canopy resistance during dry periods. However, less is known about the effects of forest replacement land covers other than pasture. In this study, field measurements of meteorological processes, stomatal resistance, and Leaf Area Index (LAI) were taken over various deforested land surfaces in the eastern Amazon Basin and in northern Thailand. Based on these measurements, evaporation and sensible heat flux were estimated over each site. Results show the degree to which different land covers replacing tropical forest affect energy partitioning. In comparison with forest, non‐irrigated, actively and recently cultivated sites had sharply lower rates of ev...

Mathematical and Computer Modelling, 2007

Fuzzy set theory has serious difficulties in producing valid answers in decision-making by fuzzif... more Fuzzy set theory has serious difficulties in producing valid answers in decision-making by fuzzifying judgments. No theorems are available about its workability when it is applied indiscriminately as a number crunching approach to numerical measurements that represent judgments. When judgments are allowed to vary in choice over the values of a fundamental scale, as in the Analytic Hierarchy Process, these judgments are themselves already fuzzy. To make them fuzzier can make the validity of the outcome, when the actual outcome is known, worse, as shown by several examples in this paper. Also, improving the consistency of a judgment matrix does not necessarily improve the validity of the outcome. Validity is the goal in decision-making, not consistency, which can be successively improved by manipulating the judgments as the answer gets farther and farther from reality. An example of this is included.

Diseases of Aquatic Organisms, 2000

Serious shrimp-disease outbreaks have reduced shrimp production and slowed industry growth since ... more Serious shrimp-disease outbreaks have reduced shrimp production and slowed industry growth since 1991. This paper tests factors such as farm siting and design, and farm-management practices for relationships with disease occurrence. Logistic regression is used to analyze farm-level data from 3951 shrimp farms in 13 Asian countries. Disease occurrence is modeled as a 0-1 variable where 1 = disease loss of 220% to any 1 crop, and 0 = losses of <20%. Logistic regression is performed for each of 3 levels of shrimp culture intensity, i.e. extensive, semi-intensive, and intensive. Attempts to apply logistic regression models to each country were not successful due to insufficient data for most countries. Factors affecting disease occurrences were quite different for different farming intensities. Farms that had larger pond production areas, with larger number of farms discharging effluent into their water supply canals, and removed silt had greater disease occurrence. On the other hand, farms that practiced polyculture and took water from the sea through a canal had lower disease occurrence.

... 3, Multiple stressors in ecological risk and impact assessment Foran, A - 1999. 3, Predicti... more ... 3, Multiple stressors in ecological risk and impact assessment Foran, A - 1999. 3, Predicting the potential invasive distributions of four alien plant species in North America Peterson, Papes, et al. ... 2, Stressor identification guidance document Cormier, Norton, et al. - 2000. ...

Agricultural and Forest Meteorology, 2003

A field study was conducted of microclimate and transpiration within a 12 ha patch of advanced se... more A field study was conducted of microclimate and transpiration within a 12 ha patch of advanced secondary forest surrounded by active or recently abandoned swidden fields. Differences in microclimate among stations located within and near the patch, give evidence of the effects of the adjacent clearing on the environment in the patch. Volumetric soil moisture content at the end of the dry season was lowest at the two edge sites, suggesting greater cumulative dry season evapotranspiration (ET) there than at swidden and forest interior sites. Total evaporation, based on energy balance methods, was also higher at the two edge sites than at the swidden or forest interior sites. Spatial differences in evaporation decreased as conditions became wetter. Measurements of sap flow in nine trees near the southwestern edge of the patch and nine trees in the patch interior indicate considerable variability in transpiration among the three monitored tree species, Vernicia montana, Alphonsea tonkinensis, and Garcinia planchonii. Dry-period transpiration averaged about 39 and 43% of total evaporation for edge and interior trees, respectively, increasing to 60 and 68% after the start of rains. Transpiration in both zones was well-correlated with micrometeorological conditions in the adjacent clearing, implying that transpiration edge effect is greatest when conditions are favorable for high positive heat advection from the clearing to the forest edge. Transpiration rates of well-exposed trees were higher than poorly-exposed trees, and decreased with distance from the edge at a statistically significant rate of −0.0135 mm per day m −1. Although the results on the strength of transpiration edge effect are somewhat equivocal due to variability within the small sample, there is clear evidence that ET within the patch is influenced by the surrounding clearings. If edges experience higher ET, greater fragmentation would result in higher regional evaporative flux, which would partly compensate for the reduction in regional ET due to deforestation.

Environmental Monitoring and Assessment, 2004

The U.S. Environmental Protections Agency's (U.S. EPA) Regional Vulnerability Assessment (ReVA) p... more The U.S. Environmental Protections Agency's (U.S. EPA) Regional Vulnerability Assessment (ReVA) program has focused much of its research over the last five years on developing and evaluating integration methods for spatial data. An initial strategic priority was to use existing data from monitoring programs, model results, and other spatial data. Because most of these data were not collected with an intention of integrating into a regional assessment of conditions and vulnerabilities, issues exist that may preclude the use of some methods or require some sort of data preparation. Additionally, to support multi-criteria decision-making, methods need to be able to address a series of assessment questions that provide insights into where environmental risks are a priority. This paper provides an overview of twelve spatial integration methods that can be applied towards regional assessment, along with preliminary results as to how sensitive each method is to data issues that will likely be encountered with the use of existing data.

Forests, 2020

Bioenergy crops are considered as potential biomass feedstocks to support the bioenergy industry ... more Bioenergy crops are considered as potential biomass feedstocks to support the bioenergy industry in the southern US. Even though there are suitable areas to grow bioenergy crops, commercial scale production of bioenergy crops has not been established to meet the increasing energy demand. Establishing bioenergy crops in the region requires landowners’ participation and it is crucial to understand whether they intend to promote bioenergy crop production. This study evaluated landowners’ perception of bioenergy and their willingness to supply lands for bioenergy crops in northern Kentucky. A questionnaire survey of randomly selected landowners was administered in four selected counties. Results indicated that landowners’ land use decisions for bioenergy crop production were based on their current land management practices, socio-economic and environmental factors. Overall, there was a low willingness of landowners to participate in bioenergy crop production. Those who were interested i...

Estimating invasion dynamic is important to the management of invasive species, and geopolitical-... more Estimating invasion dynamic is important to the management of invasive species, and geopolitical-unit level data are usually the most abundant and available records of invasive species. Here, for the first time we evaluated performances and similarities of eight common methods to estimate spread pattern and spread dynamic of invasive species with geopolitical-unit level data, and assessed impacts of variations in geopolitical-units on each method using simulated spread data. We also formulated a concave hull boundary displacement method (i.e., CEB) and an area-based regression method (i.e., AER) for estimating spread with geopolitical-unit data. Three regions with different sized counties in the United States (U.S.) were selected to conduct simulations and three spread scenarios were simulated. R2 and root mean square error were used to evaluate the abilities of all methods to estimate spread. Correlation coefficients were used to assess the similarity pattern of all methods. Finall...

The Journal of Wildlife Management, 2017

Bats roosting in buildings are a challenge for wildlife managers because of their conservation ne... more Bats roosting in buildings are a challenge for wildlife managers because of their conservation needs, capacity to transmit disease, and potential to damage structures. An understanding of roost selection by bats in buildings is important for effective management but was lacking in the southeastern United States. During 2015 and 2016, we surveyed 140 buildings in Great Smoky Mountains National Park in eastern Tennessee and western North Carolina, USA for bats, identifying 48 roost sites and detecting 5 species. We compared the microclimate conditions, building features, and habitat patch characteristics of buildings used and unused by bats using an information-theoretic approach. Averaged parameter estimates from logistic regression models developed with survey data indicated bat presence was more likely in old buildings with dark conditions surrounded by low road density. Of all roost buildings surveyed, 65.9% were accessed regularly by tourists and 68.2% were managed as historical structures. We present alternative management strategies that may be implemented to ensure human health and safety and preserve historical sites while protecting bats during the reproductive period.

GeoJournal, 2019

This research assesses the social vulnerability of five villages (Jora, Kiteghe, Makwasinyi, Bung... more This research assesses the social vulnerability of five villages (Jora, Kiteghe, Makwasinyi, Bungule, and Rukanga) in Mt. Kasigau, Kenya. Our goal was to develop a social vulnerability model by adopting a vulnerability conceptual framework that conceptualizes vulnerability into three major components: exposure, sensitivity, and adaptive capacity and using the analytical hierarchy process (AHP). Employing the AHP, the three components of vulnerability were decomposed into its constituent components and structured into a hierarchical format where each component was represented by different societal and environmental criterions and stressors. Next, we performed a pairwise comparison at each level of the hierarchy to obtain local priorities. Finally, we aggregated the local priorities from the bottom up to obtain global priorities of the social vulnerability of each village. The results from this study revealed that Makwasinyi was the most vulnerable village followed by Bungule, Kiteghe, Jora, and Rukanga respectively. Further, the results suggested that adaptive capacity and exposure played a critical role in determining the social vulnerability compared to sensitivity. Considering this, reducing social vulnerability in the area should focus much on improving the adaptive capacity of the people and reducing their exposure specifically in Makwasinyi village.

Ecological Indicators, 2016

The paper proposes a method for selecting a set of sustainable development indicators which can b... more The paper proposes a method for selecting a set of sustainable development indicators which can be used for various sustainability-related tasks, such as assessment of current condition, measure of progress toward specific goals of sustainable development, in general, and sustainable urban development, in particular. The method is based on variable clustering, selecting cluster representative, and multivariate linear regression in combination with experts and stakeholders' input in an interactive process. The small set of indicators derived from the proposed method was able to account for a significant amount of information from the initial indicator set while effectively assisting stakeholders in making informed decision based on objective quantitative information and meeting their preference simultaneously.

Decision Making Theories and Practices from Analysis to Strategy

Landscape Ecology, 2006

Landscape ecologists may be faced with ranking the relative environmental quality of watersheds a... more Landscape ecologists may be faced with ranking the relative environmental quality of watersheds across a region. The rankings would be based on measured or modeled variables with inherent sources of error. This paper examines the impact of data uncertainty on the ranking assigned to watersheds. The approach is Monte Carlo simulation in which the individual variables are considered to be estimated with uncertainty. The results show that watersheds in the best and the worst condition have rankings that are robust to uncertainty but intermediate watersheds may be difficult or impossible to assign to a rank.

Land Degradation & Development, 1997

Reduction of erosion and sediment-related pollution from urban construction sites or other degrad... more Reduction of erosion and sediment-related pollution from urban construction sites or other degraded hillslopes often relies on the initial application of suitable rolled erosion control systems (RECS) before natural vegetation cover can be established. However, research has not clearly explained why some RECS perform better than others, or under what particular conditions one system is more suitable than another. An important link between the application of the most suitable RECS and better product design is process-based studies relating the physical properties of products to the reduction of erosion subprocesses. This study investigates time-varying reduction of rainsplash detachment and transport by 13 commonly used RECS. The results indicate that product dierences in the protection they provide against splash processes vary over the duration of a rain event, and that this variation is related to individual product properties, especially surface coverage and thickness. These results should aid in the design of more eective erosion control products and in the selection of the most suitable RECS for particular hillslope applications.

Journal of Hydrology, 2007

fragmentation and less HOF. The study highlights the hydrological impacts associated with fragmen... more fragmentation and less HOF. The study highlights the hydrological impacts associated with fragmentation at Tan Minh, which is the product of decades of local and regional forcing factors that have dictated the degree and timing of timber removal and swiddening at the site.

Journal of Geophysical Research: Atmospheres, 1996

In recent efforts to predict the climatic impacts of tropical deforestation an extreme scenario o... more In recent efforts to predict the climatic impacts of tropical deforestation an extreme scenario of impoverished grassland has been used to represent the future deforested landscape. Currently, deforested areas of the tropics are composed of a mosaic of crops, bare soil, grassland, and secondary vegetation of various ages. The dominant feature of deforested land is often secondary vegetation. Parameter values for important forest replacement land covers, including secondary vegetation, have been shown to differ from those of forest much less than that assumed in general circulation model (GCM) deforestation experiments. For this study, the biosphere-atmosphere transfer scheme (BATS) is run in uncoupled mode using measured input data in place of GCM forcing and using the same parameter settings employed in recent deforestation experiments. Model output is compared with measurements taken over seven different deforested land surfaces in northern Thailand. Comparisons reveal that the simulation of deforested land overestimates reflected shortwave radiation, the diurnal range of surface temperature for secondary vegetation, surface soil moisture loss during periods without rain, and surface soil moisture increase at the start of a rainy period and underestimates net radiation, the diurnal range of surface temperature on recently used land surfaces, and root zone soil moisture increase at the start of a rainy period at most sites. Most deforested land surfaces, especially intermediate and advanced secondary vegetation, are more similar, in terms of land surface-atmosphere interaction, to the model simulation of forest than of deforested land as depicted in GCM experiments. These comparisons suggest that modelers aspiring to make realistic simulations of deforestation should adopt parameter settings representative of the diverse range of forest replacement land covers, instead of again using the grassland scenario. ha yr '1 [Houghton, 1994]. The chief concerns surrounding rapid tropical deforestation are the consequent impacts on species diversity, atmospheric chemistry, and land surfaceatmosphere interaction. The latter concern has led to numerous attempts to identify possible regional and global climatic impacts of large-scale tropical deforestation on the basis of general circulation model (GCM) experiments. Investigators have attempted to simulate the effects of the shift in land surface characteristics, especially changes in Copyright 1996 by the American Geophysical Union. Paper number 96JD01966. 0148-0227/96/96JD-01966509.00 radiative, aerodynamic, and soil hydraulic properties [Wright et al., 1996], accompanying a shift from multistoried forest canopy to grassland. While early efforts [Henderson-Sellers and Gornitz, 1984] used simplistic representations of land surface processes, modelers now incorporate more realistic soil-vegetation-atmosphere transfer schemes (SVATS) into their GCMs, allowing the effects of deforestation to be represented by changes in a wide range of parameters [Dickinson and Henderson-Sellers, 1988]. The biosphere-atmosphere transfer scheme (BATS) [Dickinson et al., 1986, 1993] has been used extensively for this purpose. Recent GCM simulations of complete tropical forest removal [Henderson-Sellers et al., 1996; McGuffie et al., 1995; Sud et al., 1996] have shown that precipitation in the Amazon Basin and Southeast Asia would be significantly reduced as a result of lower regional evaporation and reduced moisture convergence (Table 1). Recent simulation runs predicted evaporation for the Amazon Basin would be reduced by 23 to 39% due to conversion of tropical rain forest to grassland [Xue et al., 1996]. Experiments have also indicated significant changes in the atmospheric general circulation as a result of tropical deforestation, affecting the climate of regions outside the deforested areas. Henderson-Sellers et al. [1993a] found diminished vertical ascent in the intertropical convergence 25,867 25,868 GIAMBELLUCA ET AL.' SOIL-VEGETATION-ATMOSPHERE PROCESSES Table 1. Results of general circulation model (GCM) Deforestation Experiment [Henderson-Sellers et al., 1996]; Changes in Simulated Values due to Deforestation Instrument Amazon Southeast Asia Mean maximum air temperature, K + 1.4 Mean minimum air temperature, K-0.3 Mean maximum radiative surface temperature, K +2.1 Mean minimum radiative surface temperature, K-1.1 Evaporation, %-18 Rainfall, %-21 +0.8-0.4 +0.8-1.1-10-8 zone (ITCZ) over South and Central America and, to a lesser extent, Southeast Asia. Associated Hadley cell descent in the subtropics of both hemispheres was diminished as well. To ascertain whether any significant regional or global climate changes due to tropical land surface change are possible, modelers have elected, in most experiments to date, to use an extreme scenario for the deforestation case, usually described as degraded pasture or impoverished grassland. In selecting grassland to represent the postforest land cover, modelers have intentionally chosen a land cover which contrasts strongly with forest in order to examine the sensitivity of the simulated coupled climate system to land cover change. As Henderson-Sellers and Gornitz [1984] stated in describing the first GCM deforestation experiment, the objective was to "... try to estimate the maximum impact likely to occur as a result of tropical deforestation by maximizing the changes important to climate." This was clearly a sound strategy at the outset of such experiments, in that were significant climatic changes not predicted under the most extreme and extensive land surface change, other less extreme scenarios would not then need to be examined. But statements by modelers such as Polcher and Laval [1994], who refer to the replacement of the Amazonian forest by grassland as "... a realistic scenario if deforestation continues at the present rate," encourage readers to forget that grassland was intentionally selected as an extreme case. Actual land cover in tropical deforested regions is composed of a mosaic of crops, bare soil, grassland, and secondary vegetation of various ages. The cultural and economic incentives to clear forest depend on location, leading to different forest replacement covers in different changes simulated for a more realistic deforestation scenario, while likely to be significant, would be less pronounced than those simulated in current deforestation ET AL.: SOIL-VEGETATION-ATMOSPHERE PROCESSES 25,869