學術發表
Rainfall frequency analysis using event-maximum rainfalls – An event-based mixture distribution modeling approach
KE-SHENG CHENG 鄭克聲
Rainfall frequency analysis, an essential work for water resources management, is often conducted by using the annual maximum rainfall series. For rainfall stations with short record lengths and outliers presence, the use of annual maximum series for rainfall frequency analysis may yield design rainfall estimates of higher uncertainties. Moreover, for regions with cyclostationary climate patterns, the annual maximum rainfalls may be caused by different prevalent storm types, which differ in terms of their occurrence frequency and storm rainfall characteristics. In this study, we propose a novel event-maximum-rainfall-based mixture distribution modeling approach for rainfall frequency analysis. By considering the event-maximum rainfalls of individual storm events, the sample size for parameter estimation increases, and the uncertainty of design rainfall estimates reduces. Mixture distribution modeling enables a thorough investigation of the contributing probabilities of different storm types to the annual maximum rainfall. Through rigorous stochastic simulation, we demonstrated the superiority of the proposed approach over the conventional annual maximum rainfall approach. The proposed approach was applied to four representative rainfall stations in Taiwan, and the results revealed that the proposed approach is more robust than the conventional annual maximum rainfall approach. The results provide insights into the contributions of individual storm types to the annual maximum rainfall.
10.1016/j.wace.2023.100634
Fluvial flood adaptation using nature-based solutions: A comprehensive and effective assessment of hydro-meteorological risks
KUO-WEI LIAO 廖國偉
The growing prominence of Nature-based Solutions (NbS) for disaster risk reduction (DRR) has sparked increased interest. This study is motivated by the need to establish a quantifiable and standardized method for assessing the risks mitigated by NbS in engineering applications. The goal is to establish a comprehensive and effective system framework for assessing hydro-meteorological risks related to NbS in engineering applications. The proposed framework considers flood disaster mechanisms, uncertain factors, and ecosystem services, integrating them to comprehensively assess the benefits of NbS. Specifically, 2-D hydraulic analysis and an in-house adaptive Kriging-based reliability analysis are developed and applied to establish flood prevention standards for NbS. Additionally, the InVEST toolkit is utilized to evaluate ecosystem services. To demonstrate the applicability of the framework, the Baoli River Watershed located in Pingtung County of Taiwan is selected as a case study. It is found that NbS can effectively withstand a 25-year return period flood and reduce flooding on agricultural land by 46.03 %. Furthermore, the probability of flooding decreased from 100 % to 27 % for a 20-year return period flood. NbS was found to provide approximately NT$1.20–4.65 million more in total benefit value compared to the engineering governance strategy. The supporting source codes are available at https://github.com/johnthedy/Adaptive-Kriging-Using-PSO-HHs-in-HECRAS3D.git.
10.1016/j.scitotenv.2023.169329
The impacts of climate change on groundwater quality: A review
CHIHHAO FAN 范致豪
Groundwater has been known as the second largest freshwater storage in the world, following surface water. Over the years, groundwater has already been under overwhelming pressure to satisfy human needs for artificial activities around the world. Meanwhile, the most noticeable footprint of human activities is the impact of climate change. Climate change has the potential to change the physical and chemical properties of groundwater, thereby affecting its ecological functions. This study summarizes existing research affiliated with the possible effects of a changing climate on the quality of groundwater, including changes in water availability, increased salinity and pollution from extreme weather events, and the potentiality of seawater intrusion into coastal aquifers. Previous works dealing with groundwater-induced responses to the climate system and climate impacts on groundwater quality through natural and anthropogenic processes have been reviewed. The climate-induced changes in groundwater quality including pH, dissolved oxygen level, salinity, and concentrations of organic and inorganic compounds were assessed. Some future research directions are proposed, including exploring the potential changes in the occurrences and fate of micropollutants in groundwater, examining the relationship between the increase of microcystin in groundwater and climate change, studying the changes in the stability of metals and metal complexation, and completing studies across different regional climate regions.
10.1016/j.scitotenv.2023.169241
Watershed groundwater level multistep ahead forecasts by fusing convolutional-based autoencoder and LSTM models
FI-JOHN CHANG 張斐章
The development of deep learning-based groundwater level forecast models can tackle the challenge of high dimensional groundwater dynamics, predict groundwater variation trends accurately, and manage groundwater resources effectively, thereby contributing to sustainable water resources management. This study proposed a novel ConvAE-LSTM model, which fused a Convolutional-based Autoencoder model (ConvAE) and a Long Short-Term Memory Neural Network model (LSTM), to provide accurate spatiotemporal groundwater level forecasts over the next three months. The HBV-light and LSTM models are chosen as benchmarks. An ensemble of point data and the corresponding derived images concerning the past (observations) and the future (forecasts from a conceptual model) of groundwater levels at 33 groundwater wells in Jhuoshuei River basin of Taiwan between 2000 and 2019 constituted the case study. The findings showcase the effectiveness of the ConvAE-LSTM model in extracting crucial features from both point and imagery datasets. This model successfully establishes spatiotemporal dependencies between regional images and groundwater level data over diverse time frames, leading to accurate multi-step-ahead forecasts of groundwater levels. Notably, the ConvAE-LSTM model exhibits a substantial improvement, with the R-squared values showing an increase of more than 18%, 22%, and 49% for the R1, R2, and R3 regions, respectively, compared to the HBV-light model. Additionally, it outperforms the LSTM model in this regard. This study represents a noteworthy milestone in environmental modeling, offering key insights for designing sustainable groundwater management strategies to ensure the long-term availability of this vital resource.
10.1016/j.jenvman.2023.119789
A Novel Cellular Automata Framework for Modeling Depth-Averaged Solute Transport during Pluvial and Fluvial Floods
TSANG-JUNG CHANG 張倉榮
Currently, for modeling two-dimensional (2D) solute transport during pluvial and fluvial floods, the finite volume (FV) models are widely used because of their strong ability to handle steep concentration and velocity gradients from the flow advection term. However, heavy computational requirements are subsequently introduced which limit the numerical efficiency. To further increase numerical efficiency but keep the required accuracy, this study proposes a novel Solute Transport Modeling based on Cellular Automata framework (STMCA) to simulate solute transport due to the flow advection, turbulent diffusion, and material decay mechanisms in several sets of explicit algebraic equations. Four studied cases involving steep gradients of solute concentration and velocities in steady/unsteady violent flow conditions are used to compare the accuracy of the STMCA approach with a Godunov-type FV solute transport approach with a total variation diminishing (TVD) scheme. Then, the performances of the two approaches on water quality modeling are assessed through the E. Coli transport modeling during pluvial/fluvial floods on a real-scale terrain. The proposed STMCA approach is found to achieve almost the same accuracy as the FV approach. As to the numerical efficiency, the STMCA approach is faster than the FV approach by 289.6–328.6%. Hence, the proposed STMCA approach is proven to be an effective tool for simulating solute transport.
10.3390/w16010129
Ecological Carrying Capacity Estimation of the Trails in a Protected Area: Integrating a Path Analysis Model and the Stakeholders’ Evaluation
CHENG-I HSIEH 謝正義
Trails are important recreation settings; determining an appropriate trail usage amount to avoid unacceptable ecological impacts is important for protected areas. However, there is a lack of studies examining trail usage’s direct and indirect relationships and the influence of landscape-level conditions to evaluate ecological carrying capacity. This study integrated a path analysis model and stakeholder assessment to estimate the ecological carrying capacity of trails in a protected area. This study surveyed the biophysical environment along the trails and conducted a path analysis to establish the use–impact model for the trails in the study area. Based on the use–impact model, this study developed four-level usage scenarios and collected the stakeholders’ acceptance evaluation to determine the ecological carrying capacity range. The results showed that the weekly usage of the trails directly affected the soil hardness and plant coverage of the trail. The trail’s soil hardness directly affected the surrounding soil hardness, decreasing its plant coverage, while the vegetation type and slope also affected its plant cover. The stakeholders of the Mt. Xiaoguanyin Area reached a consensus on the ecological carrying capacity range, which was 288 to 404 total weekly hikers. The study results revealed the effect paths of the landscape-level conditions and usage impacts and provided managers with an implementable ecological carrying capacity. The estimation framework could be a reference for determining ecological carrying capacity in other protected areas.
10.3390/f14122400
Fertilization-induced reactive nitrogen gases and carbon dioxide emissions: insight to the carbon-nitrogen cycles
SHU-YUAN PAN 潘述元
Different agricultural practices can pose significant threats to environmental quality and human health. This study aimed to assess the emissions of reactive nitrogen (NH3, NOx, and N2O) and carbon dioxide (CO2) induced by fertilization in spinach and cabbage farmlands. Field and pot experiments were conducted to analyze the emission fluxes and intensities of reactive nitrogen gases and CO2. The findings revealed that the total emissions of reactive nitrogen for cabbage and spinach ranged from 21 to 798 kg-N ha−1 and 1.1 to 489 kg-N ha−1, respectively. Generally, organic fertilizers exhibited higher emission intensities of NH3 compared to N2O. While slow-release fertilizers effectively reduced NH3 emissions, they resulted in increased soil N2O emissions. Furthermore, the total emissions of reactive nitrogen from the soil showed a positive correlation with soil CO2 emissions. Particularly, organic farming practices, especially in the case of cabbage, led to increased CO2 emissions from farmlands. Based on the experimental findings, three priority directions were suggested to achieve sustainable soil carbon and nitrogen management in order to minimize emissions from farmlands. This study provides valuable insights for future soil carbon and nitrogen management in subtropical regions.
10.1186/s42834-023-00185-8
Energy performance of school roofing materials in hot and humid climates
KUO-TSANG HUANG 黃國倉
Effective roof insulation plays a pivotal role in reducing the energy used for air-conditioning, particularly in Taiwan's extreme summer climate. In the present study, 1108 cases of rooftop insulation renovations in Taiwanese schools between 2018 and 2022 were investigated, and the thermal insulation performance and air-conditioning-related electricity savings associated with these renovations were analyzed through a cost–benefit assessment of the investment in insulation. The EnergyPlus software was used to model typical classroom roofs in seven climate zones in Taiwan. All the adopted thermal insulation methods considerably reduce air-conditioning-related electricity use; however, diminishing returns occur faster for thicker thermal insulation. The four main roof insulation materials used in the analyzed cases are galvanized corrugated steel, foam concrete, polystyrene sheets, and insulating bricks, which are associated with average maximum electricity-saving ratios of 17%, 15.3%, 10.2%, and 9.7%, respectively, and payback periods of 6.1, 6.4, 4.5, and 9.3 years, respectively. Electricity savings are greater and the payback period is shorter for the hotter southern zones of Taiwan than for the cooler northern zones. Galvanized corrugated steel has average energy efficiency of 21% and 13% in the southern and northern zones, respectively. The selection of roof construction materials strongly influences the consumption of energy for air-conditioning. Moreover, different construction costs result in distinct payback periods. The results of this study serve as a reference for school administrators and governments in the selection of insulation methods and design of building energy conservation and management, respectively.
10.1016/j.cscm.2023.e02586
Strategies analysis for improving SWAT model accuracy and representativeness of calibrated parameters in sediment simulation for various land use and climate conditions
LI-CHI CHIANG 江莉琦
Sediment yields in a watershed are usually affected by various natural disturbances and anthropogenic activities, and can be simulated by using hydrological models. However, due to the availability and type of data (i.e., continuous or discrete) of measured sediment data, model calibration and validation performances could be significantly affected and the calibrated parameters may not be representative for the area. In this study, the sediment rating curves (SRCs) were developed to increase measurements of sediments for model calibration, and five strategies of using measured and estimated sediment data on improving a hydrological model (Soil and Water Assessment Tool, SWAT) calibration and validation for multiple sediment stations were analyzed. The five strategies were: using measured sediment data (S1), using measured data and different portions of estimated sediment during typhoon events (S2 to S4), and using estimated sediment data during entire simulation period (S5). The results showed that although the S1 mostly performed better than other sediment strategies, S4 and S5 were also suitable for improving sediment simulation at the downstream stations (STN1, 2, and 3) and upstream station (STN4), respectively. Moreover, the impact of incorporating different portions of typhoon-induced sediment data (S2, S3, and S4) on the model performance showed differently at stations. In sum, the proposed analytical procedure is expected to be useful for calibrating sediment parameters of hydrological models with limited or highly unevenly distributed measured sediment data.
10.1016/j.jhydrol.2023.130124
Application of FBG Multilevel Well on Hydraulic Tomography for a Contaminated Site in Taiwan
JUI-PIN TSAI 蔡瑞彬
The work demonstrates a method for employing the FBG MLMS and sequential multi- depth injections for an HT survey at a low to moderate heterogeneity sedimentary aquifer. While the desired degree of imaging accuracy (resolution and accuracy of the estimated parameters) is usually problem-specific, the results suggest that increasing the number of injection points at various depths could improve imaging accuracy. Moreover, the FBG MLMS efficiently collects groundwater measurements at different depths inside a well. Thus, using MLMS wells, the increase in the injection/pumping points can lead to an effective increase in the number of cross-hole tests; in turn, the collected head observations can effectively reach ergodicity.
10.3997/2214-4609.202378018
Characterizing basin-scale subsurface hydraulic heterogeneity with multiscale geological and hydrological measurements
YU-LI WANG 王昱力
Mapping aquifer heterogeneity is a pressing need for managing regional groundwater resources. Many studies have shown that combining hydraulic tomographic surveys with point-scale geological information is viable for detailing meter-scale to kilometer-scale hydraulic heterogeneity of aquifers. However, due to the complexity of aquifer systems, few field investigations have been conducted on basin-scale systems. In this study, we collected datasets of stream stages, groundwater levels, and borehole logs from 35 wells in a river plain during the wet season, when flood events altered the groundwater flow fields. We then analyzed these datasets using correlation analysis and a geostatistical inverse model. The hydraulic transmissivity and storage coefficient distributions were inverted based on different numbers of geological zones. By validating the estimated parameter fields with independent datasets, we demonstrated that appropriate selection of the number of geological zones, using point-scale geological information and clustering, improved the estimated fields. Further increasing the number of zones beyond an appropriate number deteriorated the estimates at the basin-scale site. The proposed method offers a cost-effective approach for basin-scale characterization. The better knowledge of subsurface hydraulic heterogeneity can support water resource management decisions.
10.1016/j.jhydrol.2023.130061
Thermodynamic sensitivity of ammonia oxidizers-driven N2O fluxes under oxic-suboxic realms
YU-PIN LIN 林裕彬
In terrestrial ecosystems, the nitrogen dynamics, including N2O production, are majorly regulated by a complex consortium of microbes favored by different substrates and environmental conditions. To better predict the daily, seasonal and annual variation in N2O fluxes, it is critical to estimate the temperature sensitivity of different microbial groups for N2O fluxes under oxic and suboxic conditions prevalent in soil and wetlands. Here, we studied the temperature sensitivity of two groups of ammonia oxidizers, archaea (AOA) and bacteria (AOB), in relation to N2O fluxes through both nitrification and nitrifier-denitrification pathways across a wide temperature gradient (10–55 °C). Using square root theory (SQRT) and macromolecular rate theory (MMRT) models, we estimated thermodynamic parameters and cardinal temperatures, including maximum temperature sensitivity (TSmax). The distinction between N2O pathways was facilitated by microbial-specific inhibitors (PTIO and C2H2) and controlled oxygen supply environments (oxic: ambient level; and suboxic: ∼4%). We found that nitrification supported by AOA (NtA) and AOB (NtB) dominated N2O production in an oxic climate, while only AOB-supported nitrifier-denitrification (NDB) majorly contributed (>90%) to suboxic N2O budget. The models predicted significantly higher optimum temperature (Topt) and TSmax for NtA and NDB compared to NtB. Intriguingly, both NtB and NDB exhibited significantly wider temperature ranges than NtA. Altogether, our results suggest that temperature and oxygen supply control the dominance of specific AOA- and AOB-supported N2O pathways in soil and sediments. This emergent understanding can potentially contribute toward novel targeted N2O inhibitors for GHG mitigation under global warming.
10.1016/j.chemosphere.2023.138872
Estimating hydrogeological parameters at groundwater level observation wells without pumping well information
HWA-LUNG YU 余化龍
Aquifer pumping is a common method of meeting human water needs, but it can also disrupt the natural flow of groundwater and cause fluctuations in groundwater levels. These fluctuations, however, can provide useful insights into hydrogeological properties when measured in an observation well. Traditional modeling methods are not well suited for analyzing such data because they lack essential details about the pumping wells, such as their number, distance from the observation well, and pumping rates. To address this issue, new impulse response function for transfer function modeling is developed that accurately describes the confined flow in such situations. The proposed function is based on the Theis solution, which uniformly distributes the effects of multiple pumping wells within a circular area around the observation well. This allows our function to accurately estimate hydrogeological parameters and pumping rates without knowing the number and specific location of pumping wells. The effects of well distance, spatial arrangement, and aquifer anisotropy on the accuracy of our function are also analyzed using synthetic experiments and Morris sensitivity analysis. The results show that the proposed function is effective in estimating essential hydrogeological parameters, such as the aquifer storativity, using only drawdown time series data from a observation well.
10.1016/j.jhydrol.2023.129873
The Displacement of the Resident Wetting Fluid by the Invading Wetting Fluid in Porous Media Using Direct Numerical Simulation
SHAO-YIU HSU 許少瑜
Understanding the displacement of the resident wetting fluid in porous media is crucial to the remediation strategy. When pollutants or nutrients are dissolved in the surface wetting fluid and enter the unsaturated zone, the resident wetting fluid in the porous system may remain or be easily flushed out and finally arrive in the groundwater. The fate and transport of the resident wetting fluid determine the policy priorities on soil or groundwater. In this study, the displacement of the resident wetting fluid by the invading wetting fluid in porous media was simulated using direct numerical simulation (DNS). Based on the simulations of the displacements in porous media, the effect of the non-wetting fluid on the displacement was evaluated by observation and quantification, which were difficult to achieve in laboratory experiments. The result can also explain the unknown phenomenon in previous column experiments, namely that the old water is continuously released from the unsaturated porous media even after a long period of flushing with the new water. The effects of the interfacial tension, contact angle, and injection rate, which affected the immiscible fluid–fluid flow pattern, were also evaluated. Since pollutants dissolved in the wetting fluid could change the physical properties of the wetting fluid, the interfacial tensions of the resident wetting fluid and the invading wetting fluid were set separately in the simulation. Moreover, our simulation demonstrated that the consecutive drainage–imbibition cycles could improve the displacement of the resident wetting fluid in porous media. The successful simulation in this study implied that this method can be applied to predict other immiscible fluid–fluid flow in natural or industrial processes.
10.3390/w15142636
Macroenvironmental interactions as driving indicators for detecting tetracycline resistance spread among A. hydrophila exposure to environmentally relevant oxytetracycline levels
CHUNG-MIN LIAO 廖中明
There have been efforts dedicating to investigating the effect of high levels of oxytetracycline (OTC) on tetracycline (TC) resistance among zoonotic pathogen Aeromonas hydrophila (AH), an antibiotic-resistant bacterial indicator. However, the dynamic behavior of TC-resistant AH in response to environmentally relevant OTC concentrations at a population-level has not been fully understood. Here we developed a bacterial population dynamic model to quantify TC-resistant AH posed by OTC-dependent resistance selection pressure. The key environmental factors known as water temperature, water activity, and pH were incorporated into model to produce pattern-oriented simulation outcomes. We estimated resistance acquisition number (R0) and showed that R0 was >1 at water temperature <26 °C, indicating coexistence of resistant- and susceptible-AH. Sensitivity tests revealed that cell density-dependent conjugation rate indicated crucial for influencing R0 estimation. Our results also indicated that maximum fraction of TC-resistant AH was mostly affected by temperature/activity in water and increased with increasing of OTC concentrations. We estimated OTC concentrations causing 50 % maximum fold-change of TC-resistant AH fraction ranging from 7 to 19 µg/L. Our findings suggest that control of TC resistance in AH requires particularly attention to water with temperature 26 °C lower, water activity 0.95 higher with pH ∼ 5–8. Our mechanistic framework provides a useful tool-kit to improve our understanding of the critical role of OTC stress-induced macroenvironmental interactions in a TC resistance − AH system and highlights the potential for antimicrobial management to promote resilience in aquatic ecosystems.
10.1016/j.ecolind.2023.109873