Geology topics

Y. Wu

Publications and source records attributed to Y. Wu.

8 recordsLinked to original sources

USGS2012

Impacts of biofuels production alternatives on water quantity and quality in the Iowa River Basin

Corn stover as well as perennial grasses like switchgrass (Panicum virgatum) and miscanthus are being considered as candidates for the second generation biofuel feedstocks. However, the challenges to biofuel development are its effects on the environment, especially water quality. This study evaluates the long-term impacts of biofuel production alternatives (e.g., elevated corn stover removal rates and the potential land cover change) on an ecosystem with a focus on biomass production, soil erosion, water quantity and quality, and soil nitrate nitrogen concentration at the watershed scale. The Soil and Water Assessment Tool (SWAT) was modified for setting land cover change scenarios and applied to the Iowa River Basin (a tributary of the Upper Mississippi River Basin). Results show that biomass production can be sustained with an increased stover removal rate as long as the crop demand for nutrients is met with appropriate fertilization. Although a drastic increase (4.7–70.6%) in sediment yield due to erosion and a slight decrease (1.2–3.2%) in water yield were estimated with the stover removal rate ranging between 40% and 100%, the nitrate nitrogen load declined about 6–10.1%. In comparison to growing corn, growing either switchgrass or miscanthus can reduce sediment erosion greatly. However, land cover changes from native grass to switchgrass or miscanthus would lead to a decrease in water yield and an increase in nitrate nitrogen load. In contrast to growing switchgrass, growing miscanthus is more productive in generating biomass, but its higher water demand may reduce water availability in the study area.

Iowa;Minnesota↗

USGS2012

Automating calibration, sensitivity and uncertainty analysis of complex models using the R package Flexible Modeling Environment (FME): SWAT as an example

Parameter optimization and uncertainty issues are a great challenge for the application of large environmental models like the Soil and Water Assessment Tool (SWAT), which is a physically-based hydrological model for simulating water and nutrient cycles at the watershed scale. In this study, we present a comprehensive modeling environment for SWAT, including automated calibration, and sensitivity and uncertainty analysis capabilities through integration with the R package Flexible Modeling Environment (FME). To address challenges (e.g., calling the model in R and transferring variables between Fortran and R) in developing such a two-language coupling framework, 1) we converted the Fortran-based SWAT model to an R function (R-SWAT) using the RFortran platform, and alternatively 2) we compiled SWAT as a Dynamic Link Library (DLL). We then wrapped SWAT (via R-SWAT) with FME to perform complex applications including parameter identifiability, inverse modeling, and sensitivity and uncertainty analysis in the R environment. The final R-SWAT-FME framework has the following key functionalities: automatic initialization of R, running Fortran-based SWAT and R commands in parallel, transferring parameters and model output between SWAT and R, and inverse modeling with visualization. To examine this framework and demonstrate how it works, a case study simulating streamflow in the Cedar River Basin in Iowa in the United Sates was used, and we compared it with the built-in auto-calibration tool of SWAT in parameter optimization. Results indicate that both methods performed well and similarly in searching a set of optimal parameters. Nonetheless, the R-SWAT-FME is more attractive due to its instant visualization, and potential to take advantage of other R packages (e.g., inverse modeling and statistical graphics). The methods presented in the paper are readily adaptable to other model applications that require capability for automated calibration, and sensitivity and uncertainty analysis.

Environmental Modelling and Software↗

USGS2011

Quantifying the hydrological responses to climate change in an intact forested small watershed in southern China

Responses of hydrological processes to climate change are key components in the Intergovernmental Panel for Climate Change (IPCC) assessment. Understanding these responses is critical for developing appropriate mitigation and adaptation strategies for sustainable water resources management and protection of public safety. However, these responses are not well understood and little long-term evidence exists. Herein, we show how climate change, specifically increased air temperature and storm intensity, can affect soil moisture dynamics and hydrological variables based on both long-term observation and model simulations using the Soil and Water Assessment Tool (SWAT) in an intact forested watershed (the Dinghushan Biosphere Reserve) in Southern China. Our results show that, although total annual precipitation changed little from 1950 to 2009, soil moisture decreased significantly. A significant decline was also found in the monthly 7-day low flow from 2000 to 2009. However, the maximum daily streamflow in the wet season and unconfined groundwater tables have significantly increased during the same 10-year period. The significant decreasing trends on soil moisture and low flow variables suggest that the study watershed is moving towards drought-like condition. Our analysis indicates that the intensification of rainfall storms and the increasing number of annual no-rain days were responsible for the increasing chance of both droughts and floods. We conclude that climate change has indeed induced more extreme hydrological events (e.g. droughts and floods) in this watershed and perhaps other areas of Southern China. This study also demonstrated usefulness of our research methodology and its possible applications on quantifying the impacts of climate change on hydrology in any other watersheds where long-term data are available and human disturbance is negligible.

Guangdong Province↗

USGS2011

Hydrological effects of the increased CO 2 and climate change in the Upper Mississippi River Basin using a modified SWAT

Increased atmospheric CO 2 concentration and climate change may significantly impact the hydrological and meteorological processes of a watershed system. Quantifying and understanding hydrological responses to elevated ambient CO 2 and climate change is, therefore, critical for formulating adaptive strategies for an appropriate management of water resources. In this study, the Soil and Water Assessment Tool (SWAT) model was applied to assess the effects of increased CO 2 concentration and climate change in the Upper Mississippi River Basin (UMRB). The standard SWAT model was modified to represent more mechanistic vegetation type specific responses of stomatal conductance reduction and leaf area increase to elevated CO 2 based on physiological studies. For estimating the historical impacts of increased CO 2 in the recent past decades, the incremental (i.e., dynamic) rises of CO 2 concentration at a monthly time-scale were also introduced into the model. Our study results indicated that about 1–4% of the streamflow in the UMRB during 1986 through 2008 could be attributed to the elevated CO 2 concentration. In addition to evaluating a range of future climate sensitivity scenarios, the climate projections by four General Circulation Models (GCMs) under different greenhouse gas emission scenarios were used to predict the hydrological effects in the late twenty-first century (2071–2100). Our simulations demonstrated that the water yield would increase in spring and substantially decrease in summer, while soil moisture would rise in spring and decline in summer. Such an uneven distribution of water with higher variability compared to the baseline level (1961–1990) may cause an increased risk of both flooding and drought events in the basin.

Mississippi River Basin↗

USGS2009

Patterns of forest succession and impacts of flood in the Upper Mississippi River floodplain ecosystem

The widespread loss of oak-hickory forests and the impacts of flood have been major issues of ecological interest concerning forest succession in the Upper Mississippi River (UMR) floodplain. The data analysis from two comprehensive field surveys indicated that Quercus was one of the dominant genera in the UMR floodplain ecosystem prior to the 1993 flood and constituted 14% of the total number of trees and 28% of the total basal area. During the post-flood recovery period through 2006, Quercus demonstrated slower recovery rates in both the number of trees (4%) and basal area (17%). In the same period, Carya recovered greatly from the 1993 flood in terms of the number of trees (11%) and basal area (2%), compared to its minor status before the flood. Further analyses suggested that different species responded to the 1993 flood with varying tolerance and different succession strategies. In this study, the relation of flood-caused mortality rates and DBH, f m (d), can be expressed in negative exponential functions for each species. The results of this research also indicate that the growth functions are different for each species and might also be different between pre- and post-flood time periods. These functions indicate different survival strategies and emergent properties in responding to flood impacts. This research enhances our understanding of forest succession patterns in space and time in the UPR floodplain. And such understanding might be used to predict long-term impacts of floods on UMR floodplain forest dynamics in support of management and restoration. ?? 2009 Elsevier B.V.

Ecological Complexity↗

USGS2007

State of the art and progress in the earthquake early warning system in Taiwan

We report here the recent progress and future development of real-time seismic monitoring in Taiwan, especially on earthquake early warning system (EWS) developed at the Central Weather Bureau (CWB), using the telemetered signals from strong-motion instruments. Utilizing a quick magnitude determination based on the first 10 sec of signals from a virtual and sub-network which is configured automatically, we were able to reduce the earthquake rapid reporting time to about 30 sec or less. This represents a significant step towards a more realistic earthquake early warning capability. This early warning system has been in operation at CWB since 2002. Comprehensive earthquake reports have been issued mostly in less than 30 sec, with an average of about 22 sec from the origin time. At 3 km/sec for a typical crustal shear-wave velocity, the present operation is not useful if an earthquake occurs less than about 70 km from a city, but the lead time will increase to more than 10 sec for cities at distances greater than 100 km from the earthquake source. In the latter case, a lead time of several seconds will allow pre-programmed emergency response to take place prior to the arrival of strong ground shaking. In order to offer earlier warning within an epicentral distance of less than 70 km, a τ c and Pd method was experimented. We used the Taiwan Strong-Motion Instrumentation Program (TSMIP) accelerograms recorded within epicentral distances of less than 30 km from Mw > 5.0 crustal earthquakes. This method uses the first 3-sec length records from the onset of P-waves and could issue an on-site early warning within 10 sec after the event origin time, reducing the radius of the blind zone from 70 to 25 km from the epicenter.

Book chapter↗

USGS2000

Performance of the Taiwan Rapid Earthquake Information Release System (RTD) during the 1999 Chi-Chi (Taiwan) Earthquake

A major earthquake occurred near the town of Chi-Chi in Nantou County, Taiwan, at 1:47 am (local time), 21 September 1999, about 150 km south of Taipei. This is the largest earthquake to have occurred on land in Taiwan during the 20th century. Although Taiwan has an earthquake building code, thousands of buildings collapsed due to the earthquake, leaving more than 100,000 people homeless. The death toll exceeded 2,300 with more than 10,000 injured. Within 102 seconds after the earthquake's origin time, a good estimate of the hypocenter (23.87° N, 120.75° E, Depth = 10 km) and magnitude ( M L = 7.3), and a shaking map were determined automatically by the RTD system. The result was immediately disseminated to governmental emergency response agencies electronically in four ways, by e-mail, World Wide Web, fax, and pager. This rapid information system has been successfully operating in Taiwan for more than four years. During the Chi-Chi earthquake, the rapid availability of earthquake information facilitated the emergency response. The RTD system worked very well throughout the whole aftershock sequence (several aftershocks had local magnitude of 6 or larger). Again this timely information was useful to the emergency response teams. In this paper, we briefly describe the RTD system and summarize its performance during the Chi-Chi earthquake.

Seismological Research Letters↗

USGS1999

Development of an integrated earthquake early warning system in Taiwan - Case for the Hualien area earthquakes

In order to explore the feasibility of an earthquake early warning system for Taipei, two prototype seismic early warning systems have been implemented in Hualien, about 120 km away. The Taiwan Rapid Earthquake Information Release (TREIRS) can routinely determine earthquake location and magnitude in about one minute after the earthquake occurred. However, this reporting time is too long for earthquake early warning purposes. A dense, real-time monitoring system composed of 8 strong-motion stations was installed in Hualien area for testing earthquake early warning capability. For the 27 earthquakes occurred during August 1998 to April 1999, this system has successfully reported earthquake information in about 18 sec after the origin time. Therefore, it provided about 15 sec of early warning time before shear waves arrival in the Taipei urban area. Based on our experience of these two systems, we are encouraged to proceed forward in the development of an earthquake early warning system.

Terrestrial, Atmospheric and Oceanic Sciences↗