Francisco Olivera | Texas A&M University (original) (raw)

Papers by Francisco Olivera

Journal of Hydrologic Engineering, 2012

Stochastic rainfall generators are used in hydrologic analysis because they can provide precipita... more Stochastic rainfall generators are used in hydrologic analysis because they can provide precipitation input to models whenever data are not available, and their parameters are calculated so that the long-term statistics of the synthetic rainfall time series match those of the rainfall records. However, although mentioned in the literature, the relative importance of each rainfall statistic on the watershed response has not been addressed yet, and no guidance on how to account for it has been provided. In this paper, this relative importance is estimated and used to ponder each statistic differently in the calibration of rainfall generators so that it better reflects the watershed hydrology. Rainfall records of 1,249 rain gauges throughout the contiguous United States were used in the study. It was found that when synthetic rainfall time series are generated by weighting the precipitation statistics according to their relative importance, predicted runoff depths and peak flows are underestimated by 4 and 3%, respectively, whereas when they are generated by giving the same weight to all statistics, the underestimation is by 20 and 14%, respectively. These results, based on a significant number of rain gauges, confirm the benefit of weighing the statistics differently for watershed analysis.

The capacity of a watershed to urbanize without changing its hydrologic response and the relation... more The capacity of a watershed to urbanize without changing its hydrologic response and the relation- ship between that response and the spatial configuration of the developed areas was studied. The study was con- ducted in the Whiteoak Bayou watershed (223 km2), located northwest of Houston, Texas, over an analysis period from 1949 to 2000. Annual development data were derived from

Water Resources Research, Jun 1, 2010

1] Advanced land surface models (LSMs) offer detailed estimates of distributed hydrological fluxe... more 1] Advanced land surface models (LSMs) offer detailed estimates of distributed hydrological fluxes and storages. These estimates are extremely valuable for studies of climate and water resources, but they are difficult to verify as field measurements of soil moisture, evapotranspiration, and surface and subsurface runoff are sparse in most regions. In contrast, river discharge is a hydrologic flux that is recorded regularly and with good accuracy for many of the world's major rivers. These measurements of discharge spatially integrate all upstream hydrological processes. As such, they can be used to evaluate distributed LSMs, but only if the simulated runoff is properly routed through the river basins. In this study, a rapid, computationally efficient source-to-sink (STS) routing scheme is presented that generates estimates of river discharge at gauge locations based on gridded runoff output. We applied the scheme as a postprocessor to archived output of the Global Land Data Assimilation System (GLDAS). GLDAS integrates satellite and ground-based data within multiple offline LSMs to produce fields of land surface states and fluxes. The application of the STS routing scheme allows for evaluation of GLDAS products in regions that lack distributed in situ hydrological measurements. We found that the four LSMs included in GLDAS yield very different estimates of river discharge and that there are distinct geographic patterns in the accuracy of each model as evaluated against gauged discharge. The choice of atmospheric forcing data set also had a significant influence on the accuracy of simulated discharge.

Recent concerns about global climate change and a series of large-scale hydrologic events such as... more Recent concerns about global climate change and a series of large-scale hydrologic events such as the Mid-West flood of 1993 and the El Nino of 1997 have focused attention on the need to track the flow of water through the entire hydrologic cycle. On the land surface, databases of routing parameters and routing models are required to describe the movement of runoff generated by Global Circulation Models (GCMs) and other soil water balance models over the earth's surface. In this study, a terrain analysis is performed using 30 arcsecond Digital Elevation Model (DEM) data to develop a global database of terrain derived routing parameters. A computationally efficient grid based routing model, called a source to sink (STS) model, is implemented in this study. It routes flow directly from the point of generation to the desired observation point. The STS model also allows for easy interaction with models of other phases of the viii hydrologic cycle by incorporating the boundaries of their modeling units into the definition of its own modeling units. A continental scale STS model is created and parameterized for each continent using datasets derived from the terrain analysis. A process is defined for determining additional velocity and dispersion parameters from observed flow data. Another continental scale routing model is developed using the watershed based approach of the Hydrologic Modeling System (HMS). Hydrologic elements and routing parameters for the HMS model are derived from the same terrain data used in parameterizing the STS model. Basin responses from the two models are compared for various spatial and temporal resolutions and parameter distributions to determine the implications of their respective conceptual models. These comparisons show that basin responses in the STS model are relatively independent of spatial and temporal scale while the HMS model is scale dependent with regard to both spatial and temporal resolution. Basin responses for a fine resolution HMS models were successfully duplicated in a STS model for both the uniform and non-uniformly distributed velocity and dispersion parameter case. ix

Coastal Engineering, 2014

ABSTRACT Abstract In this study we investigated the impacts of potential changes of land cover du... more ABSTRACT Abstract In this study we investigated the impacts of potential changes of land cover due to sea-level rise (SLR) on storm surge (i.e., the rise of water above normal sea level, namely mean-sea level and the astronomical tide, caused by hurricane winds and pressure) response inside bays on the lower Texas coast. We applied a hydrodynamic and wave model (ADCIRC + SWAN) forced by hurricane wind and pressure fields to quantify the importance of SLR-induced land cover changes, considering its impacts by changing bottom friction and the transfer of wind momentum to the water column, on the peak surge inside coastal bays. The SLR increments considered, 0.5 m to 2.0 m, significantly impacted the surge response inside the bays. The contribution of land cover changes due to SLR to the surge response, on average, ranged from a mean surge increase of 2% (SLR of 0.5 m) to 15% (SLR of 2.0 m), in addition to the SLR increments. The increase in surge response strongly depended on storm condition, with larger increases for more intense storms, and geographical location. Although land cover changes had little impact on the surge increase for SLR increments lower than 1.0 m, intense storms resulted in surge increase of up to 10% even for SLR below 1.0 m, but in most cases, the geometry changes were the major factor impacting the surge response due to SLR. We also found a strong relationship between changes in bottom friction and the surge response intensification; demonstrating the importance of considering land cover changes in coastal regions that are highly susceptible to SLR when planning for climate change.

Journal of Geophysical Research: Oceans, 2014

ABSTRACT storm surge is one of the most costly natural hazards in the United States. Numerical mo... more ABSTRACT storm surge is one of the most costly natural hazards in the United States. Numerical modeling to predict and estimate hurricane surge flooding is currently widely used for research, planning, decision making, and emergency response. Land cover plays an important role in hurricane surge numerical modeling because of its impacts on the forcing (changes in wind momentum transfer to water column) and dissipation (bottom friction) mechanisms of storm surge. In this study, the hydrodynamic model ADCIRC was used to investigate predicted surge response in bays on the central and lower Texas coast using different land cover data sets: (1) Coastal Change Analysis Program for 1996, 2001, and 2006; (2) the National Land Cover Dataset for 1992, 2001, and 2006; and (3) the National Wetlands Inventory for 1993. Hypothetical storms were simulated with varying the storm track, forward speed, central pressure, and radius to maximum wind, totaling 140 simulations. Data set choice impacts the mean of maximum surges throughout the study area, and variability in the surge prediction due to land cover data set choice strongly depends on storm characteristics and geographical location of the bay in relation to storm track. Errors in surge estimation due to land cover choice are approximately 7% of the surge value, with change in surge prediction varying by as much as 1 m, depending on location and storm condition. Finally, the impact of land cover choice on the accuracy of simulating surges for Hurricane Bret in 1999 is evaluated.

World Environmental and Water Resources Congress 2010, 2010

Stream and watershed delineation based on Digital Elevation Models (DEM) is currently standard pr... more Stream and watershed delineation based on Digital Elevation Models (DEM) is currently standard practice in hydrologic studies. For the United States, DEMs with a horizontal resolution (ie, cell size) of 30 meters is publicly available from the National Elevation ...

Coastal Engineering Proceedings, 2011

Critical Transitions in Water and Environmental Resources Management, 2004

ArcGIS‐SWAT, a GIS interface for the Soil and Water Assessment Tool SWAT has been developed. It i... more ArcGIS‐SWAT, a GIS interface for the Soil and Water Assessment Tool SWAT has been developed. It is an ArcView 8.x extension that uses objects defined according to the ArcObjects standard, which conform to the Component Object Model (COM) protocol; and its code ...

World Water & Environmental Resources Congress 2003, 2003

In this paper, the use of the Arc Hydro data model for integrating hydrologic computer applicatio... more In this paper, the use of the Arc Hydro data model for integrating hydrologic computer applications is presented. Arc Hydro is a template for the storage of spatial and temporal hydrologic information, in which the different objects of the system are assembled together by virtue ...

ABSTRACT In this paper an effort was made to find an optimal route between any two given points s... more ABSTRACT In this paper an effort was made to find an optimal route between any two given points subject to some constraints. The constraints used in this study were related to the reliability of travel time. The reliability of travel time was defined based on the standard ...

Different flow routing approaches for large and small watersheds respond to the need of represent... more Different flow routing approaches for large and small watersheds respond to the need of representing different physical processes. The relative importance of advective with respect to hydrodynamic dispersive processes in the runoff flow is discussed. It is shown that in small watersheds hydrodynamic dispersion prevails, while in large watersheds the catchment geomorphology plays a dominant role. Consequently, in large watersheds,

A flow routing model in which the terrain is discretized into a set of interconnected square cell... more A flow routing model in which the terrain is discretized into a set of interconnected square cells, each of which is represented by a cascade of identical linear reservoirs or by a single linear reservoir, is presented. The advantages and disadvantages of using either option, in the light of results of applying the model to watersheds of different size and