Browsing by Author "Barros, Ana"

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Open Access
The Integrated Precipitation and Hydrology Experiment - Hydrologic Applications for the Southeast US (IPHEx-H4SE) Part III: High-Resolution Ensemble Rainfall Products
(2014-01-14) Barros, Ana
The first stage of the Integrated Precipitation and Hydrology Experiment (IPHEX) includes the 37 development of quality-controlled data sets of different hydrometeorological and landscape attributes at high spatial and temporal resolutions (respectively 1km×1km and 1 hour). These data sets will facilitate the intercomparison of hydrological models and provide support to the ground validation campaign of GPM over the Southern Appalachian region. In the present report we focus on the spatial downscaling of Stage IV precipitation data (Baldwin and Mitchell, 1996; Lin and Mitchell, 2005; see online at http://www.emc.ncep.noaa.gov/mmb/ylin/pcpanl/stage4) from 4km to 1km resolution for the period 2007-2011. First, we describe the 44 methodologies utilized to develop the various QPE products and in particular the use of modified fractal downscaling methodologies, which conserve the spatial structure of the coarse resolution while enhancing sub-grid scale variability. Three different (hourly, 1km2) precipitation datasets were produced: 1) Stage IV bilinear interpolated fields; 2) Stage IV fractal downscaled fields using (with 50 ensemble realizations for each hour); and 3) Stage IV fractal downscaled fields using a transient (with 50 ensemble realizations for each hour). The realizations 50 provided for each hour in the fractal downscaled cases should be particularly useful to ensemble hydrologic applications and analysis of uncertainty propagation. The performance of the downscaled QPE (Quantitative Precipitation Estimation) products is subsequently evaluated for selected headwater basins in the Southern Appalachians for individual events and for 5 year continuous simulations in three watersheds, which are intended to highlight that, in long-term hydrological modeling and prediction and the precipitation forcing is de facto not accurate, the uncertainty varies in time, and this is further modulated by storage, evapotranspiration and subsurface flow in the hydrological model, a highly nonlinear system. The results show improved performance of an uncalibrated hydrological model using the downscaled Stage IV product using modified fractal interpolation methods as compared to bilinear interpolation. Finally, a survey of basic skill metrics indicates that current precipitation estimates are significantly poor in the inner mountain region of the Southern Appalachians where NEXRAD (Next Generation Radar Data) data used to inform the Stage IV product is compromised, which is expected in regions of complex terrain.
Open Access
The Integrated Precipitation and Hydrology Experiment - Hydrologic Applications for the Southeast US (IPHEx-H4SE). Part II: Atmospheric Forcing and Topographic Corrections
(2014-01-02) Barros, Ana
In order to prepare atmospheric forcing data sets to drive the hydrologic models at high spatial resolution, it is necessary to apply appropriate downscale methods and bias correction schemes to the coarse reanalysis products. In this manuscript, first we describe the methodology to derive a high-resolution (1×1 km2, hourly) atmospheric forcing data set from 3-hr NARR (North American Regional Reanalysis) products originally at 32×32km resolution, and second we illustrate the value and utility of the downscaled products to drive hydrologic models offline through analysis of a long-term (5-year) continuous simulation of water and energy budgets in the Southern Appalachians against flux tower observations. The IPHEx-H4SE atmospheric forcing data set includes elevation corrected air temperature and lapse rate, specific humidity, 46 friction velocity, surface layer winds, incoming longwave radiation, and topographically and cloudiness corrected incoming shortwave radiation that enable simulating water and energy fluxes from diurnal to annual time-scales, and for extreme events. Although the 5-year simulation presented here was conducted with a randomly selected rainfall product among those recommended in the companion report ( EPL-2013-H4SE-3) without re-initialization or data assimilation, and therefore does not represent an optimal simulation with the hydrological model but rather a baseline control simulation that integrates and propagates the uncertainty in all forcing data sets, the results clearly illustrate the benefit of using the bias corrected NARR atmospheric forcing fields made available here.
Open Access
The Integrated Precipitation and Hydrology Experiment. Part I: Quality High-Resolution Landscape Attributes Datasets.
(2014-01-02) Barros, Ana
Quality-controlled datasets at high spatial and temporal resolution (1km×1km, hourly) for a five year period (2007-2011) were developed for the IPHEx-H4SE project (Integrated Precipitation and Hydrology Experiment – Hydrologic Applications for the Southeast US), to support a common platform for the intercomparison and evaluation of hydrological models using various QPE (Quantitative Precipitation Estimation) products in an operational setting in coordination with the Intense Observing Period of the IPHEx field campaign in April-July 2014 (IPHEX2014). The data sets span four major river basins in the Southeast US with headwaters in the Southern Appalachians: the Upper Tennessee, the Savannah, the Catawba-Sandee, and the Yadkin-Peedee. Quality control and post processing were conducted to correct and improve the hydrometeorological forcing data sets. In this manuscript, we present the procedures and methodology to develop land surface broadband albedo, broadband emissivity, leaf area index (LAI), and fractional vegetation coverage (CV) at high tempo-spatial resolution based on the MODIS (Moderate Resolution Imaging Spectroradiometer) products. Quality control, gap filling and temporal filtering were performed to correct and improve the landscape attributes derived from MODIS products mainly due to cloud or snow or foggy contamination and limitations of retrieval algorithms. The datasets were utilized to specify land attributes in a distributed hydrological model (3D-LSHM) in the Pigeon River Basin, a headwater basin of one of the four major river basins in the Southeast of interest in the IPHEx-H4SE project. Results from fiveyear continuous simulations from 2007 to 2011 are used illustrate the importance of the quality landscape attributes affect the regional water partitioning at basin scale and thus the overall the hydrologic regime.