The Integrated Precipitation and Hydrology Experiment – Hydrologic Applications for the Southeast US (IPHEX-H4SE) Part IV: High-Resolution Enhanced StageIV-Raingauge Combined Precipitation Product

The IPHEx-QPE-1.1 V1 consists of 10 years (2008-2017) hourly rainfall intensity at 1 km2 resolution over the core region of the IPHEX domain, centered in the Pigeon River basin in The Southern Appalachian Mountains in North Carolina. Two data sets are the basis of the IPHEx RQPE: 1) the national combined radar-raingauge StageIV product (hourly, 16km2 spatial resolution); and 2) independent raingauge measurements from a network of high elevation raingauges in the region installed in support of NASA TRMM and GPM ground validation (GV) activities. First, fractal downscaling is applied to the Stage IV product to bring it to the 1 km2 resolution (STIVD). Regional event bias correction is then applied to the hourly downscaled StageIV product (STIVDB), followed by ordinary kriging (OK) to distribute errors among STIVDB and co-located raingauge observations to generate the final product STIVDBK. Evaluation of STIVDBK indicates that cumulative rainfall errors are as small as 1-3% while STIVD data have errors about 10-15%. However, assessment against the 10-year raingauge climatology revealed that significant biases at specific times-of-the day remain in STIVDBK, which also exhibit seasonality. These biases reflect radar operations and viewing geometry that have preferential impact for shallow precipitation systems and isolated intense convection. Consequently, light and convective rainfall corrections were applied to derive the final product (STIVDBKC) that is IPHEx-QPE-1.1 V. Performance metrics such as Threat Score (TS) and Heidke Skill Scores (HSS) are on average > 0.8 and close to 1 respectively for various rainfall thresholds over the 10-year period, and > 0.5 at the event time-scale(hourly). The root mean square error (RMSE) at the gauges is below 0.1 mm/hr and 0.5% for seasonal-scale accumulations. Evaluation against an independent disdrometer data set consisting of disdrometers at various locations indicates large overestimation errors (~30%) in the inner mountain region and at low elevations during the IPHEX IOP. This is in part attributed to the lack of low elevation raingauges and the overshooting of both NEXRAD radars that contribute to the Stage IV product over the region, and challenges in handling isolated convection. Work toward developing the forthcoming IPHEX-QPE 1.2 V2 reference product will focus on correcting low elevation rainfall using information from low elevation disdrometers and from NWP model simulations. Spatial intermittency will be addressed through a modified fractal downscaling methodology conditional on the rain support (i.e. the perimeter) of precipitation clusters in StageIV.

This product is generated with spatial and temporal resolution of 0.01degree and 1 hour using the same fractal downscaling techniques used in Nogueira and Barros, 2015, and bias correction and kriging. Data files are in ASCII format, each ASCII file has 104 lines: the first 4 lines are data header and the following 100 lines contain rainfall intensity data (in mm) in a matrix of 100 columns by 100 rows.

Spatial resolution: 0.01 degree.
Temporal resolution: 1 hour accumulation.
Units: mm
Spatial coverage: 35N to 36N and 83.6W to 82.6W
Upper left corner pixel (1, 1) – (35.005, -83.595)
Time period: 2008 – 2017
Missing data - 'NaN'

File naming convention: ST4DBKC_<yyyymmddhh>.txt
yyyymmddhh - year month day hour - ending time of the accumulation period. 

Missing Period:
2008042007, 2008110200-2008110223, 2008031400, 2008031500, 2008031600, 2008031700, 2008031900, 2008032000, 2008032100, 2008032200, 2008032300, 2008032400, 2008032500, 2008032518-2008032600, 2009100216-2009100300, 2012012100-2012012109.

Documentation: Merging Raingauge and Radar Measurements using Fractal Downscaling and Kriging\The IPHEx QPE+Rainfall Product

References:
Nogueira, M., and Barros, A.P., 2015: Transient Stochastic Downscaling of Quantitative Precipitation Estimates for Hydrological Applications.  J. Hydrology, No. 529, 1407-1421. DoI:10.1016/j.jhydrol.2015.08.041.
Liao, M. and Barros, A.P, 2019: The Integrated Precipitation and Hydrology Experiment – Hydrologic Applications for the Southeast US (IPHEX-H4SE). Part IV: High-Resolution Enhanced StageIV-Raingauge Combined Precipitation Product.  Duke University, Environmental Physics Laboratory, Report EPL-2019-IPHEX-H4SE-4, 28pp.

These data files are also made available through the Global Hydrology Resource Center. 
Data Citation: Liao, Mochi and Ana P Barros. 2019. GPM Ground Validation Reference Precipitation IPHEx [indicate subset used]. Dataset available online from the NASA Global Hydrology Resource Center DAAC, Huntsville, Alabama, U.S.A.
DOI: http://dx.doi.org/10.5067/GPMGV/IPHEX/GAUGES/DATA401