During early September 2011, as East Coast, Middle Atlantic, and New England states of the United States were still recovering from record flooding caused by Hurricane Irene, Tropical Storm (TS) Lee poured huge amounts of water on top of the already saturated Northeast and again inundated many inland cities. This extreme event can be viewed, analyzed, and studied with the North American Land Data Assimilation System Phase 2 (NLDAS-2) data. Examples of these data views are shown below.
As an animation of hourly precipitation from the NLDAS-2 Primary Forcing product (Figure 1) shows, from September 2-4, TS Lee produced heavy rains that saturated Louisiana, stalled off the coast, continuously expanded and intensified, and then slowly weakened and moved northeastward, spreading rain to Mississippi and Alabama. The animation also shows that, as Lee dissipated and moved northeastward, the rain system interacted with subtropical and middle-latitude systems and brought heavy rain to Virginia, Maryland, Pennsylvania, and New York. NLDAS-2 accumulated precipitation between 08Z Sep. 02 and 12Z Sep. 09 (Figure 2) shows three heavy rain centers, one over Louisiana and Mississippi, another over Alabama/Georgia/Tennessee, and another over Pennsylvania, with accumulated rainfall exceeding 10 inches (254 mm). “Z” refers to Coordinate Universal Time (UTC), also known as Greenwich Mean Time.
Figure 2. NLDAS-2 accumulated precipitation between 08Z Sep. 02 and 12Z Sep. 09, 2011. The boxes indicate the regions analyzed in the time series plots shown below.
Figure 3, with three overlying time series of NLDAS-2 hourly precipitation for the three heavy rain regions depicted by the boxes in Figure 2, (92W ~ 89W, 29N ~ 31N), (87W ~ 84W, 34N ~ 36N), and (77.5W ~ 75.5, 39N ~ 42N), clearly shows when the heaviest rain started and ended. These time series display area-averaged hourly rain rate for each region.
Figure 3. Time series of NLDAS-2 hourly precipitation for the three heavy rain regions (92W ~ 89W, 29N ~ 31N – parts of Louisiana/Mississippi), (87W ~ 84W, 34N ~ 36N – parts of Alabama/Georgia/Tennessee), and (77.5W ~ 75.5, 39N ~ 42N – parts of Pennsylvania).
An animation of surface (0 – 10 cm) soil moisture data generated by the NLDAS-2 Mosaic model (Figure 4) shows the soil moisture increasing as rainfall passed over the affected areas. Figure 5 is the combined time series of NLDAS-2 precipitation and soil moisture for the three heavy rain regions. Each set of time series shows that soil moisture was increasing with strong rainfall and reached its peak after the corresponding rainfall peak. As the rainfall decreased, soil moisture still remained high, with a very slow decrease.
Animation of soil moisture (0 – 10 cm) of NLDAS-2 Mosaic model, from 08Z Sep. 2 to 12Z Sep. 9, 2011, generated by the Giovanni NLDAS hourly portal
Figure 5. Time series of NLDAS-2 precipitation and soil moisture for the three heavy rain regions. The persistence of high soil moisture content after the heavy rains from TS Lee contributed to flash flooding in many areas caused by subsequent storms in the South and Northeast.
NLDAS, with high spatial and temporal resolutions (0.125° x 0.125° hourly) and various water- and energy-related variables (precipitation, soil moisture, evapotranspiration, latent heat, etc.) is an excellent data source for supporting water and energy cycle investigations. NLDAS can also provide data for case studies of extreme events, such as Tropical Storm Lee, Hurricane Irene, the July 2011 heat wave in the United States, and the current drought conditions in Texas. NLDAS data can be accessed from GES DISC Hydrology Data Holdings Portal
To further facilitate access and use of the data, NLDAS has been made available via the Giovanni NLDAS hourly portal
. The Giovanni portal provides a simple and intuitive way to visualize, analyze, and intercompare NLDAS data without having to download the data.
Images courtesy NASA Goddard Earth Sciences Data and Information Services Center (GES DISC) and Hydrological Sciences Branch, Goddard Space Flight Center.
The GES DISC is a NASA earth science data center, part of the NASA Earth Science Data and Information System (ESDIS) Project.