N.American Land Data Assimilation System
North American Land Data Assimilation System
The North American Land Data Assimilation System (NLDAS) is a multi-model land modeling and assimilation system run in an uncoupled mode on a common one-eighth degree grid covering the Continental United States (CONUS) along with northern Mexico and southern Canada, and driven by atmospheric forcing. The NLDAS is a multi-institutional collaborative project that has comprised two major phases so far. Phase 1 (NLDAS-1, Mitchell et al., 2004 ) was initiated in 1999 with the purpose of establishing a land data assimilation framework that includes four land surface models (Figure 1), high-quality meteorological forcing, soil and vegetation parameters, and validation datasets. Phase 2 (NLDAS-2, Xia et al., 2012a; 2013a ) is an extension of the Phase 1 with the key purpose of producing quality-controlled long-term and near real-time products to support the national operational drought monitoring, prediction, and water resource information needs of various government agencies, academia, and enterprises.
Figure 1: Four Land Surface Models used in NLDAS-1 and NLDAS-2 (clockwise from upper-left: Noah, Mosaic, VIC, and SAC).
NLDAS Phase 2 provides retrospective and near real-time (with 3.5-day delay) high-resolution water and energy cycle products, such as surface fluxes, soil moisture, snow cover, and runoff/streamflow, along with the near-surface atmospheric and precipitation data sets used as forcing for the NLDAS land models. These products support drought monitoring, seasonal hydrological prediction, weather and climate forecasting, model evaluation, and land-hydrology research within various communities. To provide reliable NLDAS-2 products, we comprehensively evaluate many variables such as soil moisture (Xia et al., 2014; Xia et al., 2015a; 2015b; Cai et al., 2016), soil temperature (Xia et al., 2013b), total runoff/streamflow (Xia et al., 2012b; Cai et al., 2016), snow water equivalent (Livneh et al., 2010) and evapotranspiration (Peters-Lidard et al., 2011; Xia et al., 2015c; Nearing et al., 2016). The weaknesses and strengths of the NLDAS-2 system and individual model products are detailed in these studies. For more details, users can see the �Publications Tab� and the �Presentations Tab� of the EMC and the NASA NLDAS websites listed below.
The near real-time NLDAS-2 was implemented into NCEP operations in 2014 after a ~35-year (1979-2014) retrospective component of NLDAS-2. The advances and prospective of NLDAS including models and system upgrade (e.g., NLDAS v2.5, NLDAS v3.0, and beyond) are well described in a recently-released NCEP LDAS white paper (Ek et al., 2017). The real-time NLDAS v2.5 (Figure 2) is being tested and will be operationally implemented at NCEP soon.
Figure 2: Schematic Flow Chart for NLDAS v2.5
The NLDAS Phase 3 system, sponsored by the NOAA CPO (Climate Program Office), is a research-based system that is jointly developed by the NCEP and NASA NLDAS team. NLDAS-3 will use the NASA-developed Land Information System (LIS, Kumar et al., 2006) software framework, upgraded land surface models, and soil moisture and snowpack data assimilation processes. The SAC model (Burnash et al., 1973) will be replaced by the Noah-MP model (Niu et al., 2011), and the Mosaic (Koster and Suarez, 1994) model will be replaced by the NASA Catchment land surface model (CLSM, Koster et al., 2000). These new NLDAS models include groundwater physics, which were recently evaluated by Xia et al. (2017). The Noah (Chen et al., 1997) and VIC (Liang et al., 1994) models will also be upgraded to versions 3.6 and 4.1.2, respectively. The 39-year (1979-2017) retrospective run and some science-related experiments are being performed in NASA, and it is proposed to transition this system to NCEP to perform a R2O task sponsored by the Climate Testbed. The similarity between various LSMs from NLDAS-2 and from the research-based NLDAS-3 is analyzed and evaluated (Kumar et al., 2017). Comparison, evaluation, and benchmarking of the NLDAS-3 LSMs as compared to NLDAS-2 are also being performed as part of the NLDAS Science Testbed.
For additional information on the NLDAS, please see the websites listed below:
Burnash, R.J.C., R.L. Ferral, and R.A. McGuire, 1973: A generalized streamflow simulation system: Conceptual models for digital computer, technical report, Joint Fed.-State River Forecast Cent., U.S. Natl. Weather Serv. And Calif. Dep. Of Water Resour., Sacramento, Calif., United States.
Chen, F., Z. Janjic, and K. E. Mitchell, 1997: Impact of atmospheric surface layer parameterization in the new land surface scheme of the NCEP mesoscale Eta model. Boundary Layer Meteor., 85, 391-421.
Ek, M.B., C.D. Peters-Lidard, Y. Xia, D.M. Mocko, J. Meng, S.V. Kumar, H. Wei, J. Dong, A. Getirana, and S. Wang, 2017: Next Phase of the NCEP Unified Land Data Assimilation System (NULDAS): Vision, Requirements, and Implementation. The LDAS white paper, NCEP, College Park, Maryland, USA (see http://www.emc.ncep.noaa.gov/mmb/nldas/White_Paper_for_Next_Phase_LDAS_final.pdf)
Koster, R.D., and M. Suarez, 1994: The components of the SVAT scheme and their effects on a GCM's hydrological cycle. Adv. Water Resour., 17, 61-78.
Koster, R.D., M.J. Suarez, A. Ducharne, M. Stieglitz, and P. Kumar, 2000: A catchment-based approach to modeling land surface processes in a GCM, Part 1, Model structure. J. Geophys. Res., 105, 24,809-24,822.
Kumar, S.V., C.D. Peters-Lidard, Y. Tian, P.R. Houser, J. Geiger, S. Olden, L. Lighty, J.L. Eastman, B. Doty, P. Dirmeyer, J. Adams, K. Mitchell, E.F. Wood, and J. Sheffield, 2006: Land Information System - An Interoperable Framework for High Resolution Land Surface Modeling. Environmental Modelling & Software, 21, 1402-1415, doi:10.1016/j.envsoft.2005.07.004
Liang, X., D.P. Lettenmaier, E.F. Wood, and S.J. Burges, 1994: A simple hydrologically based model of land surface water and energy fluxes for GCMs. J. Geophys. Res., 99, 14,415-14,428.
Xia, Y., K. E. Mitchell, M. B. Ek, J. Sheffield, B. Cosgrove, E. Wood, L. Luo, C. Alonge, H. Wei, J. Meng, B. Livneh, D. Lettenmaier, V. Koren, Q. Duan, K. Mo, Y. Fan, and D. Mocko, 2012a: Continental Water and Energy Flux Analysis and Validation for North-American Land Data Assimilation System Project Phase 2, Part 1: Comparison Analysis of Multi-model Results. J. Geophys. Res-Atmos., 117, D03109, doi:10.1029/2011JD016048.
Xia, Y., K. E. Mitchell, M. B. Ek, B. Cosgrove, J. Sheffield, L. Luo, C. Alonge, H. Wei, J. Meng, B. Livneh, Q. Duan, and D. Lohmann, 2012b: Continental Water and Energy Flux Analysis and Validation for North-American Land Data Assimilation System Project Phase 2, Part 2: Comparison Analysis of Multi-model Results. J. Geophys. Res-Atmos., 117, D03109, doi:10.1029/2011JD016048.
Xia, Y., B. Cosgrove, M. B. Ek, J. Sheffield, L. Luo, E. F. Wood, K. Mo, and NLDAS team, 2013a: Overview of North American Land Data Assimilation System, Chapter 11 in Land Data Observation, Modeling and Assimilation, edited by Liang et al., pp333-377, World Scientific (http://www.worldscientific.com/doi/abs/10.1142/9789814472616_0011).
Xia, Y., M. Ek, J. Sheffield, B. Livneh, M. Huang, H. Wei, S. Feng, L. Luo, J. Meng, and E. Wood,, 2013b: Validation of Noah-simulated Soil temperature in the North American Land Data Assimilation System Phase 2. J. Climate App. Meteor., 52, 455-471.
Xia, Y., J. Sheffield, M.B. Ek, J. Dong, N. Chaney, H. Wei, J. Meng, and E.F. Wood, 2014: Evaluation of Multi-Model Simulated Soil Moisture in NLDAS-2. J. Hydrology, 512, 107-125.
Xia, Y., D.M. Mocko, M. Huang, B. Li, M. Rodell, K.E. Mitchell, X. Cai, and M.B. Ek, 2017: Comparison and Assessment of Three Advanced Land Surface Models in Simulating Terrestrial Water Storage Components over the United States. J. Hydrometeor., 18, 625-649, doi: http://dx.doi.org/10.1175/JHM-D-16-0112.1.