Drought Depiction in the Noah-MP (Multiphysics) Land Surface Model in the North American Land Data Assimilation System (NLDAS)

The next phase of the North American Land Data Assimilation System (NLDAS) will contain new and upgraded land-surface models, with advanced physics and representation of physical processes not contained in the current NLDAS LSMs. NLDAS is a collaboration project among NOAA/EMC, NASA/GSFC, and other governmental agencies and universities; it runs operationally at NOAA, and produces a drought monitor with a daily update. The current operational system (NLDAS Phase 2) runs four different LSMs; an ensemble mean of these LSMs is also available on the drought monitor webpage. For the next phase, these LSMs either will be upgraded to their latest versions or replaced with state-of-the-art LSMs that are being updated with new physical processes and are used in modern modeling systems. One such new LSM is Noah-MP (Multi-Physics), which was jointly developed by the Univ. of Texas at Austin, NCAR, and NCEP. Noah-MP is included in the NCAR Weather Research and Forecasting (WRF) model as well as the NOAA/National Water Center’s National Water Model. Along with the other upgraded and new LSMs for the next phase of NLDAS, Noah-MP has been integrated into the NASA-developed Land Information System (LIS) software framework. Noah-MP includes numerous physics options, including a representation of groundwater as well as a dynamic vegetation option. Simulations using NLDAS-2 forcing from 1979 to 2017 were run with four of the new/upgraded LSMs in LIS. Drought percentiles were calculated and compared to the four current operational NLDAS-2 LSMs, including their ensemble means, as well as against drought extent from the U.S. Drought Monitor. Several historical severe drought case studies were examined in detail, including depictions of simulated soil moisture, groundwater, and terrestrial water storage. Using the various physics options in Noah-MP, several additional simulations were conducted, testing the ability of Noah-MP to represent these droughts when changing the groundwater scheme, turning on or off the dynamic vegetation module, and modifying other physics options. Comparisons are also made to observations of soil moisture, vegetation (LAI/greenness), and streamflow. The evaluations are performed using the NASA-developed Land Verification Toolkit (LVT) software within the NLDAS Science Testbed. Recommendations of optimal Noah-MP physics options for representing the depiction of drought for the next phase of NLDAS will be presented.