The Role of Land-Atmosphere Interactions on Droughts [INVITED]

Improving the representations of land-atmosphere interactions is important to correctly simulate the regional and global water cycle. The southwestern US is projected to experience more intense and prolonged drought conditions in the future due to global warming. To improve our ability to predict droughts, the Variable Infiltration Capacity (VIC) and Community Land Model (CLM) are being extended to include several components such as hydraulic redistribution and groundwater table dynamics that are important for simulating surface and subsurface processes in semi-arid regions. Simulations have been performed to assess the impacts of groundwater table dynamics on regional climate. In most areas in the US, groundwater table dynamics increases surface soil moisture at the expense of the subsurface, except in regions with very shallow groundwater table. The change in soil water partitioning between the surface and subsurface is found to strongly correlate with the partitioning of surface sensible and latent heat fluxes. The evaporative fraction is generally higher during summer when groundwater table dynamics is included. This is accompanied by increased cloudiness, reduced diurnal temperature range, cooler surface temperature, and increased cloud top height. By altering the groundwater table depth, land use change and groundwater withdrawal can alter land surface response and feedback to the climate system.