Leveraging deep roots to elucidate the connection between subsurface moisture and the atmosphere

Abstract:

Roots allow plants to take up subsurface moisture which is subsequently lost to the atmosphere through stomata. For this reason, they are crucial pathways of moisture and hydrologic memory. However, detailed representation of deep roots is largely excluded from most land-atmosphere modeling infrastructures. Deep roots are important in regions with seasonal rainfall and accessible groundwater. Plants access water from the capillary fringe when surface moisture (supplied by precipitation) is insufficient. This allows them to maintain productivity even when surface conditions are dry. Moreover, subsurface moisture variability occurs on long timescales (annual to interannual), whereas variability of surface processes (such as precipitation) occurs on shorter timescales, with important daily and seasonal components. Thus, surface and subsurface conditions can be decoupled but linked by plant roots. This study evaluates the effects of including deep roots in the Noah-Multiparameterization (Noah-MP) land surface model. The model is run for a small region in South America and changes in surface fluxes such as evapotranspiration are analyzed. Model output is compared with tower observations from the Large-Scale Atmosphere-Biosphere Experiment in Amazonia (LBA) as well as water table depth observations in the region. Deep soil moisture observations are also examined to determine timescales of variability at differing depths. This research is critical for more realistic representation of the soil-plant-atmosphere system in numerical modeling frameworks. As the land surface is an important component of atmospheric predictability, inclusion of deep roots can potentially contribute to improved simulations of atmospheric processes.