PNNL

Abstract

Recent studies have shown that direct root water uptake from the capillary fringe and groundwater can lead to transpiration that is greater than precipitation by a factor of 10 in hyper-arid conditions. In this study, a dynamic root water uptake scheme in the Noah-MP land surface model has been coupled to the Weather Research and Forecasting (WRF) model to investigate its impact on the surface climate variables and land-atmosphere interactions. Different from the traditional big-leaf approach that parameterizes transpiration as function of soil moisture states, the root water uptake scheme explicitly represents plant water storage and its impact on transpiration. The dynamic root scheme shows promising results by alleviating biases in the simulated gross primary product, leaf area index, precipitation, temperature, surface energy fluxes, and soil moisture. Two different mechanisms through which root affects land-atmosphere coupling have been identified. Over the transitional climate zone between the dry and wet climate, the dynamic root affects surface climate and land-atmosphere coupling mainly through changes in soil moisture through hydraulic redistribution by plant root system. Over the energy-limited mesic zone, the dynamic root affects regional land-atmosphere coupling mainly through changes in carbon allocation. Deficiency in evapotranspiration partitioning is identified, underscoring the need for future improvement.