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Article

Abstract

Substantial evolution of Normalized Difference Vegetation Index (NVDI)-derived vegetation cover (Fg)exists in the southwestern United States and Mexico. The intraseasonal and wet-/dry-year fluctuations of Fgare linked to observed precipitation in the North American monsoon system (NAMS). The manner in whichthe spatial and temporal variability of Fg influences the land–atmosphere energy and moisture fluxes, andassociated likelihood of moist convection in the NAMS regions, is examined. For this, the regional climatemodel (RCM) is employed, with three different Fg boundary conditions to examine the influence ofintraseasonal and wet-/dry-year vegetation variability. Results show that a strong link exists between evaporativefraction (EF), surface temperature, and relative humidity in the boundary layer (BL), which isconsistent with a positive soil moisture feedback. However, contrary to expectations, higher Fg does notconsistently enhance EF across the NAMS region. This is because the low soil moisture values simulated bythe land surface model (LSM) yield high canopy resistance values throughout the monsoon season. As aresult, the experiment with the lowest Fg yields the greatest EF and precipitation in the NAMS region, andalso modulates regional atmospheric circulation that steers the track of tropical cyclones. In conclusion, thesimulated influence of vegetation on land–atmosphere exchanges depends strongly on the canopy stressindex parameterized in the LSM. Therefore, a reliable dataset, at appropriate scales, is needed to calibratetranspiration schemes and to assess simulated and realistic vegetation–atmosphere interactions in theNAMS region.

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