Technical Abstract: Our goal was to evaluate the effects of a broad-scale change in vegetation from grasslands in the mid-1800s to shrublands in the late 1900’s on weather and climate. Vegetation and soil maps for 1858 and 1998 were used to run a fully coupled atmospheric-biospheric model for two times during the growing season. Model simulations were conducted for the Jornada Experimental Range, a site located in the northern Chihuahuan Desert. Overall, the shift from a grass-dominated vegetation cover in 1858 to shrub-dominated cover in 1998 led to a small change in sensible heat and a pronounced increase in latent heat. Changes in surface fluxes and the associated changes in near-surface temperature were spatially heterogeneous: conversion from grass to mesquite cools the near-surface atmosphere and from grass to creosotebush warms it. Albedo was the dominant parameter controlling the energy budget. The shift from grassland to shrubland observed in this area led to complex interactions between biophysical and physiological characteristics of the land and surface fluxes. These results clearly demonstrate that vegetation itself is a weather and climate variable as it significantly influences temperature and humidity, which then feedbacks to and affects the vegetation.