DIAGNOSTICS OF LAND-SURFACE SPATIAL VARIABILITY AND WATER-VAPOR FLUX

To assess the spatial variability of the water vapor (i.e., latent hea t) flux LE, it is convenient to scale it with its equilibrium analog L E(e). From an analysis of the data from the First International Satell ite Land Surface Climatology Project (ISLSCP) Field Experiment, or FIF E, the spatial distribution of daily values of this dimensionless evap oration, alpha = LE/LE(e), was found to be strongly related to the dis tributions of soil moisture and of the state of the vegetation. Howeve r, the relative strengths of these relationships depended on the soil moisture content and on its distribution. When the mean soil moisture content SM was high, in excess of about 27%, the distribution of evapo ration was quite uniform regardless of the vegetation uniformity. In t he intermediate range, with 20 < SM < 27%, both soil moisture and vege tation contributed to the spatial distribution of alpha. This distribu tion was controlled by the vegetation, when the soil moisture was unif orm; under nonuniform soil moisture conditions, however, soil moisture exerted the major control. For SM < 20%, soil moisture normally was n onuniform, and it was found to hold the primary control of the spatial variation of alpha. The daily distribution of soil moisture content w as largely independent from that of the state of the vegetation, due t o the different timescales involved.