ARS | Publication request: Observed relation between evapotranspiration and soil moisture in the North American monsoon region 1985

Submitted to: Geophysical Research Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 16, 2008
Publication Date: October 26, 2008
Citation: Vivoni, E.R., Moreno, H.A., Mascaro, G., Rodriguez, J.C., Watts, C.J., Garatuza-Payan, J., Scott, R.L. 2008. Observed relation between evapotranspiration and soil moisture in the North American monsoon region. Geophysical Research Letters. 35, L22403. doi:10.1029/ 2008GL036001.

Interpretive Summary: Evapotranspiration (ET) is a process that links the surface water, energy and carbon balances with the physiological activity of plants, especially for water-limited ecosystems. In the southwest U.S. and northwest Mexico, the strong seasonal grouping of optimal growing conditions and abundant rainfall during the North American monsoon leads to regional ecosystem responses in terms of vegetation greenness. While the influence of the greening of monsoon-dominated ecosystems on the surface energy exchange has been recognized, little is known of its effects on the relationship between soil moisture and ET. In this study, we utilize a set of multi-year observations within the monsoon region to determine the relationship between soil moisture and ET and how it changes in response to vegetation activity. This analysis can be used to improve the understanding and prediction of land-atmosphere interactions in the water-limited ecosystems of the monsoon region.

Technical Abstract: Soil moisture control on evapotranspiration is poorly understood in ecosystems experiencing seasonal greening. In this study, we utilize a set of multi-year observations at four eddy covariance sites along a latitudinal gradient in vegetation greening to infer the ET-' relation during the North American monsoon. Results reveal significant seasonal, interannual and ecosystem variations in the observed ET-' relation directly linked to vegetation greening. In particular, monsoon-dominated ecosystems adjust their ET-' relation, through changes in unstressed ET and plant stress threshold, to cope with differences in water availability. Comparisons of the observed relations to the North American Regional Reanalysis dataset reveal large biases that increase where vegetation greening is more significant. The analysis presented here can be used to guide improvements in land surface model parameterization in water-limited ecosystems.