A modeling approach reveals differences in evapotranspiration and its partitioning in two semiarid ecosystems in Northwest Mexico

Abstract

Seasonal vegetation changes during the North American monsoon play a major role in modifying water, energy, and momentum fluxes. Nevertheless, most models parameterize plants as a static component or with averaged seasonal variations that ignore interannual differences and their potential impact on evapotranspiration (ET) and its components. Here vegetation parameters derived from remote sensing data were coupled with a hydrologic model at two eddy covariance (EC) sites with observations spanning multiple summers. Sinaloan thornscrub (ST) and Madrean woodland (MW) sites, arranged at intermediate and high elevations along mountain fronts in northwest Mexico, occupy specific niches related to climate conditions and water availability that are poorly understood. We found that simulations with a dynamic representation of vegetation greening tracked well the seasonal evolution of observed ET and soil moisture (SM). A switch in the dominant component of ET from soil evaporation (E) to plant transpiration (T) was observed for each ecosystem depending on the timing and magnitude of vegetation greening that is directly tied to rainfall characteristics. Differences in vegetation greening at the ST and MW sites lead to a dominance of transpiration at ST (T/ET 5 57%), but evaporation-dominant conditions at MW (T/ET 5 19%). Peak transpiration occurred at 5 and 20 days after the full canopy development in the ST and MW sites, respectively. These results indicate that evapotranspiration timing and partitioning varies considerably in the two studied ecosystems in accordance with different modes of vegetation greening. Intermediateelevation ecosystems follow an intensive water use strategy with a rapid and robust transpiration response to water availability. In contrast, higher elevation sites have delayed and attenuated transpiration, suggesting an extensive water use strategy persisting beyond the North American monsoon.

Hyperresolution hydrologic modeling in a regional watershed and its interpretation using empirical orthogonal functions

“…The RSM basin represents a challenging study site for hyperresolution simulations due to its complex hydrologic response resulting from the interaction of heterogeneous terrain and soil properties with a seasonal, semiarid climate dominated by the North American monsoon that dramatically affects ecosystem properties. Previously, tRIBS has been applied in this region to small catchments (<100 km 2 ) during summer periods [53,61,81,89], demonstrating the potential of these hyperresolution simulations to capture the spatiotemporal variability of the hydrologic processes. Building upon these previous works, we extend the spatial scale of the simulations up to a regional watershed and their duration from the summer months to a multiyear period.…”

Influence of initial soil moisture and vegetation conditions on monsoon precipitation events in northwest México

“…The NAM region is characterized by a strong seasonality in vegetation greenness and biomass that is closely linked to interannual changes in precipitation (Forzieri et al, 2011(Forzieri et al, , 2014. The seasonal progression of vegetation greening has been quantified using a number of different remote sensing platforms and incorporated into modeling studies (e.g., Matsui et al, 2005;Watts et al, 2007;Castro et al, 2009;Vivoni, 2012;Tang et al, 2012;Méndez-Barroso et al, 2014). However, the intraseasonal variations of vegetation greenness and their link to available soil moisture have not been studied extensively, despite their importance for setting the land surface conditions prior to the occurrence of individual storm events.…”

Modeling the distributed effects of forest thinning on the long-term water balance and streamflow extremes for a semi-arid basin in the southwestern US

“…The below-canopy distribution of the vertical wind speed follows a decay-exponential function depending on the biometric features of the forest determined by projected leaf area index (LAI) and vegetation height (see Appendix B) (Sypka and Starzak, 2013;Yi, 2008). Evapotranspiration partitioning depends on the ability of E soil and T to extract soil water from the surface and root zones and is determined by constant model stress factors (Ivanov et al, 2004a;Mendez-Barroso et al, 2013). A kinematic approximation for unsaturated flow is used to compute infiltration and propagate soil moisture fronts in an anisotropic soil column according to an exponentially decaying hydraulic conductivity condition (Cabral et al, 1992;Garrote and Bras, 1995;Ivanov et al, 2004a).…”

“…Vegetation fraction and LAI values for non-ponderosa covered areas were extracted from the 2006 Landfire products (http://landfire.gov/) and derived from existing literature (Mendez-Barroso et al, 2013;Mitchell et al, 2004), respectively. Free throughfall coefficient (p), which accounts for the fraction of rainfall not captured by plants, and canopy capacity (S), were derived from the expressions B3 and B4 (Carlyle-Moses and Price, 2007;Mendez-Barroso et al, 2013;Pitman, 1989):…”