Effects of long-term rainfall variability on evapotranspiration and soil water distribution in the Chihuahuan Desert: A modeling analysis

摘要: We used the patch arid land simulator (PALS-FT) – a simple, mechanistic ecosystem model to explore long-term variation in evapotranspiration (ET) as function of variability rainfall and plant functional type (FT) at warm desert site southern New Mexico. PALS-FT predicts soil evaporation transpiration canopy composed five principal FTs: annuals, perennial forbs, C4 grasses, sub-shrubs, evergreen shrubs. For each FT, fractional contribution depends upon phenological activity cover well daily leaf stomatal conductance, which is water potential, calculated from root-weighted potential six layers. Simulations loss two community types (grass- vs. shrub-dominated) were carried out for Jornada Basin, Mexico, using 100 years precipitation data (1891–1990). In order emphasize associated with fundamental differences FT composition between communities, seasonal patterns perennials held constant year year. Because relative amount winter summer annual species highly variable this ecosystem, we examined their influence on predictions ET by allowing be variable, fixed, or absent. Over entire 100-yr period, total correlated both types, although T E alone are less strongly rainfall, nearly 3 times greater than 2 (CV = 35%). Water use shows relatively high similarity grass- shrub-dominated average T/ET 34% communities. However, based year-by-year comparison was significantly grass-dominated community, reflecting fact that over long term more half rain occurs slightly efficiently (T?E) C4-grass shrub found some resulted much given Percent lost (T/ET) suggests while there general trend toward increased extremely simulation, especially normal below amounts (T/ET values range 1 58% 6 60% site). These suggest because shallow distribution water, little opportunity vertical partitioning resource differential rooting depths FTs, contrast two-layer hypothesis Walter (1971). may avoid competition keying particular `windows' moisture availability via phenologies. very average, T, E, when The results our simulations help reconcile disparate conclusions drawn experimental studies about evapotranspiration, primarily revealing great year-to-year possible.