Modeling the ecohydrological role of aspect-controlled radiation on tree-grass-shrub coexistence in a semiarid climate

Xiaochi Zhou, Erkan Istanbulluoglu, Enrique Vivoni

Research output: Contribution to journalArticlepeer-review

50 Scopus citations


In this study, an ecohydrological Cellular Automata Tree-Grass-Shrub Simulator (CATGraSS) is presented. CATGraSS is driven by pulses of rainfall and daily solar radiation. In the model, each cell can hold a single plant type (tree, shrub, tree seedlings, shrub seedlings, grass) or can be bare soil. Plant competition is modeled explicitly by keeping track of mortality and establishment of plants, both calculated probabilistically based on soil moisture stress. Topographic influence on incoming shortwave radiation is treated explicitly, which leads to spatial variations in potential evapotranspiration and soil moisture over storm and interstorm time scales, and plant distribution over annual time scales. The model is implemented in a small basin (3.3 km2) in central New Mexico, USA, where north facing slopes are characterized by a juniper pine and grass savanna, and south facing slopes by creosotebush shrubs and grasses. Representing the current climate by a seasonal-varying Poisson rectangular pulse rainfall model, CATGraSS is calibrated against the existing plant patterns in the study catchment. The model is then used in a series of numerical experiments. CATGraSS is first run on flat terrain to examine the role of topography on plant patterns. Consistent with our observation in the region, this "flat run" gave a shrubland ecosystem with scattered grasses and trees. Model sensitivity to rainfall is investigated in a limited number of simulations by altering rainfall frequency-magnitude statistics, and seasonality. The sensitivity runs suggest that changes in the storm characteristics could lead to a dramatic reorganization of the plant composition on topography in central New Mexico. CATGraSS results underscore the importance of solar irradiance in determining vegetation composition over complex terrain under a water-limited ecosystem.

Original languageEnglish (US)
Pages (from-to)2872-2895
Number of pages24
JournalWater Resources Research
Issue number5
StatePublished - May 2013


  • cellular automata
  • ecohydrology
  • solar radiation
  • topography

ASJC Scopus subject areas

  • Water Science and Technology


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