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- Creators: Vivoni, Enrique R
Description
Land surface fluxes of energy and mass developed over heterogeneous mountain landscapes are fundamental to atmospheric processes. However, due to their high complexity and the lack of spatial observations, land surface processes and land-atmosphere interactions are not fully understood in mountain regions. This thesis investigates land surface processes and their impact on convective precipitation by conducting numerical modeling experiments at multiple scales over the North American Monsoon (NAM) region. Specifically, the following scientific questions are addressed: (1) how do land surface conditions evolve during the monsoon season, and what are their main controls?, (2) how do the diurnal cycles of surface energy fluxes vary during the monsoon season for the major ecosystems?, and (3) what are the impacts of surface soil moisture and vegetation condition on convective precipitation?
Hydrologic simulation using the TIN-based Real-time Integrated Basin Simulator (tRIBS) is firstly carried out to examine the seasonal evolution of land surface conditions. Results reveal that the spatial heterogeneity of land surface temperature and soil moisture increases dramatically with the onset of monsoon, which is related to seasonal changes in topographic and vegetation controls. Similar results are found at regional basin scale using the uncoupled WRF-Hydro model. Meanwhile, the diurnal cycles of surface energy fluxes show large variation between the major ecosystems. Differences in both the peak magnitude and peak timing of plant transpiration induce mesoscale heterogeneity in land surface conditions. Lastly, this dissertation examines the upscale effect of land surface heterogeneity on atmospheric condition through fully-coupled WRF-Hydro simulations. A series of process-based experiments were conducted to identify the pathways of soil moisture-rainfall feedback mechanism over the NAM region. While modeling experiments confirm the existence of positive soil moisture/vegetation-rainfall feedback, their exact pathways are slightly different. Interactions between soil moisture, vegetation cover, and rainfall through a series of land surface and atmospheric boundary layer processes highlight the strong land-atmosphere coupling in the NAM region, and have important implications on convective rainfall prediction. Overall, this dissertation advances the study of complex land surface processes over the NAM region, and made important contributions in linking complex hydrologic, ecologic and atmospheric processes through numerical modeling.
Hydrologic simulation using the TIN-based Real-time Integrated Basin Simulator (tRIBS) is firstly carried out to examine the seasonal evolution of land surface conditions. Results reveal that the spatial heterogeneity of land surface temperature and soil moisture increases dramatically with the onset of monsoon, which is related to seasonal changes in topographic and vegetation controls. Similar results are found at regional basin scale using the uncoupled WRF-Hydro model. Meanwhile, the diurnal cycles of surface energy fluxes show large variation between the major ecosystems. Differences in both the peak magnitude and peak timing of plant transpiration induce mesoscale heterogeneity in land surface conditions. Lastly, this dissertation examines the upscale effect of land surface heterogeneity on atmospheric condition through fully-coupled WRF-Hydro simulations. A series of process-based experiments were conducted to identify the pathways of soil moisture-rainfall feedback mechanism over the NAM region. While modeling experiments confirm the existence of positive soil moisture/vegetation-rainfall feedback, their exact pathways are slightly different. Interactions between soil moisture, vegetation cover, and rainfall through a series of land surface and atmospheric boundary layer processes highlight the strong land-atmosphere coupling in the NAM region, and have important implications on convective rainfall prediction. Overall, this dissertation advances the study of complex land surface processes over the NAM region, and made important contributions in linking complex hydrologic, ecologic and atmospheric processes through numerical modeling.
ContributorsXiang, Tiantian (Author) / Vivoni, Enrique R (Thesis advisor) / Gochis, David J (Committee member) / Huang, Huei-Ping (Committee member) / Mascaro, Giuseppe (Committee member) / Wang, Zhihua (Committee member) / Arizona State University (Publisher)
Created2016
Description
Ecohydrological responses to rainfall in the North American monsoon (NAM) region lead to complex surface-atmosphere interactions. In early summer, it is expected that soil properties and topography act as primary controls in hydrologic processes. Under the presence of strongly dynamic ecosystems, catchment hydrology is expected to vary substantially in comparison to other semiarid areas, affecting our understanding of ecohydrological processes and the parameterization of predictive models. A large impediment toward making progress in this field is the lack of spatially extensive observational data. As a result, it is critical to integrate numerical models, remote sensing observations and ground data to understand and predict ecohydrological dynamics in space and time, including soil moisture, evapotranspiration and runoff generation dynamics. In this thesis, a set of novel ecohydrological simulations that integrate remote sensing and ground observations were conducted at three spatial scales in a semiarid river basin in northern Sonora, Mexico. First, single site simulations spanning several summers were carried out in two contrasting mountain ecosystems to predict evapotranspiration partitioning. Second, a catchment-scale simulation was conducted to evaluate the effects of spatially-variable soil thickness and textural properties on water fluxes and states during one monsoon season. Finally, a river basin modeling effort spanning seven years was applied to understand interannual variability in ecohydrological dynamics. Results indicated that ecohydrological simulations with a dynamic representation of vegetation greening tracked well the seasonal evolution of observed evapotranspiration and soil moisture at two measurement locations. A switch in the dominant component of evapotranspiration from soil evaporation to plant transpiration was observed for each ecosystem, depending on the timing and magnitude of vegetation greening. Furthermore, spatially variable soil thickness affects subsurface flow while soil texture controls patterns of surface soil moisture and evapotranspiration during the transition from dry to wet conditions. Finally, the ratio of transformation of precipitation into evapotranspiration (ET/P) and run off (Q/P) changed in space and time as summer monsoon progresses. The results of this research improve the understanding of the ecohydrology of NAM region, which can be useful for developing sustainable watershed management plans in the face of anticipated land cover and climate changes.
ContributorsMéndez-Barroso, Luis A (Author) / Vivoni, Enrique R (Thesis advisor) / Whipple, Kelin X (Committee member) / Christensen, Phillip R (Committee member) / Sala, Osvaldo E. (Committee member) / Yepez, Enrico A (Committee member) / Ruddell, Benjamin L (Committee member) / Arizona State University (Publisher)
Created2014