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Hydrologic effects and implications of vegetation in semiarid mountain regions

Hydrologic effects and implications of vegetation in semiarid mountain regions. Huade Guan Advisor: Dr. John Wilson SAHRA 4 th Annual meeting Oct. 15, 2004. N. South Baldy, Magdalena Mountains, New Mexico, 2001. SAHRA Scientific Question and My Study.

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Hydrologic effects and implications of vegetation in semiarid mountain regions

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  1. Hydrologic effects and implications of vegetation in semiarid mountain regions Huade Guan Advisor: Dr. John Wilson SAHRA 4th Annual meeting Oct. 15, 2004

  2. N South Baldy, Magdalena Mountains, New Mexico, 2001

  3. SAHRA Scientific Question and My Study • SAHRA vegetation question: What are the impacts of vegetation change on the basin-scale water balance? • Today I’ll focus on two issues related to understanding and modeling vegetation hydrologic effects in mountain areas. • Effects of vegetation on hydrologic processes • Mountain Block Recharge (MBR) at hillslope scale under various conditions, including vegetation types, and vegetation change

  4. Precipitation Precipitation Evapotranspiration ? Percolation Interflow Bedrock Soil Soil water Surface Fault Trace FS From this percolation, what is the distributed recharge to the mountain block? Bedrock DS FR DR What is the contribution of distributed recharge to mountain-front recharge? FAULT FAULT MASTER FAULT OBLIQUEFAULT How does water partition on the mountain hillslopes? In particular, what is the percolation across the soil-bedrock interface?

  5. Precipitation Soil Soil water Bedrock Effects of vegetation on hydrologic processes • Modifies surface albedo • Intercepts precipitation • Transpires soil water, actively responds to the atmospheric condition and soil moisture • Modifies soil structure and hydraulic conductivity

  6. Effects of vegetation on hydrologic processes We separate these effects into two categories, • one contributes to the boundary of the model: PE and PT (including Fr, albedo, interception, stomatal resistance, vegetation structure, etc); • the other contributes to the model parameters: K, root water uptake model.

  7. PT PE Modified from Shuttleworth and Wallace (1985) Root macropore Hydrologic effects of vegetation New surface energy partitioning model that we use to separately generate PE and PT on mountain hillslope: SEP4HillET Hydrologic modeling of the surface and vadose zone: currently HYDRUS

  8. PE=83%, PT=17% SEP4HillET model: Considers effects of the vegetation coverage and slope (aspect and steepness) on surface energy partitioning for ET (E and T separately) modeling The model was tested for estimating both potential evaporation (PE) and potential transpiration (PT) on two surfaces of Sevilleta LTER by comparing to stable isotopic measurements (Boulanger,2003) shrub grass Measured: E =79~84%, T = 16~21% Modeled: PE = 83%, PT = 17% Measured: E = 52~70%, T = 30~48% Modeled: PE = 60%, PT = 40% Modeled PE and PT PE=60%, PT=40%

  9. Test the hypothesis for distinct vegetation Different atmospheric demands for ET lead to different soil moisture regimes, and support different vegetation. N

  10. Duration of dry root zone soil 30 cm soil 100 cm soil

  11. N Long-term vegetation changes with climate Boundary P/PET ~ 0.2 Juniper: P/PET ~ 0.24 Creosote: P/PET ~ 0.18 Model results with 8-year micrometeological Data at Red Tank station, Sevilleta LTER Picture from Bruce Harrison

  12. Precipitation Soil Soil water Bedrock Mountain Block Recharge (MBR) at hillslope scale • under various conditions, • including vegetation types, and vegetation change

  13. Granite Granite Tuff Tuff Generic hillslope hydrologic modeling MBR sensitivity to: bedrock permeability, soil thickness, vegetation coverage, and slope aspect. (climate variability, rainfall intensity, soil structure change and erosion due to vegetation change not considered) 2% 3% 4% 6% Soil and bedrock effects Percolation: in % of Precip Soil 1% 4% 7% 0.3% 16% 23% 31% 43% Aspect effect Aspect effect Soil 17% 22% 1.8% 6% Vegetation control S N S N Annual P=565mm Fr=50% Annual P=565mm Fr=5%

  14. Tuff Simulations of Los Alamos hillslope experiments Los Alamos hillslope experiments (data from Newman, 2003) • Site description: • ponderosa pine, • 6% slope, • ~ 500 mm annual precip, • permeable tuff • However, little recharge

  15. Because of root macropore ! Root zone Impeding layer for percolation Tuff Simulations of Los Alamos hillslope experiments Soil is layered, with lowest measured hydraulic conductivity at 40 cm. However the soil moisture ponds at 60-70 cm. Why? Lab measured K

  16. P=52cm P=52cm P=38cm Q1: Does ponderosa pine site naturally leads to soil impeding layer? Juniper root zone root zone root zone root zone barrier tuff tuff tuff tuff Simulations of Los Alamos hillslope experiments Ponderosa Q2: Percolation < ?

  17. Los Alamos hillslope experiments (data from Newman, 2003) Valles Caldera field sites Hillslope modeling Of the Los Alamos experiments suggests an impeding soil layer below the root zone of ponderosa pine forest. What about Valles Caldera? Impeding layer for percolation What controls soil thickness at these sites?Impeding soil layer?What is the distributed MBR? Root zone Permeable Tuff

  18. Thank you！

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