Topic%202%20Hydrology%20notes

Topic%202%20Hydrology%20notes - Trees and Forest(2010...

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Trees and Forest (2010) Forest Hydrology Water is a critical component within forest ecosystems: 1. Universal solvent - chemical weathering 2. Transport agent - nutrient (leaching) and sediment transport (erosion) - transport processes in soil formation - global hydrologic cycle 3. Essential for biological system - physiological processes Water moves through a foreest ecosystem in response to forces resulting primarily from evapotranspiration and gravity . Water is an essential component of biological systems: Globally, availability of water is the single most important factor determining the growth of land plants. Actual evapotranspiration (AET) is a good predictor of net primary productivity because it integrates solar radiation and water availability. If all the rainfall on land were spread out evenly over the surface, 70 cm/yr of precipitation would fall. The amount in the atmosphere at any one time is equal to about 0.3 cm of rainfall over the entire earth's surface. Hydrologic mass balance for a watershed: Precipitation = drainage + runoff + soil water storage + evapotranspiration In watershed studies, evapotranspiration is determined by difference and thus includes all the estimation errors of the other terms. Important Components of a Forest Hydrologic Budget 1. Precipitation Precipitation (rain, snow and fog) is measured directly; both the total volume and intensity (cm/hr) are important. Fog inputs may be a major component of the water budget, especially in coastal redwood forests where fog represents 20-40% of total annual precipitation inputs. 2. Interception, canopy throughfall and stemflow Interception - the precipitation that does not pass through the above-ground canopy to the soil surface. A given tree canopy can hold 1-5 mm of water before any significant water will fall to the soil surface. Much of this water is evaporated directly back to the atmosphere. Canopy interception in humid regions generally ranges between 20-35% and depends on
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This note was uploaded on 04/22/2011 for the course PLS 144 taught by Professor Rice during the Fall '08 term at UC Davis.

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Topic%202%20Hydrology%20notes - Trees and Forest(2010...

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