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exam 2 study guide GEOG 2050

exam 2 study guide GEOG 2050 - Geography Study Guide Exam 2...

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Geography Study Guide- Exam 2 Chapter 9 The Hydrologic Cycle: Transpiration- the movement of water vapor out through the pores in leaves; the water is drawn by the plant roots from soil-moisture storage Precipitation- rain, snow, sleet, and hail—the moisture supply (78% falls on the ocean and 22% falls on land) Evaporation- a weather instrument consisting of a standardized pan from which evaporation occurs, with water automatically replaced and measured Percolation- the process by which water permeates the soil or porous rock into the subsurface environment Infiltration- water access to subsurface regions of soil moisture storage through penetration of soil surface The Soil-Water-Balance Equation: A soil-water-budget can be established for any area of earth’s surface by measuring the precipitation input and the output of various water demands in the area considered Groundwater is the largest potential freshwater source in the hydrologic cycle and is tied to surface supplies The moisture supply to earth’s surface is precipitation arriving as rain, sleet, snow and hail. Precipitation is measured with the rain gauge. Evaporation is the net movement of free water molecules away from a wet surface into air. Transpiration in the movement of water through plants and back into the atmosphere; it is a cooling mechanism fro plants. Evaporation and transpiration are combined into one term—evapotranspiration. The ultimate demand for moisture is potential evapotranspiration, the amount of water that would evaporate and transpire under optimum moisture conditions. Evapotranspiration is measured with an evaporation pan or the more elaborate lysimeter. Unsatisfied potential evapotranspiration is deficit. By subtracting deficit from potential evapotranspiration, we determine actual evapotranspiration. Ideally, potential evapotranspiration and actual evapotranspiration are about the same, so that plants have sufficient water. If potential evapotranspiration is satisfied and the soil is full of moisture, then additional water input becomes surplus, which may puddle on the surface, flow across the surface toward stream channels, or
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percolate underground through the soil. The overland flow to streams includes precipitation and groundwater flows into river channels to make up the total runoff from the area. A “saving account” of water that receives deposits and provides withdrawals as water-balance conditions change is the soil-moisture storage. This is the volume of water stored in the soil that is accessible to plant roots. In soil, hygroscopic water is inaccessible because it is a molecule-thin layer that is tightly bound to each soil particle by hydrogen bonding. As available water is utilized, soil reaches the wilting point. Capillary water is generally accessible to plant roots because it is held in the soil by surface tension and hydrogen bonding between water and soil. Almost all capillary water that remains in the soil is available water in soil-
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