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This document explores the distribution of Earth’s water, which totals 1.36 billion km³, occurring in three states—liquid, solid, and gas—and stored in major reservoirs such as oceans, the atmosphere, rivers, lakes, groundwater, and glaciers. The hydrologic cycle describes the movement of water among these reservoirs driven by solar energy, involving processes like evaporation, condensation, and precipitation. Key factors affecting runoff, infiltration, and the balance of evaporation versus precipitation are also discussed, emphasizing the importance of understanding these dynamics for environmental science.
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Exam 2 • 2.5 pt improvement over 1st exam (better than past) • 150 (63%) improved over the first exam
Distribution of Earth’s Water The Earth has 1.36 billion km3 of water. The water occurs in one of three states: • Liquid • Solid • Gas And is stored in one of the following major reservoirs • Oceans • Atmosphere • Rivers/lakes • Groundwater • Glaciers
Changes of state and energy transfers Release of Energy • Gas to solid • Gas to liquid • Liquid to solid Requires Energy (storage) • Solid to gas • Solid to liquid • Liquid to Gas
Daily Question The hydrologic cycle describes the movement of water among the different reservoirs. Using the terms on the right (which represent both reservoirs and pathways) create a conceptual model that identifies that pathways that connect the reservoirs. • Ocean • Ground water • Atmosphere • Glaciers • Surface Water • Precipitation • Evaporation • Evapotranspiration • Infiltration • Ground water flow • Runoff
Hydrologic System • Hydrologic cycle – transfer of water between reservoirs. Solar energy drives the hydrologic cycle.
Evaporation – process by which water is transferred from the land and water masses of the earth to the atmosphere. • Transpiration – transfer of water from plants to the atmosphere, soil moisture taken up by vegetation is eventually evaporated as it exits plant pores. • Evapotranspiration – combination of evaporation and transpiration.
Conditions for Precipitation • Cooling of the air mass • Condensation – phase change from gas to liquid • Requires condensation nuclei: small particle of dust, previously formed ice or water drop, salt from ocean, clays, nitrogen oxides, etc. • Coalescence of water particles to form drops • Growth of drops until gravity is able to bring to Earth’s surface without evaporating first
Hydrologic Cycle • Precipitation – 4.2 trillion gallons per day • 66% is lost as evapotranspiration • 31% is runoff • 3% infiltrates into the subsurface
Infiltration and Ground water flow • Infiltration - the movement of water from the surface to subsurface • Could be from surface water reservoirs • Could follow rain event • Ground water flow is the movement of water in the subsurface • Can move back to surface water reservoir • Can move to the ocean
Runoff • The collective term describing the movement of water on the Earth’s surface, (primarily stream transport) • Factors affecting runoff • Geology - is it soil, unconsolidated material, or bedrock. Is it fractured? Is it porous? • Slope - a high angle of slope increases runoff • Vegetation covering - the more vegetation the less runoff • Time of the year - frozen ground vs. non-frozen ground, lower evapotranspiration vs. high evapotranspiration • Soil Saturation - if the soil is saturated there is no room for water to infiltrate • Type of precipitation - fast, hard rain increases runoff, slow soft rains allow for infiltration, snow vs. rain
Distribution of Evaporation & Precipitation More evaporation than precipitation occurs over the ocean More precipitation than evaporation occurs over land In the end, output from the ocean = input to the ocean and output from the land = input onto the land
