EESA07 note2.1

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Environmental Science
Jovan Stefanovic

EESA07_notech2 Chapter 2- Quantity and Quality : Introduction to Water Resource Science  Introduction of basics: o Hydrology and water quality  Scientific disciplines: o Fluvial geomorphology o Aquatic ecology 2.1 – Following the Hydrologic Cycle  hydrologic cycle: the movement of water in the environment o cycle: reflects the fact that the amount of water on Earth is fixed o water is continually moving from ocean  atmosphere  soil  river  back again  PRECIPITATION o Ex. rain, sleet, hail, snow o Occurs as a result of adiabatic cooling  a process which air mass rises, expands and cools  cold air holds less water than warm air  cooled air can become supersaturated with water vapor  leads to form clouds and drops of condensed water  fall as rain o Precipitation with different characteristics:  Orographic  Moisture-laden (mountains) air is forced upward leading to adiabatic cooling & precipitation on the windward side of the mountains  Less rain since descending air mass can hold more moisture  Frontal  Precipitation often forms along the boundaries of air masses of different temperatures & densities  Cold frontal moving under warmer air = short, high-intensity rainfall  Cold air push warm air up  Warm front displacing cooler air = more extended, lower-intensity precipitation  Warm air moves along the cold air by slowly going upward  Tropical cyclones (hurricanes) = low- pressure systems (can drop massive amount of rain in short time)  Convective  Heating of air near the surface can cause it to rise = short, intense precipitation (often in form of thunderstorms) o The amount of precipitation can be measured by rain gauges or can be estimated by radar  A graph of precipitation over time = hyetograph o Precipitation:  expressed in depth per unit time  Ex. mm/day  Expressed in total depth over a given event  Ex. mm o Drop of water  hit the ground directly = throughfall  encounter vegetation surface (tree, etc) = interception  intercepted moisture will either flow down to ground (stemflow) or evaporate  when on ground, drop may run off or infiltrate into soil (become part of the soil moisture pool)  porosity= maximum amount of water that soil hold (a dimension-less ratio: pore volume divided by total volume)  when pore space is completely occupied with water, the soil is saturated, however soild near the surface is unsaturated o with volume moisture content (volume of water divided by total volume) somewhere between zero & porosity  EVAPORATION o Drop of water can return to atmosphere either by evaporation (water from liquid to gas) or traspiration (biological movement of water from soil into plant then out from leaves as water vapor)  Transpiration  Essential for plant growth  For CO2 for photosynthesis  plants, tres, open stomates and in process release water vapor  Evaporation & transpiration = evapotranspiration (ET)  Depth per unit time (ex. mm/day)  ET’s measurement is called potential evaporatranspiration (PET)  PET = reflect potential for water vaporization in given time & place o Can be approximated by pan evaporation (loss of water from water-filled pan of defined size & shape o PET is controlled by temperature, humidity, wind & solar radiation  ET = less than PET o Lower water availability in soil = lower evaporation
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