GEOG 203.pdf

Lecture 2 – September 5th Topic: Introduction to environmental systems: structure and function Learning objectives: - Identify the Earth’s 4 systems/spheres - Describe what is an environmental system - Explain the differences between an open/closed system - Understand and provide examp...

Lecture 2 – September 5th Topic: Introduction to environmental systems: structure and function Learning objectives: - Identify the Earth’s 4 systems/spheres - Describe what is an environmental system - Explain the differences between an open/closed system - Understand and provide examples of positive/negative feedback - Describe the attributes of environmental systems - Explain the concept of equilibrium states Atmosphere: contains all air in earth’s system. Upper portion protects the organisms of the biosphere from the sun’s UV radiation. Absorbs and emits heat. When air T in the lower portion of atmosphere changes, weather occurs. Hydrosphere: contains all solid, liquid and gaseous water. Extends from lithosphere into atmosphere. Small portion of freshwater Lithosphere: solid, outer part of earth. Includes the upper portion of the mantle and the crust, the outermost layers of earth’s structure. Biosphere: where all the living organisms and components of the earth. Communities referred to as “biomes”. Environmental system: any ordered, interrelated set of things linked by flow of energy. Systems must me conceptually separated from surrounding environment outside the system (boundary). Ex: a lake could be a system Questions to ask ourselves - How does this system behave? - What controls the system - How do we characterize these systems - How have humans influenced these systems Open system: is going to exchange energy+ mass with the outside environment. You can have energy conversion. Ex: forests provide oxygen and that’s an output. à Car is example of open system: input of fuel, actions, output of exhaust gases heat energy, etc. à River system: input from rain, output into ocean à Earth is an open system bc we get energy from the sun (input) and output is radiation emitted Closed system: more contained, not exchanging energy or mass with the outside. Input – output = Δ storage (for a given substance or for energy) Ex: 1. Nutrient budget of an ecosystem: nutrients in (weathering, atmosphere) – loss of nutrients (leaching) = Δ nutrients 2. Mass of sediment in river reach: input of sediments (upstream) – sed. Output (downstream) = Δ storage in reach Attributes of environmental systems: function, scale, feedbacks, equilibrium states Functions of a forest: stores carbon within the system, input of sunlight, output of oxygen, action of carbohydrates used for plantgrowth - Human-earth relation: forests store carbon, creating carbon sink, roots stabilize soil which prevents landslides Scale: time scale, space scale, etc. Feedback - Positive feedback: amplify the initial disturbance. What’s going on in the system will enhance the disturbance. Tends to bring to another new state à Global warming - Negative feedback: dampens the initial change, stabilizing feedback. Tend to bring the system back to its original state *Ice-albedo feedback (+): T° increase, ice melts and exposes darker ocean surface, reflectivity (albedo) is altered bc ocean reflects less sunlight, ocean absorbs more heat and cycle goes on. * permafrost (+): T° rises, permafrost thaws, releases GHG and cycle goes on Equilibrium states - Steady-state: inputs ≅ outputs - Dynamic equilibrium: input < 𝑜𝑟 > outputs - Tend to assume systems are steady-state: input=output à water budget (amount of water in lakes)over all is roughly going to stay constant Our systems are adjusting to changes in the carbon concentration. Our ecosystems help us contain some emissions. Earth system isn’t quite in a steady-state bc absorbing more radiation than it’s letting out. Imbalance in earth system. Over time, some natural systems vary between grassland dominated or forest dominated, but if we add anthropological energy, we can force these systems to change from one state to another. Cyclical behaviours = cyclical equilibrium, for ex: seasonal variation in atmospheric CO2 Episodic - Stable state: negative feedback dominates - Unstable state: positive feedback dominates - Equilibrium states: stable through, unstable peaks Climate tipping points: thresholds that if you cross, you’re going to get a new state, dramatic change. Ex: thawing of permafrost, thawing of Greenland ice sheet how does this system behave - what are its possible states? what controls or stabilizes the system - what keeps it in its most frequent states? how have humans influenced the system? how can we better manage the system? Example: earth’s climate Lecture 3 – September 10th Topic: The atmosphere and solar radiation - define solar radiation and know the solar constant - explain insolation patterns (specifically how much solar radiation reaches earth at various places and times? How does it cause seasons? - Understand global energy budgets and latitudinal imbalance (overheating of the tropics) - Describe how atmospheric pressure and density change with height - Know the composition of the atmosphere and describe the layers of the atmosphere - Explain the greenhouse effect - Assess if the ozone layer is a success story Electromagnetic radiation: - Radiant energy in the form of electromagnetic waves is emitted by all objects with T° above absolute zero Solar shortwave vs. terrestrial longwave 1. Hotter objects emit shorter wavelengths (ex. Sun is hotter than earth which emits mostly longwave) 2. Hotter objects emit more energy than cooler objects 3. Energy emitted is dependant on T° Sun emits primarily shortwave radiation Earth emits mostly long wavelength radiation Radiation reception: transmissivity, reflectivity, absorptivity Solar constant: avrg value of this insolation when Earth is at its avrg distance from the sun. 1370 W/m2. *Change is isolation is not driving global warming Photosynthetically active radiation (PAR) is the radiation used for photosynthesis. Used by chlorophyll a and b for photosynthesis. Reasons for variations in insolation with time and place (and seasons) - Earth’s axis is tilted, and this results in predictable changes in duration of daylight and amount of sunlight received at any latitude through a year. These changes cause the annual cycle of seasons and associated temperature changes. Rotation (24 hours): determines daylength Revolution (365,25 days) around the sun Tilt: 23,5 ° Sphericity of the Earth produces the uneven receipt of insolation from pole to pole Parallel axis = the fact that the Earth’s tilt never changes Components of Earth’s movement and position - Subsolar point: the single point at which Sun’s rays are perpendicular to Earth’s surface at or near noon (during the equinox, it’s at the equator). Latitude of subsolar point is also called solar declination - The tilt doesn’t change - Circle of illumination: the line separating day from night where sunrise and sunset occur - Solar altitude: angle of the sun above the horizon, varies from equator to poles due to earth’s curvature This means that the Tropics receive 2,5 x more insolation than the poles Together, the changing solar altitude and the changing length of daylight hours produce Earth’s seasonality Warm summer days are the result of both more intense sunlight and increased daylight hours This would not happen if it weren’t for the tilt of Earth’s axis. Atmosphere: the envelope of gases that surrounds Earth Karman Line: one widely accepted definition of the top of the atmosphere at 100 km The atmosphere is made of:  - permanent gases (called permanent bc their proportions change only a little), mainly nitrogen and oxygen - variable gases (that exist in extremely small quantities and change in their proportions As radiation moves through the atmosphere (either downward or up…) - Transmission is the passage of parts of shortwave and longwave radiation through the atmosphere - Atmospheric scattering or reflection is when the atmosphere interacts with insolation though processes of scattering, a redirection of radiation through refraction from particles - Atmospheric absorption is when some of the short and longwave radiation is absorbed and heats up some constituents in atmosphere The greenhouse effect - If Earth was a “blackbody”, it’s avrg temp. would be 255 K - Yet, it’s 288 K - Thus, the difference between those 2 temps, is the magnitude of greenhouse effect - Increases in greenhouse gases contributes to global warming and climate change through an enhanced GHG effect Air density, pressure and height - Air density is amount of gas molecules in a given volume - Air pressure is weight of the atmosphere above a point - Density and height decrease exponentially with height Troposphere (1st layer) - All weather occurs here, turbulence & winds - Contains 80 % of atmosphere’s mass - Highest water vapor content and concentration of aerosols Environmental lapse rate: rate of cooling with increasing altitude in the troposphere. Avrg is 6,5 ° per 1000 m Stratosphere (2nd layer) - Permanent temp inversion - High concentrations of ozone - Absorbs UV radiation *Uv absorption in atmosphere: T° inversion in stratosphere is caused by absorption of UV radiation by stratospheric ozone. UV = solar radiation with shorter wavelengths than visible light. Ozonosphere = region of stratosphere with high concentrations of ozone molecules that block UV radiation. Montreal protocole: initial discussions on how do we go about protecting and restauring the ozone hole. Mesosphere: - Most meteors burn up here - Coldest region of atmosphere Thermosphere: - Hottest part of atmosphere (molecules are energized by intense solar radiation) - Many spacecrafts orbit there - Absorbs UV, X-rays and gamma radiation - Auroras form here Lecture 4 – September 12th Topic: Energy balance at the Earth’s surface Energy balance at the Earth’s surface - Explain what happens to radiation as it goes through Earth’s atmosphere - Define “albedo” and know the controls on surface albedo - Understand the Earth-atmosphere radiation balance (at the top of the atmosphere and surface) - Be able to interpret radiation and energy balances over various ground surfaces - Explain spatial patterns of net radiation, latent heat and sensible heat Why doesn’t all solar radiation make it down to the surface? - It can be transmitted: unimpeded movement of electromagnetic energy through air, water, etc. - It can be scattered: redirection of light by gas and molecules without changing its direction (reason why sky is blue) - Refracted - Reflected: energy that bounces off the surface so it does not provide heat (albedo high albedo reflects more, albedo = constant throughout the day except if it rains or snows) - Absorbed: molecules take in and convert radiation from one form to another (ex: shortwave à longwave). Different gases and molecules are going to absorb at different wavelengths. In atmosphere, gasses and cloud droplets absorb UV radiation Albedo is measured as % of received shortwave that is reflected Absorbed insolation at the surface  - Dark surfaces = low albedo = high absorption - When absorbed, insolation may be converted to heat (sensible/latent) or chemical energy (photosynthesis) and may radiate back out via longwave radiation Scientists measure quantity of radiation flowing using radiation balance equations Global radiation budget - Input of SW arriving from the sun - Ourput of LW radiate to space - Q* = SW¯ (insolation)− SW­ (reflection)− LW­ = net radiation - Net Q* of 0 annually on averg for the globe - Planetary Q* is balanced globally over a long term, otherwise atmosphere would heat up over time. We are warming up bc not perfect balance - Radiation surplus at low latitudes, deficit near the poles so this surplus drives ocean and atmospheric circulation Q* = SW¯− SW­ + LW¯ (infrared in) − LW­ What happens to the energy surplus Net radiation? - Goes into sensible heat and latent heat - Residual accumulates as global warming which is warming the oceans Daily radiation curve at a single location - At night, no sun - Tend to have a surplus during the day - Varies during the day Surface energy balance - Q* is split as it goes into various forms of energy includinc: - Latent heat (evaporation) - Sensible heat transfer into the atmosphere via conduction and primary convection - Heat conduction into the ground Heat = other form of energy along with radiation - Sensible heat transfer: surrounding bodies are heated - Latent heat: uptake and release of energy as water changes phase from solid to liquid to gas - Heat tends to move from areas of high heat to area of lower heat - Net Q* is mainly expended through latent heat flux. Heat transfer processes - Conduction: molecule to molecule transfer of sensible heat - Convection: energy transfer by movement through gas/fluid - Advection: horizontal movement of warm air (wind)  - Latent heat: heat energy released or absorbed during the transition from one phase to another. Moves heat from surface to atmosphere in vapour - What are thermals? Convection - turbulent convective transfer of heat from surface to atmosphere. Places with - Ample water: latent heat devours and hides heat, making it feel cooler - Little water: sensible heat transfers surplus radiation, making it feel hotter Summary: - Daily surplus radiation (Q*) goes into Sensible and Latent heat - This energy then used up and dissipated via transfers of sensible and latent heat Lecture 5 – September 17th Topic : Circulation patterns - Describe what drives ocean winds and currents - Explain atmospheric cells, including dominant pressure belts and prevailing wind patterns - Understand surface ocean currents and thermohaline circulation - Explain natural oscillations - Define temperature and heat - Describe controls on temperature and be able to understand and explain temperature patterns across the globe Wind: - What is it? Horizontal motion of air - How does wind behave (move)? From high to low pressure - What drives this motion? Wind speed and direction: - 3 forces control wind speed and direction near Earth’s surface: pressure- gradient force, Coriolis force and friction force - Directions: winds are named from whence they come. Westerly wind comes from the west and goes towards the east. Pressure gradient force: - Force resulting from changes in barometric pressure across Earth’s surface. Air pressure is a result of denser air going to the bottom, warmer air rising above. - Most important factor in determining wind speed and direction - Air flows from areas of high pressure to areas of low pressure - The greater the pressure difference, the faster the air will flow between them.  - We can express pressure in kPa Coriolis force: - Due to Earth’s eastward rotation - Deflects objects traveling in the atmosphere - Produces an apparent deflection to flying objects, regardless of their direction of motion - Impact the direction of flow but not impact wind speeds - Corolis force increases with wind speeds - Deflection is zero near the equator, but it increases as latitude increases - Upper-level winds are high above, they’re not being slowed down by friction at the surface. Friction force: - More towards the surface (mountains, etc.) - Cause wind speeds to slow down, decrease Coriolis force and cause a deflection in the wind near the surface. - Rather than the winds flying parallel to isobars, they’re going to cross the isobars - Air spiraling out of high pressure system Cyclones and anticyclones: - Cyclone: region of low pressure with counterclockwise circulation in the northern hemisphere (hurricanes). Rotate clockwise in the southern hemisphere - Anticyclone: region of high pressure with clockwise rotation in the northern hemisphere. ITZG (Intertropical convergence zone) - Discontinued band of thermal low pressure and thunderstorms that encircles the planet in the tropics - Creates heavy thunderstorm precipitation near the equator - Latent heat reeased through condensation within thunderstorms enhances instability - Shifts northward/southward impacts regional climates Subtropical high: - Area of high pressure roughly 30°N north and south latitude - Where we find most of earth’s deserts - Dry air cells sinks, is compressed and that’s going to prevent formation of clouds and create formation of these deserts Subpolar Low and polar High: - Discontinuous belt of dynamic low pressure - Cyclonic systems that bring frequent precipitation due to frontal lifting  - Polar high: an area of cold, dense air at each pole that forms a zone of thermal high pressure, creates polar deserts Prevailing global wind patterns: - Trade winds: goind towards the tropic, as these winds go towards the equator, they deflect towards the right - Westerlies winds: surface winds exiting the subtropical high pressure cells heading North toward the polar front Circulation cells are defined by winds that create “borders”. Jet stream: - Strong wind that blows - Climate change impacts jet stream behavior Natural oscillations in global circulation; - North Atlantic and arctiv oscillation go together, when one is positive, the other is negative. The world’s hottest rainiest climates occur where the NE and SE trade winds meet, converge. World’s major deserts occur at 30° N and S latitudes, beneath the subtropical highs Lecture 6 – September 19th - Provide an overview of the global water cycle - Understand the watershed as an environmental system - Describe the controls on key hydrological processes: interception, infiltration, soil moisture retention, evapotranspiration, groundwater, runoff - Explain hoe the water budget equations are applied to soil layers and drainage basins - Explain the generation of streamflow and runoff. Patterns of temperature and precipitation Temperature: measure of kinetic energy of molecules, different scales (°C, K). Absolute zero is at -273 °C, it’s where molecular motion ceases. Heat: energy transmitted between materials. With temperature increase, objects feel hotter bc heat flows from high temperature to colder temperature. Daily temperature is related to insolation energy balance. You’d be most likely to get heatstroke at 4 pm. Controls on temperature:  - Altitude: the higher you go, the colder it gets, atmosphere thins with altitude so decrease in atmospheric ability to absorb and re-radiate heat with elevation. Nearer sea level = higher mean T and less day/night contrast - Latitude: more radiation at lower latitudes, mean avrg temperature higher across the tropics - Presence of water: difference between coastal and continental, proximity to large water bodies = more temperate bc of latent heat evaporation, high specific heat (water gains and loses heat slowly), movement/mixing - Cloud cover (colder than sunny) Global temperature patterns are the combined effect of all these factors Small amount of water that is available to humans. We are depleting our water resources. Much of the evaporation occurs over the oceans, remaining comes from over the land. Transpiration is the water that goes through plants. Water balance equation: Precipitation = evapotranspiration + runoff (surplus) = change is soil moisture storage. Precipitation: measurements are simple. Global mean annual precipitation ( a lot around tropical regions, not a lot in continental regions). Interception: capture of incoming precipitation on surface of vegetation. Stemflow = rain that runs down branches and trucks of trees to reach the ground Water demand: potential evapotranspiration - Amount of water that would evaporate and transpire under optimum moisture conditions - Maximum rate of water freely available - Assumes healthy, full coverage of foliage and no lack of soil water - This demand for water can be satisfied by precipitation, soil moisture or irrigation - PET is estimated theoretically Actual evapotranspiration (AET): what’s actually going on - Actual rate can be < PET - Reach zero at the wilting point. When soil moisture is so low that plant can’t extract water from soil - Measured by evaporation pans, soil lysimeters, eddy covariance for ecosystem-scale measurements of AET Evaporation varies across different land use types. Mean annual PET is highest in the south and decrease as we go towards the north Infiltration of water into soil surface - Depends on soil type/texture - As rain falls on surface, it goes through pores in soil and gravity pulls it down - Infiltration tends to be highest at beginning of rainfall event and slows down as pores get saturated - Soil characteristics - If soil is healthy, it absorbs better than if it’s too compact - Status of vegetation influences ( a lot or a little) - Only extremely intense rains can exceed infiltration capacity of well- forested soil Soil moisture: - Water that will drain under the influence of gravity, from saturated conditions, emptying largest of pores. - Field capacity: soil moisture left after draining of gravitational water - Capillary water: water that’s going to be available to plants - Hygroscopic water: inaccessible to plants bc it sticks to soil particules - Wilting point: when only hygroscopic water is left - Components of the soil water budget: precipitation, water evaporation. Difference between input and output How does water balance in soil change over the year? Seasonal soil water budget: water surplus in winter bc of snow, summertime = more evaporation so soil water shortage. Once soil has filled up with water, the excess precipitation can go off as runoff. Percolation: Water infiltrating the soils can be lost as throughflow, can be utilized by growing plants or can continue to migrate downwards under the pull of gravity to pass into and through soil Water table: typically follows topography of area. Relief Groundwater system: water percolated downwards. Drinking source. This is where you get natural springs. Gaining stream: effluent stream base flow (contributed byground water) is partially supplied by high water table. Losing stream: river water percolating downwards, stream is losing water to the surrounding subsurface. Runoff travels to perennial or intermittent streams, originating from surplus surface-water runoff, subsurface throughflow and groundwater movement beneath the water table. Globally, runoff is closely correlated with climatic region. If rainfall intensity> infiltration capacity, precipitation excess overland occurs We measure stream runoff with Discharge (Q) = velocity x area, faster towards the top of the stream. Runoff as depth of runoff, we can compare precipitation to runoff. Storm hydrograph: how does our discharge change over time. There are high and low intensity storms, it appears on the graph with different catchment characteristics. Very little evapotranspiration in tundra, so a lot of it’s going to runoff. Varying seasonal runoff pattern. Lecture 7 – September 24th Topic: Ecohydrology and the effects of land-use change on climate and hydrology. - Describe how deforestation affects hydrology. Specifically, how are interception, evapotranspiration, runoff and flow paths impacted? - Provide examples of how deforestation influences microclimates - Define the term urban heat island - Describe the altered energy terms leading to the UHI and the urban energy balance equation - Explain the hydrological effects of urbanization Deforestation effects on hydrology and microclimate: - Extensive land use change in most forested ecosystems (boreal, tropical) - Large forested areas replaced by bare soil or proactive reforestation - Cut areas can be large and intense (removal of all trees over several hectares) - What are the hydrologic and microclimatic changes? - Equation Hydrologic effects of deforestation: - Hubbard Brook catchment in New Hampshire where they experimented on impacts of deforestation. - Reduced interception: more water reaches soil surface - Less transpiration because fewer rots, though surface temperature will be higher in clearcut sites = higher evaporation. But forest debris tends to act as mulch to lower temperatures and evaporation rates  - Greater runoff. Magnitude of change dependent on type of forestry operation, proportion of catchment affected and precipitation/evaporation rates. - Changes in flowpaths. Higher moisture leads to greater throughflow, overland flow and thus change in magnitude and frequency of flow and shorter lag between precipitation and hydrograph peaks. Potential solutions: green roofs, rain gardens, stormwater curb extensions, etc. UHI: - Relative warmth of urban areas compared to their non-urbanized surrondings - Places with parks are cooler - Nocturnal phenomenon. Urban energy balance: Q* + QF = QH + QE + ΔQs à where QF = energy flux density released by human activity (heating our homes, driving our cars, etc.) at the urban-atmosphere interface and ΔQs = heat storage in the ground, buildings, air, vegetation Altered energy terms leading to UHI - Increased long-wave radiation from the sky due to air pollution (aerosols that increase absorption and re-emission) - Increased short-wave absorption due to canyon geometry (greater surface area and ‘trapping’ by multiple reflections) - Decreased long-wave radiation loss due to canyon geometry - Increased storage heat flux (ΔQs) due to building / paving materials and increased surface area - Decreased evapotranspiration (QE) due to impervious surfaces increased - Anthropogenic heat release (QF) term added to the urban energy balance) - The canopy-layer urban heat island is small (or negative) during day, but positive at night - hence a night-time phenomena. Urban activity is increasing atmospheric pollutants. Correlation between heat and income/vulnerability for example age (seniors) Strategies to combat UHI: - Increase surface albedo with white roofs. Cities tend to be dark. Reflect more radiation, new types of concrete that have higher albedo - Reduce heat loss from buildings and vehicles - Install air conditioning, improve access to cool places, preventative healthcare - Increase biomass, greenery bc it increases latent heat exchange, prevents radiation being absorbed and stored by impervious surfaces like concrete, more evaporation = more cooling  - Green roofs increases latent heat exchange Hydrological effects of urbanization: - Changes/increase in precipitation over urban areas. Cities can modify air flow around them so bc there’s cloud formation over cities - Higher temperatures but less water availability so overall decrease - Increased runoff. Less evaporation, concrete can’t absorb water - Increase in impervious areas (roads, buildings) leads to overland flow - Sewerage systems increase rates of subsurface flow and lower water table - Both lead to increased peak runoff (floods) and low flow runoff - Creates urban rivers - Quicker discharge (response) peaking early, Questions midterm: - Answer key points in question - Long answer question 1 ½ Page 15 sur 15 - Have to remember some equations, have a ballpark idea (what’s high/low albedo), in desert would all the rainfall go as runoff or be absorbed by soil During el nina = reverse el nino. Moves trade winds backwards, changes area of low pressure, change winds and precipitation and global ramification El nino: - Normally, trade winds blow from east to west, push warm water westwards, so cold water is pulled up in phenomenon = upwelling, creates an area of uncertain weather. Sets up atmospheric circulation around the world. - During el nino: trade winds reversed, so less push of warm water to west and less upwelling. This cancels out normal temperature difference. This changes rainfall patterns around equatorial pacific. Main impacts in tropics (increased risks of floods) - Each El Nino event is different How does water get to the stream, overland flow water