Yan

• Hydrology


  A branch of scientific and engineering discipline that deals with the occurrence, distribution, movement, and properties of the waters of the earth
• Hydrological cycle


  1. Evaporation

  2. Condensation

  3. Precipitation

  4. Transpiration

  5. Surface runoff

  6. Infiltration

  7. Percolation
• Water distribution


  • 97.5% salt water
  • 2.5% fresh water
  • 96.5% water in ocean
• Residence time


  The average duration for a water molecule to pass through a water body, derived by dividing the volume of water by the flow rate
• The total amount of water available to the earth is finite and conserved. Although the total volume of water in the global hydrologic cycle remains constant, the distribution of this water is continually changing on continents, in regions and local catchments
• Catchment


  An extent of land where water from rain or snow melt drains downhill into a body of water, such as a river, lake, reservoir, estuary, wetland, sea or ocean
• Evaporation


  A process by which water gets converted from a liquid form to vapor form
• Factors affecting evaporation


  • Temperature
  • Wind
  • Humidity
  • Surface area
• Evapotranspiration


  The water loss occurring from the processes of evaporation and transpiration
• Evaporation


  Occurs when water becomes vapor from bodies of water
• Transpiration


  Occurs when water leaves a plant as a vapor
• Flux


  Inflow-outflow water relationship in groundwater system, the rate of flow of a property per unit area
• Vapour pressure


  The partial pressure contributed by water vapour. When the pressure is in equilibrium, it is called saturated vapour pressure
• Sensible heat


  Heat you can feel, or sense, responsible for liquid water temperature change
• Latent heat


  Heat used to vaporise liquid water into water vapour, varies slightly with temperature
• Evaporation pan


  Provides a measurement of the combined effect of temperature, humidity, wind speed and sunshine on the reference crop evapotranspiration
• Lysimeter


  Devices typically tanks or containers, that define a specific boundary to contain soil water and permit measurement of either the soil water balance or the volume of water percolating vertically and or its quality
• Eddy covariance


  A statistical method that analyses high-frequency wind and scalar atmospheric data series, and yields values of evaporation or evapotranspiration
• Precipitation


  Part of the atmosphere water and derived from water vapour. Atmospheric water mostly exists as vapour, but briefly and locally it becomes a liquid (rainfall and cloud water droplets) or a solid (snowfall, cloud ice crystal and hails)
• The sun is the driving force for the hydrological cycle. Precipitation comes from water vapour generated by the solar radiation from land and ocean. Water is made of H2O hence water vapour is lighter than air (low air pressure is linked with high moisture, hence more likely to rain)
• Processes that can induce precipitation

  • Ice Crystal Process
  • Coalescence Process
• Major categories of precipitation

  • Convective/Convectional Precipitation
  • Orographic/Relief Precipitation
  • Cyclonic/Frontal Precipitation
• Precipitation data


  Precipitation events are recorded by gauges at specific locations. Point precipitation data are used collectively to estimate areal variability of rain and snow. Rainfall data are usually represented as mm/hour, mm/day, etc.
• Gauge


  A device that measures the amount or quantity of something and shows the amount measured
• Examples of gauges


  • Rain Gauges
  • Temperature Gauges
  • Pressure Gauges
• Rain gauge


  Used to study the present as well as the future condition of water resources, to determine the amount of rainfall with respect to the time at a particular place or area, to predict the water precipitation at a particular place to make a stable structure like a dam, road, etc., and to design the drainage by showing the discharge of precipitation at given interval of time
• Recording gauge


  An instrument that automatically records the amount of precipitation collected as a function of time
• Non-recording gauge


  Only displays the amount of rain that has fallen, cannot tell when the rain started, when it stopped, what the intensity of the rain was, or how much the intensity of the rain varied over the course of the storm
• Importance of rain gauges

  • Keeping plants and grass well-watered
  • Identifying weather patterns and trends for your neighborhood
  • Knowing the best times for planting
  • Identifying potential conditions for flooding
  • Getting better rainfall data
• Areal rainfall


  Precipitation in a specific area expressed as an average depth of liquid water over the area
• Methods to compute rainfall

  • Arithmetic mean method
  • Thiessen polygon method
  • Isohyetal method