Hydro Definitions Flashcards
PET
The theoretical maximum amount of ET that would occur from an area of continuous, uniform vegetation that covers the whole ground - with an unlimited supply of water
Aridity Index
A = P/PET = numerical indicator of the degree of dryness of the climate at a given location <0.05 = hyperarid 0.05-0.20 = arid 0.20-0.50 = semiarid 0.50-0.65 = subhumid >0.65 = humid
Evaporative Index
Determines the portioning of P —> ET and Q and is used in the Budyko Curve
Dryness Index
Characterises climatic conditions and is used in the Budyko Curve
Hydrologic Design
The process of assessing the impact of hydrologic events on a water resource system and choosing values for the key variables of the system so it will perform adequately.
What are hydraulic design estimates based on?
Hydraulic design estimates are based on either the largest event we can imagine (ELV) or the expected return period of an event.
Probability of an event
Inverse of the return period. P(X>Xt) = 1/T
What’s the problem with trying to do statistical frequency analysis in developing countries?
It requires a lot of data and developing countries are generally data poor
Return Period
Average length of time between occurrences of a storm of a given magnitude or greater. Also known as recurrence interval. An estimate of the liklihood of an event.
What is a streamflow gauge?
A streamflow gauge is a device/structure that continuously measures the discharge in a river
Describe the processes of the Hydrological Cycle
Precipitation –> Infiltration/Interception/Percolation –> Surface runoff/GW base subsurface flow –> ET and Evap –> Surface outflow/GW outflow –> Evap from oceans.
Residence time
Residence time is the average travel time, Tr, for water to pass through a subsystem of the hydrological cycle. Tr = S/Q
Green water
Water from precipitation that is stored in the root zone of the soil/on top of the soil or in vegetation which is evaporated/transpired/incorporated by plants. Particularly relevant in agricultural and forestry production.
Blue Water
Freshwater, surface water or ground water. It is either evaporated, transferred from one body of water to another or used for the production of a product. Relevant for irrigated agriculture, industry and domestic water use.
Grey Water
Grey water is polluted. It comes about a result of domestic activities
What are the assumptions we use in the water balance equation?
- Groundwater in is equal to groundwater out. We assume this because we assume that the catchment is very large. And also that hydrogeological characteristics are not that important.
- We assume that there is no change in storage over long periods of time.
Sources of Evapotranspiration
Evaporation
- Open Water
- Soil
- Vegetation surfaces
Transpiration
- Plants
Evaporation
Collective term, covers all the ways in which (liquid) water is transferred as water vapour to the atmosphere. Includes evaporation from open water (lakes & reservoirs), soil surfaces and water intercepted by vegetative surfaces.
Transpiration
Evaporation of water vapour through the leaves of plants via leaf stomata (pores)
Three types of classification used for the Budyko curve?
Land Cover
Climate
Soil Type
What does the Budyko framework do?
Describes the long term water and energy balance of a catchment. It depicts the partitioning of P.
3 reasons for falling off the Budyko curve?
Budyko is more reliable using long-term averages (»1yr) and large catchments (>10,000km2)
- Inadequate observations of precipitation, temperature and discharge.
- Inadequate representation of (potential) ET
- Inadequate representation of discharge
What are inadequate observations caused by? (reason for falling off Budyko curve)
- Instrument errors - systematic bias, equipment malfunction, replaced sensors, sensor ‘drift’ (gets worse over time
- Lack of spatial coverage - low vs. high elevation, minimum number of sensors per catchment, generally more in lower regions
What causes an inadequate representation of (potential) ET? (reason for falling of Budyko)
ET underestimated shifts right
- Failure to consider net radiation (insolation)
- Relative humidity and wind speed for PET and ET computation results in shifts away from the curve.
What causes an inadequate representation of discharge? (reason for falling off Budyko)
GW loss underestimated shifts down
Failure to consider additional groundwater loses of precipitation
Responsivity
The degree to which Q (runoff) is synchronised with P (precipitation).
Responsivity corresponds to a vertical or horizontal gap on the Budyko?
And the bigger the gap the ________ the responsivity?
Vertical, lower
Elasticity corresponds to ______ and ______ changes on the Budyko
A big vertical gap and a small horizontal gap correlates to __________ elasticity
Horizontal and vertical
low
Elasticity
How quick a catchment can return to normal functioning after perturbations.
What are ground based measurements? And what are 4 examples?
They can support stochastic (random) hydrology and help design and validate hydrological models. Stream flow gauge, radar, distrometer, rain gauge.
Name 3 satellites and what they measure?
MODIS - precipitation and cloud information
GPM - precipitation
SMOS - Soil moisture
Three methods of acquiring data?
- Local ground-based observations
- Global hydrological models
- Global satellite remote sensing products
What are the advantages (2) and disadvantages (3) of local ground-based observations?
Adv:
- Accurate
- Highly instrumented catchments will retrieve lots of data
Disadv:
- Physical installation is costly and requires trained personell
- It collects point data
- Sensors require calibration
- Can be restricting as you can put them in hard to reach places so don’t collect any data here
What are the advantages (5) and disadvantages (5) of global hydrological models?
Adv:
- Easy, low effort
- Cheap
- Better temporal resolution vs. satellites
- They allow for estimations where you can’t measure directly
- Model info can be used for planning and design
Disadv:
- Usually uses US/EU validation data so ignores characteristics from unmeasured places (Africa)
- Relies on several individual datasets
- Based on assumptions
- Non physical parameters are hard to be traced
What are the advantages (3) and disadvantages (2) of global satellite remote sensing products?
Adv:
- Potentially cover the whole globe
- Cheap for the user
- Easy to download
Disadv:
- Lower temporal resolution than the model
at are the 4 different categories of models?
- Perceptual
- Conceptual
- Symbolic
- Numerical
What is a perceptual model?
Helps you to understand the key processes of a system.
- Not constrained by math
- Perception of model may differ among different hypothesis adopted
What is a conceptual model?
Provides a synthesis (simplification) of the perceptual model.
- May differ among different hypothesis adopted
What is a statistical model?
Take advantage of rich datasets to build mathematical rules to explain/predict processes for a given location.
- quality and length of data are important
- single or multi variable models
What is a numerical model?
Codifies the rules captured by conceptual models into a programming language.
- Spatial discretisation (lumped vs distributed) and and temporal integration of equations
- Empiricism can still happen (i.e. transferability from other places)
- Can be very complex, relying on several input data and prescribed parameters
- Calibration is an option but depends on observations
What is a reservoir?
Natural or artificial lake used to store water. Created in river valleys by the construction of a dam.
Rainfall excess
The rainfall that is neither retained on the land surface nor infiltrated into the soil. It flows over land.
Rainfall runoff analysis
Effective rainfall, is rainfall that is neither retained on the land surface nor infiltrated into the soil
What is antecedent moisture? And what effect does it have?
The relative wetness of dryness of a watershed. ACM 1 means low moisture content (dry) therefore there is more potential infiltration and the CN is higher
What are the 10 indicators of climate change?
Which have the potential to cause floods or drought?
- Increasing surface temperature of seas
- Increasing ocean heat content
- Melting sea ice
- Rising sea levels
- Increasing humidity
- Increasing temperature near surface (trophosphere)
- Increasing temp over oceans
- Glaciers melting
- Snow cover reducing
- Increasing temp over land
Three key messages of freshwater availability?
- Tools are available for the analysis of water use on people and the environment
- Scale is challenging for water issues but there are tools for moving between scales
- Groundwater is not well integrated into these tools
How is environmental flow maintained?
If you keep your river/streamflow within 20% of long-term normals then the environment of that river will probably maintained.
What is a watershed?
Area of land that drains to a water body
What is a tool? And what are the three categories of tool used?
An intellectual/technical equation/method/algorithm/model/that can be used in water management.
People
Ppl & environment
Environment
What are the three specific tools under ‘people’ and what do they do?
Water stress - (total water withdrawn)/(renewable freshwater resources) its a human stress
Wedges - where a number of solutions can be used in combination to achieve a particular target
Water crowding - Water resources available per capita. >1000m3 = water scarcity, >1700m3 = water stress
What is the tool under ‘people and the environment’?
Planetary boundaries - the physical/biophysical limits on what we can do to earth and still maintain a habitable state for humanity
What are the tools under ‘environment’?
Water footprints - the volume of water required to produce a good or service, can be split up into different colours of water
GW footprint - area required to sustain GW use and GW dependent ecosystem services of a region of interest
