Space,%20Time%20and%20Variables%20in%20Hydrology

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Space, Time and Variables in Hydrology

• David R. Maidment
• Feb 7, 2008

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Hydrologic Cycle
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Hydrologic System
Take a watershed and extrude it vertically into
the atmosphere and subsurface, Applied Hydrology,
p.7- 8 A hydrologic system is a structure or
volume in space surrounded by a boundary, that
accepts water and other inputs, operates on them
internally, and produces them as outputs
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Reynolds Transport Theorem
Rate of change of B stored in the control volume
Total rate of change of B in the fluid system
Net outflow of B across the control surface
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Geography
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Geographic Things
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Data Cube
A simple data model
Time, T
When
D
Where
Space, L
Variables, V
What
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ArcHydro Time Series
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Continuous Space-Time Model NetCDF (Unidata)
Time, T
Coordinate dimensions X
D
Space, L
Variable dimensions Y
Variables, V
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Discrete Space-Time Data ModelArcHydro
Time, TSDateTime
TSValue
Space, FeatureID
Variables, TSTypeID
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CUAHSI Observations Data Model

• A relational database at the single observation
  level (atomic model)
• Stores observation data made at points
• Metadata for unambiguous interpretation
• Traceable heritage from raw measurements to
  usable information

Streamflow
Groundwater levels
Precipitation Climate
Soil moisture data
Flux tower data
Water Quality
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Space, Time, Variables and Observations
An observations data model archives values of
variables at particular spatial locations and
points in time

• Observations Data Model
• Data from sensors (regular time series)
• Data from field sampling (irregular time points)

Variables (VariableID)
Space (HydroID)
Time
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Space, Time, Variables and Simulation
A process simulaton model computes values of sets
of variables at particular spatial locations at
regular intervals of time

• Process Simulation Model
• A space-time point is unique
• At each point there is a set of variables

Variables (VariableID)
Space (HydroID)
Time
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Space, Time, Variables and Statistics
A statistical distribution is defined for a
particular variable defined over a particular
space and time domain

• Statistical distribution
• Represented as probability, value
• Summarized by statistics (mean, variance,
  standard deviation)

Variables (VariableID)
Space (HydroID)
Time