WEATHER DATA

1
WEATHER DATA
2
Weather Data

• Objectives and learning points
• Review of type of data used in NPS modeling and
  how it is used in various simulation module
• Review how weather data is stored in BASINS
• Introduce structure of WDM file
• GIS representation of weather stations (exercise
  on selecting a weather station)

3
Weather Data

• Nonpoint source pollution is weather-driven
  process
• Hydrologic processes are time varying and depends
  on changes in environmental conditions, i.e.
• Precipitation
• Temperature
• Wind speed

4
Weather Data

• Weather Parameters
• Precipitation
• Potential Evaporation
• Air Temperature
• Wind Speed
• Solar Radiation
• Dewpoint Temperature
• Cloud Cover

Spatial variability

• Highly variable
• Low variability
• Daily/seasonal
• Moderately variable
• Fairly variable
• Low variability

• Moderately variable

5
Weather Data Requirements for HSPF
6
How Precipitation is Used in HSPF

• Surface runoff is directly dependent on
  precipitation
• Detachment of soil matrix by the impact of rain
  and transport of detached sediment depend on
  precipitation.
• Soil/Ag. chem. is removed by overland flow and
  may be associated with detached soil.
• Rain falling directly on the water surface of a
  reach and its temperature may be considered
  optionally.
• Two different lapse rates are used in temperature
  correction for elevation difference -- one when
  precipitation occurs and another during dry
  periods (Lapse rate Rate of drop in temperature)

7
How Evaporation is Used in HSPF

• Evapotranspiration comprises evaporation
  directly from the soil layers, from vegetation
  surface, and from transpiration through plants.
• Evapotranspiration is used in runoff computation
• Direct loss of water from water surface or from
  snow pack to atmosphere
• Loss of water through transpiration from
  vegetaion surface
• Evaporation is used in water balance calculation

8
How Air Temperature is Used in HSPF

• Function of Elevation
• Corrected using elevation difference between the
  weather station elevation and the subwatershed
  mean elevation
• Snow and Snow Melt
• Determine when precipitation is rain or snow
• Calculate density of snow
• Calculate snow melt
• Soil Temperature
• Heat transfer through soil surface
• Heat exchange and water temperature
• Determine conductive-convective heat transport

9
How Wind Speed is Used in HSPF

• Evaporation from snow pack
• Directly proportional to wind speed
• Heat exchange rates
• Condensation heat flux to snowpack is directly
  proportional to wind speed
• Heat balance in water bodies
• Evaporative heat loss increases with wind speed
• Conductive-convective heat transfer between air
  and water is wind speed driven
• Reaeration rate
• Lake reaeration rate is expressed as a function
  of wind speed only.
• Volatilization rate
• Indirectly dependent on wind speed as
  volitization of a chemical from water is related
  to oxygen reaeration coefficient

10
How Solar Radiation is Used in HSPF

• Contributes to snow melt (shortwave radiation)
• Heat balance in water bodies
• Estimate shortwave solar radiation
• Plankton growth rate
• Determine the light limiting conditions

11
Dewpoint Temperature

• Snow
• Determine when precipitation is considered as
  snow
• Heat balance in water bodies

12
Cloud Cover

• Heat balance in water bodies
• Cloud cover reduces longwave radiation from the
  water body
• Photolysis
• Loss of general quality constituent due to
  photolysis decreases as cloud cover increases

13
Weather Data Format

• Weather data are time series (hourly, daily,
  etc.)
• Recommended time interval for nonpoint source
  modeling is hourly
• No missing data allowed
• Analyze multiple stations to estimate missing
  data
• Base on understanding of weather parameter
  spatial and temporal variability
• Large set of weather data can be efficiently
  managed by use of a special binary file - called
  Watershed Data Management (WDM) file.
• BASINS includes WDM files already built for
  nonpoint source modeling

14
WDM File

• A WDM file can contain a large number of time
  series data.
• HSPF can manipulate (e.g. read, replace) the data
  contained in a WDM file.
• Annie program can assist in creating the WDM
  file from raw (ASCII) data sets

15
WDM File Structure

• Conceptual structure of a WDM file

Station 1
Station 2
Station 3
Column
02 03 04 05 06 07 08 09 ... ...
... PREC EVAP ATEM CLOU WIND SOLR DEWP PREC ...
... ... ... ... ... ... Data ... ... ... ...
... ... ... ... ... ... ... ... ...
Field Name

• Limitation No additional information, besides
  the four character field names, can be stored.

16
Supplementary Information to a WDM File

• NPSM overcomes the WDM limitation by implementing
  an INF file.
• An INF file has the same first name as the WDM
  file.
• INF file format Time period, name and location
  of weather stations

1971 1 1 0 1993 12 31 24 //start/end time 9
//Number of stations "State
Station Name" "StationID" "METELEV"
"EVAPCOEF" "PREC" "EVAP" //
(ft) in
in "GA ATHENS MUNI AP" GA00013873
1234 0.76 11 12 "GA
ATLANTA HARTSFIELD" GA00013874 1232
0.77 31 32 "GA AUGUSTA BUSH
FIELD" GA00003820 123 0.80 51
52
17
Processing of Meteorogical Data in BASINS-HSPF
18
Meteorological Data in BASINS
19
Weather Data in the HSPF Input

• References to the WDM file and the data sets are
  located in two places of the input file.
• FILES block Specify files to be used by the run
  and their Unit Numbers
• EXT SOURCES block Specify input time series
  from WDM file

FILES
WDM 15 C\Basins\Models\Npsm\Tutorial.wd
m END FILES
EXT SOURCES
SsysSgapTran
tem strgstrg
WDM 2 PREC
ENGLZERO SAME PERLND 1 EXTNL
PREC END EXT SOURCES
Unit 206-19
20
GIS WDM Weather StationsExercise

• BASINS includes a WDM weather station coverage
  and associated attribute tables
• Display the station from the BASINS View
• Activate the theme
• Use the identification tool to explore the
  stations

21
Identification of WDM Weather Stations

• Use the identification tool to explore the
  stations
• Elevation of each station
• Geographical location and distribution across the
  state
• For a given watershed which station will you
  select?

Station ID
Source Stations for WDM Data