Precipitation:Spatially and Temporally Varied Precipitation

Assignment of spatially and temporally varied rainfall requires the creation of a rainfall input file. Like the project file, the rainfall input file is card based. The precipitation input file can contain multiple “events’. The following rainfall cards, Table 9, are recognized by GSSHA, and valid for use only in the precipitation input file (not in the project file):

Card	Argument	Description
EVENT	“character string”	Denotes the beginning of a new event in the precipitation input file. The optional character string can be used to annotate the file. Card-REQUIRED, argument-OPTIONAL. Optional string MUST be in double quotes.
NRGAG	integer	Denotes the number of gages that recorded data for this event. The card and argument are REQUIRED for each EVENT.
NRPDS	integer	Denotes the number of periods of rain rate observations for this EVENT. The card and argument are REQUIRED for each EVENT.
COORD₁ COORD_NRGAG	real real “char string” “char string”	Denotes the UTM coordinates of the gage, in the format easting northing. Two optional strings, which must be in double quotes are provided to annotate the file. One COORD card is REQUIRED for each gage. The number of COORD cards in an EVENT must equal NRGAG.
GAGES₁ GAGES_NRPDS	date time val_1,1..val_1,NRGAG date time val_NRPDS,1..val_NRPDS,NRGAG	Rain accumulations (mm) recorded at the end of the sampling period. The number of GAGES cards in each EVENT must equal NRPDS. Each GAGES card must have the date and time of the recording, and be followed by NRGAG real values of rain accumulation during that period.
RADAR₁ RADAR_NRPDS	date time val_1,1..val_1,NRGAG date time val_NRPDS,1..val_NRPDS,NRGAG	Rain rates (mm/h) recorded at the end of the sampling period. The number of RADAR cards in each EVENT must equal NRPDS. Each RADAR card must have the date and time of the recording. There are two radar formats that can be put here: a set (NRGAG in size) of values similar to a set of gage points of rain rate or a sequence of file names of Arc/Info ASCII grids of rainfall rates (one per time step). If a set of values is used, the NRGAG should be the number of points. If the file version is used, then NRGAG should equal -1 and no coordinate locations should be defined.
RATES₁ RATES_NRPDS	date time val_1,1..val_1,NRGAG date time val_NRPDS,1..val_NRPDS,NRGAG	Rain rates (mm/h) recorded at the beginning of the sampling period. The number of RATES cards in each EVENT must equal NRPDS. Each RATES card must have the date and time of the recording, and be followed by NRGAG real values of rain rate.
ACCUM₁ ACCUM_NRPDS	date time val_1,1..val_1,NRGAG date time val_NRPDS,1..val_NRPDS,NRGAG	Cumulative amount of rainfall (mm) recorded at the end of the sampling period. The number of ACCUM cards in each EVENT must equal NRPDS. Each ACCUM card must have the date and time of the recording, and be followed by NRGAG real values of cumulative rainfall. The values must increase monotonically for each gage.

Table 9 – Types of rainfall inputs

The following information on developing rainfall input should also be noted:

In a given EVENT, the rainfall data source type (GAGES, RADAR, RATES, ACCUM) may NOT change.
The data source type may change from one EVENT to the next.
The number and location of rain gages may change from one event to the next.
If only one gage is present, rainfall interpolation is impossible. The location of the gage is irrelevant and the gage coordinates are ignored. Rainfall is applied uniformly in space. This provides a means to apply a temporal distribution of rain in a spatially uniform fashion. Such temporally varying, spatially uniform rainfall distributions are commonly used in flood frequency analysis, i.e. TP40.
A separate line with its own time of recording is used to input each instance of rainfall, allowing varying temporal resolution rainfall data to be input. This feature is particularly useful when using radar-rainfall estimates, since the temporal resolution can vary considerably.
Avoid using precipitation data with temporal resolution coarser than 1 hour.
The finest temporal resolution of GSSHA rainfall input is 1 minute. Rainfall rates change on integer minutes. Seconds are not allowed in the time field.
The COORD card must be followed by the easting and northing of the rain gage. Easting and northing must be in coordinates in the same frame of reference as the header of all ASCII GRASS input maps. If the gage and map coordinates are not in the same system, the gages will not be placed at the correct location in relation to the watershed.
If used, the optional strings must be enclosed in double quotes “like this”
Tabs or spaces are used to delimit the file. DO NOT USE COMMAS.
To improve readability, line feeds are allowed in the data file.
If radar rainfall files are used they should be in the same projection as the model, which should be a UTM projection.

The following is an example of a multiple-event precipitation input file using radar-rainfall estimates for the first event, rain gage data for the second event, and radar ascii text files for the third event. (unlikely but illustrative):

EVENT “Event of 30 June 1995- rainfall stops on July 1st”
NRPDS 5 
NRGAG 3
COORD 205150.0 4750212.0 "center of radar pixel #1" 
COORD 205045.0 4750104.0 "center of radar pixel #2" 
COORD 205320.0  4751173.0 "center of radar pixel #3" 
RADAR 1995 06  30  22  56  0.00  0.00  0.00 
RADAR 1995 06  30  23  18  10.75  2.25  5.80 
RADAR 1995 06  30  23  39  21.16  1.80  41.50 
RADAR 1995 06  30  23  57  12.13  20.90  20.70 
RADAR 1995 07  01  00  09  11.71  16.50  2.30 

EVENT "Event of 4 July 1995- new raingage network data" 
NRPDS  4 
NRGAG  4 
COORD 204555.0  4751268.0 "location of raingage #1" 
COORD 205642.0  4750491.0 "location of raingage #2" 
COORD 205921.0  4750330.0 "location of raingage #3" 
COORD 206170.0  4749611.0 "location of raingage #4" 
GAGES 1995 07  04  09  47  0.0  0.0  0.0  0.0 
GAGES 1995 07  04  10  01  38.0  2.0  0.0  0.0 
GAGES 1995 07  04  10  16  16.0  14.0  3.0  0.0 
GAGES 1995 07  04  10  35  19.0  20.0  16.0  8.0 

EVENT "Event of 6 July 1995- new radar data" 
NRPDS  8 
NRGAG  -1 
RADAR 1995 07  06  10  54  kzmx_07_06_10_54.asc
RADAR 1995 07  06  11  00  kzmx_07_06_11_00.asc
RADAR 1995 07  06  11  06  kzmx_07_06_11_06.asc
RADAR 1995 07  06  11  12  kzmx_07_06_11_12.asc
RADAR 1995 07  06  11  18  kzmx_07_06_11_18.asc
RADAR 1995 07  06  11  24  kzmx_07_06_11_24.asc
RADAR 1995 07  06  11  30  kzmx_07_06_11_30.asc
RADAR 1995 07  06  11  36  kzmx_07_06_11_36.asc