tr-55

A Python implementation of TR-55.

Functions

simulate_all_tiles and simulate_year are the two functions intended for consumers of this module.

simulate_all_tiles

The simulate_all_tiles function simulates the events of a single day. It takes three arguments:

1. parameters which is either a date object (which is mapped to precipitation and evapotranspiration using sample year data) or that argument is a single day's precipitation and evapotranspiration as a tuple of two floats (in units of inches).

   If the sample year data are to be considered typical, precipitation should generally be between 0 and 3 inches daily, and evapotranspiration should be between 0 and 0.2 inches daily.

2. tile_census is a dictionary containing the number of appearances of each type of tile in the query area, e.g.

    {
        "result": {
            "cell_count": 147,
            "distribution": {
                "d:hi_residential": 33,
                "c:commercial": 42,
                "a:deciduous_forest": 72
            }
        }
    }

Here, "d:hi_residential" indicates High-Intensity Residential land use on top of Type D soil.

3. pre_columbian is a boolean argument which controls whether or not to simulate the given area under pre-Columbian conditions. When this is set to true, all land-uses other than water and wetland are treated as mixed forest.

The algorithm used is close to TR-55 (the algorithm found in the USDA's Technical Release 55, revised 1986), but with a few differences. The main differences are:

• it applies the TR-55 algorithm on a tile-by-tile basis and aggregates the results rather than running the TR-55 algorithm once over the entire area
• it uses the Pitt Small Storm Hydrology Model on tiles which are of a "built-type" when precipitation is two inches or less

and there are numerous other small differences, as well.

simulate_all_tiles returns a triple of runoff, evapotranspiration, and infiltration (all in units of inches).

simulate_year

The simulate_year function takes two parameters, tile_census and pre_columbian as described above, and simulates an entire year using a year's worth of sample precipitation and evapotranspiration data. It returns a triple of runoff, evapotranspiration, and infiltration for the given area over the entire sample year.

Usage Example

The following program:

from tr55.model import simulate_year

tiles = {
    "result": {
        "cell_count": 147,
        "distribution": {
            "d:hi_residential": 33,
            "c:commercial": 42,
            "a:deciduous_forest": 72
        }
    }
}

(q, et, inf) = simulate_year(tiles)
print("%f inches of runoff" % q)
print("%f inches of et" % et)
print("%f inches of infiltration" % inf)

should produce the following output:

17.614212 inches of runoff
15.167862 inches of et
20.245580 inches of infiltration

Testing

Run nosetests from within the project directory.

License

This project is licensed under the terms of the Apache 2.0 license.