Rainfall Intensities

The staley2017 (s17) module module works strictly with rainfall accumulations (mm of accumulation over a duration). However, many users find it useful to work with rainfall intensities (mm/hour) instead, and the gartner2014 (g14) module additionally expects rainfall intensities as input. As such, utils.intensity module provides functions to convert between these two formats.

To Accumulation

The to_accumulation command converts input rainfall intensities to accumulations, given a rainfall duration (in minutes):

>>> from pfdf.utils import intensity
>>> I = [16, 20, 24, 40]  # Rainfall intensity in mm/hour
>>> R = intensity.to_accumulation(I, duration=15)
>>> print(R) # mm accumulated over a 15 minute interval
array([ 4.,  5.,  6., 10.])

You can alternatively provide a specific duration for each input intensity:

>>> I = [16, 20, 24, 40]
>>> durations = [15, 30, 60, 60]  # in minutes
>>> R = intensity.to_accumulation(I, durations)
>>> print(R) # mm accumulated over the relevant interval
array([ 4., 10., 24., 40.])

From Accumulation

The from_accumulation command converts from rainfall accumulations to intensities, again given the relevant durations (in minutes). By default, this command is intended for output from the s17.accumulation command, so the input durations are broadcast along the final dimension of the input accumulations array:

>>> from pfdf.utils import intensity
>>> import numpy as np

>>> # Mimic s17 output, 5 segments x 3 durations
>>> R = np.array([
    [10, 21, 43],
    [5, 11, 22],
    [11, 22, 45],
    [1, 3, 7],
    [7, 14, 29],
])

>>> # Durations (in minutes) are broadcast over the columns
>>> durations = [15, 30, 60]
>>> I = intensity.from_accumulation(R, durations)
>>> print(I) # mm/hour
array([[40., 42., 43.],
       [20., 22., 22.],
       [44., 44., 45.],
       [ 4.,  6.,  7.],
       [28., 28., 29.]])

Alternatively, you can use the dim option to specify the index of the dimension over which to broadcast durations. For example:

>>> R = np.array([
    [1, 2],
    [2, 4],
    [4, 8],
])
>>> durations = [15, 30, 60]
>>> I = intensity.from_accumulation(R, durations, dim=0),
>>> print(I)
array([[4., 8.],
       [4., 8.],
       [4., 8.]]),