No reproducibility of steps blended nowcast when using noise_stddev_adj='auto'

[mpvginde]

When running 2 identical blended nowcasts with pysteps.blending.steps.forecast using
a fixed seed
and setting
noise_stddev_adj = 'auto',
the results (sometimes) differ.

I suspect this behavior is coming from the
pysteps.noise.utils.compute_noise_stddev_adjs function.

This function takes the seed argument, but inside the function the seed is always set to None:

pysteps/pysteps/noise/utils.py

Lines 102 to 106 in be8eea4

	randstates = []
	seed = None
	for k in range(num_iter):
	randstates.append(np.random.RandomState(seed=seed))
	seed = np.random.randint(0, high=1e9)

Leading to different normalization weights for every run and impacting the final results, preventing reproducibility.

Kind regards,
@mpvginde

[dnerini]

Hi @mpvginde thanks for reporting this issue! Do you want to go ahead and submit a pr (looks like a simple fix)? Otherwise I'll try to have a look on it

[mpvginde]

Sure @dnerini. I'll have a look at it.

[mpvginde]

A small update:
The issue might be more complex as I initially thought.
When I fix passing the seed in the pysteps.noise.utils.compute_noise_stddev_adjs results become reproducable for the pysteps.blending.steps.forecast routine.
However, for pysteps.nowcast.steps.forecast results still differ between identical runs.
Only when I disable the dask parallel workers in the _update helper routine in nowcasts.steps the results become reproducable.
I suspect this might be linked to issue #337, I will investigate further.

[mpvginde]

See #337 (comment)

Should be fixed with PR #347