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117 lines
3.0 KiB
Python
117 lines
3.0 KiB
Python
"""Calculate probability distributions for IPCC sea level rise forecasts.
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This will calculate the values required to Cauchy Distributions for
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different SLR projections.
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Reads:
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'IPCC AR6.xlsx'
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Writes:
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'cauchy-values.csv'
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D. Howe
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d.howe@wrl.unsw.edu.au
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2022-05-12
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"""
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import os
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import re
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import numpy as np
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import pandas as pd
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from scipy import stats, optimize
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import matplotlib.pyplot as plt
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PLOT = True
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def cauchy_cdf(x, loc, scale):
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"""Calculate cumulative density function, using Cauchy distribution."""
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return stats.cauchy(loc=loc, scale=scale).cdf(x)
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# Read data
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df = pd.read_excel('IPCC AR6.xlsx', index_col=[0, 1, 2, 3, 4])
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df = df.sort_index()
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# Use all 'medium' confidence scenarios for intermediate quantiles
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scenarios = ['ssp119', 'ssp126', 'ssp245', 'ssp370', 'ssp585']
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dff = df.loc[838, 'total', 'medium', scenarios].groupby('quantile').mean()
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# Use ssp119/ssp585 for 5th and 95th quantiles
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dff.loc[5] = df.loc[838, 'total', 'medium', 'ssp119', 5]
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dff.loc[95] = df.loc[838, 'total', 'medium', 'ssp585', 95]
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dff = dff.T
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dff.index.name = 'year'
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percentiles = dff.columns.values / 100
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for i, row in dff.iterrows():
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values = row.values
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x_min = values.min() - 0.2
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x_max = values.max() + 0.2
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x = np.linspace(x_min, x_max, num=1000)
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# Fit distribution
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loc, scale = optimize.curve_fit(cauchy_cdf, values, percentiles)[0]
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p = {'loc': loc, 'scale': scale}
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dff.loc[i, 'loc'] = loc
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dff.loc[i, 'scale'] = scale
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if not PLOT:
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continue
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fig, ax = plt.subplots(1, 2, figsize=(10, 3))
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ax[0].plot(x, 100 * stats.cauchy.cdf(x, **p))
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ax[0].plot(values, 100 * percentiles, '.', c='#444444')
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ax[1].plot(x, stats.cauchy.pdf(x, **p), label='Cauchy')
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ax[1].plot([], [], '.', c='#444444', label='IPCC data')
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ax[1].legend()
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ax[0].set_ylabel('Percentile', labelpad=10)
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ax[0].set_title('Cumulative distribution')
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ax[1].set_title('Probability density')
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ax[0].annotate(i, (-0.3, 1),
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xycoords='axes fraction',
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clip_on=False,
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size=14)
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for a in ax:
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a.set_xlabel('SLR (m)', labelpad=10)
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a.spines['top'].set_visible(False)
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a.spines['right'].set_visible(False)
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plt.show()
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# Save distribution parameters
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dff[['loc', 'scale']].to_csv('cauchy-values.csv', float_format='%0.3f')
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if PLOT:
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# Plot all distributions
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fig, ax = plt.subplots(1, 1, figsize=(8, 4))
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cmap = plt.cm.get_cmap('RdBu_r', len(dff))
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c = list(cmap(range(cmap.N)))
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j = -1
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for i, row in dff.iterrows():
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j += 1
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y = stats.cauchy(loc=row['loc'], scale=row['scale']).pdf(x)
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ax.plot(x, y * row['scale'], c=c[j])
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if j % 2 == 0:
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ax.annotate(f' {i}', (x[y.argmax()], 1),
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ha='center',
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va='bottom',
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rotation=90)
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ax.set_xlabel('SLR (m)', labelpad=10)
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ax.set_ylabel('Probability density (-)', labelpad=10)
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ax.spines['top'].set_visible(False)
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ax.spines['right'].set_visible(False)
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plt.show()
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