Add 'generate_slr.py'

probabilistic-analysis/generate_slr.py

@@ -0,0 +1,94 @@
+import os
+import re
+import numpy as np
+import pandas as pd
+from scipy import stats, optimize
+
+WORKBOOK = '../inputs/20220505_Probabilistic_Erosion_Parameters_5th_JTC_REVIEWED_IPCC_SLR_OFFSET.xlsx'  # noqa
+SHEET = 'IPCC AR6 WRL FINAL'
+VERSION = 'WRL V5 corrected to 2020'  # First row of data
+
+
+def get_cdf(x, loc, scale):
+    """Calculate cumulative density function, using Cauchy distribution."""
+    return stats.cauchy(loc=loc, scale=scale).cdf(x)
+
+
+def cauchy(n_runs, start_year, end_year):
+    """
+    Use Monte Carlo simulation to generate sea level rise trajectories by
+    fitting IPCC data to a Cauchy distribution.
+
+    Args:
+        n_runs     (int): number of runs
+        start_year (int): first year of model
+        end_year   (int): last year of model
+
+    Returns:
+        the simulated sea level rise (m)
+    """
+
+    # Load IPCC SLR data
+    df = pd.read_excel(WORKBOOK, sheet_name=SHEET, index_col='psmsl_id')
+    idx = df.index.get_loc(VERSION)  # First row containing values we want
+    df = df.iloc[idx:idx + 5].set_index('quantile')
+    df = df.drop(columns=['process', 'confidence', 'scenario']).T
+    df.index.name = 'year'
+    percentiles = df.columns.values / 100
+
+    for i, row in df.iterrows():
+        values = row.values
+
+        # Set valid range of probability distribution function
+        x_min = row[5] + (row[5] - row[50])
+        x_max = row[95] + (row[95] - row[50])
+        x = np.linspace(x_min, x_max, num=1000)
+
+        # Fit Cauchy distribution
+        loc, scale = optimize.curve_fit(get_cdf, values, percentiles)[0]
+
+        if x_min == x_max:
+            # Harcode values for start year (when everything is zero)
+            scale = 0.001
+            x_min = -0.001
+            x_max = 0.001
+
+        df.loc[i, 'loc'] = loc
+        df.loc[i, 'scale'] = scale
+        df.loc[i, 'min'] = x_min
+        df.loc[i, 'max'] = x_max
+
+    # Interpolate intermediate values
+    index = np.arange(df.index.min(), df.index.max() + 1)
+    df = df.reindex(index).interpolate(method='linear')
+    df = df.loc[start_year:end_year]  # Trim dataframe to given range
+
+    # Prepare array for SLR values
+    slr = np.zeros([len(df), n_runs], dtype=float)
+
+    for i, (year, row) in enumerate(df.iterrows()):
+        # Get probability distribution for current year
+        dist = stats.cauchy(loc=row['loc'], scale=row['scale'])
+
+        # Generate random samples
+        for factor in range(2, 1000):
+            s_raw = dist.rvs(n_runs * factor)
+
+            # Take first samples within valid range
+            s = s_raw[(s_raw > row['min']) & (s_raw < row['max'])]
+
+            if len(s) > n_runs:
+                break  # Success
+            else:
+                continue  # We need more samples, so try larger factor
+
+        # Add the requried number of samples
+        slr[i] = s[:n_runs]
+
+    # Sort each row to make SLR trajectories smooth
+    slr = np.sort(slr, axis=1)
+
+    # Randomise run order (column-wise)
+    slr = np.random.permutation(slr.T).T
+
+    return slr