Carbon Flux#

datashadergeoviews
profileJim Bednar
profileJean-Luc Stevens
Published: November 28, 2018 · Updated: November 14, 2024
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Carbon Monitoring Project#

FluxNet is a worldwide collection of sensor stations that record a number of local variables relating to atmospheric conditions, solar flux and soil moisture. This notebook visualizes the data used in the NASA Goddard/University of Alabama carbon monitoring project NEE Data Fusion (Grey Nearing et al., 2018), but using Python tools rather than Matlab.

The scientific goals of this notebook are to:

  • examine the carbon flux measurements from each site (net C02 ecosystem exchange, or NEE)

  • determine the feasibility of using a model to predict the carbon flux at one site from every other site.

  • generate and explain model

The “meta” goal is to show how Python tools let you solve the scientific goals, so that you can apply these tools to your own problems.

import numpy as np
import pandas as pd
import hvplot.pandas  # noqa

pd.options.display.max_columns = 10

Download data#

In order to get the full dataset for this notebook, you should run anaconda-project run pre-build to get the .csv files needed in the later sections of this notebook.

Load metadata#

First we will load in the fluxnet_metadata containing some site information for each of the fluxnet sites. Included in these data are the lat and lon of each site and the vegetation encoding (more on this below). In the next cell we will read in these data and take a look at a random few lines:

path = 'data/allflux_metadata.txt'

metadata = pd.read_csv(
    path,
    header=None,
    names=['site', 'lat', 'lon', 'igbp', 'network'],
    usecols=['site', 'lat', 'lon', 'igbp'],
)

metadata.sample(5)
site lat lon igbp
43 US-CaV 39.0633 -79.4208 GRA
201 CZ-wet 49.0247 14.7704 WET
187 CH-Oe1 47.2858 7.7319 GRA
186 CH-Lae 47.4781 8.3650 MF
255 JP-MBF 44.3869 142.3186 DBF

The vegetation type is classified according to the categories set out in the International Geosphere–Biosphere Programme (igbp) with several additional categories defined on the FluxNet website.

igbp_vegetation = {
    'WAT': '00 - Water',
    'ENF': '01 - Evergreen Needleleaf Forest',
    'EBF': '02 - Evergreen Broadleaf Forest',
    'DNF': '03 - Deciduous Needleleaf Forest',
    'DBF': '04 - Deciduous Broadleaf Forest',
    'MF' : '05 - Mixed Forest',
    'CSH': '06 - Closed Shrublands',
    'OSH': '07 - Open shrublands',
    'WSA': '08 - Woody Savannas',
    'SAV': '09 - Savannas',
    'GRA': '10 - Grasslands',
    'WET': '11 - Permanent Wetlands',
    'CRO': '12 - Croplands',
    'URB': '13 - Urban and Built-up',
    'CNV': '14 - Cropland/Nartural Vegetation Mosaics',
    'SNO': '15 - Snow and Ice',
    'BSV': '16 - Baren or Sparsely Vegetated'
}

We can use the dictionary above to map from igbp codes to longer labels - creating a new column on our metadata. We will make this column an ordered categorical to improve visualizations.

from pandas.api.types import CategoricalDtype

dtype = CategoricalDtype(ordered=True, categories=sorted(igbp_vegetation.values()))
metadata['vegetation'] = metadata['igbp'].map(igbp_vegetation).astype(dtype)

metadata.sample(5)
site lat lon igbp vegetation
157 BE-Bra 51.3076 4.5198 MF 05 - Mixed Forest
159 BE-Vie 50.3050 5.9981 MF 05 - Mixed Forest
49 US-Dk1 35.9712 -79.0934 GRA 10 - Grasslands
93 US-Ro5 44.6910 -93.0576 CRO 12 - Croplands
231 FI-Sod 67.3624 26.6386 ENF 01 - Evergreen Needleleaf Forest

Visualize the fluxdata sites#

The PyViz ecosystem strives to make it always straightforward to visualize your data, to encourage you to be aware of it and understand it at each stage of a workflow. Here we will use Open Street Map tiles from geoviews to make a quick map of where the different sites are located and the vegetation at each site.

metadata.hvplot.points('lon', 'lat', geo=True, color='vegetation',
                       height=420, width=800, cmap='Category20', tiles='OSM')

Loading FluxNet data#

The data in the nee_data_fusion repository is expressed as a collection of CSV files where the site names are expressed in the filenames.

This cell defines a function to:

  • read in the data from all sites

  • discard columns that we don’t need

  • calculate day of year

  • caculate the season (spring, summer, fall, winter)

data_columns = ['P_ERA', 'TA_ERA', 'PA_ERA', 'SW_IN_ERA', 'LW_IN_ERA', 'WS_ERA',
                'VPD_ERA', 'TIMESTAMP', 'site', 'NEE_CUT_USTAR50']
soil_data_columns = ['SWC_F_MDS_1', 'SWC_F_MDS_2', 'SWC_F_MDS_3',
                     'TS_F_MDS_1', 'TS_F_MDS_2', 'TS_F_MDS_3']

keep_from_csv = data_columns + soil_data_columns

y_variable = 'NEE_CUT_USTAR50'

def season(df, site, metadata):
    """Add season column based on latitude and month."""
    lat = metadata[metadata['site'] == site]['lat'].item()
    if lat > 0:
        seasons = {3: 'spring', 4: 'spring', 5: 'spring',
                   6: 'summer', 7: 'summer', 8: 'summer',
                   9: 'fall', 10: 'fall', 11: 'fall',
                   12: 'winter', 1: 'winter', 2: 'winter'}
    else:
        seasons = {3: 'fall', 4: 'fall', 5: 'fall',
                   6: 'winter', 7: 'winter', 8: 'winter',
                   9: 'spring', 10: 'spring', 11: 'spring',
                   12: 'summer', 1: 'summer', 2: 'summer'}

    def map_month_to_season(partition):
        partition['season'] = partition['TIMESTAMP'].dt.month.map(seasons)
        return partition

    meta = df._meta.copy()
    meta['season'] = pd.Series(dtype='category')

    df = df.map_partitions(map_month_to_season, meta=meta)

    return df

def clean_data(df, site):
    """
    Clean data columns:

    * Add NaN for missing columns
    * Keep only needed columns
    * Add day of year and year columns
    """
    df = df.assign(**{col: np.nan for col in keep_from_csv if col not in df.columns})
    df = df[keep_from_csv]

    df = df.assign(DOY=df.TIMESTAMP.dt.dayofyear)
    df = df.assign(year=df.TIMESTAMP.dt.year)
    df = season(df, site, metadata)

    return df

Read and clean data#

First we will iterate over all the .csv files, read, and munge the data in each one. This is necessary since the columns in each file don’t necessarily match the columns in the other files. Before we concatenate across sites, we need to do some cleaning.

import os
import glob
import dask.dataframe as dd

file_pattern = 'data/FLX*.csv'
local_paths = glob.glob(file_pattern)

datasets = []
skipped = []
used = []

print(f"Processing {len(local_paths)} files...")
for local_path in local_paths:
    try:
        ddf = dd.read_csv(
            local_path,
            assume_missing=True,
            na_values=[-9999],
            parse_dates=['TIMESTAMP']
        )

        filename = os.path.basename(local_path)
        site = filename.split('_')[1]
        ddf['site'] = site

        if not set(ddf.columns) >= set(data_columns):
            skipped.append(site)
            continue

        datasets.append(clean_data(ddf, site))
        used.append(site)

    except Exception as e:
        print(f'\nError processing {local_path}: {e}')
        skipped.append(local_path)
        continue

print(f'Found {len(used)} fluxnet sites with enough data to use - skipped {len(skipped)}')

Processing 209 files...

Found 179 fluxnet sites with enough data to use - skipped 30

Now that we have a list of datasets, we will concatenate across all rows. Since the data is loaded lazily - using dask - we need to explicitly call compute to get the data in memory.

data = dd.concat(datasets).compute()
data.columns

Index(['P_ERA', 'TA_ERA', 'PA_ERA', 'SW_IN_ERA', 'LW_IN_ERA', 'WS_ERA',
       'VPD_ERA', 'TIMESTAMP', 'site', 'NEE_CUT_USTAR50', 'SWC_F_MDS_1',
       'SWC_F_MDS_2', 'SWC_F_MDS_3', 'TS_F_MDS_1', 'TS_F_MDS_2', 'TS_F_MDS_3',
       'DOY', 'year', 'season'],
      dtype='object')

We’ll also set the data type of 'site' to 'category'. This will come in handy later.

data['site'] = data['site'].astype('category')

Visualizing Data Available at Sites#

We can look at the sites for which we have data. We’ll plot the sites on a world map again - this time using a custom colormap to denote sites with valid data, sites where data exist but were not loaded because too many fields were missing, and sites where no data was available. In addition to this map we’ll get the count of different vegetation types at the sites.

def mapper(x):
    if x in used:
        return 'valid'
    elif x in skipped:
        return 'skipped'
    else:
        return 'no data'
    
cmap = {'valid': 'green', 'skipped': 'red', 'no data': 'darkgray'}

QA = metadata.copy()
QA['quality'] = QA['site'].map(mapper)

all_points = QA.hvplot.points('lon', 'lat', geo=True, color='quality', 
                              cmap=cmap, hover_cols=['site', 'vegetation'],
                              height=420, width=500, tiles='OSM').options(tools=['hover', 'tap'], 
                                                             legend_position='top')

def veg_count(data):
    veg_count = data['vegetation'].value_counts().sort_index(ascending=False)
    return veg_count.hvplot.barh(height=420, width=500)

hist = veg_count(QA[QA.quality=='valid']).relabel('Vegetation counts for valid sites')

all_points + hist

We’ll make a couple of functions that generate plots on the full set of data or a subset of the data. We will use these in a dashboard below.

import holoviews as hv
hv.extension('bokeh')

def site_timeseries(data):
    """Timeseries plot showing the mean carbon flux at each DOY as well as the min and max"""
    
    tseries = hv.Overlay([
        (data.groupby(['DOY', 'year'])[y_variable]
             .mean().groupby('DOY').agg(['min', 'max'])
             .hvplot.area('DOY', 'min', 'max', alpha=0.2, fields={'min': y_variable})),
        data.groupby('DOY')[y_variable].mean().hvplot()])
    
    return tseries.options(width=450, height=400)

def site_count_plot(data):
    """Plot of the number of observations of each of the non-mandatory variables."""
    return data[soil_data_columns + ['site']].count().hvplot.bar(rot=90, width=300, height=400)

timeseries = site_timeseries(data)
count_plot = site_count_plot(data)
timeseries + count_plot

Dashboard#

Using the plots and functions defined above, we can make a Panel dashboard of sites where by clicking on a site, you get the timeseries and variable count for that particular site.

from holoviews.streams import Selection1D
import panel as pn

stream = Selection1D(source=all_points)
empty = timeseries.relabel('No selection') + count_plot.relabel('No selection')

def site_selection(index):
    if not index:
        return empty
    i = index[0]
    if i in QA[QA['quality']=='valid'].index:
        site = QA.iloc[i]['site']
        ts = site_timeseries(data[data['site'] == site]).relabel(site)
        ct = site_count_plot(data[data['site'] == site]).relabel(site)
        return ts + ct
    else:
        return empty

one_site = hv.DynamicMap(site_selection, streams=[stream])

pn.Column(pn.Row(all_points, hist), pn.Row(one_site))

Merge data#

Now that the data are loaded in we can merge the daily data with the metadata from before.

In order to use the categorical igbp field with machine-learning tools, we will create a one-hot encoding where each column corresponds to one of the igbp types, the rows correspond to observations and all the cells are filled with 0 or 1. This can be done use the method pd.get_dummies:

onehot_metadata = pd.get_dummies(metadata, columns=['igbp'])
onehot_metadata.sample(5)
site lat lon vegetation igbp_BSV ... igbp_SAV igbp_SNO igbp_WAT igbp_WET igbp_WSA
153 AU-Wac -37.4259 145.1878 02 - Evergreen Broadleaf Forest False ... False False False False False
79 US-NC1 35.8118 -76.7119 07 - Open shrublands False ... False False False False False
94 US-Ro6 44.6946 -93.0578 12 - Croplands False ... False False False False False
191 CN-Dan 30.4978 91.0664 10 - Grasslands False ... False False False False False
247 IT-Noe 40.6062 8.1512 06 - Closed Shrublands False ... False False False False False

5 rows × 19 columns

We’ll do the same for season - keeping season as a column.

data = pd.get_dummies(data, columns=['season']).assign(season=data['season'])

We’ll merge the metadata with all our daily observations - creating a tidy dataframe.

df = pd.merge(data, onehot_metadata, on='site')
df.sample(5)
P_ERA TA_ERA PA_ERA SW_IN_ERA LW_IN_ERA ... igbp_SAV igbp_SNO igbp_WAT igbp_WET igbp_WSA
332827 0.000 -16.963 94.767 167.884 176.034 ... False False False False False
531039 0.000 -2.072 70.291 115.995 206.047 ... False False False False False
274784 1.481 6.537 99.335 76.616 321.704 ... False False False False False
444483 0.000 3.496 101.213 55.438 253.971 ... False False False False False
360081 5.574 8.255 101.618 30.687 359.471 ... False False False False False

5 rows × 41 columns

Visualizing Soil Data Availability at Sites#

Now that all of our observations are merged with the site metadata, we can take a look at which sites have soil data. Some sites have soil moisture and temperature data at one depths and others have the data at all 3 depths. We’ll look at the distribution of availability across sites.

import geoviews.tile_sources as gts

partial_soil_data = df[df[soil_data_columns].notnull().any(axis=1)]
partial_soil_data_sites = metadata[metadata.site.isin(partial_soil_data.site.unique())]

full_soil_data = df[df[soil_data_columns].notnull().all(1)]
full_soil_data_sites = metadata[metadata.site.isin(full_soil_data.site.unique())]

args = dict(geo=True, hover_cols=['site', 'vegetation'], height=420, width=500)

partial = partial_soil_data_sites.hvplot.points('lon', 'lat', **args).relabel('partial soil data')
full    =    full_soil_data_sites.hvplot.points('lon', 'lat', **args).relabel('full soil data')

(partial * full * gts.OSM).options(legend_position='top') +  veg_count(partial_soil_data_sites) * veg_count(full_soil_data_sites)

Since there seems to be a strong geographic pattern in the availablity of soil moisture and soil temperature data, we won’t use those columns in our model.

df = df.drop(columns=soil_data_columns)

Now we will set data to only the rows where there are no null values:

df = df[df.notnull().all(1)].reset_index(drop=True)

df['site'] = df['site'].astype('category')

Assigning roles to variables#

Before we train a model to predict carbon flux globally we need to choose which variables will be included in the input to the model. For those we should only use variables that we expect to have some relationship with the variable that we are trying to predict.

explanatory_cols = ['lat']
data_cols = ['P_ERA', 'TA_ERA', 'PA_ERA', 'SW_IN_ERA', 'LW_IN_ERA', 'WS_ERA', 'VPD_ERA']
season_cols = [col for col in df.columns if col.startswith('season_')]
igbp_cols = [col for col in df.columns if col.startswith('igbp_')]

x = df[data_cols + igbp_cols + explanatory_cols + season_cols].values
y = df[y_variable].values

Scaling the Data#

from sklearn.preprocessing import StandardScaler

# transform data matrix so 0 mean, unit variance for each feature
X = StandardScaler().fit_transform(x)

Now we are ready to train a model to predict carbon flux globally.

Training and Testing#

We’ll shuffle the sites and select 10% of them to be used as a test set. The rest we will use for training. Note that you might get better results using leave-one-out, but since we have a large amount of data, classical validation will be much faster.

from sklearn.model_selection import GroupShuffleSplit

sep = GroupShuffleSplit(train_size=0.9, test_size=0.1)
train_idx, test_idx = next(sep.split(X, y, df.site.cat.codes.values))

train_sites = df.site.iloc[train_idx].unique()
test_sites = df.site.iloc[test_idx].unique()

train_site_metadata = metadata[metadata.site.isin(train_sites)]
test_site_metadata = metadata[metadata.site.isin(test_sites)]

Let’s make a world map showing the sites that will be used as in training and those that will be used in testing:

train = train_site_metadata.hvplot.points('lon', 'lat', **args).relabel('training sites')
test  = test_site_metadata.hvplot.points( 'lon', 'lat', **args).relabel('testing sites') 

(train * test * gts.OSM).options(legend_position='top') +  veg_count(train_site_metadata) * veg_count(test_site_metadata)

This distribution seems reasonably uniform and unbiased, though a different random sampling might have allowed testing for each continent and all vegetation types.

Training the Regression Model#

We’ll construct a linear regression model using our randomly selected training sites and test sites.

from sklearn.linear_model import LinearRegression

model = LinearRegression()
model.fit(X[train_idx], y[train_idx]);

We’ll create a little function to look at observed vs predicted values

from holoviews.operation.datashader import datashade

def result_plot(predicted, observed, title, corr=None, res=0.1):
    """Plot datashaded observed vs predicted"""
    
    corr = corr if corr is not None else np.corrcoef(predicted, observed)[0][1]
    title = f'{title} (correlation: {corr:.02f})'
    scatter = hv.Scatter((predicted, observed), 'predicted', 'observed')\
                .redim.range(predicted=(observed.min(), observed.max()))
    
    return datashade(scatter, y_sampling=res, x_sampling=res).relabel(title)

(result_plot(model.predict(X[train_idx]), y[train_idx], 'Training') + \
 result_plot(model.predict(X[test_idx ]), y[test_idx],  'Testing')).options('RGB', axiswise=True, width=500)

Prediction at test sites#

We can see how well the prediction does at each of our testing sites by making another dashboard.

results = []

for site in test_sites:
    site_test_idx = df[df.site == site].index
    y_hat_test = model.predict(X[site_test_idx])
    corr =  np.corrcoef(y_hat_test, y[site_test_idx])[0][1]
    
    results.append({'site': site,
                    'observed': y[site_test_idx], 
                    'predicted': y_hat_test, 
                    'corr': corr})

test_site_results = pd.merge(test_site_metadata, pd.DataFrame(results), 
                             on='site').set_index('site', drop=False)

Now we can set up another dashboard with just the test sites, where tapping on a given site produces a plot of the predicted vs. observed carbon flux.

First we’ll set up a timeseries function.

def timeseries_observed_vs_predicted(site=None):
    """
    Make a timeseries plot showing the predicted/observed 
    mean carbon flux at each DOY as well as the min and max
    """
    if site:
        data = df[df.site == site].assign(predicted=test_site_results.loc[site, 'predicted'])
        corr = test_site_results.loc[site, 'corr']
        title = f'Site: {site}, correlation coefficient: {corr:.02f}'
    else:
        data = df.assign(predicted=np.nan)
        title = 'No Selection'

    spread = data.groupby(['DOY', 'year'])[y_variable].mean().groupby('DOY').agg(['min', 'max']) \
             .hvplot.area('DOY', 'min', 'max', alpha=0.2, fields={'min': 'observed'})
    observed  = data.groupby('DOY')[y_variable ].mean().hvplot().relabel('observed')
    predicted = data.groupby('DOY')['predicted'].mean().hvplot().relabel('predicted')
    
    return (spread * observed * predicted).options(width=800).relabel(title)

timeseries_observed_vs_predicted(test_sites[0])

Then we’ll set up the points colored by correlation coefficient.

test_points = test_site_results.hvplot.points('lon', 'lat', geo=True, c='corr', legend=False,
                                              cmap='coolwarm_r', s=150, height=420, width=800, 
                                              hover_cols=['vegetation', 'site']).options(
                                              tools=['tap', 'hover'], line_color='black')

And put it together into a dashboard. This will look very similar to the one above.

test_stream = Selection1D(source=test_points)

def test_site_selection(index):
    site = None if not index else test_sites[index[0]]
    return timeseries_observed_vs_predicted(site)

one_test_site = hv.DynamicMap(test_site_selection, streams=[test_stream])
title = 'Test sites colored by correlation: tap on site to plot long-term-mean timeseries'

dash = pn.Column((test_points * gts.OSM).relabel(title), one_test_site)
dash.servable()

Optional: Seasonal Prediction#

Clicking on some of the sites above suggests that prediction often works well for some months and not for others. Perhaps different variables are important for prediction, depending on the season? We might be able to achieve better results if we generate separate models for each season. First we’ll set up a function that computes prediction stats for a given training index, test index, array of X, array of y and array of seasons.

seasons = ['summer', 'fall', 'spring', 'winter']

def prediction_stats(train_idx, test_idx, X, y, season):
    """
    Compute prediction stats for equal length arrays X, y, and season
    split into train_idx and test_idx
    """
    pred = {}

    for s in seasons:
        season_idx = np.where(season==s)
        season_train_idx = np.intersect1d(season_idx, train_idx, assume_unique=True)
        season_test_idx = np.intersect1d(season_idx, test_idx, assume_unique=True)
        
        model = LinearRegression()
        model.fit(X[season_train_idx], y[season_train_idx])
        
        y_hat = model.predict(X[season_test_idx])
        y_test = y[season_test_idx]
        pred[s] = {'predicted': y_hat,
                   'observed': y_test,
                   'corrcoef': np.corrcoef(y_hat, y_test)[0][1],
                   'test_index': test_idx}
    return pred

Setup Dask#

With dask, we can distribute tasks over cores and do parallel computation. For more information see https://dask.org/

from distributed import Client

client = Client()
client

Client

Client-866d3165-a292-11ef-89bf-000d3a30433a

Connection method: Cluster object Cluster type: distributed.LocalCluster
Dashboard: http://127.0.0.1:8787/status

Cluster Info

Now we’ll scatter our data using dask and make a bunch of different splits. For each split we’ll compute the predicton stats for each season.

futures = []
sep = GroupShuffleSplit(n_splits=50, train_size=0.9, test_size=0.1)

X_future = client.scatter(X)
y_future = client.scatter(y)
season_future = client.scatter(df['season'].values)

for train_index, test_index in sep.split(X, y, df.site.cat.codes.values):
    futures += [client.submit(prediction_stats, train_index, test_index,
                              X_future, y_future, season_future)]

Now that we have our computations set up in dask, we can gather the results:

results = client.gather(futures)

And consolidate the results for each season.

output = {
    s: {
        'predicted': np.concatenate([i[s]['predicted'] for i in results]),
        'observed': np.concatenate([i[s]['observed'] for i in results]),
        'test_index': np.concatenate([i[s]['test_index'] for i in results]),
        'corrcoef': np.array([i[s]['corrcoef'] for i in results])
    } for s in seasons}

hv.Layout([
    result_plot(output[s]['predicted'], output[s]['observed'], s, output[s]['corrcoef'].mean())
    for s in seasons]).cols(2).options('RGB', axiswise=True, width=400)

def helper(s):
    corr = output[s]['corrcoef']
    return pd.DataFrame([corr, [s] * len(corr)], index=['corr', 'season']).T

corr = pd.concat(map(helper, seasons)).reset_index(drop=True)

corr.hvplot.hist(y='corr', groupby='season', bins=np.arange(0, .9, .05).tolist(), dynamic=False, width=500)

Suggested Next Steps#

  • Can we predict certain vegetations better than others?

  • Calculate fraction of explained variance.

  • Replace each FluxNet input variable with a remotely sensed (satellite imaged) quantity to predict carbon flux globally

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