## WEMC Tech Blog 4.5: Calculating NUTS2 Regional Averages with Land Sea Mask.

This post serves as a continuation on the techniques described in Tech Blog #4. So please familiarise with those steps beforehand.

NUTS2

As before, load in the NUTS shapefiles, this time selecting NUTS2.

NUTS2 is higher resolution and as a result, there are many more shapefiles. NUTS2 contains polygons at a regional (sub-country) level. In total there are 332 shapes for the Eurostat EU region.

Obtain the latest shapefiles from Eurostat.

Select a particular region with the 4 character NUTS_ID string.

For example, Stuttgart (DE):

``region = nuts[nuts['NUTS_ID'] == 'DE11']``

Land Sea Mask (LSM)

The land-sea mask is a field that contains, for every grid point, the proportion of land in the grid box. The values are between 0 (sea) and 1 (land).

You can obtain the ECMWF LSM NetCDF file here

A quick plot of the LSM gives this visual representation of the mask:

Calculate NUT2 Area Averages, with LSM

Now, following the same steps as described in Tech Blog #4, it is possible to calculate the area averages, with the LSM applied.

``````# contact luke.sanger@wemcouncil.org

# import packages
import iris
import geopandas as gpd
import numpy as np
import cartopy.crs as ccrs
import shapely
import iris.pandas
import iris.analysis.cartography
import os
import time

# place this file in directory where ERA5 files are located and define path below:
directory_in_str = '/data/private/wemc/100WS'

# read the NUTS shapefile and extract the polygons for a individual countries

# get the latitude-longitude grid from LSM file
cube2=cubelist2[0]
cube2=cube2.intersection(longitude=(-180, 180))

# function to check whether data is within shapefile - source: http://bit.ly/2pKXnWa

def geom_to_masked_cube(cube, geometry, x_coord, y_coord,
"""
Convert a shapefile geometry into a mask for a cube's data.

Args:

* cube:
The cube to mask.
* geometry:
A geometry from a shapefile to define a mask.
* x_coord: (str or coord)
A reference to a coord describing the cube's x-axis.
* y_coord: (str or coord)
A reference to a coord describing the cube's y-axis.

Kwargs:

* mask_excludes: (bool, default False)
If False, the mask will exclude the area of the geometry from the
cube's data. If True, the mask will include *only* the area of the
geometry in the cube's data.

.. note::
This function does *not* preserve lazy cube data.

"""
# Get horizontal coords for masking purposes.
lats = cube.coord(y_coord).points
lons = cube.coord(x_coord).points
lon2d, lat2d = np.meshgrid(lons,lats)

# Reshape to 1D for easier iteration.
lon2 = lon2d.reshape(-1)
lat2 = lat2d.reshape(-1)

# Iterate through all horizontal points in cube, and
# check for containment within the specified geometry.
for lat, lon in zip(lat2, lon2):
this_point = gpd.geoseries.Point(lon, lat)
res = geometry.contains(this_point)

# Invert the mask if we want to include the geometry's area.
# Make sure the mask is the same shape as the cube.
dim_map = (cube.coord_dims(y_coord)[0],
cube.coord_dims(x_coord)[0])

# Apply the mask to the cube's data.
data = cube.data
return cube

directory = os.fsencode(directory_in_str)

# iterate through NUTS file
for i, row in nuts.iterrows():

# select NUTS_ID as a string
cntry = str(row.NUTS_ID)

# assign row to variable based on NUTS_ID string
geom = nuts[nuts['NUTS_ID'] == cntry]

# loop through directory of NetCDF files
for file in os.listdir(directory):
filename = os.fsdecode(file)
if filename.endswith(".nc"):

# get the latitude-longitude grid from netcdf file
cube=cubelist[0]
cube=cube.intersection(longitude=(-180, 180))

# apply the geom_to_masked_cube function
geometry = geom

# apply the geom_to_masked_cube function to the LSM

# use iris function to get area weights

grid_lsm = grid_areas * grid_areaslsm

# create new time series cube with area averages
new_cube = masked_cube.collapsed(['latitude','longitude'], iris.analysis.MEAN, weights=grid_lsm)

# convert to series and retain the time series - use this!
dfs = iris.pandas.as_series(new_cube, copy=True)

#generate a new filename
edit = str(filename)
edit2 = edit.rstrip(".nc")
csv_name = cntry + "_" + edit2 + ".csv"

# save as csv
dfs.to_csv(csv_name)

# pause loop to save CPU drain
time.sleep(0.2)``````
NUTS2 Area Average

As usual, you can also get the code from my GitHub page.

by Luke Sanger (WEMC Data Engineer, 2018)

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