ERA-NUTS: interim version for 2021, daily data from January 1980 to September 2021

Interim extension for the daily ERA-NUTS dataset. This is the data used for generating the chart in this tweet: https://twitter.com/matteodefelice/status/1446144816744632320 <strong>DISCLAIMER</strong>: this version has not been completely quality-checked, the next official version (1980-2021) will be released next January. <strong>## Data</strong><br> The time-series have daily frequency and are aggregated following the NUTS 2016 classification. NUTS (Nomenclature of Territorial Units for Statistics) is a European Union standard for referencing the subdivisions of countries (member states, candidate countries and EFTA countries). This dataset contains NUTS0/1/2 time-series for the following variables obtained from the <strong>ERA5 reanalysis data</strong> (in brackets the name of the variable on the Copernicus Data Store and its unit measure): - <strong>t2m</strong>: 2-meter temperature (`2m_temperature`, Celsius degrees)<br> - <strong>ssrd</strong>: Surface solar radiation (`surface_solar_radiation_downwards`, Watt per square meter)<br> - <strong>ro</strong>: Runoff (`runoff`, millimeters)<br> <br> There are also a set of derived variables:<br> - <strong>ws100</strong>: Wind speed at 100 meters (derived by `100m_u_component_of_wind` and `100m_v_component_of_wind`, meters per second)<br> - <strong>HDD</strong>/<strong>CDD</strong>: Heating/Cooling Degree days (derived by 2-meter temperature the EUROSTAT definition).