Plotting a trend line

Software and Tools Other - Software and tools
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1

Hello guys,

im struggling with the following problem, maybe someone can help.

My plot (see the code below) is about the timeseries of a variable and i want to add a linear trend. What i already did is to figure out the necessary parameters a and b.

Is there a toolbox-function to plot a line with just these paramets requiered? Or is creating a vector out of these parameters and plotting this vector a better solution?

Any help is appreciated!

Thanks and cheers,

Tim

 Expand source 
import cdstoolbox as ct

@ct.application(title=‘Zonal mean and trend’)


@ct.output.livefigure()


def application():

data = ct.catalogue.retrieve(

‘reanalysis-era5-land-monthly-means’,

{

‘variable’: ‘2m_temperature’,

‘product_type’: ‘monthly_averaged_reanalysis’,

‘year’: [

‘2002’,‘2003’,‘2004’,‘2005’,‘2006’,‘2007’,‘2008’,‘2009’,‘2010’,‘2011’,‘2012’,

],

‘month’: [

‘01’,‘02’,‘03’,‘04’,‘05’,‘06’,‘07’,‘08’,‘09’,‘10’,‘11’,‘12’

],

‘time’: ‘00:00’,

}

)


temp = ct.cube.average(data, dim=['lat', 'lon'])

a, b, a_std, b_std = ct.stats.trend(
    temp, slope_units='°C year-1')
    
fig  = ct.chart.line(temp,
    layout_kwargs = {
        'title': 'Monthly average temperature',
        'xaxis':{
            'title': 'Time [years]',
            'range': ['2001-07','2013-06']
        },
        'yaxis': {
          'title': 'ERA5 2m Air temperature (°C)',               
          'range': [-10,1]
        }
    },
    scatter_kwargs = {
        'mode': 'lines'
    }
) 

return fig</pre>


2

Dear Tim,

I have added a trend line to your workflow in the following application:

https://cds.climate.copernicus.eu/toolbox-editor/168/forum_trend_line

The trick is to compute the linear fit of the your data using the ct.stats.extrapolate function and plot the fit.

fit = ct.stats.extrapolate(
        temp,
        date_range_kwargs=
        {
            'start': start_date, 
            'end': end_date, 
            'periods': 2
        },
        func='linear'
    )

Let me know if you have any question or want any further explanation.

Regards.

Vivien

3

Dear Vivien,

thanks, this is exactly what I want to plot. No further questions!

Thanks and regards,

Tim