Strengths and weaknesses of the new CERRA-Land &#160;surface reanalysis at 5.5 km resolution over Europe
Authors: Verrelle Antoine , Michael Glinton , Eric Bazile , Le Moigne Patrick 
Published: June 2022

&lt;p&gt;&lt;span&gt;The Copernicus Climate Change Service of the European Commission &lt;/span&gt;&lt;span&gt;aims &lt;/span&gt;&lt;span&gt;to&lt;/span&gt;&lt;span&gt; produc&lt;/span&gt;&lt;span&gt;e&lt;/span&gt;&lt;span&gt; and deliver a &lt;/span&gt;&lt;span&gt;land &lt;/span&gt;&lt;span&gt;regional reanalysis for Europe covering the period &lt;/span&gt;&lt;span&gt;from&lt;/span&gt;&lt;span&gt; 19&lt;/span&gt;&lt;span&gt;84 to &lt;/span&gt;&lt;span&gt;the present&lt;/span&gt;&lt;span&gt; at &lt;/span&gt;&lt;span&gt;a &lt;/span&gt;&lt;span&gt;horizontal &lt;/span&gt;&lt;span&gt;resolution of &lt;/span&gt;&lt;span&gt;5.5 km.&lt;/span&gt;&lt;/p&gt;&lt;p&gt;The need for precipitation and surface variables at an ever-increasing spatial and temporal resolution is a recurrent demand. These variables allow, among other things, to address water resource management issues and to conduct climate change impact studies. Regional surface reanalyses are a way to reconstruct these variables for past periods covering several years using state-of-the-art models.&lt;/p&gt;&lt;p&gt;&lt;span&gt; CERRA-&lt;/span&gt;&lt;span&gt;Land &lt;/span&gt;&lt;span&gt;(Copernicus European Regional Re-Analysis)&lt;/span&gt;&lt;span&gt; is a &lt;/span&gt;&lt;span&gt;regional&lt;/span&gt;&lt;span&gt; land surface reanalysis dataset &lt;/span&gt;&lt;span&gt;that&lt;/span&gt;&lt;span&gt; describes the evolution of soil moisture, soil temperature and &lt;/span&gt;&lt;span&gt;the&lt;/span&gt;&lt;span&gt; snowpack. &lt;/span&gt;&lt;span&gt;CERRA-Land&lt;/span&gt;&lt;span&gt; is the result of a single &lt;/span&gt;&lt;span&gt;stand alone integration of the SURFEX V8.1 land surface model driven by meteorological forcing from the CERRA atmospheric &lt;/span&gt;&lt;span&gt;reanalysis&lt;/span&gt;&lt;span&gt; and an offline &lt;/span&gt;&lt;span&gt;analysis &lt;/span&gt;&lt;span&gt;of &lt;/span&gt;&lt;span&gt;daily accumulated &lt;/span&gt;&lt;span&gt;surface&lt;/span&gt;&lt;span&gt; precipitation &lt;/span&gt;&lt;span&gt;using&lt;/span&gt; &lt;span&gt;an &lt;/span&gt;&lt;span&gt;optimal interpolation between a&lt;/span&gt;&lt;span&gt;n initial estimate (&lt;/span&gt;&lt;span&gt;first guess&lt;/span&gt;&lt;span&gt;)&lt;/span&gt; &lt;span&gt;based on CERRA &lt;/span&gt;&lt;span&gt;predicted&lt;/span&gt;&lt;span&gt; precipitation&lt;/span&gt;&lt;span&gt; and in situ rain gauges&lt;/span&gt;&lt;span&gt;. The &lt;/span&gt;&lt;span&gt;2-meter &lt;/span&gt;&lt;span&gt;temperature and relative humidity &lt;/span&gt;&lt;span&gt;forcing data &lt;/span&gt;&lt;span&gt;come &lt;/span&gt;&lt;span&gt;from&lt;/span&gt; &lt;span&gt;the &lt;/span&gt;&lt;span&gt;CERRA &lt;/span&gt;&lt;span&gt;surface analysis and the&lt;/span&gt; &lt;span&gt;shortwave and longwave &lt;/span&gt;&lt;span&gt;downw&lt;/span&gt;&lt;span&gt;elling &lt;/span&gt;&lt;span&gt;radiation, the 10-meter wind speed, and surface pressure come from the CERRA forecast output&lt;/span&gt;&lt;span&gt;s&lt;/span&gt;&lt;span&gt;. &lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;The CERRA-Land system &lt;/span&gt;&lt;span&gt;uses the tiling approach where each grid-box of the model is &lt;/span&gt;&lt;span&gt;divided into three different fraction&lt;/span&gt;&lt;span&gt;s&lt;/span&gt;&lt;span&gt;: urban, lake and natur&lt;/span&gt;&lt;span&gt;al&lt;/span&gt;&lt;span&gt;. &lt;/span&gt;&lt;span&gt;For the nature fraction, the soil is discretized into 14 layers to accurately describe the water and energy transfers between the surface and the deep soil.&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;The quality of &lt;/span&gt;&lt;span&gt;CERRA-&lt;/span&gt;&lt;span&gt;Land is assessed by compari&lt;/span&gt;&lt;span&gt;sons&lt;/span&gt; &lt;span&gt;to&lt;/span&gt;&lt;span&gt; ground-based observations, &lt;/span&gt;&lt;span&gt;such as&lt;/span&gt;&lt;span&gt; snow depth, &lt;/span&gt;&lt;span&gt;2-&lt;/span&gt;&lt;span&gt;meter temperature&lt;/span&gt;&lt;span&gt;, &lt;/span&gt;&lt;span&gt;downw&lt;/span&gt;&lt;span&gt;elling&lt;/span&gt;&lt;span&gt; shortwave radiation &lt;/span&gt;&lt;span&gt;and independent rain&lt;/span&gt;&lt;span&gt;fall&lt;/span&gt;&lt;span&gt; station&lt;/span&gt;&lt;span&gt;s&lt;/span&gt;&lt;span&gt;.&lt;/span&gt; &lt;span&gt;A comparison with E&lt;/span&gt;&lt;span&gt;RA&lt;/span&gt;&lt;span&gt;5-Land will be done and the add&lt;/span&gt;&lt;span&gt;ed&lt;/span&gt;&lt;span&gt; value of th&lt;/span&gt;&lt;span&gt;e&lt;/span&gt;&lt;span&gt; regional dataset will be discussed. &lt;/span&gt;&lt;span&gt;The entire &lt;/span&gt;&lt;span&gt;CERRA&lt;/span&gt;&lt;span&gt;-Land dataset from 19&lt;/span&gt;&lt;span&gt;84&lt;/span&gt;&lt;span&gt; to present is &lt;/span&gt;&lt;span&gt;now available in the &lt;/span&gt;&lt;span&gt;MARS&lt;/span&gt;&lt;span&gt; database &lt;/span&gt;&lt;span&gt;at ECMWF&lt;/span&gt;&lt;span&gt; and will be avai&lt;/span&gt;&lt;span&gt;lable&lt;/span&gt;&lt;span&gt; through the &lt;/span&gt;&lt;span&gt;Copernicus C&lt;/span&gt;&lt;span&gt;limate &lt;/span&gt;&lt;span&gt;D&lt;/span&gt;&lt;span&gt;ata &lt;/span&gt;&lt;span&gt;S&lt;/span&gt;&lt;span&gt;tore.&lt;/span&gt;&lt;/p&gt;