Heat waves characterization in the Iberian Peninsula over the last 70 years&#160;
Authors: Paredes Fortuny Laura , Palao Juan , Khodayar Samiro 
Published: June 2021

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&lt;p&gt;&lt;span&gt;The Iberian Peninsula is a well-known&amp;#160;&lt;/span&gt;&lt;span&gt;climate change&amp;#160;&lt;/span&gt;&lt;span&gt;hot spot&amp;#160;&lt;/span&gt;&lt;span&gt;where&lt;/span&gt;&lt;span&gt;&amp;#160;heat waves&lt;/span&gt;&lt;span&gt;&amp;#160;are a recurrent&amp;#160;&lt;/span&gt;&lt;span&gt;phenomenon&lt;/span&gt;&lt;span&gt;,&lt;/span&gt;&lt;span&gt;&amp;#160;with potentially catastrophic consequences.&amp;#160;&lt;/span&gt;&lt;span&gt;In this investigation, w&lt;/span&gt;&lt;span&gt;e aim to characterize the heat waves occurred in this region since 1951 and identify potential changes.&amp;#160;&lt;/span&gt;&lt;/p&gt;
&lt;p&gt;&lt;span&gt;We use the observational data from the SPAIN02 (about 5x5 km), from AEMET and the high-resolution convection-permitting COSMO model simulation (about 2.8km) covering the period from 1951 to 2019 the former, and the period 2000 to 2019 the later. To characterize the heat waves, the&lt;/span&gt;&lt;span&gt;ir&lt;/span&gt;&lt;span&gt;&amp;#160;intensity, the size, maximum temperature, the trajectory of the centre of mass and the heat wave magnitude index (HWMI)&lt;/span&gt;&lt;span&gt;, which characterize&amp;#160;&lt;/span&gt;&lt;span&gt;heat wave&lt;/span&gt;&lt;span&gt;s&lt;/span&gt;&lt;span&gt;&amp;#160;in terms of intensity, duration and size&lt;/span&gt;&lt;span&gt;, are investigated&lt;/span&gt;&lt;span&gt;. Furthermore, their concurrence with drought&lt;/span&gt;&lt;span&gt;&amp;#160;and&lt;/span&gt;&lt;span&gt;&amp;#160;the impact of precedent&lt;/span&gt;&lt;span&gt;&amp;#160;winter-spring&lt;/span&gt;&lt;span&gt;&amp;#160;precipitation is examined.&amp;#160;&lt;/span&gt;&lt;span&gt;&amp;#160;&lt;/span&gt;&lt;/p&gt;
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&lt;p&gt;&lt;span&gt;In general,&amp;#160;&lt;/span&gt;&lt;span&gt;we&lt;/span&gt;&lt;span&gt;&amp;#160;may&lt;/span&gt;&lt;span&gt;&amp;#160;&lt;/span&gt;&lt;span&gt;conclude that heat waves&amp;#180;&lt;/span&gt;&lt;span&gt;&amp;#160;&lt;/span&gt;&lt;span&gt;number,&lt;/span&gt;&lt;span&gt;&amp;#160;&lt;/span&gt;&lt;span&gt;and&lt;/span&gt;&lt;span&gt;&amp;#160;&lt;/span&gt;&lt;span&gt;intensity&lt;/span&gt;&lt;span&gt;&amp;#160;&lt;/span&gt;&lt;span&gt;has increased&lt;/span&gt;&lt;span&gt;&amp;#160;over the study period&lt;/span&gt;&lt;span&gt;.&lt;/span&gt;&lt;span&gt;&amp;#160;&lt;/span&gt;&lt;span&gt;The associated maximum temperature recorded each year has become higher.&lt;/span&gt;&lt;span&gt;&amp;#160;&lt;/span&gt;&lt;span&gt;Furthermore, the number of heat days defined as the days affected by a heat wave has increased.&amp;#160;&lt;/span&gt;&lt;span&gt;The duration of the heat wave periods has also increased.&lt;/span&gt;&lt;span&gt;&amp;#160;&lt;/span&gt;&lt;span&gt;Moreover, the assessment of the heat wave sizes points out an increase, although the mass centre of all the heat waves occurr&lt;/span&gt;&lt;span&gt;ing&lt;/span&gt;&lt;span&gt;&amp;#160;within a year is fixed in the centre of the peninsula, with small deviations.&amp;#160;&lt;/span&gt;&lt;span&gt;Accordingly, the HWMID shows that the magnitude of the heat waves has increased.&amp;#160;&lt;/span&gt;&lt;span&gt;&amp;#160;&lt;/span&gt;&lt;/p&gt;
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&lt;p&gt;&lt;span&gt;The assessed evolution is spatiotemporally heterogeneously distributed. &lt;/span&gt;&lt;span&gt;Although all areas suffer an increase in the number of heat days and heat wave events&lt;/span&gt;&lt;span&gt;&amp;#160;over time&lt;/span&gt;&lt;span&gt;, s&lt;/span&gt;&lt;span&gt;ome areas at the Mediterranean coast and at the northern Cantabria&lt;/span&gt;&lt;span&gt;n&lt;/span&gt;&lt;span&gt; region&amp;#160;&lt;/span&gt;&lt;span&gt;e&lt;/span&gt;&lt;span&gt;xperience&lt;/span&gt;&lt;span&gt;&amp;#160;&lt;/span&gt;&lt;span&gt;generall&lt;/span&gt;&lt;span&gt;y&amp;#160;&lt;/span&gt;&lt;span&gt;less&lt;/span&gt;&lt;span&gt;&amp;#160;heat days in comparison to the rest of the peninsula&lt;/span&gt;&lt;span&gt;,&lt;/span&gt;&lt;span&gt;&amp;#160;&lt;/span&gt;&lt;span&gt;but those&amp;#160;&lt;/span&gt;&lt;span&gt;a&lt;/span&gt;&lt;span&gt;re more intense than elsewhere&lt;/span&gt;&lt;span&gt;. Nevertheless, the central part of the peninsula &lt;/span&gt;&lt;span&gt;experiences&lt;/span&gt;&lt;span&gt;&amp;#160;&lt;/span&gt;&lt;span&gt;generally&amp;#160;&lt;/span&gt;&lt;span&gt;more heat days&lt;/span&gt;&lt;span&gt;,&amp;#160;&lt;/span&gt;&lt;span&gt;but&lt;/span&gt;&lt;span&gt;&amp;#160;with a lower associated intensity.&lt;/span&gt;&lt;span&gt;&amp;#160;These observations&amp;#160;&lt;/span&gt;&lt;span&gt;do&lt;/span&gt;&lt;span&gt;&amp;#160;not change over time.&lt;/span&gt;&lt;span&gt;&amp;#160;The increase in the number of heat days per year is also temporally heterogeneous. In the last 10 years the growth in the number of heat days has been much higher than in the previous periods studied. Some regions at the south-western&amp;#160;&lt;/span&gt;&lt;span&gt;p&lt;/span&gt;&lt;span&gt;eninsula have doubled the number of heat days in the last decade. These regions correspond to frequently affected drought zones.&amp;#160;&lt;/span&gt;&lt;/p&gt;
&lt;p&gt;&lt;span&gt;We will additionally discuss o&lt;/span&gt;&lt;span&gt;ur results&amp;#160;&lt;/span&gt;&lt;span&gt;regarding the impact of precedent winter-spring precipitation on heat waves development. A&amp;#160;&lt;/span&gt;&lt;span&gt;correlation between a low frequency of heat days and rainy preceding winters&lt;/span&gt;&lt;span&gt;&amp;#160;is found&lt;/span&gt;&lt;span&gt;.&amp;#160;&lt;/span&gt;&lt;span&gt;&amp;#160;&lt;/span&gt;&lt;/p&gt;
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