Abstract
During the second half of the 20th century, in the littoral and pre-littoral areas of the Valencia region, the diurnal temperature range (DTR) registered a significant drop in summer (July and August). Meanwhile, in the same period in the lower Ebro Valley (Ebro Observatory), to the north of the Valencia region, the maximum temperature and DTR increased steeply. In order to explain the DTR drop in the coastal areas of the Valencia region, some studies have proposed an increase in the summer sea-surface temperature (SST) and others have attributed it to the urban heat island effect. Nevertheless, this drop occurred well before the current climate change was evident and therefore, before the rise of the SST. Furthermore, regarding the second proposed explanation, the drop in the DTR does not disappear when working with selected stations away from heavily urbanized areas. In this work, we propose that both the DTR rise at the Ebro Observatory and the DTR drop in the Valencia region are linked to the same process: changes in atmospheric circulation on a synoptic-scale in the North Atlantic that occurred in the late 1960s.
Highlights
The 20th century saw a worldwide rise in temperature of 0.89 ◦ C [1] but this increase was not a uniform one all around the globe, neither spatially nor seasonally [2,3]
Minimum temperatures increased at a faster rate than maximum temperatures during the latter half of the 20th century resulting in a significant decrease in the diurnal temperature range (DTR) for this period [5]
We focus on the Northern days because, as we shall see, it is during these days when the reasons for the differential behaviour in the Tx along the eastern coast of the Iberian Peninsula (IP) becomes hand, when the meridional component of the flow is northward (42% of the days, ‘Southern days’), the IP is in general more influenced by Mediterranean and African air masses
Summary
The 20th century saw a worldwide rise in temperature of 0.89 ◦ C [1] but this increase was not a uniform one all around the globe, neither spatially nor seasonally [2,3]. This increase was not a progressive one either and was, produced during two different phases. Minimum temperatures increased at a faster rate than maximum temperatures during the latter half of the 20th century resulting in a significant decrease in the DTR (diurnal temperature range) for this period [5]. This widespread decrease in the DTR was only evident from 1950–1980 [6]; that is to say, maximum and minimum temperatures have increased roughly at the same rate from the beginning of the current period of global warming
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