Urbanisation and Geographical Signatures in Observed Air Temperature Station Trends Over the Mediterranean and the Middle East–North Africa
Panos Hadjinicolaou, Anna Tzyrkalli, George Zittis, Jos Lelieveld
Abstract
Abstract We update observed temperature trends in the Mediterranean and the Middle East–North Africa (MENA) region, assess their temporal and spatial features and investigate possible influences from urbanisation. Monthly mean temperature time-series of 370 stations are acquired from the CRUTEM4.6 and GSOD datasets and converted into suitable format for statistical analysis. The calculated annual and seasonal temperature linear trends for 1981–2020 indicate a strong warming with a MENA station average annual trend equal to $$0.36 ^\circ {\hbox {C}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>0</mml:mn> <mml:mo>.</mml:mo> <mml:msup> <mml:mn>36</mml:mn> <mml:mo>∘</mml:mo> </mml:msup> <mml:mtext>C</mml:mtext> </mml:mrow> </mml:math> /decade and a faster warming rate for spring ( $$0.43 ^\circ {\hbox {C}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>0</mml:mn> <mml:mo>.</mml:mo> <mml:msup> <mml:mn>43</mml:mn> <mml:mo>∘</mml:mo> </mml:msup> <mml:mtext>C</mml:mtext> </mml:mrow> </mml:math> /decade) and summer ( $$0.45 ^\circ {\hbox {C}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>0</mml:mn> <mml:mo>.</mml:mo> <mml:msup> <mml:mn>45</mml:mn> <mml:mo>∘</mml:mo> </mml:msup> <mml:mtext>C</mml:mtext> </mml:mrow> </mml:math> /decade). These trends are correlated with longitude, revealing faster warming rates over the eastern Mediterranean and Middle East. The stations are characterised as rural or urban centre with the use of the Global Human Settlement Model (GHS-SMOD) spatial grid that accounts for population, city size and shape for the year 2000. The trend derived for the urban centre stations is an annually averaged $$0.1 ^\circ {\hbox {C}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>0</mml:mn> <mml:mo>.</mml:mo> <mml:msup> <mml:mn>1</mml:mn> <mml:mo>∘</mml:mo> </mml:msup> <mml:mtext>C</mml:mtext> </mml:mrow> </mml:math> /decade greater than for the rural or all stations, and more prominent during summer and autumn. Hence a discernible, but small, urbanisation signature is revealed.