Urban Heat Island Effect In South America

By Paul Homewood

According to GISS there is no heat island in Asuncion

As promised, a closer look at the GISS temperature record in South America. Yesterday we saw how GHCN temperature adjustments were cooling the past there and producing an artificial warming trend. We also observed how the vast majority of stations, 29 out of 33, were urban sites. So is this distorting the temperature record?

It is well established that urban sites create an urban heat island effect and that this effect has been increasing over recent decades. In theory, GISS allow for this effect by making “Homogeneity Adjustments”, in practice increasing past temperatures at urban sites. As their website puts it :-

The goal of the homogenization effort is to avoid any impact (warming or cooling) of the changing environment that some stations experienced by changing the long term trend of any non-rural station to match the long term trend of their rural neighbors, while retaining the short term monthly and annual variations. If no such neighbors exist - or the overlap of the rural combination and the non-rural record is less than 20 years - the station is completely dropped;

So how has this worked out on the sites we identified previously? Figure 1 shows the change in mean temperatures between 1940 and 2010. As there is considerable variation from country to country, I have given average figures for each state. In Brazil and Argentina, the trend change is about half a degree higher in urban sites than in rural, although the rural sample is inevitably too small to draw any real conclusions.

SOUTH AMERICA







GISS VERSION 2 MEAN TEMPS



















1940 2010 INCREASE























SALTA URBAN ARG 16.98 16.58 -0.40 SANTIAGO URBAN ARG 20.26 19.85 -0.41 POSADAS URBAN ARG 20.86 21.74 0.88 LA RIOJA URBAN ARG 18.95 20.18 1.23 CATAMARCA URBAN ARG 19.40 20.92 1.52 CERES URBAN ARG 18.22 18.98 0.76 SAN JUAN URBAN ARG 16.63 17.97 1.34 PARANA URBAN ARG 17.57 17.82 0.25 RIO CUARTO URBAN ARG 15.49 16.25 0.76 JUNIN URBAN ARG 16.28 15.65 -0.63 SANTA ROSA URBAN ARG 15.03 15.45 0.42 DOLORES URBAN ARG 14.80 14.90 0.10 MAR DEL PLATA URBAN ARG 13.46 13.66 0.20 BAHIA URBAN ARG 14.78 14.82 0.04 BARILOCHE URBAN ARG 8.84 8.12 -0.72 ESQUEL URBAN ARG 9.20 8.21 -0.99 TRELEW URBAN ARG 13.53 13.96 0.43 COMODORO URBAN ARG 12.78 13.02 0.24 RIO GALLEGOS URBAN ARG 6.68 7.53 0.85 USHUAIA URBAN ARG 5.79 6.14 0.35 AV ARGENTINA URBAN















0.31























SAN ANTONIO RURAL ARG 15.23 14.54 -0.69 PILAR RURAL ARG 16.76 16.91 0.15 AV ARGENTINA RURAL















-0.27























LA PAZ URBAN BOL 10.04 8.29 -1.75























MANAUS URBAN BRA 26.71 27.88 1.17 SALVADOR URBAN BRA 24.93 25.71 0.78 CUIABA URBAN BRA 25.42 26.42 1.00 SAO PAOLO URBAN BRA 18.26 20.54 2.28 CURITIBA URBAN BRA 17.00 17.77 0.77 AV BRAZIL URBAN















1.20























QUIXERAMOBIN RURAL BRA 26.99 27.85 0.86







































ARICA URBAN CHI 20.01 18.72 -1.29 PUDAHUEL URBAN CHI 14.55 14.21 -0.34 PUNTA ARENAS RURAL CHI 6.85 6.08 -0.77 AV CHILE















-0.80























ASUNCION URBAN PAR 23.88 22.79 -1.09

FIGURE 1

So let’s now look at the Homogeneity Adjustments GISS have actually made.

SOUTH AMERICA



GISS VERSION 3.1























1940 1940 UHI











AFTER GHCN ADJ AFTER ADJ















HOMOGENEITY



SALTA URBAN ARG 15.88 15.88 0.00 SANTIAGO URBAN ARG 20.26 19.36 -0.90 POSADAS URBAN ARG 20.86 21.76 0.90 LA RIOJA URBAN ARG 18.95 18.85 -0.10 CATAMARCA URBAN ARG 19.40 19.40 0.00 CERES URBAN ARG 18.22 18.22 0.00 SAN JUAN URBAN ARG 16.63 16.63 0.00 PARANA URBAN ARG 17.28 17.47 0.19 RIO CUARTO URBAN ARG 15.49 15.49 0.00 JUNIN URBAN ARG 16.28 15.88 -0.40 SANTA ROSA URBAN ARG 14.64 14.64 0.00 DOLORES URBAN ARG 14.80 14.80 0.00 MAR DEL PLATA URBAN ARG 13.36 13.46 0.10 BAHIA URBAN ARG 14.78 14.78 0.00 BARILOCHE URBAN ARG 8.24 8.24 0.00 ESQUEL URBAN ARG 8.30 8.30 0.00 TRELEW URBAN ARG 13.53 13.53 0.00 COMODORO URBAN ARG 12.78 12.98 0.20 RIO GALLEGOS URBAN ARG 6.68 6.68 0.00 USHUAIA URBAN ARG 5.79 6.09 0.30 AV ARGENTINA URBAN















0.01



















0.00 SAN ANTONIO RURAL ARG 15.23 15.23 0.00 PILAR RURAL ARG 16.76 16.76 0.00 AV ARGENTINA RURAL















0.00



















0.00 LA PAZ URBAN BOL



N/A



















0.00 MANAUS URBAN BRA 26.29 26.69 0.40 SALVADOR URBAN BRA



N/A CUIABA URBAN BRA 25.42 25.92 0.50 SAO PAOLO URBAN BRA N/A CURITIBA URBAN BRA 17.00 18.20 1.20 AV BRAZIL URBAN















0.70



















0.00 QUIXERAMOBIN RURAL BRA 25.99 25.99 0.00















0.00



















0.00 ARICA URBAN CHI 20.01 20.01 0.00 PUDAHUEL URBAN CHI 13.75 14.05 0.30 AV CHILE URBAN















0.15























PUNTA ARENAS RURAL CHI 6.05 6.05 0.00 AV CHILE















0.00



















0.00 ASUNCION URBAN PAR 22.48 22.38 -0.10























AVERAGE ALL URBAN















0.10

FIGURE 2

Of the 29 urban sites, 4 have been given negative adjustments; i.e. it has been assumed that the UHI effect has produced cooling. 13 more have no UHI adjustment made at all. Overall, as a crude average, the UHI adjustment is a mere 0.10 C.

We seem to be faced with 3 explanations :-

1) The UHI effect does not exist at most of these cities.

2) The rural sites GISS use to compare with urban ones are also exhibiting UHI or other non-climatic effects of their own, thereby cancelling out the urban signals.

3) GISS’s programmes are not doing what they are designed to do.