Paper Reviewed
Ruiz-Alvarez, O., Singh, V.P., Enciso-Medina, J., Munster, C., Kaiser, R., Ontiveros-Capurata, R.E., Diaz-Garcia, L.A. and Costa dos Santos, C.A. 2019. Spatio-temporal trends in monthly pan evaporation in Aguascalientes, Mexico. Theoretical and Applied Climatology 136: 775-789.

Global warming alarmists predict that surface evaporation should be increasing throughout the world in response to rising global temperatures. However, several researchers examining this topic have observed no recent trends in pan evaporation records or even decreasing trends (meaning less evaporation is occurring; see the several studies examined in our Subject Index under the topic of Evaporation). And now, Ruiz-Alvarez et al. (2019) have added to that growing body of literature.

As their contribution, the eight scientists hailing from Mexico, Brazil and the United States analyzed trends in monthly pan evaporation at 52 weather stations in the Mexico state of Aguascalientes. Each station was managed by the National Meteorological Service and recorded daily evaporation data from type "A" pans and had durations ranging from 22 to 71 years.

Statistical analyses were performed on the monthly data from each station so as to obtain twelve trend values per station per year. In all, the scientists produced 602 monthly trend series from the 52 stations, which was slightly less than the 624 expected (12 months x 52 stations) due to missing data.

And what did those trends in pan evaporation reveal?

In line with that which has been observed elsewhere in the world, evidence was lacking for a CO2-induced global warming effect. In fact, only 107 (17.8%) of the 602 monthly series had statistically significant trends, while the vast majority of them -- 495 or 82.2% -- did not. Furthermore, of those 107 stations that had statistically significant trends, Ruiz-Alvarez et al. report that 88 of them were negative, indicative of less evaporation through time, while only 19 were positive. All in all, therefore, of the 602 monthly evaporation series, only 3.2% had statistically significant increasing trends. By any measure, that percentage represents a failure in the global warming hypothesis that predicts pan evaporation should be increasing.