Temperature trends in regions affected by increasing aridity/humidity

A paper in 1991 claimed that regions affected by desertification experience warming trends relative to neighbouring areas. To assess this, an index of aridity/humidity based on the ratio of annual precipitation to annual potential evapotranspiration totals (P/PET) is developed. This index is used to define regions experiencing increases (and those where the increase is statistically significant) in aridity and humidity. We also consider regions always arid (average values of P/PET <0.5) and always humid (P/PET >2.0). Trends of average annual and summer surface air temperature are then calculated for regions in the various aridity/humidity categories and compared to most of the rest of the world's land areas equatorward of 60°. The results indicate that most of the differences in trends between categories are not statistically significant.