Changes in the hydrological conditions of the land surface
have substantial impacts on society. Yet assessments of observed continental
dryness trends yield contradicting results. The concept that dry regions dry
out further, whereas wet regions become wetter as the climate warms has been
proposed as a simplified summary of expected as well as observed changes over land, although this concept is
mostly based on oceanic data. Here we present an analysis of more than 300
combinations of various hydrological data sets of historical land dryness
changes covering the period from 1948 to 2005. Each combination of data sets is
benchmarked against an empirical relationship between evaporation,
precipitation and aridity.