The global precipitation pattern and its changes in the 20th century:
Air temperature and measurable falling precipitation are basic meteorological parameters to be used in both observational statistics and validation (such as calibration) of general circulation models.
The preference of precipitation being a conservative element of climate may be explained by its relatively simple method of areal determination in contrast to more difficult estimates of the energy balance components, e.g. net radiation or turbulent fluxes of latent heat, which would be more suitable to check model output.
The aim of this chapter – seen against the background of the total draft of this book – is to presentproblems and limits of precipitation determination and its temporal changes above continents and oceans.