Sebastiaan,
De duur van "overlappend waarnemen" hangt af van wat je waarneemt en het verschil in ligging van de twee officieel metende waarnemingsstations.
Bijvoorbeeld temperatuur en neerslag verschillen al in waarneningsduur al gauw een factor 2.
Tussen Nederland en Belgie zijn zeker meer dan 10 jaar nodig.
Wat er bijvoorbeeld in de VS mee komt kijken vind je hier:http://journals.ametsoc.org/doi/abs/10.1175/JAMC-D-11-0267.1
Projecting ‘‘Normals’’ in a Nonstationary Climate
D. S. WILKS
Department of Earth and Atmospheric Sciences, Cornell University, Ithaca, New York
(Manuscript received 16 December 2011, in final form 4 September 2012)
ABSTRACT
Climate ‘‘normals’’ are statistical estimates of present and/or near-future climate means for such quantities
as seasonal temperature or precipitation. In a changing climate, simply averaging a large number of previous
years of data may not be the best method for estimating normals. Here eight formulations for climate normals,
including the recently proposed ‘‘hinge’’ function, are compared in artificial- and real-data settings. Although
the hinge function is attractive conceptually for representing accelerating climate changes simply, its use is in
general not yet justified for divisional U.S. seasonal temperature or precipitation. Averages of the most recent
15 and 30 yr have performed better during the recent past for U.S. divisional seasonal temperature and
precipitation, respectively; these averaging windows are longer than those currently employed for this purpose at the U.S. Climate Prediction Center"
Over de methode zelf heb ik zelf veel steun gehad aan het boek: " Methods in Climatology" van V.Conrad en L.W. Pollack en speciaal het hoofdstuk "Spatial Comparison of Climatic Elements"