Have precipitation extremes and annual totals been increasing in the
world's dry regions over the last 60 years?
Sebastian Sippel1,2, Jakob Zscheischler2, Martin Heimann1, Holger Lange3, Miguel D. Mahecha1,4,5, Geert Jan Van Oldenborgh6, Friederike E. L. Otto7, and Markus Reichstein1,4,51Max Planck Institute for Biogeochemistry, Jena, Germany 2Institute for Atmospheric and Climate Science, ETH Zürich, Zürich, Switzerland 3Norwegian Institute of Bioeconomy Research, Ås, Norway 4German Centre for Integrative Biodiversity Research (iDiv), Leipzig, Germany 5Michael Stifel Center Jena for Data-Driven and Simulation Science, Jena, Germany 6Weather and Climate Modeling, Koninklijk Nederlands Meteorologisch Instituut, De Bilt, Netherlands 7Environmental Change Institute, University of Oxford, South Parks Road, Oxford, United Kingdom
Abstract. Daily rainfall extremes and annual totals have increased in large parts of the global land area over the last decades. These observations are consistent with theoretical considerations of a warming climate. However, until recently these global tendencies have not been shown to consistently affect land regions with limited moisture availability. A recent study, published by Donat et al. (2016), now identified rapid increases in globally aggregated dry region daily extreme rainfall and annual rainfall totals. Here, we reassess the respective analysis and find that a) statistical artifacts introduced by the choice of the reference period prior to data standardization lead to an overestimation of the reported trends by up to 40 %, and also that b) the definition of "dry regions of the globe" affect the reported globally aggregated trends in extreme rainfall. Using the same observational dataset, but accounting for the statistical artifacts and using alternative, well-established dryness definitions, we find no significant increases in heavy precipitation in the world's dry regions. Adequate data pre-processing approaches and accounting for uncertainties regarding the definition of dryness are crucial to the quantification of spatially aggregated trends in the world's dry regions. In view of the high relevance of the question to many potentially affected stakeholders, we call for a cautionary consideration of specific data processing methods, including issues related to the definition of dry areas, to guarantee robustness of communicated climate change relevant findings.
Sippel, S., Zscheischler, J., Heimann, M., Lange, H., Mahecha, M. D., Van Oldenborgh, G. J., Otto, F. E. L., and Reichstein, M.: Have precipitation extremes and annual totals been increasing in the
world's dry regions over the last 60 years?, Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-452, in review, 2016.