A quantitative evaluation of the issue of drought definition: a source of disagreement in future drought assessmentsA quantitative evaluation of the issue of drought definition: a source of disagreement in future drought assessments Επιστολή Letter 2023-02-172021enA. K. acknowledges the support from the FP7 project HELIX (Grant No. 603864)Droughts are anticipated to intensify in many parts of the world due to climate change. However, the issue of drought definition, namely the diversity of drought indices, makes it difficult to compare drought assessments. This issue is widely known, but its relative importance has never been quantitatively evaluated in comparison to other sources of uncertainty. Here, encompassing three drought categories (meteorological, agricultural, and hydrological droughts) with four temporal scales of interest, we evaluated changes in the drought frequency using multi-model and multi-scenario simulations to identify areas where the definition issue could result in pronounced uncertainties and to what extent. We investigated the disagreement in the signs of changes between drought definitions and decomposed the variance into four main factors: drought definitions, greenhouse gas concentration scenarios, global climate models, and global water models, as well as their interactions. The results show that models were the primary sources of variance over 82% of the global land area. On the other hand, the drought definition was the dominant source of variance in the remaining 17%, especially in parts of northern high-latitudes. Our results highlight specific regions where differences in drought definitions result in a large spread among projections, including areas showing opposite signs of significant changes. At a global scale, 7% of the variance resulted independently from the definition issue, and that value increased to 44% when 1st and 2nd order interactions were considered. The quantitative results suggest that by clarifying hydrological processes or sectors of interest, one could avoid these uncertainties in drought assessments to obtain a clearer picture of future drought change.http://creativecommons.org/licenses/by/4.0/Environmental Research Letters1610Satoh_et_al_Environ. Res. Lett._16(10)_2021.pdfChania [Greece]Library of TUC2023-02-17application/pdf3.6 MBfree Satoh Yusuke Shiogama, Hideo Hanasaki Naota Pokhrel, Yadu Boulange Julien Burek Peter Gosling Simon N. Gryllakis Emmanouil Γρυλλακης Εμμανουηλ Koutroulis Aristeidis Κουτρουλης Αριστειδης Müller Schmied Hannes Thiery Wim Yokohata Tokuta IOP Publishing Drought projections Uncertainty The issue of drought definition Sources of uncertainty ANOVA