Editing IPCC:AR6/WGI/Chapter-11 (section)

==== 11.6.3.4 Hydrological Deficits ====

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Streamflow and groundwater are not directly simulated by ESMs, which only simulate runoff, but they are generally represented in hydrological models ( [[#Prudhomme--2014|Prudhomme et al., 2014]] ; [[#Giuntoli--2015|Giuntoli et al., 2015]] ), which are typically driven in a stand-alone manner by observed or simulated climate forcing. The simulation of hydrological deficits is much more problematic than the simulation of mean streamflow or peak flows ( [[#Fundel--2013|Fundel et al., 2013]] ; [[#Stoelzle--2013|Stoelzle et al., 2013]] ; [[#Velázquez--2013|Velázquez et al., 2013]] ; [[#Staudinger--2015|Staudinger et al., 2015]] ), since models tend to be too responsive to the climate forcing and do not satisfactorily capture low flows ( [[#Tallaksen--2014|Tallaksen and Stahl, 2014]] ). Simulations of hydrological drought metrics show uncertainties related to the contribution of both GCMs and hydrological models ( [[#Bosshard--2013|Bosshard et al., 2013]] ; [[#Giuntoli--2015|Giuntoli et al., 2015]] ; [[#Samaniego--2017|Samaniego et al., 2017]] ; [[#Vetter--2017|Vetter et al., 2017]] ), but hydrological models forced by the same climate input data also show a large spread ( [[#van%20Huijgevoort--2013|van Huijgevoort et al., 2013]] ; [[#Ukkola--2018|Ukkola et al., 2018]] ). At the catchment scale, the hydrological model uncertainty is higher than both GCM and downscaling uncertainty ( [[#Vidal--2016|Vidal et al., 2016]] ), and the hydrological models show issues in representing drought propagation throughout the hydrological cycle ( [[#Barella-Ortiz--2019|Barella-Ortiz and Quintana Seguí, 2019]] ). A study on the evaluation of streamflow droughts in seven global (hydrological and land surface) models compared with observations in near-natural catchments of Europe showed a substantial spread among models, an overestimation of the number of drought events, and an underestimation of drought duration and drought-affected area ( [[#Tallaksen--2014|Tallaksen and Stahl, 2014]] ).

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