Reviewer Comments for HESS-2019-676

Dierauer et al. 2020 present an analysis of snow and streamflow drought in four catchments in British Columbia, Canada.They use an uncalibrated process-based hydrologic model forced with downscaled climate data from four general circulation models archived in the CMIP-5 climate model database.The processbased hydrologic model includes physical representations of unsaturated zone and saturated zone groundwater flow, physical representations of overland flow/channel routing, and conceptual representations of snow accumulation and snowmelt.This allows the authors to draw inferences about possible linkages between changes in snow C1 HESSD Interactive comment Printer-friendly version Discussion paper accumulation and melt, groundwater storage, and summer and winter low streamflow, including the lowest 20% of all summer and winter flows, referred to as "streamflow drought".The authors justify their study by identifying two knowledge gaps: 1) no studies have explicitly quantified the impact of different snow drought types, i.e. dry, warm, or warm and dry, on the severity of summer/winter streamflow droughts, and 2) no studies have completed a combined analysis of snow drought and streamflow drought regimes in the context of climate change.Thereafter, the authors offer two hypotheses: 1) the snow-streamflow drought response depends on baseline mean winter temperature, and 2) the snow-streamflow drought response depends on changes in groundwater recharge/storage.Only the former is explicitly stated in the introduction, the latter is implicitly stated by the study design, reported results, and discussion.The authors use four catchments that span a range of climatic conditions, from -0.6-5.9 oC average annual temperature, and 46-235 cm average annual total precipitation.This is appropriate with respect to the first hypothesis.The catchments also differ in terms of consumptive water use demands, which ends up dominating much of the discussion despite not being related to the study hypotheses.The catchment slopes range from 2-35o.Unsaturated zone and saturated zone depths, bulk soil densities, and hydraulic conductivity values are assigned based on published data sources.The combination of physically-based groundwater modeling, realistic soil properties, and variations in catchment slope are appropriate with respect to the second hypothesis.The authors find that the distribution of future "snow droughts" into warm, dry, and warm and dry differ depending on the baseline mean annual air temperature and the future changes in air temperature and precipitation.The distribution of future low flows shifts toward less severe in winter and more severe in summer.Precipitation and temperature both increase under all future scenarios.The frequency and severity of dry and warm/dry snow droughts therefore decreases while warm snow droughts increase.Total annual runoff increases for all catchments because winter runoff increases more

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