1. Agenda and goals for the meeting Project 1: Sensitivity of hydrologic impacts assessment to downscaling methodology and spatial resolution (Reclamation/USACE funded) –Overview of results from project 1 (Martyn Clark) –Vignettes on submitted papers (Roy Rasmussen, Ethan Gutmann, and Naoki Mizukami) –Impact of different downscaling methods on simulations of the large-scale water balance (Naoki Mizukami) –Evaluation of how the choice/configuration of hydrologic model affects the portrayal of climate change impacts (Pablo Mendoza) Project 2: The predictability of streamflow across the contiguous United States (Reclamation/USACE funded) –Initial results from project 2 (Martyn Clark) Project 3: Hydrological impacts of climate change over the contiguous United States (USACE funded) –Overview of project 3 (Martyn Clark) –Improving downscaling methods (Ethan Gutmann) –Improving hydrologic simulations (Martyn Clark)

2. Sensitivity of hydrologic impacts assessment to downscaling methodology and spatial resolution: Project overview

3. Tasks (from the collaborative project summary) Task 1: Select experiment years, obtain data, and configure models –WRF: 4-km, 12-km and 36-km over the Headwaters domain for 2001-2008 for current and perturbed climate –Statistical downscaling: CONUS domain, calibration 1979-2000; validation 2001-2008 –Hydrologic model: West-wide domain, 3 headwater catchments (Animas, East, and Yampa) Task 2: Apply downscaling under historical climate and climate changed conditions –Multi-resolution WRF simulations completed for current and future climate –Statistical downscaling completed Task 3: Inter-compare results across methods and resolutions –Differences in precipitation and coupled simulations of the water balance among multi-resolution WRF simulations (Roy and Kyoko) –Differences in precipitation and temperature among statistical downscaling methods (Ethan) –Differences in hydrology simulations among statistical downscaling methods and among hydrology models (Naoki) Task 4: Hydrologic modeling –Impact of differences between statistical and dynamical downscaling methods on hydrology simulations (Naoki and Pablo) –Impacts of WRF resolution on simulations of hydrology (Naoki and Pablo) –Sensitivity of the portrayal of climate change impacts to choice of hydrologic model and the method used to infer model parameters (Pablo) Task 5: Final assessment, publications, and next steps –Roy’s water balance paper, Ethan’s statistical downscaling paper, Naoki’s model forcing paper –Many more papers (to discuss at this meeting)

4. Original research questions (from the collaborative project summary) Is the portrayal of hydrologic impacts under climate change dependent on the chosen downscaling method? –Yes… we’re in the midst of a paradigm shift –Substantial differences between statistical and dynamical downscaling methods (results from 4-km WRF simulations very different from current guidance being provided to water managers) –Substantial differences among statistical downscaling methods (Ethan’s paper went viral!) At what space and time scales does impacts portrayal begin to be sensitive to methods class, and for what types of hydrologic metrics? –12-km and 36-km WRF simulations have poor correspondence to observations, and very different change signals to the 4-km WRF simulations –The impact of WRF resolution on hydrology is primarily due to differences in WRF simulations and (differences in the spatial resolution of the hydrology model are still important) How do the responses to these questions vary with the spatial resolution of dynamical downscaling and the adequacy of process representation in atmospheric and hydrologic models? –Impacts of climate change on hydrology are very sensitive to both the choice of hydrologic model and the method used to infer model parameter sets