https://doi.org/10.5194/hess-2020-613 Preprint. Discussion started: 4 January 2021 c Author(s) 2021. CC BY 4.0 License. 3 and greenness were decreasing but wetness and snowcover were not changing, and [iii] in the semi-arid to sub-humid agricultural Prairies three patterns of increasing streamflow and an increase in the wetness index were observed. The largest changes in streamflow occurred in 45 the eastern Canadian Prairies, where there were only a few increases in greenness and snow indices.

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... 50 Methods The hydrometric (streamflow) stations selected for this study were all designated as 'active', 130 (i.e. were currently monitored), 'natural' (i.e. their flows are not managed), and either continuous or seasonal and shown as having more than 30 years of data in ECDataExplorer (Environment Canada 2010) at the time the data were downloaded. No attempts were made to use a common window of years -rather all analyses used the entire period of record for each station. In trend studies, time periods are selected that are a trade-off between record length 135 and network density (Hannaford et al. 2013). Many trend studies use a common period of years with an arbitrary measure of completeness such as 20 years of data in a 60 year period (e.g. Vincent et al. 2015) and rely on continuous data throughout the year so that measures such as annual mean flow, or specific monthly flows, can be assessed for trend. This generally means that only continuously observed sites would be included. The alternative approach used here 140 includes data from a large number of seasonal and continuously observed sites, which are considered using only an annual time window described below. The locations of the hydrometric stations, the main river basins, and major tributaries are shown in Figure 1. Given the northerly (Mackenzie) or easterly direction of river flow in the region the hydrometric stations generally sample basin hydrology that lies to the south or west of the 145 points shown. The number of continuous and seasonal stations in each of the larger river basins is given in Table 1. Three additional stations were purposely included, these were at Changing Cold Regions Network (CCRN) Water, Ecosystem, Cryosphere, and Climate (WECC) observatories: Marmot Creek, Alberta; Smith Creek, Saskatchewan; and Scotty Creek, Northwest Territories (Table 1), and including these stations provides a link to CCRN process-150 based studies (DeBeer et al. 2016). Streamflow data from a total of 395 stations (gauged basins) was available; 233 (59%) were operated on a seasonal basis. Water Survey of Canada station numbers are here referred to as stationID. Basin areas range from 9.1 km 2 (Marmot Creek) to 270000 km 2 (Liard River at the mouth) and station elevations range from 22 m (Anderson River below Carnwath River) to 2095 m (Mistaya River near Saskatchewan 155 Crossing). The dataset contains nested basins. Individual stations were analysed for all periods for which data were available, but clustering and statistical analysis involving multiple stations were restricted to the data in the annual common time window of the year from 21 April to 1 November when both seasonal and continuous data sets were available. Plots of missingness and annual station densities of the dataset are provided in Figure S1 .