Long-term datasets that chronicle hydrological processes within the context of climate and land management change are rare. This is especially true for cold regions with seasonally frozen ground and where remoteness and inclement weather limit continuous measurements. Long-term experimental datasets that do exist in such regions are diminishing quickly (Laudon et al., 2017). For hillslope-scale long-term experiments over seasonally frozen ground, such records are particularly uncommon. Here we present an unusually long 50-year record for a set of three monitored agricultural hillslopes in southwestern Saskatchewan, Canada, that includes runoff, runoff nutrients, snowpack, soil moisture, and soil nutrients for a 50-year period, during which the hillslopes underwent controlled, comparative changes in agricultural practices.

The hillslope-scale dataset is at the spatial scale intermediate between more traditional long-term catchment-scale datasets (e.g., Water Survey of Canada (WSC) Historical Data, the United States Geological Survey (USGS) National Streamflow Information Program, or the UK National River Flow Archive) and point-scale datasets (e.g., TERENO-SOILCan network, Pütz et al., 2016, or the Reynold's Creek soil lysimeter network, Seyfried et al., 2001). As such, hillslope-scale measurements of precipitation and runoff, together with internal measurements of soil moisture, snowpack, and soil nutrients, offer an opportunity to understand mechanistically the links between climate trends in rainfall and snowmelt inputs and runoff outputs. Further, in terms of land use change in dry agroecosystems, they offer an opportunity to understand how tillage, seeding, and crop rotational practices affect the hydrology of agricultural hillslopes as well as nutrient delivery to downstream water bodies.

The collation of our long-term hillslope database has been motivated largely by the importance of water management and sustainability for dryland agriculture on seasonally frozen, snowmelt-dominated terrain. This paper reports on an archive of downloadable data from an experimental, agriculturally managed hillslope site at Swift Current, Saskatchewan. This dataset documents the characteristics more broadly of the semiarid portions of the northern Great Plains of North America. It serves as a resource for long-term analyses and model formulation, calibration, and testing of land management and climate change effects on agricultural hillslopes.

The three hillslopes (also referred to as “watersheds” in the dataset) are located at South Farm (50∘15′53′′ N, 107∘43′53′′ W), an agricultural research site of the Swift Current Research and Development Centre of Agriculture and Agri-food Canada, approximately 5 km southeast of Swift Current, Saskatchewan (Fig. 1). The hillslopes adjoin each other and are rectangular in shape, with areas of 4.25 ha (Hillslope 1), 4.66 ha (Hillslope 2), and 4.86 ha (Hillslope 3). The hillslopes are approximately 150 m wide in the east–west direction and 300–320 m long in the north–south direction. They were artificially diked with raised grassed berms constructed in the 1950s by Agriculture and Agri-food Canada. Hydrological observations at the hillslopes began in 1962 to address the effects of agricultural land management practices on runoff water supply and quality, chemical transport, and soil erodibility.

The hillslopes have undulating topography and slope towards the north-northwest with gradients of 1 %–4 %. Digital elevation models (DEMs), obtained using a Leica Viva GS15 from 17 to 18 April 2012, are available for all three hillslopes at a 2 m horizontal resolution (Coles et al., 2018). These DEMs were obtained by mounting the Leica Viva GS15 rover to a side-by-side vehicle at a height of 2 m above the ground surface. The vehicle was driven methodically up and down each hillslope, achieving full coverage of each hillslope (Coles et al., 2018). The GPS was set to automatically collect points every 2 m and at instances when the elevation change exceeded 0.15 m (Coles et al., 2018). The survey was referenced to a permanent Agriculture and Agri-food Canada benchmark located near to the hillslopes, to give elevations in meters above sea level. Location data for these DEMs are in the projected coordinate system UTM Zone 13N with GRS 1980 datum. Two additional DEMs, obtained using an Optech ILRIS-LR Terrestrial Laser Scanner in summer 2014, are available for Hillslope 2 at a 0.25 m horizontal resolution (Coles et al., 2018b). These two finer DEMs of Hillslope 2 were obtained from surveys on 7 July 2014 and 24 September 2014, before and after a simulated seeding of the hillslope. They therefore capture the surface micro-topography of a tilled hillslope with random soil clod undulations, as well as a seeding-induced ridge-and-furrow topography. These DEMs were obtained by mounting the laser scanner at the top of a 15 ft (4.57 m) scaffolding tower located on the eastern margin of Hillslope 2 and also from the top of a vehicle parked in the northeastern corner of the hillslope. The elevation data are relative elevations (not absolute elevations). Location data for these DEMs are in the projected coordinate system UTM Zone 13N with GRS 1984 datum. Additional information on the generation of the 2 m and 0.25 m DEMs can be found in Coles et al. (2018).

The soils are Orthic Brown Chernozems (Ayres et al., 1985), specifically Swinton silt loam in the upper four-fifths of the hillslopes, where the solum is developed within loess, and Haverhill loam in the lower fifth of the hillslope, where past erosion has resulted in the solum extending into the underlying loamy till (McConkey et al., 1997). The surficial 0–15 cm soil layer consists of 50.4 % silt, 31.4 % sand, and 18.2 % clay, has a bulk density of 1.22 g cm-3, and has a saturated hydraulic conductivity of 14.2 mm h-1 (Coles and McDonnell, 2018). Silt content decreases with depth, while clay content increases with depth. Mean soil depth, as measured with a dynamic cone penetrometer, is 2.65 m (Coles and McDonnell, 2018).

The hillslopes have been predominantly under an annual rotation of wheat (Triticum aestivum L.) and fallow (Table 1). This two-crop rotation is with the exception of a period (1977–1980) of grass (Psathyrostachys juncea (Fisch.) Nevski) and a period (1982–1985) of annual wheat on Hillslopes 1 and 2; an annual rotation (1994–2010) of wheat and legume green manure (Lathyrus sativus L.) without use of herbicides or mineral fertilizers on Hillslope 1; and an annual rotation (2004–2011) of wheat and pulses (lentils and peas; Lens culinaris L. and Pisum sativum L., respectively) on Hillslope 2. The hillslopes have largely been under conventional tillage practice with a heavy-duty cultivator, with the exception of the period 1993–2011 when Hillslope 2 was switched to no tillage practice, with weed control entirely with herbicides. Unlike the other two hillslopes, Hillslope 3 has had a consistent two-crop rotation and consistent tillage management since 1962.

From 1962 to 2011, runoff, runoff nutrient concentration, snowpack characteristics, soil moisture, and soil nutrient concentration were monitored on the hillslopes. The year 2011 marked the final year of regular monitoring of the hillslopes by the Swift Current Research and Development Centre of Agriculture and Agri-food Canada. In 2013 and 2014, monitoring of runoff, snowpack characteristics, and soil moisture was undertaken in collaboration with the University of Saskatchewan; these data are presented separately (Appels et al., 2017; Coles and McDonnell, 2018). If regular monitoring of the hillslopes resumes, the data repository will be updated accordingly. Meteorological data from an Environment and Climate Change Canada meteorological station located 390 m to the south-southeast complement the hillslope dataset.

These data have proven valuable for the study of a variety of research questions related to the interactions between agricultural practices, climate, hydrology, and nutrient export. Studying the effects of agricultural practices on nutrient export and water quality, Nicholaichuk and Read (1978) showed guideline-exceeding N and P concentrations in runoff from unfertilized hillslopes. Schneider et al. (2019) used the long-term data set to show that the conversion to no-till farming caused an increase in snowmelt runoff, which subsequently increased nutrient exports. Cessna et al. (2013) found an increased amount of herbicide exported in runoff from conservation tillage hillslopes, due to the increased use of herbicides. McConkey et al. (1997) showed that soil erosion was greatest in April during snowmelt-runoff events over partially frozen soil and that erosion occurring during rainfall-runoff events was relatively unimportant. Hydrological process studies at this site include Coles et al. (2017), who explored the hierarchies of importance of various controls on snowmelt-runoff generation. Appels et al. (2017) and Coles and McDonnell (2018) used single melt season intensive data collection to quantify the spatial patterns of hydrological variables and the generation of snowmelt-runoff connectivity over low-angled terrain. Finally, climate change studies at this site have shown warming winter and spring temperatures, decreasing snowfall amounts, and a resultant decrease in snowmelt-runoff amounts, earlier spring runoff timing, and an increase in summer rainfall amounts but no change in rainfall-driven runoff (Cutforth et al., 1999; Coles et al., 2017).

The available data are summarized in Table 2 and detailed below.

Data from the three Swift Current hillslopes are available at 10.23684/hhn5-rz52 (McConkey and Thiagarajan, 2018). This depository includes the runoff, runoff nutrient concentrations, snowpack, soil moisture, soil nutrient concentrations, and crop and tillage data. Herbicide and sediment concentration data are not included in this dataset. We have also made available the digital elevation data for the site, which can be accessed at 10.20383/101.0117 (Coles et al., 2018). The Environment and Climate Change Canada meteorological data are available at http://climate.weather.gc.ca/ (last access: 30 August 2019).

This paper has presented details of a long-term (1962–2013) dataset from three 5 ha research hillslopes at the Swift Current Research and Development Centre (of Agriculture and Agri-food Canada) in southern Saskatchewan on the northern Great Plains. The hillslopes are seasonally frozen and under agricultural management. Runoff from the hillslopes is non-continuous and is dominated by spring snowmelt. The dataset includes runoff, runoff nutrient concentrations, snowpack depth, density and water equivalent, soil moisture, soil nutrient concentrations, and crop and tillage data. Digital elevation data are also available for the three hillslopes at a 2 m horizontal resolution, and, for one of the hillslopes (Hillslope 2), at a 0.25 m horizontal resolution. A nearby Environment and Climate Change standard meteorological station provides a dataset of precipitation, temperature, and other climate conditions at daily (1962 onwards) and hourly (1995 onwards) resolution. Data from the three hillslopes and the meteorological station are now available online. This rich dataset is a valuable source for hydrological response analysis and model formulation and calibration within the context of climate and land management change.