Abstract
Abstract. Water resources in cold regions in western Canada face severe risks posed by anthropogenic global warming as evapotranspiration increases and precipitation regimes shift. Although understanding the water cycle is key for addressing climate change issues, it is difficult to obtain high spatial- and temporal-resolution observations of hydroclimatic processes, especially in remote regions. Climate models are useful tools for dissecting and diagnosing these processes, especially the convection-permitting (CP) high-resolution regional climate simulation, which provides advantages over lower-resolution models by explicitly representing convection. In addition to better representing convective systems, higher spatial resolution also better represents topography, mountain meteorology, and highly heterogeneous geophysical features. However, there is little work with convection-permitting regional climate models conducted over western Canada. Focusing on the Mackenzie River and Saskatchewan River basins, this study investigated the surface water budget and atmospheric moisture balance in historical and representative concentration pathway (RCP8.5) projections using 4 km CP Weather Research and Forecasting (WRF). We compared the high-resolution 4 km CP WRF and three common reanalysis datasets, namely the North American Regional Reanalysis (NARR), the Japanese 55-year Reanalysis (JRA-55), and European Centre for Medium-Range Weather Forecasts reanalysis interim dataset (ERA-Interim). High-resolution WRF outperforms the reanalyses in balancing the surface water budget in both river basins with much lower residual terms. For the pseudo-global-warming scenario at the end of the 21st century with representative concentration pathway (RCP8.5) radiative forcing, both the Mackenzie River and Saskatchewan River basins show increases in the amplitude for precipitation and evapotranspiration and a decrease in runoff. The Saskatchewan River basin (SRB) shows a moderate increase in precipitation in the west and a small decrease in the east. Combined with a significant increase in evapotranspiration in a warmer climate, the Saskatchewan River basin would have a larger deficit of water resources than in the current climate based on the pseudo-global-warming (PGW) simulation. The high-resolution simulation also shows that the difference of atmospheric water vapour balance in the two river basins is due to flow orientation and topography differences at the western boundaries of the two basins. The sensitivity of water vapour balance to fine-scale topography and atmospheric processes shown in this study demonstrates that high-resolution dynamical downscaling is important for large-scale water balance and hydrological cycles.
Highlights
If the current pace of greenhouse gas (GHG) emissions continues, evidence points to fast-paced anthropogenic climate change in this century (Pachauri et al, 2014)
We have investigated the water balance in the Weather Research and Forecasting (WRF) simulations and the reanalyses from two perspectives, namely the surface water budget and the atmospheric moisture budget
The assimilation system of reanalyses has to adjust the model variables according to newly available observation; though water vapour is constrained by satellite observation, the dry air mass or water balance is not strongly constrained (Takacs et al, 2016)
Summary
If the current pace of greenhouse gas (GHG) emissions continues, evidence points to fast-paced anthropogenic climate change in this century (Pachauri et al, 2014). The warming climate’s impacts on water resources and ecosystems are generating considerable interest, its impact on water balance in polar and subpolar regions. Most climate projections have shown that polar and subpolar regions warm faster than the regions in lower latitudes (IPCC, 2013). S. Kurkute et al.: Water balance in convection-permitting weather research and forecasting simulations
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