Climate change poses great risks to western Canada's ecosystem and socioeconomical development. To assess these hydroclimatic risks under high-end emission scenario RCP8.5, this study used the Weather Research Forecasting (WRF) model at a convection-permitting (CP) 4 km resolution to dynamically downscale the mean projection of a 19-member CMIP5 ensemble by the end of the 21st century. The CP simulations include a retrospective simulation (CTL, 2000–2015) for verification forced by ERA-Interim and a pseudo-global warming (PGW) for climate change projection forced with climate change forcing (2071–2100 to 1976–2005) from CMIP5 ensemble added on ERA-Interim. The retrospective WRF-CTL's surface air temperature simulation was evaluated against Canadian daily analysis ANUSPLIN, showing good agreements in the geographical distribution with cold biases east of the Canadian Rockies, especially in spring. WRF-CTL captures the main pattern of observed precipitation distribution from CaPA and ANUSPLIN but shows a wet bias near the British Columbia coast in winter and over the immediate region on the lee side of the Canadian Rockies. The WRF-PGW simulation shows significant warming relative to CTL, especially over the polar region in the northeast during the cold season, and in daily minimum temperature. Precipitation changes in PGW over CTL vary with the seasons: in spring and late autumn precipitation increases in most areas, whereas in summer in the Saskatchewan River basin and southern Canadian Prairies, the precipitation change is negligible or decreased slightly. With almost no increase in precipitation and much more evapotranspiration in the future, the water availability during the growing season will be challenging for the Canadian Prairies. The WRF-PGW projected warming is less than that by the CMIP5 ensemble in all seasons. The CMIP5 ensemble projects a 10 %–20 % decrease in summer precipitation over the Canadian Prairies and generally agrees with WRF-PGW except for regions with significant terrain. This difference may be due to the much higher resolution of WRF being able to more faithfully represent small-scale summer convection and orographic lifting due to steep terrain. WRF-PGW shows an increase in high-intensity precipitation events and shifts the distribution of precipitation events toward more extremely intensive events in all seasons. Due to this shift in precipitation intensity to the higher end in the PGW simulation, the seemingly moderate increase in the total amount of precipitation in summer east of the Canadian Rockies may underestimate the increase in flooding risk and water shortage for agriculture. The change in the probability distribution of precipitation intensity also calls for innovative bias-correction methods to be developed for the application of the dataset when bias correction is required. High-quality meteorological observation over the region is needed for both forcing high-resolution climate simulation and conducting verification. The high-resolution downscaled climate simulations provide abundant opportunities both for investigating local-scale atmospheric dynamics and for studying climate impacts on hydrology, agriculture, and ecosystems.

The freeze/thaw process and the surface energy budget of the seasonally frozen ground in the source region of the Yellow River were investigated by using observed soil temperature and moisture and the energy flux from May 12, 2014, to May 11, 2015. Compared with the Maduo site, the starting date of the freezing process was later and the freezing depth was shallower at Maqu site. The maximum frozen depth was about 320 cm at Maduo site and 90 cm at Maqu site. The soil temperature of Maqu site was higher than of Maduo site due to lower latitude and altitude. The soil was the driest under the depth of 40 cm and 80 cm at Maduo and Maqu sites, respectively. The diurnal amplitudes of soil temperature of Maduo site were larger than of Maqu site at four freeze/thaw stages; the amplitudes were the largest in the completely thawed stage (9.19 °C and 4.35 °C) and minimal in the freezing stage (1.23 °C and 0.47 °C). The diurnal amplitudes of soil moisture of Maqu site were greater than of Maduo site at all stages. The net radiation Rn’s seasonal change was hardly influenced by the freeze/thaw process. The mean ground heat flux (G₀) was negative during the freezing and completely frozen stage and positive during the thawing and completely thawed stage. During the completely thawed and frozen stages, the latent heat flux (LE) and sensible heat flux (H) predominated in the surface energy distribution, respectively. Overall, the variations of fluxes were affected by both the monsoon and freeze/thaw process of the soil layer in seasonally frozen region. The freeze/thaw process had a significant effect on the diurnal change of G₀ during the freezing stage. The annual energy closure status of Maduo and Maqu sites was 0.77 and 0.58, respectively. The energy closure status was the highest during the completely thawed stage at Maduo site and during the thawing stage at Maqu site and lowest during the freezing stage among the four stages, due to the snow cover’s impact. Overall, the freeze/thaw process and the high albedo caused by snow cover had effects on the energy closure status.

An observational study of nonlinear interaction between the quasi 2 day wave (QTDW) and the diurnal and semidiurnal tides from meteor radar measurements at Maui is reported. The diurnal and semidiurnal tides show a short‐term variation with the QTDW activity. The variation of amplitude of the semidiurnal tide is opposite to that of the QTDW. The minimum amplitudes of the diurnal tide appear several days later than the maximum amplitudes of the QTDW, and the diurnal tide obviously strengthens when the QTDW drops to small amplitudes. The bispectrum analysis shows significant nonlinear interactions among the QDTW and the tidal components. The two quasi 16 h modes with periods of 16.2 h and 15.8 h generated in the interactions of the QTDW with the diurnal and semidiurnal tides can clearly be distinguished because of the slight deviation of the QTDW period from 48 h. The bicoherence spectrum demonstrates that the QTDW and the semidiurnal tide have quite strong levels of coherence, indicating that the nonlinear interaction is a mechanism responsible for the variability of the semidiurnal tide. Although there is also some interaction between the QTDW and the diurnal tide, their coherence level is low. When the QTDW drops to very weak amplitudes, the background wind decreases and reverses. During this time, the diurnal tide holds large amplitudes. These results support the notion that the variability of the diurnal tide is mainly attributable to the strong QTDW‐induced changes in the background atmosphere, which was shown in the modeling study by Chang et al. (2011). Hence, both the nonlinear interaction and the background flow changes are responsible for the observed variation of the diurnal tide.