The impact of snow loss and soil moisture on convective precipitation over the Rocky Mountains under climate warming

Warm season moist diurnal convection can be particularly sensitive to changes in land surface characteristics such as snow cover and soil moisture. Over regions of mountainous terrain, climate change is expected to reduce snow cover along the low-elevation seasonal snowpack margin. These snow reduct...

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Bibliographic Details
Published in:	Climate dynamics 2021-05, Vol.56 (9-10), p.2915-2939
Main Authors:	Wallace, Brendan, Minder, Justin R.
Format:	Article
Language:	eng
Subjects:	Albedo Albedo (solar) Ascent Boundary layer stability Boundary layers Climate change Climatology Convection Convection (Meteorology) Convective instability Convective precipitation Daytime Earth and Environmental Science Earth Sciences Elevation Environmental aspects Fluxes Geophysics/Geodesy Global warming Lifting condensation level Mesoscale phenomena Moisture content Mountain climates Mountains Oceanography Precipitation Precipitation (Meteorology) Rainfall intensity Regional climates Snow Snow cover Snowpack Soil Soil moisture Soil moisture content Surface fluxes Surface properties Terrain Thermal circulation Warm seasons Water content
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Summary:	Warm season moist diurnal convection can be particularly sensitive to changes in land surface characteristics such as snow cover and soil moisture. Over regions of mountainous terrain, climate change is expected to reduce snow cover along the low-elevation seasonal snowpack margin. These snow reductions alter surface albedo and soil moisture content, leading to changes in surface fluxes and alterations in mesoscale orographic circulations that act to transport moisture and provide ascent. A set of convection-permitting regional climate simulations centered on the Rocky Mountains of Colorado are conducted from April through July across a period of 12 years (2002–2013). These include a reanalysis forced control run (CTR), a pseudo global warming run (PGW), and an additional altered land surface run (DSURF) used to isolate the effects of the snow albedo and soil moisture changes on orographic convection. Over the mountains, daytime hourly precipitation accumulation (0900–1800 MST) decreased in PGW by an average of 4.2% while precipitation in DSURF increased by 12.5%. On days with weak synoptic forcing, the PGW response more closely follow the DSURF response with daytime hourly increases averaging 29.7% for PGW and 28.7% for DSURF. For PGW, hourly daytime precipitation intensity increases of up to 82% overcome reductions in precipitation frequency to produce higher accumulations. DSURF shows smaller increases in intensity of up to 23% and broad increases in daytime frequency indicating that surface changes act to moderate reductions in the frequency of convective precipitation. Reduced snow cover contributes to this convective response by increasing convective instability and boundary layer moisture and decreasing lifting condensation level over the high terrain. Alterations in orographic thermal circulations contribute to this response by converging moisture over the high terrain and enhancing mesoscale ascent.
ISSN:	0930-7575 1432-0894