Mapped extent of the rain-snow transition zone in the western U.S. under historic and projected climate

Detailed, high-resolution maps and GIS-ready datasets are now publicly available for download. They depict the probability of rain versus snow in the western U.S. under both historic and future (projected) climate (see research summary here). The detailed methods, data, and findings of the research are described in the publication: Klos, P. Z., T. E. Link, and J. T. Abatzoglou (2014), Extent of the rain-snow transition zone in the western U.S. under historic and projected climate, Geophys. Res. Lett., 41, doi:10.1002/2014GL060500.

 

Monthly Maps and Datasets

Monthly Map Description: The current and future extent of the strongly rain-dominated (blue), strongly snow- dominated (white), and rain-snow mix (pink to red) areas within the western U.S. based on wet-day mean temperature. Future extents are based upon the RCP8.5 scenario using a 20-model global climate model (GCM) mean. (ΔT ranging from ~1.5 to ~4°C spatially).

Klos_et_al-f01-v2

 

Monthly Datasets: GIS-ready monthly probability data of climatic snow-likelihood (ASCII Format).

1979-2012 climate period (historic) by numeric month (i.e. 1 = January): hist1 hist2 hist3 hist4 hist5 hist6 hist7 hist8 hist9 hist10 hist11 hist12

2035-2065 climate period (projected under the RCP 8.5 emissions scenario) by numeric month (i.e. 1 = January): rcp85-1 rcp85-2 rcp85-3 rcp85-4 rcp85-5 rcp85-6 rcp85-7 rcp85-8 rcp85-9 rcp85-10 rcp85-11 rcp85-12

Data Description: Data values indicate the probability of snow likelihood for each 4km pixel across the western U.S.  Due to a tangential relationship in the Dai (2008) equation, values do not reach 0 or 1.  For use/display, a threshold of 0.97 for 100% snow is suggested, as is a minimum threshold of 0.03 for 0% snow (i.e. 100% rain). The file is in ASCII format, with header rows indicating the spatial reference and resolution in lat/lon degrees.

How to import the data in an ESRI GIS framework:

Step 1: Download dataset and rename the file extension to .txt from .doc (.doc is required for WordPress import, apologies for this inconvenience).

Step 2: Open ESRI ArcMap and choose the ‘ASCII to Raster Conversion’ tool from the Toolbox. Convert your .txt file to a raster file.  All the appropriate header information is included in the ASCII file, so this should be automatically found by ArcMap. Make sure to select ‘FLOAT’ values for the output raster.

Step 3: Open your new raster dataset and reclassify the pixels appropriately based on the above data description.

 

 

Winter-aggregated Maps, Datasets, and Regional Summaries

Winter-aggregated Map Description: Current extent of strongly snow-dominated (white and light gray), strongly rain-dominated (blue), and mixed phase (pink to red) winter precipitation regimes based on the mean wet-day winter temperature (1979–2012 Climate Period, December–February (DJF)mean) and the encroachment (light gray) of the mixed-phase rain-snow transition zone into previously 100% snow-dominated areas. Inset of Yosemite National Park to display spatial resolution. Locations of selected experimental sites include: Boulder Creek Critical Zone Observatory (BCCZO), Beaver Creek Experimental Watershed (BCEW), Dry Creek E. W. (DCEW), Fraser Experimental Forest (FEF), H. J. Andrews E. F. (HJA), Jemez River Basin C. Z. O. (JRBCZO), Little Bear River WATERS testbed (LBR), Mica Creek E. W. (MCEW), Priest River E. F. (PREF), Reynolds Creek E. W., C. Z. O., and WATERS testbed (RCEW), Santa Catalina C. Z. O. (SCCZO), Sevilleta Research Site (SEV), Sheep Range Meteorological Transect (ShRMT), Snake Range M. T. (SnRMT), Southern Sierra C. Z. O. (SSCZO), and Tenderfoot Creek E. F. (TCEF).

Klos_et_al-f02-v3

 

Winter-aggregated Datasets: GIS-ready probability data of climatic snow-likelihood (ASCII Format) using a December, January, February (DJF) mean.

1979-2012 climate period (historic): histDJF

2035-2065 climate period (projected under the RCP 8.5 emissions scenario): rcp85-DJF

Data Description: Data values indicate the probability of snow likelihood for each 4km pixel across the western U.S.  Due to a tangential relationship in the Dai (2008) equation, values do not reach 0 or 1.  For use/display, a threshold of 0.97 for 100% snow is suggested, as is a minimum threshold of 0.03 for 0% snow (i.e. 100% rain). The file is in ASCII format, with header rows indicating the spatial reference and resolution in lat/lon degrees.

How to import the data in an ESRI GIS framework:

Step 1: Download dataset and rename the file extension to .txt from .doc (.doc is required for WordPress import, apologies for this inconvenience).

Step 2: Open ESRI ArcMap and choose the ‘ASCII to Raster Conversion’ tool from the Toolbox. Convert your .txt file to a raster file.  All the appropriate header information is included in the ASCII file, so this should be automatically found by ArcMap. Make sure to select ‘FLOAT’ values for the output raster.

Step 3: Open your new raster dataset and reclassify the pixels appropriately based on the above data description.

 

Winter-aggregated Regional Summary: Changes in Wintertime Precipitation Phase by Region; Based on mean snow-only and rain-only areal extent for the winter months (DJF) between historic (late20C) and projected (mid21C) climate; ranked by greatest percent loss by mid21C in the percent of late20C snow-only areal extent.

Region Snow-only extent in late20C (%) Change in snow-only extent by mid21C (%) Rain-only extent in late20C (%) Change in rain-only extent by mid21C (%)
US EPA Level-III Ecoregions
15 Northern Rockies 56 -56 0 3
77 North Cascades 48 -48 1 18
11 Blue Mountains 27 -27 0 29
80 Northern Basin and Range 18 -18 0 23
20 Colorado Plateaus 18 -18 6 50
04 Cascades 6 -6 17 42
13 Central Basin and Range 6 -6 2 66
09 Eastern Cascades Slopes and Foothills 5 -5 0 27
10 Columbia Plateau 3 -3 0 65
23 Arizona/New Mexico Mountains 1 -1 36 54
12 Snake River Plain 44 -42 0 29
16 Idaho Batholith 88 -79 0 1
19 Wasatch and Uinta Mountains 68 -60 0 8
18 Wyoming Basin 44 -37 0 0
05 Sierra Nevada 19 -14 26 26
41 Canadian Rockies 100 -67 0 0
22 Arizona/New Mexico Plateau 3 -2 20 71
17 Middle Rockies 82 -46 0 0
21 Southern Rockies 69 -34 0 3
08 Southern California Mountains 0 0 77 16
14 Mojave Basin and Range 0 0 95 4
01 Coast Range 0 0 88 11
02 Puget Lowland 0 0 95 5
03 Willamette Valley 0 0 99 1
06 Southern and Central California Chaparral and Oak Woodlands 0 0 99 1
07 Central California Valley 0 0 100 0
78 Klamath Mountains 0 0 65 30
79 Madrean Archipelago 0 0 99 1
81 Sonoran Basin and Range 0 0 100 0
USGS HUC-4 Watersheds
MIDDLE SNAKE 29 -29 0 23
GREAT SALT LAKE 16 -16 0 56
YAKIMA 16 -16 0 25
ESCALANTE DESERT SEVIER LAKE 14 -14 0 70
BLACK ROCK DESERT HUMBOLDT 14 -14 0 49
OREGON CLOSED BASINS 13 -13 0 26
UPPER COLORADO DIRTY DEVIL 12 -12 10 64
PUGET SOUND 7 -7 40 18
MIDDLE COLUMBIA 6 -6 0 54
CENTRAL LAHONTAN 5 -5 1 75
UPPER CANADIAN 4 -4 30 18
CENTRAL NEVADA DESERT BASINS 4 -4 11 53
SALT 1 -1 59 31
SACRAMENTO 1 -1 54 26
LOWER COLORADO LAKE MEAD 1 -1 59 35
NORTH LAHONTAN 1 -1 0 50
KLAMATH NORTHERN CALIFORNIA COASTAL 1 -1 46 27
WILLAMETTE 1 -1 64 25
UPPER PECOS 1 -1 71 23
BEAR 79 -76 0 3
RIO GRANDE ELEPHANT BUTTE 12 -11 22 51
UPPER COLORADO DOLORES 17 -15 0 54
LOWER SNAKE 50 -44 0 25
LOWER GREEN 55 -48 0 15
WHITE YAMPA 81 -69 0 0
POWDER TONGUE 36 -29 0 0
SAN JOAQUIN 10 -8 74 8
MISSOURI MUSSELSHELL 35 -27 0 0
MISSOURI MARIAS 44 -33 0 0
UPPER SNAKE 74 -55 0 8
LOWER YELLOWSTONE 24 -17 0 0
SAN JUAN 10 -7 1 77
LOWER COLUMBIA 3 -2 45 34
NORTHERN MOJAVE MONO LAKE 3 -2 79 11
MISSOURI HEADWATERS 69 -44 0 0
TULARE BUENA VISTA LAKES 10 -6 76 7
GREAT DIVIDE UPPER GREEN 52 -31 0 0
BIG HORN 40 -23 0 0
UPPER YELLOWSTONE 62 -32 0 0
RIO GRANDE HEADWATERS 65 -29 0 0
COLORADO HEADWATERS 73 -30 0 11
GUNNISON 68 -26 0 13
OREGON WASHINGTON COASTAL 0 0 79 15
LITTLE COLORADO 0 0 13 83
SOUTHERN CALIFORNIA COASTAL 0 0 85 3
SOUTHERN MOJAVE SALTON SEA 0 0 95 1
CENTRAL CALIFORNIA COASTAL 0 0 97 1
LOWER COLORADO 0 0 82 3
LOWER GILA 0 0 99 1
MIDDLE GILA 0 0 96 1
SAN FRANCISCO BAY 0 0 98 0
UPPER GILA 0 0 72 27

 

Citation for all data:

Klos, P. Z., T. E. Link, and J. T. Abatzoglou (2014), Extent of the rain-snow transition zone in the western U.S. under historic and projected climate, Geophys. Res. Lett., 41, doi:10.1002/2014GL060500.

Acknowledgments:

The authors provide thanks to the Oregon State Climate Group for creating and providing free online access to the PRISM climate data. Financial support was provided by the National Science Foundation’s IGERT Program (Award 0903479) and by the National Science Foundation’s CBET Program (Award 0854553).

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