Projected future climate - Revision history

JeffreyJLukas: /* Drought */

2024-10-23T20:14:24Z

Drought

← Older revision		Revision as of 16:14, 23 October 2024
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	The projected higher temperatures for the basin will likely lead to greater frequency and severity of soil-moisture droughts in the basin as the increases in evapotranspiration that will result from warming either exacerbate long-term decreases in annual precipitation (if they occur) or cancel all but the largest future increases in precipitation. CMIP5 projections of near-surface soil moisture consistently indicate decreased summer (JJA) soil moisture over the Colorado River Basin, and most parts of the Western U.S. [USGCRP 2017]		The projected higher temperatures for the basin will likely lead to greater frequency and severity of soil-moisture droughts in the basin as the increases in evapotranspiration that will result from warming either exacerbate long-term decreases in annual precipitation (if they occur) or cancel all but the largest future increases in precipitation. CMIP5 projections of near-surface soil moisture consistently indicate decreased summer (JJA) soil moisture over the Colorado River Basin, and most parts of the Western U.S. [USGCRP 2017]

	~~Future~~ projections of hydrologic drought and its key ~~indicators~~ (snowpack, runoff) ~~are detailed in~~ [[Projected future hydrology]].		For more on future projections of hydrologic drought and its key components (snowpack, runoff), see [[Projected future hydrology]].

	===Wildfire===		===Wildfire===

JeffreyJLukas: /* Hot extremes */

2024-10-23T20:13:30Z

Hot extremes

← Older revision		Revision as of 16:13, 23 October 2024
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	[[File:Increase_days_over_90F.png\|thumb\|400px\|'''Figure 4.''' Projected increase in the future number of days over 90°F in the Western U.S. for mid-century (2036-2065) compared to a 1976-2005 baseline, from the weighted average of 32 CMIP5 model projections run under the RCP8.5 emissions scenarios, with LOCA downscaling. (Figure: J. Lukas, adapted from Figure 6.9 in USGCRP, 2017: Climate Science Special Report: Fourth National Climate Assessment, Volume I; CMIP5-LOCA data: http://loca.ucsd.edu; Pierce, Cayan, and Thrasher 2014)]]		[[File:Increase_days_over_90F.png\|thumb\|400px\|'''Figure 4.''' Projected increase in the future number of days over 90°F in the Western U.S. for mid-century (2036-2065) compared to a 1976-2005 baseline, from the weighted average of 32 CMIP5 model projections run under the RCP8.5 emissions scenarios, with LOCA downscaling. (Figure: J. Lukas, adapted from Figure 6.9 in USGCRP, 2017: Climate Science Special Report: Fourth National Climate Assessment, Volume I; CMIP5-LOCA data: http://loca.ucsd.edu; Pierce, Cayan, and Thrasher 2014)]]

	Similar to what has been observed over the past 40 years in the basin and the Southwest U.S., the projected shift in the center of the distribution of temperatures (i.e., annually averaged temperature) is expected to manifest in a large ~~increase~~ in ~~extremes at the warm tail of the distribution:~~ extremely hot days and multi-day heat waves. Figure 4 shows that the number of days per year over 90°F is projected under RCP8.5 to increase by 20-60 days by mid-century over the middle and lower elevations of the basin; many high-elevation areas that do not currently experience temperatures above 90°F are expected to see them by mid-century.		Similar to what has been observed over the past 40 years in the basin and the Southwest U.S., the projected shift in the center of the distribution of temperatures (i.e., annually averaged temperature) is expected to manifest in large increases in extremely hot days and multi-day heat waves. Figure 4 shows that the number of days per year over 90°F is projected under RCP8.5 to increase by 20-60 days by mid-century over the middle and lower elevations of the basin; many high-elevation areas that do not currently experience temperatures above 90°F are expected to see them by mid-century.

	===Cold extremes===		===Cold extremes===

JeffreyJLukas at 20:09, 23 October 2024

2024-10-23T20:09:54Z

← Older revision		Revision as of 16:09, 23 October 2024
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	Wildfire occurrence and total areas burned per year are projected to increase substantially in the Rocky Mountain West by mid-century as warming leads to drying of the land surface and of fuels. [Lukas et al. 2014]. The length of the fire season is also projected to increase. While several other factors have led to increases in large fires and in area burned since 1980, and will continue to influence wildfire trends in the future (e.g., historical fire suppression, development of the wildland-urban interface, increase in human ignition sources), anthropogenic warming has been identified as a significant driver of increasing wildfire occurrence. [Williams and Abotzoglou 2018]		Wildfire occurrence and total areas burned per year are projected to increase substantially in the Rocky Mountain West by mid-century as warming leads to drying of the land surface and of fuels. [Lukas et al. 2014]. The length of the fire season is also projected to increase. While several other factors have led to increases in large fires and in area burned since 1980, and will continue to influence wildfire trends in the future (e.g., historical fire suppression, development of the wildland-urban interface, increase in human ignition sources), anthropogenic warming has been identified as a significant driver of increasing wildfire occurrence. [Williams and Abotzoglou 2018]

	~~==Other climate metrics==~~

	==Data and tools==		==Data and tools==
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	[https://wwa.colorado.edu/publications/reports/CRBreport/ColoRiver_StateOfScience_WWA_2020_Chapter_11.pdf Chapter 11] of the 2020 State of the Science report details the projected future climate for the basin, in section 11.6, as well the methods and data used in those projections: Global climate models (GCMs; 11.2); CMIP (11.3); Emissions scenarios (11.4); Downscaling (11.5).		[https://wwa.colorado.edu/publications/reports/CRBreport/ColoRiver_StateOfScience_WWA_2020_Chapter_11.pdf Chapter 11] of the 2020 State of the Science report details the projected future climate for the basin, in section 11.6, as well the methods and data used in those projections: Global climate models (GCMs; 11.2); CMIP (11.3); Emissions scenarios (11.4); Downscaling (11.5).

	===[https://science2017.globalchange.gov/ NCA4 ~~Climate Science Special Report~~]===		===[https://nca2023.globalchange.gov Fifth National Climate Assessment (NCA5)]===

			Chapter 2 (Climate Trends), Section 2.3, of the Fifth National Climate Assessment (NCA5; 2023) provides an overview of the projected impacts of climate change on temperature, precipitation, extreme heat, drought, and heavy and extreme precipitation, based on CMIP6 climate model projections.

			===[https://science2017.globalchange.gov/ Fourth National Climate Assessment (NCA4) CSSR]===

	The 2018 Climate Science Special Report (CSSR), Volume 1 of the Fourth National Climate Assessment (NCA4), describes climate models, emissions scenarios, and projections in Chapter 4, and details ~~the~~ future projections of climate variables and extreme events for the U.S. ~~in subsequent chapters~~: Temperature changes (Chapter 6); Precipitation changes (Chapter 7); Droughts, floods, wildfire (Chapter 8); Extreme storms (Chapter 9).		The 2018 Climate Science Special Report (CSSR), Volume 1 of the Fourth National Climate Assessment (NCA4), describes climate models, emissions scenarios, and projections in Chapter 4, and details future projections of climate variables and extreme events for the U.S., nased on CMIP5 climate models: Temperature changes (Chapter 6); Precipitation changes (Chapter 7); Droughts, floods, wildfire (Chapter 8); Extreme storms (Chapter 9).

JeffreyJLukas: /* Additional resources */

2024-10-21T20:54:15Z

Additional resources

← Older revision		Revision as of 16:54, 21 October 2024
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	==Additional resources==		==Additional resources==

	===State of the Science ~~Report~~===		===[https://wwa.colorado.edu/resources/colorado-river-resources/CRBreport Colorado River Basin Climate and Hydrology: State of the Science report]===

	[https://wwa.colorado.edu/publications/reports/CRBreport/ColoRiver_StateOfScience_WWA_2020_Chapter_11.pdf Chapter 11] of the State of the Science report details the projected future climate for the basin, in section 11.6, as well the methods and data used in those projections: Global climate models (GCMs; 11.2); CMIP (11.3); Emissions scenarios (11.4); Downscaling (11.5).		[https://wwa.colorado.edu/publications/reports/CRBreport/ColoRiver_StateOfScience_WWA_2020_Chapter_11.pdf Chapter 11] of the 2020 State of the Science report details the projected future climate for the basin, in section 11.6, as well the methods and data used in those projections: Global climate models (GCMs; 11.2); CMIP (11.3); Emissions scenarios (11.4); Downscaling (11.5).

	===[https://science2017.globalchange.gov/ NCA4 Climate Science Special Report]===		===[https://science2017.globalchange.gov/ NCA4 Climate Science Special Report]===

	The 2018 Climate Science Special Report (CSSR), Volume 1 of the Fourth National Climate Assessment (NCA4), describes climate models, emissions scenarios, and projections in Chapter 4, and details the future projections of climate variables and extreme events for the U.S. in subsequent chapters: Temperature changes (Chapter 6); Precipitation changes (Chapter 7); Droughts, floods, wildfire (Chapter 8); Extreme storms (Chapter 9).		The 2018 Climate Science Special Report (CSSR), Volume 1 of the Fourth National Climate Assessment (NCA4), describes climate models, emissions scenarios, and projections in Chapter 4, and details the future projections of climate variables and extreme events for the U.S. in subsequent chapters: Temperature changes (Chapter 6); Precipitation changes (Chapter 7); Droughts, floods, wildfire (Chapter 8); Extreme storms (Chapter 9).

JeffreyJLukas: /* Heavy and extreme precipitation */

2024-10-21T18:11:37Z

Heavy and extreme precipitation

← Older revision		Revision as of 14:11, 21 October 2024
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	===Heavy and extreme precipitation===		===Heavy and extreme precipitation===

	As noted in [[Recent climate change]], warmer air can hold more moisture, also known as precipitable water (PW). Observations show that globally-averaged PW has increased in recent decades at a rate consistent with physical expectations, given the observed global warming. The CMIP5 models consistently project future increases in average PW globally as warming progresses. Changes in average PW for the Western U.S. are more variable across the CMIP5 models because at the regional scale, PW is also a function of the frequency of wet weather patterns that transport and concentrate moisture--changes in which being less certain. The ~~CMIP5~~ models do project that ''extreme'' PW values for this region (e.g., highest daily PW in a 10-year period) will increase by about 15% by the 2050s.		As noted in [[Recent climate change]], warmer air can hold more moisture, also known as precipitable water (PW). Observations show that globally-averaged PW has increased in recent decades at a rate consistent with physical expectations, given the observed global warming. The CMIP5 and CMIP6 models consistently project there to be future increases in average PW globally as warming progresses. Changes in average PW for the Western U.S. are more variable across the CMIP5 and CMIP6 models because at the regional scale, PW is also a function of the frequency of wet weather patterns that transport and concentrate moisture--changes in which being less certain. The models do project that ''extreme'' PW values for this region (e.g., highest daily PW in a 10-year period) will increase, by about 10-20% by the 2050s per CMIP5.

	With these projected increases in PW on the wettest days, extreme precipitation events over the region that includes the Colorado River Basin are also projected to become more frequent and intense. Over the the Southwest US (CA, NV, UT, CO, AZ, NM), what is currently a 1-in-5-year 2-day event is projected to become, by the 2050s, a 1-in-3-year event under both RCP4.5 and RCP8.5. [Jannsen et al 2014] The 1-in-20-year 1-day event is projected to increase in magnitude (rainfall depth) by mid-century by 10% under RCP4.5 and by 12% under RCP8.5 [USGCRP 2017]. These and other studies indicate that heavy and extreme precipitation days (>95th percentile of all days with precipitation) will contribute an increasingly greater fraction of the annual precipitation.		With these projected increases in PW on the wettest days, extreme precipitation events over the region that includes the Colorado River Basin are also projected to become more frequent and intense. Over the the Southwest US (CA, NV, UT, CO, AZ, NM), what is currently a 1-in-5-year 2-day event is projected to become, by the 2050s, a 1-in-3-year event under both RCP4.5 and RCP8.5. [Jannsen et al 2014] The 1-in-20-year 1-day event is projected to increase in magnitude (rainfall depth) by mid-century by 10% under RCP4.5 and by 12% under RCP8.5 [USGCRP 2017]. These and other studies indicate that heavy and extreme precipitation days (>95th percentile of all days with precipitation) will contribute an increasingly greater fraction of the annual precipitation.

	===Drought===		===Drought===

JeffreyJLukas: /* Future basin precipitation */

2024-10-21T18:09:42Z

Future basin precipitation

← Older revision		Revision as of 14:09, 21 October 2024
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	The CMIP5 and CMIP6 GCMs show more pronounced tendencies for change in seasonal precipitation over the basin than annual precipitation. In winter (DJF), most models show increased precipitation over the Upper Basin. In spring (MAM), most models show decreased precipitation for the Lower Basin. In summer, most models show decreased precipitation for both the Upper and Lower Basins; however, the North American Monsoon is not simulated well in the GCMs, and confidence in the projected changes in summer precipitation is lower than for the other seasons.		The CMIP5 and CMIP6 GCMs show more pronounced tendencies for change in seasonal precipitation over the basin than annual precipitation. In winter (DJF), most models show increased precipitation over the Upper Basin. In spring (MAM), most models show decreased precipitation for the Lower Basin. In summer, most models show decreased precipitation for both the Upper and Lower Basins; however, the North American Monsoon is not simulated well in the GCMs, and confidence in the projected changes in summer precipitation is lower than for the other seasons.

	Multi-decadal natural variability--~~which is~~ simulated by the GCMs--strongly influences the precipitation projections, as seen in the frequent excursions in the 30-year averages in Figure 3, up and down by 5% or more. These excursions, both in the models and in the real world, make it hard to discern trends that might be attributable to the "forced" (anthropogenic) climate changes, such as shifts in average storm tracks.		Multi-decadal natural variability--as simulated by the GCMs--strongly influences the precipitation projections, as seen in the frequent excursions in the 30-year averages in Figure 3, up and down by 5% or more. These excursions, both in the models and in the real world, make it hard to discern trends that might be attributable to the "forced" (anthropogenic) climate changes, such as shifts in average storm tracks.

	The ensemble median precipitation changes of RCP4.5 and RCP8.5 throughout the 21st century are very similar, though after 2050 the RCP8.5 ensemble does have greater spread (right side of Figure 3), suggesting that at least some of the models show larger responses in precipitation as a result of the higher greenhouse gases assumed in RCP8.5.		The ensemble median precipitation changes of RCP4.5 and RCP8.5 throughout the 21st century are very similar, though after 2050 the RCP8.5 ensemble does have greater spread (right side of Figure 3), suggesting that at least some of the models show larger responses in precipitation as a result of the higher greenhouse gases assumed in RCP8.5.

JeffreyJLukas: /* Future basin precipitation */

2024-10-21T18:09:17Z

Future basin precipitation

← Older revision		Revision as of 14:09, 21 October 2024
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	[[File:UCRB_CMIP5-LOCA_Precip_45.png\|thumb\|800px\|'''Figure 3.''' Projected future annual precipitation change for the Upper Basin compared to a 1971–2000 baseline, from an ensemble of 32 CMIP5 model projections under the moderate RCP4.5 emissions scenario with LOCA downscaling. The light blue lines are the 30-year running averages, plotted on the middle (15th) year, of the individual model projections of future precipitation change, with the median projection shown as the dark dashed line. The box-whiskers plot at rights show the distribution of the 30-year average values at 2055 (2041–2070). (Figure: J. Lukas, adapted from Lukas and Payton, 2020; Data: CMIP5-LOCA; D. Pierce, Scripps Institution; http://loca.ucsd.edu; Pierce, Cayan, and Thrasher 2014)]]		[[File:UCRB_CMIP5-LOCA_Precip_45.png\|thumb\|800px\|'''Figure 3.''' Projected future annual precipitation change for the Upper Basin compared to a 1971–2000 baseline, from an ensemble of 32 CMIP5 model projections under the moderate RCP4.5 emissions scenario with LOCA downscaling. The light blue lines are the 30-year running averages, plotted on the middle (15th) year, of the individual model projections of future precipitation change, with the median projection shown as the dark dashed line. The box-whiskers plot at rights show the distribution of the 30-year average values at 2055 (2041–2070). (Figure: J. Lukas, adapted from Lukas and Payton, 2020; Data: CMIP5-LOCA; D. Pierce, Scripps Institution; http://loca.ucsd.edu; Pierce, Cayan, and Thrasher 2014)]]

	Compared to temperature, precipitation reflects a much more complex set of climate drivers and processes, and changes in precipitation are more difficult to ~~diagnose and~~ predict than changes in temperature. In general, the GCMs agree that the prevailing westerly storm tracks across western North America will shift northward on average (potentially drying the Lower Basin and parts of the Upper Basin), but also that individual weather systems will carry more moisture, consistent with the effect of warming on the atmosphere's moisture-holding capacity. The models do not agree on future changes in ENSO (El Niño/La Niña) events, which influence storm tracks and precipitation, especially in the Lower Basin.		Compared to temperature, precipitation reflects a much more complex set of climate drivers and processes, and changes in precipitation are more difficult to predict than changes in temperature. In general, the GCMs agree that the prevailing westerly storm tracks across western North America will shift northward on average (potentially drying the Lower Basin and parts of the Upper Basin), but also that individual weather systems will carry more moisture, consistent with the effect of warming on the atmosphere's moisture-holding capacity. The models do not agree on future changes in ENSO (El Niño/La Niña) events, which influence storm tracks and precipitation, especially in the Lower Basin.

	As a result of these mixed future tendencies, under ~~both RCP4.5~~ and ~~RCP8.5~~ the GCMs ~~indicate slight~~ overall tendencies toward higher annual precipitation in the Upper Basin (Figure 3) and toward lower annual precipitation in the Lower Basin~~. Those tendencies are enhanced for the northern half of the Upper Basin (wetter) and the southern half of the Lower Basin (drier), reflecting north-south gradient across the western U.S~~. For the Upper Basin, the ~~“wetter”~~ of the ~~32 projections~~ call for about 5–10% more annual precipitation by mid-century, while the ~~“drier” projections~~ call for 5–10% less precipitation. For the Lower Basin, the "wetter~~" projections~~ call for ~~0–5~~% more annual precipitation, while the drier ~~projections~~ call for 10–15% less precipitation.		As a result of these mixed future tendencies, under higher and lower emissions scenarios the CMIP5 and CMIP6 GCMs show overall tendencies toward slightly higher annual precipitation in the Upper Basin (Figure 3) and toward lower annual precipitation in the Lower Basin. For the Upper Basin, the wetter-leaning of the models call for about 5–10% more annual precipitation by mid-century, while the drier-leaning models call for 5–10% less precipitation. For the Lower Basin, the wetter models call for up to 5% more annual precipitation, while the drier models call for 10–15% less precipitation.

	The GCMs show more pronounced tendencies for change in seasonal precipitation over the basin than annual precipitation. In winter (DJF), most models show increased precipitation over the Upper Basin. In spring (MAM), most models show decreased precipitation for the Lower Basin. In summer, most models show decreased precipitation for both the Upper and Lower Basins; however, the North American Monsoon is not simulated well in the GCMs, and ~~the~~ confidence in the projected changes in summer precipitation is lower than for the other seasons.		The CMIP5 and CMIP6 GCMs show more pronounced tendencies for change in seasonal precipitation over the basin than annual precipitation. In winter (DJF), most models show increased precipitation over the Upper Basin. In spring (MAM), most models show decreased precipitation for the Lower Basin. In summer, most models show decreased precipitation for both the Upper and Lower Basins; however, the North American Monsoon is not simulated well in the GCMs, and confidence in the projected changes in summer precipitation is lower than for the other seasons.

	Multi-decadal natural variability (which is simulated by the GCMs) strongly influences the precipitation projections, as seen in the frequent excursions in the 30-year averages in Figure 3, up and down by 5% or more. These excursions, both in the models and in the real world, make it hard to discern trends that might be attributable to forced climate changes, such as shifts in average storm tracks. The ensemble medians of RCP4.5 and RCP8.5 throughout the 21st century are very similar, though after 2050 the RCP8.5 ensemble does have greater spread (right side of Figure 3), suggesting that at least some of the models show larger responses in precipitation as a result of the higher greenhouse gases in RCP8.5.		Multi-decadal natural variability--which is simulated by the GCMs--strongly influences the precipitation projections, as seen in the frequent excursions in the 30-year averages in Figure 3, up and down by 5% or more. These excursions, both in the models and in the real world, make it hard to discern trends that might be attributable to the "forced" (anthropogenic) climate changes, such as shifts in average storm tracks.

	Most GCMs also project that the variability in precipitation over the western U.S. will itself change, increasing at all time scales, including greater year-to-year variability. This would mean more frequent occurrence of both very dry and very wet years, and more frequent transitions from very dry to very wet conditions.		The ensemble median precipitation changes of RCP4.5 and RCP8.5 throughout the 21st century are very similar, though after 2050 the RCP8.5 ensemble does have greater spread (right side of Figure 3), suggesting that at least some of the models show larger responses in precipitation as a result of the higher greenhouse gases assumed in RCP8.5.

			Most CMIP5 and CMIP6 GCMs also project that the variability in precipitation over the western U.S. will itself change, increasing at all time scales, including greater year-to-year variability. This would mean more frequent occurrence of both very dry and very wet years, and more frequent transitions from very dry to very wet conditions.

	==Future climate extremes and hazards==		==Future climate extremes and hazards==

JeffreyJLukas: /* Future basin temperature */

2024-10-21T17:20:31Z

Future basin temperature

← Older revision		Revision as of 13:20, 21 October 2024
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	[[File:UCRB_CMIP5-LOCA_Temp_45.png\|thumb\|800px\|'''Figure 2.''' Projected future temperature change for the Upper Basin compared to a 1971–2000 baseline, from an ensemble of 32 CMIP5 model projections under the moderate RCP4.5 emissions scenario with LOCA downscaling. The light blue lines are the 30-year running averages, plotted on the middle (15th) year, of the individual model projections of future temperature change, with the median projection shown as the dark dashed line. The box-whiskers plot at rights show the distribution of the 30-year average values at 2055 (2041–2070). (Figure: J. Lukas, adapted from Lukas and Payton, 2020; Data: D. Pierce, Scripps Institution; http://loca.ucsd.edu; Pierce, Cayan, and Thrasher 2014)]]		[[File:UCRB_CMIP5-LOCA_Temp_45.png\|thumb\|800px\|'''Figure 2.''' Projected future temperature change for the Upper Basin compared to a 1971–2000 baseline, from an ensemble of 32 CMIP5 model projections under the moderate RCP4.5 emissions scenario with LOCA downscaling. The light blue lines are the 30-year running averages, plotted on the middle (15th) year, of the individual model projections of future temperature change, with the median projection shown as the dark dashed line. The box-whiskers plot at rights show the distribution of the 30-year average values at 2055 (2041–2070). (Figure: J. Lukas, adapted from Lukas and Payton, 2020; Data: D. Pierce, Scripps Institution; http://loca.ucsd.edu; Pierce, Cayan, and Thrasher 2014)]]

	All of the GCM projections run for CMIP5 ~~under RCP4.5~~ and ~~RCP8.5~~ indicate that the Colorado River Basin will continue to ~~rapidly~~ warm in all seasons through the during the 21st century ~~(Figure 2)~~. By mid-century (2041-2070), the basin is projected to warm by +3°F to +8°F over a 1971-2000 baseline, and by +2°F to +7°F over the most recent 30-year period (1991-2020). ~~As can be seen in Figure 2, the~~ range or uncertainty in the projected warming is due to both the emissions scenario (RCP) and the GCMs' different climate sensitivities to each increment of greenhouse gases in the atmosphere. After ~~2040~~, the range of projected warming under ~~RCP~~ 8.5 increasingly diverges from RCP 4.5, ~~reflecting the higher emissions and higher concentrations of greenhouse gases in RCP 8~~.5.		All of the GCM projections run for CMIP5 (Figure 2) and CMIP6 indicate that the Colorado River Basin will continue to warm in all seasons through the during the 21st century. By mid-century (2041-2070), the basin is projected by CMIP5 and CMIP6 models to warm by +3°F to +8°F over a 1971-2000 baseline, and by +2°F to +7°F over the most recent 30-year period (1991-2020). The range or uncertainty in the projected warming is due to both the emissions scenario (RCP) and the GCMs' different climate sensitivities to each increment of greenhouse gases in the atmosphere. After 2050, the range of projected warming under the higher-emissions scenarios (RCP8.5, SSP3-7.0, SSP5-8.5) increasingly diverges from the moderate-emissions scenarios (RCP 4.5, SSP2-4.5).

	Even under a lower-end warming outcome (+4°F above 1971-2000), the “normal” years around 2055 would be warmer than the very warmest years of the last century. Slightly greater warming is projected for the Upper Basin ~~than the~~ Lower Basin, since the Upper Basin is further from the moderating influence of the Pacific Ocean. Warming is expected to be greater in summer and fall than the other seasons due to a land-surface feedback that is more prevalent and potent in those seasons: When soils dry out, the incoming solar energy that had been evaporating soil moisture can instead warm the land surface and the air above it.		Even under a lower-end warming outcome (+4°F above 1971-2000), the “normal” years around 2055 would be warmer than the very warmest years of the last century. Slightly greater warming is consistently projected for the Upper Basin compared to Lower Basin, since the Upper Basin is further from the moderating influence of the Pacific Ocean. Warming is expected to be greater in summer and fall than the other seasons due to a land-surface feedback that is more prevalent and potent in those seasons: When soils dry out, the incoming solar energy that had been evaporating soil moisture can instead warm the land surface and the air above it.

	==Future basin precipitation==		==Future basin precipitation==

JeffreyJLukas: /* Future basin temperature */

2024-10-21T17:13:08Z

Future basin temperature

← Older revision		Revision as of 13:13, 21 October 2024
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	All of the GCM projections run for CMIP5 under RCP4.5 and RCP8.5 indicate that the Colorado River Basin will continue to rapidly warm in all seasons through the during the 21st century (Figure 2). By mid-century (2041-2070), the basin is projected to warm by +3°F to +8°F over a 1971-2000 baseline, and by +2°F to +7°F over the most recent 30-year period (1991-2020). As can be seen in Figure 2, the range or uncertainty in the projected warming is due to both the emissions scenario (RCP) and the GCMs' different climate sensitivities to each increment of greenhouse gases in the atmosphere. After 2040, the range of projected warming under RCP 8.5 increasingly diverges from RCP 4.5, reflecting the higher emissions and higher concentrations of greenhouse gases in RCP 8.5.		All of the GCM projections run for CMIP5 under RCP4.5 and RCP8.5 indicate that the Colorado River Basin will continue to rapidly warm in all seasons through the during the 21st century (Figure 2). By mid-century (2041-2070), the basin is projected to warm by +3°F to +8°F over a 1971-2000 baseline, and by +2°F to +7°F over the most recent 30-year period (1991-2020). As can be seen in Figure 2, the range or uncertainty in the projected warming is due to both the emissions scenario (RCP) and the GCMs' different climate sensitivities to each increment of greenhouse gases in the atmosphere. After 2040, the range of projected warming under RCP 8.5 increasingly diverges from RCP 4.5, reflecting the higher emissions and higher concentrations of greenhouse gases in RCP 8.5.

	Even under a lower-end warming outcome (+4°F above 1971-2000), the “normal” years around 2055 would be warmer than the very warmest years of the last century. Slightly greater warming is projected for the Upper Basin than the Lower Basin, since the Upper Basin is further from the moderating influence of the Pacific Ocean. Warming is expected to be ~~slightly~~ greater in summer than the other seasons due to a land surface feedback that is more prevalent and potent in ~~summer; when~~ soils dry out, the energy that had been evaporating soil moisture can instead warm the land surface and the air above it.		Even under a lower-end warming outcome (+4°F above 1971-2000), the “normal” years around 2055 would be warmer than the very warmest years of the last century. Slightly greater warming is projected for the Upper Basin than the Lower Basin, since the Upper Basin is further from the moderating influence of the Pacific Ocean. Warming is expected to be greater in summer and fall than the other seasons due to a land-surface feedback that is more prevalent and potent in those seasons: When soils dry out, the incoming solar energy that had been evaporating soil moisture can instead warm the land surface and the air above it.

	==Future basin precipitation==		==Future basin precipitation==

JeffreyJLukas: /* Global climate models */

2024-10-21T17:09:57Z

Global climate models

← Older revision		Revision as of 13:09, 21 October 2024
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	*SSP5-8.5		*SSP5-8.5

	Under the auspices of the Coupled Model Intercomparison Project (CMIP), the GCMs that have been developed around the world are run under standardized protocols, including emissions scenarios as described above, to produce future climate projections to support the periodic Intergovernmental Panel on Climate Change (IPCC) reports. The climate projections from CMIP's Phase 5 (CMIP5), were originally released around 2012. As of late 2024, most of the ~~currently~~ available GCM-based analyses of local impacts, e.g., for Colorado River Basin hydrology, are based on the CMIP5 projections. The most recent set of climate projections, from CMIP's Phase 5 (CMIP6), were released around 2020 and are increasingly being used in analyses for the Colorado River Basin and elsewhere.		Under the auspices of the Coupled Model Intercomparison Project (CMIP), the GCMs that have been developed around the world are run under standardized protocols, including emissions scenarios as described above, to produce future climate projections to support the periodic Intergovernmental Panel on Climate Change (IPCC) reports. The climate projections from CMIP's Phase 5 (CMIP5), were originally released around 2012. As of late 2024, most of the available GCM-based analyses of local impacts, e.g., for Colorado River Basin hydrology, are based on the CMIP5 projections. The most recent set of climate projections, from CMIP's Phase 5 (CMIP6), were released around 2020 and are increasingly being used in analyses for the Colorado River Basin and elsewhere.

	The potential climate futures (temperature and precipitation) for the Colorado River Basin as portrayed by the CMIP6 models are generally similar to those seen in the CMIP5 models under comparable emissions scenarios with the key difference being that the range of CMIP6 is shifted towards greater future warming. However, a subset of the CMIP6 GCMs (the so-called hot models) may be modeling cloud feedbacks and anthropogenic aerosols in a way that leads to implausibly high rates of warming.		The potential climate futures (temperature and precipitation) for the Colorado River Basin as portrayed by the CMIP6 models are generally similar to those seen in the CMIP5 models under comparable emissions scenarios with the key difference being that the range of CMIP6 is shifted towards greater future warming. However, a subset of the CMIP6 GCMs (the so-called hot models) may be modeling cloud feedbacks and anthropogenic aerosols in a way that leads to implausibly high rates of warming.

	===Downscaling===		===Downscaling===