Recent climate change - Revision history

JeffreyJLukas: /* Precipitation */

2024-10-31T21:12:20Z

Precipitation

← Older revision		Revision as of 17:12, 31 October 2024
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	==Precipitation==		==Precipitation==

	As discussed in [[Climate patterns and variability]], annual precipitation in the basin is highly variable, and ~~there are no~~ recent trends in annual or seasonal precipitation ~~that~~ clearly ~~emerge~~ from the background “noise” of historical year-to-year and decadal variability~~, as with~~ temperature. But the ~~most recent two decades does stand out for~~ overall ~~dryness~~, ~~which~~ is ~~accentuated~~ by ~~the preceding~~ two wet decades in the 1980s and 1990s (Figures 2 & 3~~). By slight margins, 2000-2020 has been the driest 21-year period on record in both the Upper Basin (with 94% of the 20th-century average) and Lower Basin (88% of the 20th-century average~~). The period since 2000 also includes the driest ~~single~~ water years on record in the Upper Basin (2018) and Lower Basin (2002).		As discussed in [[Climate patterns and variability]], annual precipitation in the basin is highly variable, and recent trends in annual or seasonal precipitation are not clearly distinguishable from the background “noise” of historical year-to-year and decadal variability (unlike temperature). But the period since 2000 has been dry overall, an impression that is enhanced by having been preceded by two relatively wet decades, the 1980s and 1990s (Figures 2 & 3). The period since 2000 also includes the driest water years on record in the Upper Basin (2018) and Lower Basin (2002).

	[[File:UCRB_WY_Precip_1900-2024.png\|thumb\|700px\|Figure 2. Upper Colorado River Basin water-year precipitation, 1900-2024 (green dots and line), and a smoothing filter that emphasizes multi-year variability (dark red line). (NOAA NCEI Climate-at-a-Glance; https://www.ncdc.noaa.gov/cag/)]]		[[File:UCRB_WY_Precip_1900-2024.png\|thumb\|700px\|Figure 2. Upper Colorado River Basin water-year precipitation, 1900-2024 (green dots and line), and a smoothing filter that emphasizes multi-year variability (dark red line). (NOAA NCEI Climate-at-a-Glance; https://www.ncdc.noaa.gov/cag/)]]
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	[[File:LCRB_WY_Precip_1900-2024.png\|thumb\|700px\|Figure 3. Lower Colorado River Basin water-year precipitation, 1900-2024 (green dots and line), and a smoothing filter that emphasizes multi-year variability (dark red line). (NOAA NCEI Climate-at-a-Glance; https://www.ncdc.noaa.gov/cag/)]]		[[File:LCRB_WY_Precip_1900-2024.png\|thumb\|700px\|Figure 3. Lower Colorado River Basin water-year precipitation, 1900-2024 (green dots and line), and a smoothing filter that emphasizes multi-year variability (dark red line). (NOAA NCEI Climate-at-a-Glance; https://www.ncdc.noaa.gov/cag/)]]

	Several studies have indicated that the overall lower precipitation since 2000 is likely part of natural variability in the basin’s climate, rather than due to longer-lasting changes in atmospheric circulation related to anthropogenic warming. Some ~~more~~ recent studies, however, suggest that anthropogenic climate change is in fact exerting a long-term tendency towards reduced precipitation. However, the tendency that was identified is small relative to the natural fluctuations. This ambiguity about causation of precipitation change is expected to continue; even if a systematic anthropogenic change in precipitation is occurring, it may not be obvious for several decades. This is very different than the situation with temperature change.		Several studies have indicated that the overall lower precipitation since 2000 is likely part of natural variability in the basin’s climate, rather than due to longer-lasting changes in atmospheric circulation related to anthropogenic warming. Some recent studies, however, suggest that anthropogenic climate change is in fact exerting a long-term tendency towards reduced precipitation. However, the tendency that was identified is small relative to the natural fluctuations. This ambiguity about causation of precipitation change is expected to continue; even if a systematic anthropogenic change in precipitation is in fact occurring, it may not be obvious for several decades. This is very different than the situation with temperature change.

	One well-known consequence of warming has implications for precipitation at shorter timescales (hourly, daily, weekly): warmer air can hold more moisture. So in principle, under a warmer climate, any weather pattern that brings a moist air mass into the region can generate a larger precipitation event, all else equal. Recent and substantial increases in heavy and extreme precipitation events (daily and multi-day) have been clearly observed in most parts of the world, and much of the U.S., consistent with that physical expectation.		One well-known consequence of warming has implications for precipitation at shorter timescales (hourly, daily, weekly): warmer air can hold more moisture. So in principle, under a warmer climate, any weather pattern that brings a moist air mass into the region can generate a larger precipitation event, all else equal. Recent and substantial increases in heavy and extreme precipitation events (daily and multi-day) have been clearly observed in most parts of the world, and much of the U.S., consistent with that physical expectation.

JeffreyJLukas: /* Wiki Library: Recent climate change */

2024-10-31T20:38:46Z

Wiki Library: Recent climate change

← Older revision		Revision as of 16:38, 31 October 2024
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	===[https://www.zotero.org/groups/4274378/colorado_river_science_wiki/collections/S2KWMNE8/items//item-list Wiki Library: Recent climate change]===		===[https://www.zotero.org/groups/4274378/colorado_river_science_wiki/collections/S2KWMNE8/items//item-list Wiki Library: Recent climate change]===

	The Wiki library lists over 40 research publications on recent climate change relevant to the Colorado River Basin.		The Wiki library lists over 40 research publications on recent climate change that are relevant to the Colorado River Basin.

JeffreyJLukas: /* Additional resources */

2024-10-31T20:38:17Z

Additional resources

← Older revision		Revision as of 16:38, 31 October 2024
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	[https://wwa.colorado.edu/publications/reports/CRBreport/ColoRiver_StateOfScience_WWA_2020_Chapter_2.pdf Chapter 2] of the 2020 State of the Science report describes the basin's recent climate changes in greater detail, in section 2.10.		[https://wwa.colorado.edu/publications/reports/CRBreport/ColoRiver_StateOfScience_WWA_2020_Chapter_2.pdf Chapter 2] of the 2020 State of the Science report describes the basin's recent climate changes in greater detail, in section 2.10.

	===[https://www.zotero.org/groups/4274378/colorado_river_science_wiki/collections/S2KWMNE8/items//item-list Wiki Library: Recent climate change		===[https://www.zotero.org/groups/4274378/colorado_river_science_wiki/collections/S2KWMNE8/items//item-list Wiki Library: Recent climate change]===

	The Wiki library lists over 40 research publications on recent climate change relevant to the Colorado River Basin.		The Wiki library lists over 40 research publications on recent climate change relevant to the Colorado River Basin.

JeffreyJLukas: /* Additional resources */

2024-10-31T20:38:07Z

Additional resources

← Older revision		Revision as of 16:38, 31 October 2024
Line 59:		Line 59:
	[https://wwa.colorado.edu/publications/reports/CRBreport/ColoRiver_StateOfScience_WWA_2020_Chapter_2.pdf Chapter 2] of the 2020 State of the Science report describes the basin's recent climate changes in greater detail, in section 2.10.		[https://wwa.colorado.edu/publications/reports/CRBreport/ColoRiver_StateOfScience_WWA_2020_Chapter_2.pdf Chapter 2] of the 2020 State of the Science report describes the basin's recent climate changes in greater detail, in section 2.10.

	===[https://~~science2017~~.~~globalchange~~.~~gov~~/ ~~NCA4 Climate Science Special Report]===~~		===[https://www.zotero.org/groups/4274378/colorado_river_science_wiki/collections/S2KWMNE8/items//item-list Wiki Library: Recent climate change

	The ~~2018 Climate Science Special Report (CSSR), Volume 1 of the Fourth National Climate Assessment (NCA4), describes the historical record and likely causes of recent temperature change (Ch 6.1, 6.2) and~~ recent ~~precipitation~~ change ~~(Ch. 7.1) in~~ the ~~U.S~~.		The Wiki library lists over 40 research publications on recent climate change relevant to the Colorado River Basin.

JeffreyJLukas: /* Drought indicators */

2024-10-29T15:09:14Z

Drought indicators

← Older revision		Revision as of 11:09, 29 October 2024
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	The Palmer Drought Index is a simple emulation of the balance of moisture inputs (via monthly precipitation) and evaporative losses (temperature) from the soil column, accounting for the memory of water storage in the soil. It is widely used in agriculture as well as general drought monitoring. Figure 5 shows the historical record of August PDSI, reflecting drought conditions leading up to and through the growing season, for the Upper Basin.		The Palmer Drought Index is a simple emulation of the balance of moisture inputs (via monthly precipitation) and evaporative losses (temperature) from the soil column, accounting for the memory of water storage in the soil. It is widely used in agriculture as well as general drought monitoring. Figure 5 shows the historical record of August PDSI, reflecting drought conditions leading up to and through the growing season, for the Upper Basin.

	[[File:UCRB_Aug_PDSI_1900-2024.~~jpg~~\|thumb\|700px\|Figure 5. August Palmer Drought Severity Index for the Upper Colorado River Basin, 1900-2024. Between 2000 and 2024, eight years have exceeded the threshold for ''extreme drought'' (-4.0), compared to only six such years between 1900 and 1999. The red line is a smoothing spline that emphasizes multi-year variability. (Chart: NOAA NCEI Climate at a Glance, https://www.ncdc.noaa.gov/cag/]]		[[File:UCRB_Aug_PDSI_1900-2024.png\|thumb\|700px\|Figure 5. August Palmer Drought Severity Index for the Upper Colorado River Basin, 1900-2024. Between 2000 and 2024, eight years have exceeded the threshold for ''extreme drought'' (-4.0), compared to only six such years between 1900 and 1999. The red line is a smoothing spline that emphasizes multi-year variability. (Chart: NOAA NCEI Climate at a Glance, https://www.ncdc.noaa.gov/cag/]]

	It shows that fluctuations in PDSI are mainly driven by precipitation variability, but accentuated by the warmer temperatures that typically accompany drier-than-average years. It also shows show the impact of systematically warming temperatures over the last 40 years in causing a steeper decline in PDSI (i.e., increasing drought) than in precipitation over that period (compare with figures X and X). The ''average'' August PDSI in the Upper Basin (-2.59) as well as in the Lower Basin (-2.79) since 2000 would be classified as ''moderate drought'', with over a third of those years falling under ''extreme drought''.		It shows that fluctuations in PDSI are mainly driven by precipitation variability, but accentuated by the warmer temperatures that typically accompany drier-than-average years. It also shows show the impact of systematically warming temperatures over the last 40 years in causing a steeper decline in PDSI (i.e., increasing drought) than in precipitation over that period (compare with figures X and X). The ''average'' August PDSI in the Upper Basin (-2.59) as well as in the Lower Basin (-2.79) since 2000 would be classified as ''moderate drought'', with over a third of those years falling under ''extreme drought''.

JeffreyJLukas: /* Drought indicators */

2024-10-29T15:08:33Z

Drought indicators

← Older revision		Revision as of 11:08, 29 October 2024
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	The Palmer Drought Index is a simple emulation of the balance of moisture inputs (via monthly precipitation) and evaporative losses (temperature) from the soil column, accounting for the memory of water storage in the soil. It is widely used in agriculture as well as general drought monitoring. Figure 5 shows the historical record of August PDSI, reflecting drought conditions leading up to and through the growing season, for the Upper Basin.		The Palmer Drought Index is a simple emulation of the balance of moisture inputs (via monthly precipitation) and evaporative losses (temperature) from the soil column, accounting for the memory of water storage in the soil. It is widely used in agriculture as well as general drought monitoring. Figure 5 shows the historical record of August PDSI, reflecting drought conditions leading up to and through the growing season, for the Upper Basin.

	[[File:~~UB_PDSI_Figure~~.~~png~~\|thumb\|700px\|Figure 5. August Palmer Drought Severity Index for the Upper Colorado River Basin, ~~1895~~-~~2020~~. ~~Since~~ 2000, ~~a larger proportion of~~ years have exceeded the ~~thresholds~~ for ''~~moderate~~ drought'' (-~~2.0), ''severe drought'' (-3~~.0), and ~~''extreme drought'' (-4.0)~~. The red line is a smoothing spline that emphasizes multi-year variability. (Chart: NOAA NCEI Climate at a Glance, https://www.ncdc.noaa.gov/cag/]]		[[File:UCRB_Aug_PDSI_1900-2024.jpg\|thumb\|700px\|Figure 5. August Palmer Drought Severity Index for the Upper Colorado River Basin, 1900-2024. Between 2000 and 2024, eight years have exceeded the threshold for ''extreme drought'' (-4.0), compared to only six such years between 1900 and 1999. The red line is a smoothing spline that emphasizes multi-year variability. (Chart: NOAA NCEI Climate at a Glance, https://www.ncdc.noaa.gov/cag/]]

	It shows that fluctuations in PDSI are mainly driven by precipitation variability, but accentuated by the warmer temperatures that typically accompany drier-than-average years. It also shows show the impact of systematically warming temperatures over the last 40 years in causing a steeper decline in PDSI (i.e., increasing drought) than in precipitation over that period (compare with figures X and X). The ''average'' August PDSI in the Upper Basin (-2.59) as well as in the Lower Basin (-2.79) since 2000 would be classified as ''moderate drought'', with over a third of those years falling under ''extreme drought''.		It shows that fluctuations in PDSI are mainly driven by precipitation variability, but accentuated by the warmer temperatures that typically accompany drier-than-average years. It also shows show the impact of systematically warming temperatures over the last 40 years in causing a steeper decline in PDSI (i.e., increasing drought) than in precipitation over that period (compare with figures X and X). The ''average'' August PDSI in the Upper Basin (-2.59) as well as in the Lower Basin (-2.79) since 2000 would be classified as ''moderate drought'', with over a third of those years falling under ''extreme drought''.

JeffreyJLukas: /* Precipitation */

2024-10-29T14:53:42Z

Precipitation

← Older revision		Revision as of 10:53, 29 October 2024
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	==Precipitation==		==Precipitation==

	As discussed in [[Climate patterns and variability]], annual precipitation in the basin is highly variable, and there are no recent trends in annual or seasonal precipitation that clearly emerge from the background “noise” of historical year-to-year and decadal variability, as with temperature. But the most recent two decades does stand out for overall dryness, which is accentuated by the preceding two wet decades in the 1980s and 1990s (Figures 3 ~~& 4~~). By slight margins, 2000-2020 has been the driest 21-year period on record in both the Upper Basin (with 94% of the 20th-century average) and Lower Basin (88% of the 20th-century average). The period since 2000 also includes the driest single water years on record in the Upper Basin (2018) and Lower Basin (2002).		As discussed in [[Climate patterns and variability]], annual precipitation in the basin is highly variable, and there are no recent trends in annual or seasonal precipitation that clearly emerge from the background “noise” of historical year-to-year and decadal variability, as with temperature. But the most recent two decades does stand out for overall dryness, which is accentuated by the preceding two wet decades in the 1980s and 1990s (Figures 2 & 3). By slight margins, 2000-2020 has been the driest 21-year period on record in both the Upper Basin (with 94% of the 20th-century average) and Lower Basin (88% of the 20th-century average). The period since 2000 also includes the driest single water years on record in the Upper Basin (2018) and Lower Basin (2002).

	[[File:UCRB_WY_Precip_1900-2024.png\|thumb\|700px\|Figure 3. Upper Colorado River Basin water-year precipitation, 1900-2024 (green dots and line), and a smoothing filter that emphasizes multi-year variability (dark red line). (NOAA NCEI Climate-at-a-Glance; https://www.ncdc.noaa.gov/cag/)]]		[[File:UCRB_WY_Precip_1900-2024.png\|thumb\|700px\|Figure 2. Upper Colorado River Basin water-year precipitation, 1900-2024 (green dots and line), and a smoothing filter that emphasizes multi-year variability (dark red line). (NOAA NCEI Climate-at-a-Glance; https://www.ncdc.noaa.gov/cag/)]]

	[[File:LCRB_WY_Precip_1900-2024.png\|thumb\|700px\|Figure 4. Lower Colorado River Basin water-year precipitation, 1900-2024 (green dots and line), and a smoothing filter that emphasizes multi-year variability (dark red line). (NOAA NCEI Climate-at-a-Glance; https://www.ncdc.noaa.gov/cag/)]]		[[File:LCRB_WY_Precip_1900-2024.png\|thumb\|700px\|Figure 3. Lower Colorado River Basin water-year precipitation, 1900-2024 (green dots and line), and a smoothing filter that emphasizes multi-year variability (dark red line). (NOAA NCEI Climate-at-a-Glance; https://www.ncdc.noaa.gov/cag/)]]

	Several studies have indicated that the overall lower precipitation since 2000 is likely part of natural variability in the basin’s climate, rather than due to longer-lasting changes in atmospheric circulation related to anthropogenic warming. Some more recent studies, however, suggest that anthropogenic climate change is in fact exerting a long-term tendency towards reduced precipitation. However, the tendency that was identified is small relative to the natural fluctuations. This ambiguity about causation of precipitation change is expected to continue; even if a systematic anthropogenic change in precipitation is occurring, it may not be obvious for several decades. This is very different than the situation with temperature change.		Several studies have indicated that the overall lower precipitation since 2000 is likely part of natural variability in the basin’s climate, rather than due to longer-lasting changes in atmospheric circulation related to anthropogenic warming. Some more recent studies, however, suggest that anthropogenic climate change is in fact exerting a long-term tendency towards reduced precipitation. However, the tendency that was identified is small relative to the natural fluctuations. This ambiguity about causation of precipitation change is expected to continue; even if a systematic anthropogenic change in precipitation is occurring, it may not be obvious for several decades. This is very different than the situation with temperature change.

JeffreyJLukas at 14:53, 29 October 2024

2024-10-29T14:53:05Z

← Older revision		Revision as of 10:53, 29 October 2024
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	==Overview==		==Overview==
	[[File:UCRB_WY_Tave_1900-2024.png\|thumb\|700px\|Figure 1. Annually averaged (water-year) temperature over the Upper Colorado River Basin, 1900-2024 (orange dots and line), and a LOESS curve that emphasizes multi-decadal variability (green line). The LOESS curve since 1980 indicates over 2°F of warming since 1980 (NOAA NCEI Climate-at-a-Glance; https://www.ncdc.noaa.gov/cag/)]]

	The climate of the Colorado River Basin has clearly changed in the past several decades, becoming substantially warmer, by over 2°F since 1980. This observed warming in the basin is synchronous with warming over that same period on regional, continental and global scales that has been attributed to the emission of greenhouse gases. The pervasive increase in the basin’s temperature has significant implications for the the basin's surface water balance and hydrology.		The climate of the Colorado River Basin has clearly changed in the past several decades, becoming substantially warmer, by over 2°F since 1980. This observed warming in the basin is synchronous with warming over that same period on regional, continental and global scales that has been attributed to the emission of greenhouse gases. The pervasive increase in the basin’s temperature has significant implications for the the basin's surface water balance and hydrology.
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	==Temperature==		==Temperature==
			[[File:UCRB_WY_Tave_1900-2024.png\|thumb\|700px\|Figure 1. Annually averaged (water-year) temperature over the Upper Colorado River Basin, 1900-2024 (orange dots and line), and a LOESS curve that emphasizes multi-decadal variability (green line). The LOESS curve since 1980 indicates over 2°F of warming since 1980 (NOAA NCEI Climate-at-a-Glance; https://www.ncdc.noaa.gov/cag/)]]

	After seeing little overall warming from the beginning of observations in the late 1800s to the 1970s, annually averaged temperatures in the basin have risen sharply, with a persistent warming trend of about 0.5°F per decade since 1980. The warming trends in the Upper Basin (Figure 1) and Lower Basin are comparable. Figure 1 shows that of the 10 warmest water years in the Upper Basin on record, 8 have occurred since 2000, with 7 of them since 2012. Each of the four meteorological seasons has warmed at rates similar to the trend in annual temperatures.		After seeing little overall warming from the beginning of observations in the late 1800s to the 1970s, annually averaged temperatures in the basin have risen sharply, with a persistent warming trend of about 0.5°F per decade since 1980. The warming trends in the Upper Basin (Figure 1) and Lower Basin are comparable. Figure 1 shows that of the 10 warmest water years in the Upper Basin on record, 8 have occurred since 2000, with 7 of them since 2012. Each of the four meteorological seasons has warmed at rates similar to the trend in annual temperatures.

JeffreyJLukas: /* Temperature */

2024-10-29T14:52:25Z

Temperature

← Older revision		Revision as of 10:52, 29 October 2024
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	==Temperature==		==Temperature==

	[[File:Southwest_JJA_Tmax_figure.png\|thumb\|700px\|Figure 2. Fraction of the area of the Southwest U.S. (UT, CO, AZ, NM) experiencing extremely warm (upper 10%; red bars) and extremely cool (lower 10%; blue bars) daily high temperatures averaged over the summer (June-August), 1895-2020. Note the abrupt increase in the area experiencing extremely warm summer daily highs after 1995. The green line is a 9-point smoothing filter to emphasize decadal-scale variability. (Chart: NOAA NCEI https://www.ncdc.noaa.gov/extremes/cei/; annotation on y-axis by Jeff Lukas)]]

	After seeing little overall warming from the beginning of observations in the late 1800s to the 1970s, annually averaged temperatures in the basin have risen sharply, with a persistent warming trend of about 0.5°F per decade since 1980. The warming trends in the Upper Basin (Figure 1) and Lower Basin are comparable. Figure 1 shows that of the 10 warmest water years in the Upper Basin on record, 8 have occurred since 2000, with 7 of them since 2012. Each of the four meteorological seasons has warmed at rates similar to the trend in annual temperatures.		After seeing little overall warming from the beginning of observations in the late 1800s to the 1970s, annually averaged temperatures in the basin have risen sharply, with a persistent warming trend of about 0.5°F per decade since 1980. The warming trends in the Upper Basin (Figure 1) and Lower Basin are comparable. Figure 1 shows that of the 10 warmest water years in the Upper Basin on record, 8 have occurred since 2000, with 7 of them since 2012. Each of the four meteorological seasons has warmed at rates similar to the trend in annual temperatures.

JeffreyJLukas: /* Precipitation */

2024-10-29T14:52:00Z

Precipitation

← Older revision		Revision as of 10:52, 29 October 2024
Line 22:		Line 22:
	As discussed in [[Climate patterns and variability]], annual precipitation in the basin is highly variable, and there are no recent trends in annual or seasonal precipitation that clearly emerge from the background “noise” of historical year-to-year and decadal variability, as with temperature. But the most recent two decades does stand out for overall dryness, which is accentuated by the preceding two wet decades in the 1980s and 1990s (Figures 3 & 4). By slight margins, 2000-2020 has been the driest 21-year period on record in both the Upper Basin (with 94% of the 20th-century average) and Lower Basin (88% of the 20th-century average). The period since 2000 also includes the driest single water years on record in the Upper Basin (2018) and Lower Basin (2002).		As discussed in [[Climate patterns and variability]], annual precipitation in the basin is highly variable, and there are no recent trends in annual or seasonal precipitation that clearly emerge from the background “noise” of historical year-to-year and decadal variability, as with temperature. But the most recent two decades does stand out for overall dryness, which is accentuated by the preceding two wet decades in the 1980s and 1990s (Figures 3 & 4). By slight margins, 2000-2020 has been the driest 21-year period on record in both the Upper Basin (with 94% of the 20th-century average) and Lower Basin (88% of the 20th-century average). The period since 2000 also includes the driest single water years on record in the Upper Basin (2018) and Lower Basin (2002).

	[[File:~~UCRB_precip_WY~~.png\|thumb\|700px\|Figure 3. Upper Colorado River Basin water-year precipitation, 1900-~~2020~~ (green dots and line), ~~with~~ smoothing filter that emphasizes multi-year variability (dark red line). (NOAA NCEI Climate-at-a-Glance; https://www.ncdc.noaa.gov/cag/)]]		[[File:UCRB_WY_Precip_1900-2024.png\|thumb\|700px\|Figure 3. Upper Colorado River Basin water-year precipitation, 1900-2024 (green dots and line), and a smoothing filter that emphasizes multi-year variability (dark red line). (NOAA NCEI Climate-at-a-Glance; https://www.ncdc.noaa.gov/cag/)]]

	[[File:~~LCRB_precip_WY~~.png\|thumb\|700px\|Figure 4. Lower Colorado River Basin water-year precipitation, 1900-~~2020~~ (green dots and line), ~~with~~ smoothing filter that emphasizes multi-year variability (dark red line). (NOAA NCEI Climate-at-a-Glance; https://www.ncdc.noaa.gov/cag/)]]		[[File:LCRB_WY_Precip_1900-2024.png\|thumb\|700px\|Figure 4. Lower Colorado River Basin water-year precipitation, 1900-2024 (green dots and line), and a smoothing filter that emphasizes multi-year variability (dark red line). (NOAA NCEI Climate-at-a-Glance; https://www.ncdc.noaa.gov/cag/)]]

	Several studies have indicated that the overall lower precipitation since 2000 is likely part of natural variability in the basin’s climate, rather than due to longer-lasting changes in atmospheric circulation related to anthropogenic warming. Some more recent studies, however, suggest that anthropogenic climate change is in fact exerting a long-term tendency towards reduced precipitation. However, the tendency that was identified is small relative to the natural fluctuations. This ambiguity about causation of precipitation change is expected to continue; even if a systematic anthropogenic change in precipitation is occurring, it may not be obvious for several decades. This is very different than the situation with temperature change.		Several studies have indicated that the overall lower precipitation since 2000 is likely part of natural variability in the basin’s climate, rather than due to longer-lasting changes in atmospheric circulation related to anthropogenic warming. Some more recent studies, however, suggest that anthropogenic climate change is in fact exerting a long-term tendency towards reduced precipitation. However, the tendency that was identified is small relative to the natural fluctuations. This ambiguity about causation of precipitation change is expected to continue; even if a systematic anthropogenic change in precipitation is occurring, it may not be obvious for several decades. This is very different than the situation with temperature change.