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==Overview==
==Overview==
Monitoring the climate of the Colorado River Basin and describing its patterns and changes over space and time is made possible by an extensive ground-based system of observations of atmospheric variables such as temperature, precipitation, humidity, and winds. This ad-hoc system is comprised of a number of different station networks that have been developed and expanded over time, usually to serve particular monitoring purposes (e.g., agriculture, water supply, aviation).
[[File:Huntsman_Mesa_CO_RAWS.jpg|thumb|550px|Figure 1. The Huntsman Mesa Remote Automated Weather Station (RAWS) located in the Gunnison Basin of western Colorado. There are about 2200 stations in the RAWS network nationwide, and about 100 stations within the Colorado River Basin. Source: Western Regional Climate Center, https://raws.dri.edu/]]
Currently, there are about 1,000 active weather stations in formal monitoring networks within or adjacent to the boundaries of the basin. Very few of these networks were established specifically for detecting long-term climate trends, but with careful adjustments for changes in station location and instrumentation, their data have been used for that purpose as well.
Monitoring the weather and climate of the Colorado River Basin is made possible by an extensive network of regular observations of weather variables such as temperature, precipitation, humidity, and winds. This "meta-network" actually comprises many individual weather station networks (e.g., RAWS; Figure 1) that have been separately established and maintained, usually to serve particular monitoring purposes (e.g., agriculture, water supply). Data from the vast majority of these weather stations can be accessed in near-real-time (with lags from 5 minutes to one day) from online portals (see Data and tools below); archived data from previous months and years are also typically available.
Site-specific data from the vast majority of these weather stations can be accessed in near-real-time (with lags from 5 minutes to one day) from online portals (see Data and tools below); archived data from previous months and years are also typically available. The data from these weather stations is also gathered and processed into widely used Gridded climate products.
The data from these weather stations are also gathered and processed into widely used gridded climate products. These gridded climate products are designed to alleviate inadequacies of the station data in two important ways:
* Spatial distribution: Stations are not evenly distributed across the landscape; gridded products interpolate between station observations to provide continuous spatial coverage.
* Temporal consistency: Individual stations may only be active for a few decades or less, and over time a station may experience changes in location, instrumentation, or time of observation; gridded products adjust for these "inhomogeneities" to provide consistent data over time.
Most of the gridded climate products share at least some baseline observational data from weather station networks and use similar processing, so they are not independent of each other.
==Relevance==
Observations from weather station networks are directly consulted and used throughout the basin for many weather and climate monitoring applications, such as agriculture, water supply, wildfire management, aviation, road safety, and drought monitoring. One key water-supply application is NOAA CBRFC's use of real-time precipitation and temperature observations from SNOTEL and COOP stations to initialize their streamflow forecasting system with the current moisture conditions for each catchment. Once real-time weather station observations are processed into gridded climate products, those products are widely used for near-real-time to seasonal monitoring applications, and also for historical analyses.
Data directly from weather station networks is used extensively in monitoring
In the Colorado River Basin, as elsewhere in the West, high-elevation weather stations were extremely sparse before the establishment of the SNOTEL network starting in the late 1970s. So the gridded climate data for mountain watersheds critical to water supply is much less reliable prior to 1980.
==Topography and elevation==
==Data and tools==
<onlyinclude>
[[File:Elev_Temp_Precip maps Figure.png|thumb|900px|Figure 1. Colorado River Basin, showing close correspondence of elevation (left) with annual average temperature (1981-2010; center) and annual average precipitation (1981-2010; right). (Elevation map: Reclamation 2020; Climate maps: Lukas and Payton 2020, based on gridded climate data from Livneh et al. 2013.)]]
===Weather station data===
====[https://mesowest.utah.edu/ MesoWest]====
The most important spatial gradients and patterns in average climate arise from the topography and resulting differences in elevation. In general, seasonal and annual precipitation is significantly greater at higher elevations in a given area, due mainly to orographic lift: moist air masses are forced upslope by the terrain, causing water vapor to cool, condense and precipitate (Figure 1). Conversely, rain shadows occur in basins downwind (typically, east) of mountain ranges as downslope flow leads to warming and drying of air masses. Altogether, the crests of mountain ranges receive 2 to 5 times more precipitation on an annual basis than the basins or valleys below. Higher elevations also experience cooler temperatures as a consequence of the lower atmospheric pressure; air masses (whether moist or dry) expand and cool at higher elevation (Figure 1).
This site created by the University of Utah provides map-based access to thousands of weather observing sites from the NWS and FAA (ASOS/AWOS) automated networks, RAWS, SNOTEL, APRSWXNET/CWOP (citizen weather stations), and many other networks. Very useful for real-time monitoring of temperature, winds, humidity, and recent precipitation; users can also access historical observations.
Other mechanisms create gradients in climate at broader scales. Average temperatures increase dramatically from north to south, not only due to the lower elevations in southern Arizona and California compared to Wyoming, but also because of increasing proximity to the tropics and the greater solar heating there. Precipitation also is also lower in the southern parts of the basin because of the increasing influence of the subtropical high pressure belt that tends to deflect storm systems, especially in the cooler months.
==Dynamics and seasonality of precipitation==
[[File:Seasonal Moisture_Precip maps Figure.png|thumb|700px|Figure 2. Schematic showing the predominant oceanic moisture sources in each season (blue arrows), the main dynamical mechanisms for precipitation (purple text), and average seasonal precipitation (blue contours) for the Colorado River Basin. (Design: Jeff Lukas; precipitation maps: Climate Engine/gridMET; https://app.climateengine.org)]]
All precipitation over land requires two things: (1) the horizontal transport of water vapor from a moisture source--typically an ocean--to that area, and (2) a mechanism to vertically lift that water vapor so that it can cool, condense, and fall as rain or snow. For the Colorado River Basin, seasonally varying atmospheric dynamics and weather patterns bring different moisture sources into play while also influencing the mechanisms of lift that dominate in a particular season and location (Figure 2).
Overall, the climate feature most important to the basin's hydrology is the series of mid-latitude cyclonic storms (i.e., low-pressure systems) and lesser disturbances, entraining moisture from the Pacific Ocean, that track across the interior West throughout the cool season from October-May. The frequency and specific track of these systems, which generally follow the jet stream, are the main determinants of water year precipitation in the headwaters and thus, of the basin's annual streamflow as well. In mid-winter (Dec-Feb), the moisture delivery of some of these storms is greatly enhanced by accompanying “atmospheric rivers” (ARs) that periodically penetrate inland into the basin. The Lower Basin has a distinct peak in storm activity in mid-winter, while the Upper Basin tends to get a more even distribution of storms throughout the cool season, at least on average.
In summer and early fall (Jun-Sep), the jet stream weakens and shifts off to the north, setting the stage for the North American Monsoon (NAM). The NAM is a pattern which brings moist subtropical air northward from the Gulf of California and also the Gulf of Mexico, firing up regular if not daily convective storms (i.e., thunderstorms) across the Lower Basin and into parts of the Upper Basin. In the spring and summer, moisture for storms may also be “recycled” evapotranspiration (ET) from the land surface. From late summer into October, periodic landfalling Pacific tropical storms may douse the Lower Basin as intact systems, or at least juice the monsoonal storms with additional moisture.
These maps, generated from weather station observations from the NWS COOP network and updated daily by the High Plains Regional Climate Center (HPRCC), are very helpful for monitoring conditions from weekly to annual timescales. Note that the "shaded" maps are created using a very simple interpolation, unlike that used for gridded climate products.
The previous sections describe the average tendencies of climate over the historical record. But as all water users and water managers know, the basin’s climate can vary dramatically from year to year, and also from decade to decade, especially precipitation and related drought and moisture variables. This regional climate variability is associated, at least in part, with identified modes of global climate variability, principally El Nino-Southern Oscillation (ENSO). The predictability of the basin’s climate on seasonal and interannual timescales mainly stems from ENSO events and the "memory" imparted by long-term soil-moisture anomalies. For temperature, the long-term warming trend also imparts predictability; i.e., it is likely that every year will be warmer than a historical average. But most of the variability in precipitation from year to year appears to be unpredictable.
===Gridded climate products===
====[https://www.ncdc.noaa.gov/cag/ NOAA NCEI Climate at a Glance]====
This versatile tool can be used to generate many types of charts, maps, and analyses from NOAA’s official nClimGrid 5-km gridded climate dataset, updated monthly.
As noted previously, the annual precipitation of the Upper Basin has varied two-fold between the wettest and driest years (Figure 3), while the Lower Basin is more variable, with a three-fold difference between the wettest and driest years (Figure 4). The wettest years are those in which the tracks mid-latitude cyclones over the basin were especially active throughout the cool season (Oct-May), while in the driest years those storm tracks were unusually inactive and/or shifted north of the basin, and often the North American Monsoon was much weaker as well, disproportionately affecting the Lower Basin.
This toolset, developed by researchers at the U. of California-Merced and partners, generates many different types of charts and analyses from the gridMET 4-km gridded climate dataset, updated daily.
[[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: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/)]]
The basin’s precipitation also varies on decadal time scales, and these multi-year and longer excursions towards wet and dry can lead the large reservoirs on the mainstem Colorado River to fill and spill, or experience great stresses. Average annual precipitation in the Upper Basin from 1977-1986 was almost 20% higher than for the preceding 10 years, 1968-1977. The presence of this substantial natural decadal variability makes it difficult to discern long-term trends, and one cannot assume that a trend, if detected, will continue.
Temperatures in the basin also vary from year to year, though this temperature variability is more spatially coherent than precipitation variability; accordingly, a single time-series for the entire Colorado River Basin tells the story for both the Upper Basin and Lower Basin (Figure 5). The effects of temperature variability on water resources and ecosystems are more subtle than the effects of precipitation variability. The two variables are physically and statistically related; drier years, especially over the April-October warm season, tend to be warmer than average, while wetter years tend to be cooler, since the underlying weather patterns tie together dry-sunny-warm conditions, and conversely, wet-cloudy-cool conditions.
[[File:CRB_ann_temp_1895-2020.png|thumb|700px|Figure 1. Annually averaged temperature over the Colorado River Basin, 1895-2020, shown with the blue and red bars as anomalies from a late 20th- century (1971-2000) baseline. The gray line is a 10-year running average plotted on the 6th year, and the. The dashed yellow line is the linear trend from 1980-2020, showing 2.1°F of warming over that period. (Design: Jeff Lukas, updated from Lukas and Payton 2020, based on gridded climate data from NOAA NCEI Climate-at-a-Glance; https://www.ncdc.noaa.gov/cag/.)]]
The most obvious feature of the observed temperature record in the basin is the substantial warming trend, of about 2°F over the past 40 years. This trend has a magnitude similar to the interannual variability in temperature, meaning that the range of temperatures, not just the average, is shifting away from the past climate. The warming trend is described in greater detail in [[Recent climate change]].
==Data and tools==
There are several climate tools that are useful for plotting and examining time-series and recent trends in temperature, precipitation, and other climate variables over specific areas (states, counties, river basins, etc.). Each tool depicts one or more Gridded climate datasets (LINK), so users of the tools may want to familiarize themselves with these datasets as well.
<onlyinclude>
===[https://www.ncdc.noaa.gov/cag/ NOAA NCEI Climate at a Glance]===
The “CAG” tool is a versatile tool that can be used to generate many types of charts, maps, and analyses from NOAA’s official nClimGrid monthly gridded climate dataset. Selecting "Regional" and "Time series" at top brings up several dozen region options, including the Upper Basin and Lower Basin. Selecting "Regional" and "Mapping" allows data to be mapped with river basin boundaries.
This tool, developed by researchers at the U. of California-Merced and partners, generates climographs of average (1981-2010) monthly temperature and precipitation for any point, county, HUC8 watershed, or user-selected area, from the gridMET gridded (4 km) climate dataset.
These maps display the PRISM 4-km gridded climate product, updated monthly, for climate (temperature, precipitation) variables as well as drought indices (PDSI, SPI, SPEI). The "Percentile" maps show how unusual recent conditions are relative to the historical record.
</onlyinclude>
</onlyinclude>
==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_2.pdf Chapter 2] of the State of the Science report describes these patterns, mechanisms, and trends in much greater detail, in sections 2.2, 2.3, 2.4, 2.7, 2.8, and 2.10.
===Assessment of Climate Change in the Southwest United States===
Chapters 4 (Present Weather and Climate: Average Conditions) and 5 (Present Weather and Climate: Evolving Conditions) of the 2013 [https://www.swcarr.arizona.edu/ Southwest Climate Change Assessment] cover the climate processes and patterns and climate variability and trends, respectively, of the six states of the Southwest region (CA, NV, UT, CO, NM, AZ).
==Research directions==
==New and Notable Research (2020-present)==
[https://wwa.colorado.edu/publications/reports/CRBreport/ColoRiver_StateOfScience_WWA_2020_Chapter_4.pdf Chapter 4] of the 2020 State of the Science report describes weather station data and networks, and gridded climate products, in much greater detail.
'''[<URL FOR PAPER>]'''
===[https://www.zotero.org/groups/4274378/colorado_river_science_wiki/collections/KFS9HQFJ Wiki Library: Weather and climate monitoring]===
''Summary''
The Wiki library lists over 20 research publications on weather and climate monitoring that discuss monitoring networks, products, and/or methods that are relevant to the Colorado River Basin.
Latest revision as of 16:41, 31 October 2024
Overview
Figure 1. The Huntsman Mesa Remote Automated Weather Station (RAWS) located in the Gunnison Basin of western Colorado. There are about 2200 stations in the RAWS network nationwide, and about 100 stations within the Colorado River Basin. Source: Western Regional Climate Center, https://raws.dri.edu/
Monitoring the weather and climate of the Colorado River Basin is made possible by an extensive network of regular observations of weather variables such as temperature, precipitation, humidity, and winds. This "meta-network" actually comprises many individual weather station networks (e.g., RAWS; Figure 1) that have been separately established and maintained, usually to serve particular monitoring purposes (e.g., agriculture, water supply). Data from the vast majority of these weather stations can be accessed in near-real-time (with lags from 5 minutes to one day) from online portals (see Data and tools below); archived data from previous months and years are also typically available.
The data from these weather stations are also gathered and processed into widely used gridded climate products. These gridded climate products are designed to alleviate inadequacies of the station data in two important ways:
Spatial distribution: Stations are not evenly distributed across the landscape; gridded products interpolate between station observations to provide continuous spatial coverage.
Temporal consistency: Individual stations may only be active for a few decades or less, and over time a station may experience changes in location, instrumentation, or time of observation; gridded products adjust for these "inhomogeneities" to provide consistent data over time.
Most of the gridded climate products share at least some baseline observational data from weather station networks and use similar processing, so they are not independent of each other.
Observations from weather station networks are directly consulted and used throughout the basin for many weather and climate monitoring applications, such as agriculture, water supply, wildfire management, aviation, road safety, and drought monitoring. One key water-supply application is NOAA CBRFC's use of real-time precipitation and temperature observations from SNOTEL and COOP stations to initialize their streamflow forecasting system with the current moisture conditions for each catchment. Once real-time weather station observations are processed into gridded climate products, those products are widely used for near-real-time to seasonal monitoring applications, and also for historical analyses.
In the Colorado River Basin, as elsewhere in the West, high-elevation weather stations were extremely sparse before the establishment of the SNOTEL network starting in the late 1970s. So the gridded climate data for mountain watersheds critical to water supply is much less reliable prior to 1980.
This site created by the University of Utah provides map-based access to thousands of weather observing sites from the NWS and FAA (ASOS/AWOS) automated networks, RAWS, SNOTEL, APRSWXNET/CWOP (citizen weather stations), and many other networks. Very useful for real-time monitoring of temperature, winds, humidity, and recent precipitation; users can also access historical observations.
These maps, generated from weather station observations from the NWS COOP network and updated daily by the High Plains Regional Climate Center (HPRCC), are very helpful for monitoring conditions from weekly to annual timescales. Note that the "shaded" maps are created using a very simple interpolation, unlike that used for gridded climate products.
This versatile tool can be used to generate many types of charts, maps, and analyses from NOAA’s official nClimGrid 5-km gridded climate dataset, updated monthly.
This toolset, developed by researchers at the U. of California-Merced and partners, generates many different types of charts and analyses from the gridMET 4-km gridded climate dataset, updated daily.
These maps display the PRISM 4-km gridded climate product, updated monthly, for climate (temperature, precipitation) variables as well as drought indices (PDSI, SPI, SPEI). The "Percentile" maps show how unusual recent conditions are relative to the historical record.
The Wiki library lists over 20 research publications on weather and climate monitoring that discuss monitoring networks, products, and/or methods that are relevant to the Colorado River Basin.
