#Snowpack news (April 15, 2021): Hoping for another peak this week

Click on a thumbnail graphic to view a gallery of snowpack data from the NRCS.

Here’s the Westwide SNOTEL basin filled map for April 14, 2021.

Westwide SNOTEL basin filled map April 14, 2021 via the NRCS.

@Northern_Water Increases Colorado-Big Thompson Quota to 70% #ColoradoRiver #COriver #aridification

Moraine Park and the headwaters of the Big Thompson River in Rocky Mountain National Park. Moraine Park is on the east side of the park and of the continental divide, near the town of Estes Park. This region has a number of areas call “parks”, which refer to open, level areas in the mountains, usage which comes from the French word parque. The names of these areas predate the establishment of the national park and are unrelated to the use of the word “park” in that context. By The original uploader was Kbh3rd at English Wikipedia. – Transferred from en.wikipedia to Commons., CC SA 1.0, https://commons.wikimedia.org/w/index.php?curid=1009783

From Northern Water:

Adequate native water supplies coupled with improved Front Range soil moisture from March snowstorms prompted the Northern Water Board of Directors to increase its 2021 quota allocation for the Colorado-Big Thompson Project to 70 percent.

The Board unanimously approved the allocation at its meeting Thursday, April 8, 2021, with several board members participating remotely because of the ongoing pandemic. The Board also directed Northern Water staff to update them in May and June to determine whether an additional allocation would be advisable during the peak demand season.

Emily Carbone, an engineer in the Water Resources Department at Northern Water, outlined snowpack and forecasted streamflows, and the Board also heard about the available native water supplies in regional reservoirs. In addition, the Board heard a presentation about the potential water resources impacts caused by the 2020 East Troublesome Fire. Public input was also considered.

The Board has been setting C-BT quota since 1957 and 70 percent is the most common quota declared. It was also the quota set for the 2019 water delivery season, while the 2020 quota was set at 80 percent. The quota reflects the amount of water to be delivered through the C-BT Project.

The quota increases available C-BT Project water supplies by 62,000 acre-feet from the initial 50 percent quota made available in November. Water from the C-BT Project supplements other sources for 33 cities and towns, 120 agricultural irrigation companies, various industries and other water users within Northern Water’s 1.6 million-acre service area. According to recent census figures, more than 1 million residents now live inside Northern Water’s boundaries. To learn more about Northern Water and the C-BT quota, visit http://www.northernwater.org.

#ClimateChange and the #aridification of North America — PNAS

Click here to read the paper (Jonathan Overpeck and Bradley Udall). Here’s an excerpt:

Discussions of droughts and their impacts often center on the lack of precipitation, just as assessments of hydrologic impacts under a changing climate most often focus on how average precipitation in a given locale is likely to change in the future. Within climate science, however, focus has begun to include the growing role warming temperatures are playing as a potent driver of greater aridity: hotter climate extremes; drier soil conditions; more severe drought; and the impacts of hydrologic stress on rivers, forests, agriculture, and other systems. This shift in the hydrologic paradigm is most clear in the American Southwest, where declining flows in the region’s two most important rivers, the Colorado (Fig. 1) and Rio Grande, have been attributed in part to increasing temperatures caused by human activities, most notably the burning of fossil fuels. Warmer summers are also likely to reduce flows in the Columbia River, as well as in rivers along the Sierra Nevada in California. Now, an important study documents how warming is also causing flow declines in the northern Rocky Mountains and in the largest river basin in the United States, the Missouri. This work further highlights the mechanisms behind the temperature-driven river flow declines and places more focus on how anthropogenic climate warming is progressively increasing the risk of hot drought and more arid conditions across an expanding swath of the United States.

Climate change is causing the Southwest to aridify. (Left) Since the 1930s, increasing temperatures have caused the percentage of precipitation going to evapotranspiration (ET) to increase at the expense of precipitation going to Colorado River flow, resulting in an unprecedented and still ongoing megadrought (shading) starting in 1999 (8). (Right) Higher temperatures have already reduced Colorado River flow by 13%, and projected additional warming, assuming continued high emissions of greenhouse gases, will increase ET while reducing river flow even more through the 21st century. Data on Left are 20-y running means from ref. 5, and data on Right are calculated from Representative Concentration Pathways (RCP) 8.5 multimodel Coupled Model Intercomparison Project–Phase 5 (CMIP5) ensemble temperature increases projected for the Upper Colorado River Basin combined with temperature sensitivity of −9.3%/°C estimated by ref. 5, assuming no change in precipitation.