{"id":286535,"date":"2023-11-04T19:05:25","date_gmt":"2023-11-04T18:05:25","guid":{"rendered":"https:\/\/climatescience.press\/?p=286535"},"modified":"2023-11-04T19:05:28","modified_gmt":"2023-11-04T18:05:28","slug":"colorado-river-flow-data-disproves-climate-change-warming-computer-model-flow-reduction-claims","status":"publish","type":"post","link":"https:\/\/climatescience.press\/?p=286535","title":{"rendered":"Colorado River Flow Data Disproves \u201cClimate Change Warming\u201d Computer Model Flow Reduction Claims"},"content":{"rendered":"\n
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The next question is, does climate change even predict future reductions of precipitation over the Colorado River watershed? The following plot shows an average of 183 climate model simulations of average yearly precipitation in an area approximating the Colorado River watershed. The models suggest a slight increase in total precipitation with warming.<\/em><\/strong><\/p>\n\n\n\n

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From Watts Up With That?<\/a><\/p>\n\n\n\n

 Guest essay by Larry Hamlin<\/strong><\/p>\n\n\n\n

The\u00a0Orange County Register published a prior Denver Post article<\/a>\u00a0claiming that \u201cclimate change warming\u201d had caused a 20% reduction in Colorado River flow since 1900 as shown below.<\/p>\n\n\n\n

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The Denver Post article (as published in the Orange County Register) notes: <\/p>\n\n\n\n

\u201cFirst, the river is drying as the West becomes warmer and more arid. Warmer temperatures speed evaporation, further reducing a lack of water from less precipitation. One report<\/strong> by the U.S. Geological Survey<\/a> found the Colorado River\u2019s flows have dropped by 20% since 1900 primarily due to warming.\u201d<\/p>\n\n\n\n

The U.S. Geological Survey report<\/strong> referenced<\/a> in the Denver Post article then references a February 2020 study<\/strong> \u201crecently published in Science\u201d<\/strong><\/a> <\/strong>which notes: <\/p>\n\n\n\n

\u201cThe sensitivity of river discharge to climate-system warming is highly uncertain, and the processes that govern river discharge are poorly understood, which impedes climate-change adaptation.\u201d <\/p>\n\n\n\n

\u201cA Monte Carlo simulation<\/strong> with a radiation-aware hydrologic model resolves the longstanding, wide disparity in sensitivity estimates and reveals the controlling physical processes.\u201d<\/p>\n\n\n\n

This computer model simulation<\/strong> is then used to \u201cestimate\u201d the following outcome for Colorado River flows as: <\/p>\n\n\n\n

\u201cWe estimate that annual mean discharge has been decreasing by 9.3% per degree Celsius of warming because of increased evapotranspiration, mainly driven by snow loss and a consequent decrease in reflection of solar radiation.\u201d<\/p>\n\n\n\n

Thus, the claim that \u201cthe Colorado River flows have dropped by 20% since 1900 primarily due to warming\u201d is driven by a \u201ccomputer model simulation\u201d which was intended to reveal the \u201ccontrolling physical processes\u201d regarding Colorado River flows into Lake Mead. <\/p>\n\n\n\n

The Denver Post article never addresses any measured data regarding Colorado River flows into Lake Mead with this data readily available from the U.S. Bureau of Reclamation covering the period from 1930-2019. <\/p>\n\n\n\n

Additionally, neither data of the Upper Colorado River Basin Snowpack levels during this same period that feed the Colorado River nor data of the changing supply and demands from the Colorado River water\u2019s many users during this period is addressed in the Denver Post article.<\/p>\n\n\n\n

The peer review \u201cstudy\u201d published in Science assumes the lower levels of Lake Mead are caused by reduced flows from the Colorado River and then uses a \u201cMonte Carlo simulation\u201d computer model to determine how \u201cclimate change warming\u201d caused this reduced flow of the Colorado that resulted in lower water levels in Lake Mead.             <\/p>\n\n\n\n

Climate scientist Dr. Roy Spencer evaluated measurement records of inflows<\/a> of the Colorado River at Lees Ferry starting in the 1930s as well as measurements of snow levels at the upper Colorado basis over this period which is the primary source supplying Colorado River flows arriving at Lees Ferry.<\/p>\n\n\n\n

Dr. Spencer\u2019s study and analysis of measured data regarding the Lake Mead Elevation changes since 1940 and the Colorado inflows since 1930 is shown below.<\/p>\n\n\n

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Key highlights from the study are noted as:<\/p>\n\n\n\n