<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body style="overflow-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;"><p style="font-family: Arial, Helvetica, sans-serif; font-size: small; font-variant-ligatures: normal; orphans: 2; widows: 2; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial; margin: 0px; line-height: normal; font-size-adjust: none; font-kerning: auto; font-variant-alternates: normal; font-variant-numeric: normal; font-variant-east-asian: normal; font-feature-settings: normal; color: rgb(11, 11, 11); background-color: rgb(255, 255, 255);"><span style="line-height: normal; font-size-adjust: none; font-kerning: auto; font-variant-alternates: normal; font-variant-ligatures: normal; font-variant-numeric: normal; font-variant-east-asian: normal; font-feature-settings: normal; color: rgb(0, 0, 0);">PNAS </span><span style="font-kerning: none;">September 22, 2025</span></p><p style="color: rgb(34, 34, 34); font-family: Arial, Helvetica, sans-serif; font-size: small; font-variant-ligatures: normal; orphans: 2; widows: 2; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial; margin: 0px; line-height: normal; font-size-adjust: none; font-kerning: auto; font-variant-alternates: normal; font-variant-numeric: normal; font-variant-east-asian: normal; font-feature-settings: normal; background-color: rgb(255, 255, 255); min-height: 14px;"><br></p><p style="font-family: Arial, Helvetica, sans-serif; font-size: small; font-variant-ligatures: normal; orphans: 2; widows: 2; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial; margin: 0px; line-height: normal; font-size-adjust: none; font-kerning: auto; font-variant-alternates: normal; font-variant-numeric: normal; font-variant-east-asian: normal; font-feature-settings: normal; color: rgb(11, 11, 11); background-color: rgb(255, 255, 255);"><span style="font-kerning: none;"><b>Riverine heat waves on the rise, outpacing air heat waves</b></span></p><p style="font-family: Arial, Helvetica, sans-serif; font-size: small; font-variant-ligatures: normal; orphans: 2; widows: 2; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial; margin: 0px; line-height: normal; font-size-adjust: none; font-kerning: auto; font-variant-alternates: normal; font-variant-numeric: normal; font-variant-east-asian: normal; font-feature-settings: normal; color: rgb(83, 83, 83); background-color: rgb(255, 255, 255);"><span style="text-decoration: underline; font-kerning: none;"><a href="https://www.pnas.org/doi/10.1073/pnas.2503160122#con1" target="_blank" data-saferedirecturl="https://www.google.com/url?q=https://www.pnas.org/doi/10.1073/pnas.2503160122%23con1&source=gmail&ust=1758843318386000&usg=AOvVaw09laJh33E5PJIV6P_pFGgD" style="color: rgb(17, 85, 204);">Kayalvizhi Sadayappan</a></span><span style="font-kerning: none; color: rgb(29, 29, 29);"> and <a href="https://www.pnas.org/doi/10.1073/pnas.2503160122#con2" target="_blank" data-saferedirecturl="https://www.google.com/url?q=https://www.pnas.org/doi/10.1073/pnas.2503160122%23con2&source=gmail&ust=1758843318386000&usg=AOvVaw0fmOW2zKkCJfpiLSNbzAxj" style="color: rgb(17, 85, 204);"><span style="font-kerning: none; color: rgb(83, 83, 83);">Li <wbr>Li</span></a> </span></p><p style="font-family: Arial, Helvetica, sans-serif; font-size: small; font-variant-ligatures: normal; orphans: 2; widows: 2; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial; margin: 0px; line-height: normal; font-size-adjust: none; font-kerning: auto; font-variant-alternates: normal; font-variant-numeric: normal; font-variant-east-asian: normal; font-feature-settings: normal; color: rgb(11, 11, 11); background-color: rgb(255, 255, 255); min-height: 12px;"><span style="font-kerning: none;"></span><br></p><p style="font-family: Arial, Helvetica, sans-serif; font-size: small; font-variant-ligatures: normal; orphans: 2; widows: 2; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial; margin: 0px; line-height: normal; font-size-adjust: none; font-kerning: auto; font-variant-alternates: normal; font-variant-numeric: normal; font-variant-east-asian: normal; font-feature-settings: normal; color: rgb(27, 95, 170); background-color: rgb(255, 255, 255);"><span style="text-decoration: underline; font-kerning: none;"><a href="https://doi.org/10.1073/pnas.2503160122" target="_blank" data-saferedirecturl="https://www.google.com/url?q=https://doi.org/10.1073/pnas.2503160122&source=gmail&ust=1758843318386000&usg=AOvVaw2C2Myut6z9foD4Xv-F-Pfd" style="color: rgb(17, 85, 204);">https://doi.org/10.1073/pnas.<wbr>2503160122<span style="font-kerning: none; color: rgb(27, 95, 170);"></span></a></span></p><ul style="color: rgb(34, 34, 34); font-family: Arial, Helvetica, sans-serif; font-size: small; font-variant-ligatures: normal; orphans: 2; widows: 2; background-color: rgb(255, 255, 255); text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial; list-style-type: none;"><li style="margin: 0px; line-height: normal; font-size-adjust: none; font-kerning: auto; font-variant-alternates: normal; font-variant-ligatures: normal; font-variant-numeric: normal; font-variant-east-asian: normal; font-feature-settings: normal; color: rgb(29, 29, 29); min-height: 22px;"><span style="font-kerning: none;"></span><br></li></ul><p style="font-family: Arial, Helvetica, sans-serif; font-size: small; font-variant-ligatures: normal; orphans: 2; widows: 2; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial; margin: 0px 0px 12px; line-height: normal; font-size-adjust: none; font-kerning: auto; font-variant-alternates: normal; font-variant-numeric: normal; font-variant-east-asian: normal; font-feature-settings: normal; color: rgb(11, 11, 11); background-color: rgb(255, 255, 255);"><span style="font-kerning: none;"><b>Significance</b></span></p><p style="font-family: Arial, Helvetica, sans-serif; font-size: small; font-variant-ligatures: normal; orphans: 2; widows: 2; background-color: rgb(255, 255, 255); text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial; margin: 0px; line-height: normal; font-size-adjust: none; font-kerning: auto; font-variant-alternates: normal; font-variant-numeric: normal; font-variant-east-asian: normal; font-feature-settings: normal; color: rgb(29, 29, 29);"><span style="font-kerning: none;">Riverine heat wave events\u2014periods of abnormally high riverine water temperatures (WT)\u2014can substantially impair aquatic ecosystems, water quality, and food and energy production. However, comprehensive analysis of riverine heat waves is still emerging, long hindered by fragmented and discontinuous WT data. Here, we used a deep learning model and reconstructed consistent daily WT in 1471 U.S. river sites (1980\u20132022). <span style="background-color: rgb(255, 251, 0);">Results show that riverine heat wave events occur less frequently and intensively but last nearly twice as long as air heat waves. Alarmingly, riverine heat waves have risen at much faster rates than air heat waves.</span> Results here underscore the need for coordinated monitoring and data consolidation efforts for riverine heat waves, and their incorporation into global climate risk assessment and adaptation policies.</span></p><p style="font-family: Arial, Helvetica, sans-serif; font-size: small; font-variant-ligatures: normal; orphans: 2; widows: 2; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial; margin: 0px; line-height: normal; font-size-adjust: none; font-kerning: auto; font-variant-alternates: normal; font-variant-numeric: normal; font-variant-east-asian: normal; font-feature-settings: normal; color: rgb(29, 29, 29); background-color: rgb(255, 255, 255);"><span style="font-kerning: none;"><br></span></p><p style="font-family: Arial, Helvetica, sans-serif; font-size: small; font-variant-ligatures: normal; orphans: 2; widows: 2; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial; margin: 0px 0px 12px; line-height: normal; font-size-adjust: none; font-kerning: auto; font-variant-alternates: normal; font-variant-numeric: normal; font-variant-east-asian: normal; font-feature-settings: normal; color: rgb(11, 11, 11); background-color: rgb(255, 255, 255);"><span style="font-kerning: none;"><b>Abstract</b></span></p><p style="font-family: Arial, Helvetica, sans-serif; font-size: small; font-variant-ligatures: normal; orphans: 2; widows: 2; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial; margin: 0px; line-height: normal; font-size-adjust: none; font-kerning: auto; font-variant-alternates: normal; font-variant-numeric: normal; font-variant-east-asian: normal; font-feature-settings: normal; color: rgb(29, 29, 29);"><span style="font-kerning: none;"><span style="background-color: rgb(255, 251, 0);">While air heat waves often grab headlines, riverine heat waves have gone quietly unnoticed because rivers are commonly perceived as cool refuges. </span><span style="background-color: rgb(255, 255, 255);">Analysis of riverine heat waves has been hindered by fragmented datasets, despite a proliferation in water-temperature monitoring with sensors and satellites. Here, we analyze riverine heat wave events by training one single deep learning (long short-term memory) model and reconstructing consistent and continuous daily water temperatures (WT) in 1471 sites in the Contiguous United States (1980\u20132022). We show that riverine heat waves occur at about half the frequency (2.3 versus 4.6 events/year), a third intensity (2.6 versus 7.7 °C/event), but almost double the duration (7.2 versus 4.0 d/event) of air heat waves. </span><span style="background-color: rgb(255, 251, 0);">Riverine heat wave events have increased at double to quadruple rates of air heat wave events, amounting to an additional 1.8 events/year in frequency, 0.43 °C/event in intensity, 3.4 d/event in duration, and 7 to 15 additional thermal stress days for aquatic ecosystems in 2022 compared to 1980. Rising<b> riverine heat waves have outpaced those of air heat waves in 65 to 76% of the sites, particularly in regions experiencing accelerated warming (e.g., the Rockies).</b></span><b style="background-color: rgb(255, 255, 255);"> </b><span style="background-color: rgb(255, 255, 255);">Riverine heat wave trends are driven predominantly by climate-induced changes such as warming and dwindling snowpacks and water flow. Human activities do play important roles: large dams elongate, whereas agriculture reduces heat waves. These results highlight anthropogenic climate change as the primary external driver, whereas human-induced structural changes as the secondary internal modulators of river response to heat disturbance. </span><span style="background-color: rgb(255, 251, 0);">The widespread rise of riverine heat waves threatens aquatic ecosystems and water-energy-food security</span><span style="background-color: rgb(255, 255, 255);">, underscoring the need for their global characterization and risk assessment.</span></span></p><div style="color: rgb(34, 34, 34); font-family: Arial, Helvetica, sans-serif; font-size: small; font-variant-ligatures: normal; orphans: 2; widows: 2; background-color: rgb(255, 255, 255); text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;"><span style="font-kerning: none;"><br></span></div><div style="color: rgb(34, 34, 34); font-family: Arial, Helvetica, sans-serif; font-size: small; font-variant-ligatures: normal; orphans: 2; widows: 2; background-color: rgb(255, 255, 255); text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;"><br class="Apple-interchange-newline"></div><div>
<meta charset="UTF-8"><div style="font-family: Verdana; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; text-decoration: none; caret-color: rgb(0, 0, 0); color: rgb(0, 0, 0);"><br class="Apple-interchange-newline"><br></div><div style="font-family: Verdana; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; text-decoration: none; caret-color: rgb(0, 0, 0); color: rgb(0, 0, 0);">=\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014------===-------------------------------------------------=<br><br>\u201cFull of recent references and statistics, Harvesting the Biosphere adds to the growing chorus of warnings about the current trajectory of human activity on a finite planet, of which climate change is only one dimension. <br><br>\u201cOne can quibble with some assumptions or tweak Smil\u2019s calculations, but the bottom line will not change, only the time it may take humanity to reach a crisis point.\u201d<br><br>Stephen Running. \u201cApproaching the Limits\u201d Science 15 March 2013.<br><br>Book review. Harvesting the Biosphere: What we have taken from Nature. by Vaclav Smil . MIT Press, Cambridge, MA, 2012. 315 pp. $29, £19.95. ISBN 9780262018562.<br><br>=\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014-----------------------===\u2014----------------------------\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014=<br><br>\u201cMan \u2026 is alone, abandoned on earth in the midst of his infinite responsibilities, without help, with no other aim than the one he sets himself, with no other destiny than the one he forges for himself on this earth.\u201d<br><br>Jean-Paul Sartre (1905-1980)<br><br></div>
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