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<front>
<journal-meta>
<journal-id journal-id-type="publisher">EGUsphere</journal-id>
<journal-title-group>
<journal-title>EGUsphere</journal-title>
<abbrev-journal-title abbrev-type="publisher">EGUsphere</abbrev-journal-title>
<abbrev-journal-title abbrev-type="nlm-ta">EGUsphere</abbrev-journal-title>
</journal-title-group>
<issn pub-type="epub"></issn>
<publisher><publisher-name>Copernicus Publications</publisher-name>
<publisher-loc>Göttingen, Germany</publisher-loc>
</publisher>
</journal-meta>
<article-meta>
<article-id pub-id-type="doi">10.5194/egusphere-2026-2895</article-id>
<title-group>
<article-title>Assessing summertime hydrological cycle acceleration through drought indices</article-title>
</title-group>
<contrib-group><contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Sabin</surname>
<given-names>Matthew Walter</given-names>
<ext-link>https://orcid.org/0009-0009-9199-4234</ext-link>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
</contrib>
<contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Bjarke</surname>
<given-names>Nels R.</given-names>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
<xref ref-type="aff" rid="aff3">
<sup>3</sup>
</xref>
</contrib>
<contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Livneh</surname>
<given-names>Ben</given-names>
<ext-link>https://orcid.org/0000-0001-5445-2473</ext-link>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
<xref ref-type="aff" rid="aff3">
<sup>3</sup>
</xref>
</contrib>
</contrib-group><aff id="aff1">
<label>1</label>
<addr-line>Department of Civil, Environmental, and Architectural Engineering, University of Colorado, Boulder, 80309, United States</addr-line>
</aff>
<aff id="aff2">
<label>2</label>
<addr-line>Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, 80309, United States</addr-line>
</aff>
<aff id="aff3">
<label>3</label>
<addr-line>Western Water Assessment, University of Colorado, Boulder, 80309, United States</addr-line>
</aff>
<pub-date pub-type="epub">
<day>18</day>
<month>06</month>
<year>2026</year>
</pub-date>
<volume>2026</volume>
<fpage>1</fpage>
<lpage>30</lpage>
<permissions>
<copyright-statement>Copyright: &#x000a9; 2026 Matthew Walter Sabin et al.</copyright-statement>
<copyright-year>2026</copyright-year>
<license license-type="open-access">
<license-p>This work is licensed under the Creative Commons Attribution 4.0 International License. To view a copy of this licence, visit <ext-link ext-link-type="uri"  xlink:href="https://creativecommons.org/licenses/by/4.0/">https://creativecommons.org/licenses/by/4.0/</ext-link></license-p>
</license>
</permissions>
<self-uri xlink:href="https://egusphere.copernicus.org/preprints/2026/egusphere-2026-2895/">This article is available from https://egusphere.copernicus.org/preprints/2026/egusphere-2026-2895/</self-uri>
<self-uri xlink:href="https://egusphere.copernicus.org/preprints/2026/egusphere-2026-2895/egusphere-2026-2895.pdf">The full text article is available as a PDF file from https://egusphere.copernicus.org/preprints/2026/egusphere-2026-2895/egusphere-2026-2895.pdf</self-uri>
<abstract>
<p>The rate (or velocity) of the hydrological cycle affects water availability for agriculture, energy production, and planning for droughts or floods. Therefore, acceleration in the velocity of the hydrological cycle is likely to impact multiple hydrological domains and management practices. Previous work has primarily studied hydrological cycle velocity and acceleration through the lens of flux magnitudes and their change. Motivated to expand this definition to characterize temporal coupling between stages in the hydrological cycle, we introduce a novel definition of hydrological cycle velocity and acceleration derived from the concept of drought propagation. We define the hydrological cycle velocity as the response time between the 1-month Standardized Precipitation Index (SPI) and the 1-month Standardized Soil Moisture Index (SSI) and define acceleration as the change in response time between an early time period and a late period. Using gridded reanalysis data over the conterminous United States (CONUS) from 1951&amp;ndash;2020, we analyzed the summer period (June, July, August) to minimize the lagging-effects of cold-season processes. Response times exceeded 100 days in southwestern CONUS (indicating a slower hydrological cycle velocity), but were substantially shorter elsewhere, 10&amp;ndash;20 days, indicating a faster hydrological cycle velocity. A Random Forest variable importance analysis revealed strong negative associations of response time and mean annual flux magnitudes, with higher precipitation and evaporation associated with shorter response times. Regarding potential acceleration between an earlier (1951&amp;ndash;1985) and later (1986&amp;ndash;2020) period, 48.47 % of reanalysis grid cells experienced a deceleration (lengthening of response time) of their local summer hydrological cycle, while 39.32 % of grid cells experienced an acceleration (shortening of response time). However, a false detection rate correction found a lack of robust field significance (a&lt;sub&gt;FDR&lt;/sub&gt;=0.05), a finding reinforced by a regional decadal trend analysis. By framing hydrological cycle acceleration in terms of propagation of meteorological anomalies to land surface anomalies, we expand the conceptual basis for diagnosing changes in the hydrological cycle.</p>
</abstract>
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<funding-group>
<award-group id="gs1">
<funding-source>National Oceanic and Atmospheric Administration</funding-source>
<award-id>NA22OAR4320151</award-id>
</award-group>
</funding-group>
</article-meta>
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