Imprints of evaporative conditions and vegetation type in diurnal temperature variations
<p>Diurnal temperature variations are strongly shaped by the absorption of solar radiation, but evaporation, or the latent heat flux, also plays an important role. Generally, evaporation cools. Its relation to diurnal temperature variations, however, is unclear. This study investigates the diu...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2020-10-01
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| Series: | Hydrology and Earth System Sciences |
| Online Access: | https://hess.copernicus.org/articles/24/4923/2020/hess-24-4923-2020.pdf |
| _version_ | 1819208896038830080 |
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| author | A. Panwar M. Renner M. Renner A. Kleidon |
| author_facet | A. Panwar M. Renner M. Renner A. Kleidon |
| author_sort | A. Panwar |
| collection | DOAJ |
| description | <p>Diurnal temperature variations are strongly shaped by the absorption of solar radiation, but evaporation, or the latent heat flux, also plays an important role. Generally, evaporation cools. Its relation to diurnal temperature variations, however, is unclear. This study investigates the diurnal response of surface and air temperatures to evaporative conditions for different vegetation types. We use the warming rate, defined as the increase in temperature in response to absorbed solar radiation in the morning, and evaluate how it changes with evaporative fraction, which is an indicator of the evaporative conditions. Results for 51 FLUXNET sites show that the warming rate of air temperature carries very weak imprints of evaporative fraction across all vegetation types. However, the warming rate
of surface temperature is highly sensitive to evaporative fraction with a
value of <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M1" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>∼</mo><mn mathvariant="normal">23</mn><mo>×</mo><msup><mn mathvariant="normal">10</mn><mrow><mo>-</mo><mn mathvariant="normal">3</mn></mrow></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="58pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="d45125934b2b5fc04c7ccaed99796c32"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="hess-24-4923-2020-ie00001.svg" width="58pt" height="14pt" src="hess-24-4923-2020-ie00001.png"/></svg:svg></span></span> K (W m<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M2" display="inline" overflow="scroll" dspmath="mathml"><mrow><msup><mi/><mrow><mo>-</mo><mn mathvariant="normal">2</mn></mrow></msup><msup><mo>)</mo><mrow><mo>-</mo><mn mathvariant="normal">1</mn></mrow></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="26pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="6b270f3edcdfec640fbb2e1a73dfed1f"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="hess-24-4923-2020-ie00002.svg" width="26pt" height="15pt" src="hess-24-4923-2020-ie00002.png"/></svg:svg></span></span>, indicating stronger evaporative cooling for moister conditions. Contrarily, the warming rates of surface and air temperatures are similar at forest sites and carry literally no imprints of evaporative fraction. We explain these contrasting patterns with an analytical surface energy balance model. The derived expressions reproduce the observed warming rates and their sensitivity to evaporative fraction in all vegetation types. Multiplying the warming rate with daily maximum solar radiation gives an approximation for the diurnal surface temperature range (DT<span class="inline-formula"><sub>s</sub></span>R). We use our model to compare the individual contributions of solar radiation, evaporative conditions, and vegetation (by its aerodynamic conductance) in shaping DT<span class="inline-formula"><sub>s</sub></span>R and show that the high aerodynamic conductance of forests reduces DT<span class="inline-formula"><sub>s</sub></span>R substantially more (<span class="inline-formula">−56</span> %) than evaporative cooling (<span class="inline-formula">−22</span> %). We further show that the strong diurnal variation in aerodynamic conductance (<span class="inline-formula">∼2.5</span> times of the mean across vegetation types) reduces DT<span class="inline-formula"><sub>s</sub></span>R by <span class="inline-formula">∼35</span> % in short vegetation and savanna but only by <span class="inline-formula">∼22</span> % in forests. We conclude that diurnal
temperature variations may be useful for predicting evaporation for short
vegetation. In forests, however, the diurnal variations in temperatures are
mainly governed by their high aerodynamic conductance, resulting in negligible imprints of evaporative conditions.</p> |
| first_indexed | 2024-12-23T05:46:40Z |
| format | Article |
| id | doaj.art-edddeddbc4d24892bac5a1f244dc59ac |
| institution | Directory Open Access Journal |
| issn | 1027-5606 1607-7938 |
| language | English |
| last_indexed | 2024-12-23T05:46:40Z |
| publishDate | 2020-10-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Hydrology and Earth System Sciences |
| spelling | doaj.art-edddeddbc4d24892bac5a1f244dc59ac2022-12-21T17:58:04ZengCopernicus PublicationsHydrology and Earth System Sciences1027-56061607-79382020-10-01244923494210.5194/hess-24-4923-2020Imprints of evaporative conditions and vegetation type in diurnal temperature variationsA. Panwar0M. Renner1M. Renner2A. Kleidon3Biospheric Theory and Modeling group, Max Planck Institute for Biogeochemistry, 07745 Jena, GermanyBiospheric Theory and Modeling group, Max Planck Institute for Biogeochemistry, 07745 Jena, Germanynow at: Brandenburg State Office for Environment, Flood Monitoring Centre, 15236 Frankfurt (Oder), GermanyBiospheric Theory and Modeling group, Max Planck Institute for Biogeochemistry, 07745 Jena, Germany<p>Diurnal temperature variations are strongly shaped by the absorption of solar radiation, but evaporation, or the latent heat flux, also plays an important role. Generally, evaporation cools. Its relation to diurnal temperature variations, however, is unclear. This study investigates the diurnal response of surface and air temperatures to evaporative conditions for different vegetation types. We use the warming rate, defined as the increase in temperature in response to absorbed solar radiation in the morning, and evaluate how it changes with evaporative fraction, which is an indicator of the evaporative conditions. Results for 51 FLUXNET sites show that the warming rate of air temperature carries very weak imprints of evaporative fraction across all vegetation types. However, the warming rate of surface temperature is highly sensitive to evaporative fraction with a value of <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M1" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>∼</mo><mn mathvariant="normal">23</mn><mo>×</mo><msup><mn mathvariant="normal">10</mn><mrow><mo>-</mo><mn mathvariant="normal">3</mn></mrow></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="58pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="d45125934b2b5fc04c7ccaed99796c32"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="hess-24-4923-2020-ie00001.svg" width="58pt" height="14pt" src="hess-24-4923-2020-ie00001.png"/></svg:svg></span></span> K (W m<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M2" display="inline" overflow="scroll" dspmath="mathml"><mrow><msup><mi/><mrow><mo>-</mo><mn mathvariant="normal">2</mn></mrow></msup><msup><mo>)</mo><mrow><mo>-</mo><mn mathvariant="normal">1</mn></mrow></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="26pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="6b270f3edcdfec640fbb2e1a73dfed1f"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="hess-24-4923-2020-ie00002.svg" width="26pt" height="15pt" src="hess-24-4923-2020-ie00002.png"/></svg:svg></span></span>, indicating stronger evaporative cooling for moister conditions. Contrarily, the warming rates of surface and air temperatures are similar at forest sites and carry literally no imprints of evaporative fraction. We explain these contrasting patterns with an analytical surface energy balance model. The derived expressions reproduce the observed warming rates and their sensitivity to evaporative fraction in all vegetation types. Multiplying the warming rate with daily maximum solar radiation gives an approximation for the diurnal surface temperature range (DT<span class="inline-formula"><sub>s</sub></span>R). We use our model to compare the individual contributions of solar radiation, evaporative conditions, and vegetation (by its aerodynamic conductance) in shaping DT<span class="inline-formula"><sub>s</sub></span>R and show that the high aerodynamic conductance of forests reduces DT<span class="inline-formula"><sub>s</sub></span>R substantially more (<span class="inline-formula">−56</span> %) than evaporative cooling (<span class="inline-formula">−22</span> %). We further show that the strong diurnal variation in aerodynamic conductance (<span class="inline-formula">∼2.5</span> times of the mean across vegetation types) reduces DT<span class="inline-formula"><sub>s</sub></span>R by <span class="inline-formula">∼35</span> % in short vegetation and savanna but only by <span class="inline-formula">∼22</span> % in forests. We conclude that diurnal temperature variations may be useful for predicting evaporation for short vegetation. In forests, however, the diurnal variations in temperatures are mainly governed by their high aerodynamic conductance, resulting in negligible imprints of evaporative conditions.</p>https://hess.copernicus.org/articles/24/4923/2020/hess-24-4923-2020.pdf |
| spellingShingle | A. Panwar M. Renner M. Renner A. Kleidon Imprints of evaporative conditions and vegetation type in diurnal temperature variations Hydrology and Earth System Sciences |
| title | Imprints of evaporative conditions and vegetation type in diurnal temperature variations |
| title_full | Imprints of evaporative conditions and vegetation type in diurnal temperature variations |
| title_fullStr | Imprints of evaporative conditions and vegetation type in diurnal temperature variations |
| title_full_unstemmed | Imprints of evaporative conditions and vegetation type in diurnal temperature variations |
| title_short | Imprints of evaporative conditions and vegetation type in diurnal temperature variations |
| title_sort | imprints of evaporative conditions and vegetation type in diurnal temperature variations |
| url | https://hess.copernicus.org/articles/24/4923/2020/hess-24-4923-2020.pdf |
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