Journal cover Journal topic
Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
Journal topic

Journal metrics

Journal metrics

  • IF value: 4.936 IF 4.936
  • IF 5-year value: 5.615 IF 5-year
    5.615
  • CiteScore value: 4.94 CiteScore
    4.94
  • SNIP value: 1.612 SNIP 1.612
  • IPP value: 4.70 IPP 4.70
  • SJR value: 2.134 SJR 2.134
  • Scimago H <br class='hide-on-tablet hide-on-mobile'>index value: 107 Scimago H
    index 107
  • h5-index value: 63 h5-index 63
Preprints
https://doi.org/10.5194/hess-2019-651
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/hess-2019-651
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 10 Jan 2020

Submitted as: research article | 10 Jan 2020

Review status
This preprint is currently under review for the journal HESS.

The effect of rainfall amount and timing on annual transpiration in grazed savanna grassland

Matti Räsänen1, Mika Aurela2, Ville Vakkari2, Johan P. Beukes3, Juha-Pekka Tuovinen2, Pieter G. Van Zyl3, Miroslav Josipovic3, Stefan J. Siebert3, Tuomas Laurila2, Markku Kulmala1, Lauri Laakso2,3, Janne Rinne4, Ram Oren5,6, and Gabriel Katul5,7 Matti Räsänen et al.
  • 1Institute for Atmospheric and Earth System Research, University of Helsinki, Finland
  • 2Finnish Meteorological Institute, Helsinki, Finland
  • 3Unit for Environmental Sciences and Management, North-West University, South Africa
  • 4Department of Physical Geography and Ecosystem Science, Lund University, Sweden
  • 5Nicholas School of the Environment, Duke University, Durham, North Carolina, USA
  • 6Department of Forest Science, University of Helsinki, Finland
  • 7Department of Civil and Environmental Engineering, Duke University, Durham, North Carolina, USA

Abstract. The role of precipitation (P) variability on evapotranspiration (ET) and its two components transpiration (T) and evaporation (E) rates from savannas continues to draw significant research interest given its relevance to a number of eco-hydrological applications. The work here reports on six years of measured ET and energy flux components, and estimated T from a grazed savanna grassland collected at a research site situated in Welgegund, South Africa. During this period, annual P varied considerably in amount (421 mm to 614 mm), rainy season length and precipitation intensity. T was estimated using annual water use efficiency and gross primary production determined from eddy-covariance measurements of net ecosystem CO2 exchange rates. The computed annual T was highly constrained to 352 ± 8 mm (T/ET = 0.55) for four wet years when rainfall was near or above the long-term mean. This is explained by the near constant annual tree transpiration and moderate water stress of C4 grasses during these years. In a drought year with intermittent rainfall, the annual ecosystem T was reduced due to grass dieback-regrowth that alters the temporal dynamics of bare soil cover and infiltration, and complicates monthly T/ET relation to leaf-area index (LAI). However, annual ET remains approximately equal to annual precipitation (P) even during the drought year due to increased soil evaporation. Indeed, at annual scales, ET ≈ P and annual T is conservative despite variation in amount and timing in rainfall, due to constant water use of mature trees, and the ability of C4 grasses to maintain transpiration at moderate water stress and effectively use pulsed rainfall.

Matti Räsänen et al.

Interactive discussion

Status: open (extended)
Status: open (extended)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
[Subscribe to comment alert] Printer-friendly Version - Printer-friendly version Supplement - Supplement

Matti Räsänen et al.

Data sets

Dataset for "The effect of rainfall amount and timing on annual transpiration in grazed savanna grassland" M. Räsänen, M. Aurela, V. Vakkari, P. Beukes Tuovinen, J.-P. S. Siebert, P. Van Zyl, M. Josipovic, T. Laurila, M. Kulmala, L. Laakso, J. Rinne, R. Oren, and G. G. Katul https://doi.org/10.6084/m9.figshare.11322464

Matti Räsänen et al.

Viewed

Total article views: 276 (including HTML, PDF, and XML)
HTML PDF XML Total Supplement BibTeX EndNote
196 76 4 276 25 7 11
  • HTML: 196
  • PDF: 76
  • XML: 4
  • Total: 276
  • Supplement: 25
  • BibTeX: 7
  • EndNote: 11
Views and downloads (calculated since 10 Jan 2020)
Cumulative views and downloads (calculated since 10 Jan 2020)

Viewed (geographical distribution)

Total article views: 185 (including HTML, PDF, and XML) Thereof 174 with geography defined and 11 with unknown origin.
Country # Views %
  • 1
1
 
 
 
 

Cited

Saved

No saved metrics found.

Discussed

No discussed metrics found.
Latest update: 30 May 2020
Publications Copernicus
Download
Short summary
The annual ET is approximately equal to precipitation during six measured years for grazed savanna grassland. The computed annual transpiration was highly constrained when rainfall was near or above the long-term mean but was reduced during severe drought year. The developed methodologies can be used in a wide range of arid and semi-arid ecosystems.
The annual ET is approximately equal to precipitation during six measured years for grazed...
Citation