Root-zone soil moisture variability across African savannas: From pulsed rainfall to land‐cover switches

Matti Räsänen, Lutz Merbold, Ville Vakkari, Mika Aurela, Lauri Laakso, Johan P. Beukes, Pieter G. Van Zyl, Miroslav Josipovic, Gregor Feig, Petri Pellikka, Janne Rinne, Gabriel Katul

Research output: Contribution to journalArticleScientific

Abstract

The main source of soil moisture variability in savanna ecosystems is pulsed rainfall. Rainfall pulsing impacts water-stress durations, soil moisture switching between wet-to-dry and dry-to-wet states, and soil moisture spectra as well as derived measures from it such as soil moisture memory. Rainfall pulsing is also responsible for rapid changes in grassland leaf area and concomitant changes in evapotranspirational (ET) losses, which then impact soil moisture variability. With the use of a hierarchy of models and soil moisture measurements, temporal variability in root-zone soil moisture and water-stress periods are analysed at four African sites ranging from grass to miombo savannas. The normalized difference vegetation index (NDVI) and potential ET (PET)-adjusted ET model predict memory timescale and dry persistence in agreement with measurements. The model comparisons demonstrate that dry persistence and mean annual dry periods must account for seasonal and interannual changes in maximum ET represented by NDVI and to a lesser extent PET. Interestingly, the precipitation intensity and soil moisture memory were linearly related across three savannas with ET/infiltration similar to 1.0. This relation and the variability of length and timing of dry periods are also discussed.

Original languageEnglish
Article number2213
JournalEcohydrology
Volume13
Issue number5
Number of pages20
ISSN1936-0584
DOIs
Publication statusPublished - Jul 2020
MoE publication typeB1 Journal article

Fields of Science

  • 1181 Ecology, evolutionary biology
  • 1171 Geosciences
  • memory
  • persistence
  • precipitation intensity
  • savanna
  • WATER-CONTROLLED ECOSYSTEMS
  • VOLATILE ORGANIC-COMPOUNDS
  • HYDROLOGIC PROCESSES
  • ACTIVE-ROLE
  • CLIMATE
  • BALANCE
  • MODEL
  • STRESS
  • PLANTS
  • DISTRIBUTIONS

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