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Global warming could have serious consequences for soil degradation and downstream waterway silting in Madagascar. This is especially true for the country’s upland areas, the most vulnerable and populated part of the island. However, whether soil erosion is induced by local human activities (farming) or global impact is still questionable. In order to reveal the contribution of each factor and to observe the impact of climate change, the temporal variation of the soil erosion rate in agricultural fields has been investigated by the Cs-137 fallout radionuclide resampling approach. At the agricultural erosion study site, land use has remained unchanged over time, and the expected change can then be correlated to climate variability. The catchment study area is located in the eastern central highland of Madagascar. The first sampling campaign was carried out in 2010, and the resampling one was conducted in 2019 in the same field, following the same transect protocol and sampling strategy. The 137Cs measurements were performed using an HPGe gamma spectrometry detector. The mass balance conversion model (MBM2) has been used to estimate water-induced soil erosion rates. Results show that during the 9-year time span, the Mean erosion rate has increased from 9.1 to 11.1 t ha−1 yr−1 (+22%), the Net erosion rate from 7.4 to 10.1 t ha−1 yr−1 (+36%), and the Sediment Delivery Ratio (SDR) from 89% to 99.8% (i.e.,+12%). In any case, SDR is the most suitable to represent the erosion-deposition-sedimentation dynamics of the study site. Caesium-137 inferred soil erosion values are averaged from 1954, the onset of global fallout, to the sampling time, meaning these changes may reflect a more intense phenomenon. Assuming a steady linear increase as a model of the soil erosion rate change, an increase rate of 0.675 t ha−1 yr−1 per year can be deduced from 1954 to the present time, or 6.75 t ha−1 yr−1 per decade. To summarize, the magnitude of the upstream on-site erosion phenomenon and the downstream SDR have increased during the last decade and could be related to the trend in climate variability. A mitigation strategy could then be developed accordingly.

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Investigating Effects of Climate Change on Madagascar’s Agricultural Land, Using Cs-137 Resampling Approach

  • 会议论文

  • 发表日期：

    2026年

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  • Naivo Rabesiranana,
  • Ramanantoanina Silvère Tsaravola,
  • Asivelo Fanantenansoa Solonjara,
  • Rovatiana Fanjanirina Randrianantenaina,
  • Martin Rasolonirina

摘要

Global warming could have serious consequences for soil degradation and downstream waterway silting in Madagascar. This is especially true for the country’s upland areas, the most vulnerable and populated part of the island. However, whether soil erosion is induced by local human activities (farming) or global impact is still questionable. In order to reveal the contribution of each factor and to observe the impact of climate change, the temporal variation of the soil erosion rate in agricultural fields has been investigated by the Cs-137 fallout radionuclide resampling approach. At the agricultural erosion study site, land use has remained unchanged over time, and the expected change can then be correlated to climate variability. The catchment study area is located in the eastern central highland of Madagascar. The first sampling campaign was carried out in 2010, and the resampling one was conducted in 2019 in the same field, following the same transect protocol and sampling strategy. The 137Cs measurements were performed using an HPGe gamma spectrometry detector. The mass balance conversion model (MBM2) has been used to estimate water-induced soil erosion rates. Results show that during the 9-year time span, the Mean erosion rate has increased from 9.1 to 11.1 t ha−1 yr−1 (+22%), the Net erosion rate from 7.4 to 10.1 t ha−1 yr−1 (+36%), and the Sediment Delivery Ratio (SDR) from 89% to 99.8% (i.e.,+12%). In any case, SDR is the most suitable to represent the erosion-deposition-sedimentation dynamics of the study site. Caesium-137 inferred soil erosion values are averaged from 1954, the onset of global fallout, to the sampling time, meaning these changes may reflect a more intense phenomenon. Assuming a steady linear increase as a model of the soil erosion rate change, an increase rate of 0.675 t ha−1 yr−1 per year can be deduced from 1954 to the present time, or 6.75 t ha−1 yr−1 per decade. To summarize, the magnitude of the upstream on-site erosion phenomenon and the downstream SDR have increased during the last decade and could be related to the trend in climate variability. A mitigation strategy could then be developed accordingly.