Multiscale TROPical CatchmentS (M-TROPICS)

Experimental Tropical Watersheds

M-TROPICS Critical Zone Observatories

The CZO Multiscale TROPIcal CatchmentS (M-TROPICS) provides the international scientific community with unique decennial time series of meteorological, hydrological, geochemical, and ecological variables in tropical environments. The CZO M-TROPICS involves academic and governmental partners in tropical countries (Cameroun, India, Lao PDR, and Vietnam) and is included in the Research Infrastructure OZCAR, the French contribution to the international CZO initiative.


  • Long-term monitoring of the variables needed for establishing water, biogeochemical (including particulate matter), and energy budgets: water and inorganic and organic matter in solution (major anions and cations, carbon), in suspension (suspended particulate matter, including organic carbon), and bed particulate matter
  • Impact assessment of global change (land-use, climate) on water fluxes, chemical weathering, and physical erosion
  • Data and information dissemination to the scientific and stakeholder communities
  • Capacity building in the field of catchment hydrology and soil erosion, through on-the-job training, teaching, and student internships, and basic geochemistry through analytical platforms
  • Recommendations on land use policy to the national authorities


  • Multiscale approach, both spatially (from microplot to catchment and larger river basins scales) and temporally (from sub-hourly to multi-decennial time-series)
  • Multidisciplinary approach, currently involving hydrology, biogeochemistry, soil science, agronomy, ecology, remote sensing, experimentation, and modelling


Besides data collection and dissemination, the achievements of M-TROPICS on June 2021 are:

  • 241 scientific publications in international journals
  • 32 scientific publications in national journals
  • 1 special issue in the Lao Journal of Agriculture and Forestry (2008): Management of soil erosion and water resources in the uplands of Lao P.D.R., by Ribolzi O. (Ed.), Pierret A. (Ed.), Gebbie L. (Ed.), Sengtaheuanghoung O. (Ed.), and Chanphengxay M. (Pref.)
  • 57 PhDs, 7 post-docs, and 281 MSc, BSc and Agric. Eng. degrees


Hand pump well, Berambadi catchment.

The Earth Critical Zone (CZ) is defined as the thin layer between the top of the canopy and the bottom of groundwater aquifer in which complex interactions involving rock, soil water, air and living organisms regulate the natural habitat and determine the availability of life sustaining resources. This concept brings together scientific disciplines in the aim to tackle crucial environmental issues regarding how the various components of the CZ react to global changes, including land use and climate changes:

  • What are the water, solute, and particulate fluxes exported from tropical catchments?
  • What is the impact of rapid land use changes on hydrology, water quality, soil resources?

The strategies adopted to answer these questions are often integrated approaches on experimental catchments, where hydrological, sedimentary, biogeochemical and ecological studies can be coupled. Acquiring simultaneous time series of meteorological, hydrological, geochemical, and ecological data over decades on river systems (both small experimental watersheds and larger basins) representative of the diversity of ecosystems is pivotal for the understanding of these processes, building integrated modelling and for proposing predictive scenarios.

Houay Pano catchment.

Among the Critical Zone Observatories (CZOs) that have been implemented by the Earth Science community in the past 30 years, very few were set up in the Tropics despite the huge importance of these regions in terms of population density, fast-changing land use, biodiversity hotspots, biomass stock on continents (humid forests), size of river systems. In addition, rainfall in the Tropics is mostly governed by monsoon systems, which are particularly sensitive to climate change.


Soil organic carbon stocks and quality in small-scale tropical, sub-humid and semi-arid watersheds under shrubland and dry deciduous forest in southwestern India

Soil organic carbon stocks and quality in small-scale tropical, sub-humid and semi-arid watersheds under shrubland and dry deciduous forest in southwestern India. Soil organic carbon is regulated by a dynamic interaction between vegetation inputs, organic matter degradation, and stabilization processes in soils, and its redistribution in the landscape. Many processes of the soil carbon cycle […]


Dissemination of pathogenic bacteria in tropical hydrosystems: transport and fate of Escherichia coli in the Mekong watershed in Lao PDR

Paty Nakhle, PhD student within M-TROPICS CZO, defended her PhD thesis today at GET. Fecal contamination of surface water remains a major threat to public health especially in the rural areas of developing countries. Over 70 million people depend on unimproved water resources in the lower Mekong basin. Diarrheal diseases are a leading cause of […]


In-stream Escherichia coli modeling using high-temporal-resolution data with deep learning and process-based models

Contamination of surface waters with microbiological pollutants is a major concern to public health. Although long-term and high-frequency Escherichia coli (E. coli) monitoring can help prevent diseases from fecal pathogenic microorganisms, such monitoring is timeconsuming and expensive. Process-driven models are an alternative means for estimating concentrations of fecal pathogens. However, process-based modeling still has limitations […]


Overland flow during a storm event strongly affects stream water chemistry and bacterial community structure

As flood events are expected to become more frequent due to climate change, investigating how overland flow exports terrestrial nutrients, carbon and living organisms into aquatic systems is essential for understanding both soil and stream ecosystem status. In this paper led by Huong Le, former PhD student at iEES Paris, the authors assessed how dissolved […]


Land use, surface runoff, soil erosion: multi-scale impact assessment of teak tree plantation management in a tropical humid mountainous agro-ecosystem

Layheang Song, PhD student within M-TROPICS CZO, defended his thesis today at GET. His thesis work was under the international double degree program between the University Paul Sabatier and the Institute of Technology of Cambodia. Soil erosion is one of the most concerning environmental problems on the global scale. Soil erosion is increasingly driven by […]


Interactions between surface and deep critical zone: case of South India ecosystems and agrosystems

One of the major interests of long-term critical zone observatories is to study and model the interactions between the different compartments that compose the critical zone, and in particular the feedback loops between surface and deep critical zone that affect the hydrological and geochemical cycles. The importance of these feedbacks was illustrated by salient results […]