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CP 17 Project. Rainwater Harvesting (RWH) in Limpopo Basin - Challenges. 4 th Scientific Workshop, JHB 15 th to 18 th June 2009. Limpopo River Basin. Limpopo Basin - Rainfall. Pafuri average annual rainfall: 380.0 mm. Xai-Xai average annual rainfall: 953.0 mm.

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rainwater harvesting rwh in limpopo basin challenges
CP 17 Project

Rainwater Harvesting (RWH) in Limpopo Basin - Challenges

4th Scientific Workshop, JHB 15th to 18th June 2009

rainfall distribution and waterbalance

average annual rainfall: 380.0 mm


average annual rainfall: 953.0 mm

Rainfall Distribution and Waterbalance
options in rainfed agriculture
Options in Rainfed Agriculture

poverty trap

what to do

to reverse trends

  • Climate:
  • rainfall harvest
  • rainfall storage
  • Crops:
  • length
  • tolerance
  • root
  • Soil:
  • soil structure
  • soil management
conceptual model


Conceptual Model
  • Low Cost Interventions:
    • explore rainfall pattern;
    • crop (ETc);
    • soil storage.
  • Other possible interventions:
    • rainfall harvest and storage-supplementary irrigation;
    • medium to large dams and irrigation.
et crop kc x eto kc kcb ke
ET crop = Kc x ETo(Kc = Kcb + Ke)
  • Decrease Crop Failure Hazard:
    • mulching to decrease soil evaporation;
    • increase rainfall collecting area;
    • soil/root water storage reservoir
rainfall water harvest techniques1
Macro catchment

Micro catchment

Flood water catchment

Barreira trapezoidal

Barreira de pedra

Represa de terra

Barreira semi circular

Barreira semi circular

Rainfall Water Harvest Techniques
computer models to assess potential rwh
Computer Models to Assess Potential RWH
  • Visual Water Balance Processes for In-Field RainWater Harvesting – VISWBP-IRWH)- animation program to explain farmers and extension officers
  • CROPWAT model
  • SWAT model
  • PARCHED THIRST (PT) - process-based model, which combines the simulation of hydrology with growth and yield of a crop.

Decision support tool that addresses challenges of low and unreliable crop production in semi arid areas

conceptual model1


Conceptual Model
  • Crop growth model: water and soil fertility issues
  • Integrated Pest Management
  • Economical aspects
economical feasibility of rwh technology
Economical Feasibility of RWH Technology
  • Comparison of the performance of good RWH for maize, paddy and vegetable enterprises over a period of 5 years

Source: Hatibuet al (2004)

rainfall water harvest techniques5
Rainfall Water Harvest Techniques
  • Plastic-covered ridge and furrow rainfall harvesting for corn production

*Except labor cost

Source: Yan Li et al (2001)

  • Adoption of RWH improve the yields and reduce crop failure.
  • Economic benefits of RWH are greater when coupled with high value crops associated to other agricultural inputs (fertilizers, IPM).
  • Successful water harvesting projects are often based on farmers’ experience and trial and error rather than on scientifically well established techniques. There are still big challenges in hydrological and crop modelling associated to economical analysis in different environments.
  • Although RWH can increase the water availability, the climatic risks still existing.
  • Planting dates are crucial, but should be based in rainfall events and other factors (soil, pests) versus risk management (e.g. two consecutive rainy days totalizing 35 mm and planting several periods in a year).
rainwater harvesting rwh in limpopo basin challenges2
CP 17 Project

Thank you

Rainwater Harvesting (RWH) in Limpopo basin - Challenges

4th Scientific Workshop, JHB 15th to 18th June 2009