What is the possible range of Runoff Coefficient (Runoff / Rainfall ratio) of tropical rain-forests with sloping terrain and experience over 2000 mm average annual rainfall? What are the theoretical methods of estimation of average values of Runoff Ratio for ungauged catchments with different land uses and soil types?
As a first-order preliminary estimate, you may want to evaluate the applicability of the Budyko framework to your watershed(s). This may give you some fairly good preliminary estimates of values (and range) for Runoff/Rainfall without a lot of detailed investigation.
This seems to be two questions. The first focuses on tropical rainforests on sloping terrain, the second looking at ungauged catchments, taking into account land use and soil types (presumably generalising the first question to consider either different forest types, or considering the impact of deforestation and conversion to other land uses?).
For the first question, you could start with the Budyko framework as James suggests. Given that you are interested in tropical rainforests, then you are looking at energy limited systems, so things become simpler. In addition to the annual rainfall, you should consider the separation into wet and dry seasons (the shorter the wet season, the higher the runoff coefficient).
For the second question, this does depend on what range of land use you are interested in. The slope will also be a factor as well as soil structure (rather than just type), and if you are considering deforestation, then you need to consider the impacts of human activities (e.g. terracing).
First, I thank both of you. I am not familiar with Budiko framework you mentioned. If you can recommend me a technical paper or textbook, which can guide me, it will be useful. My question regards to a catchment covered with tropical rainforest and soil with moderate infiltration. Catchment remains wet throughout the year and evapo-transpiration may be close to potential values. As an initial estimate, can I take the runoff as the difference between annual rainfall and potential evapo-transpiration (since the infiltrated water is also added to either river flow or transpiration).
There are many papers on the Budyko curve/framework, so a simple search should turn up a suite of papers. Even if you don't have subscriptions, there will be open access papers you can read. For catchments that are wet throughout the year (these will be energy limited rather than water limited), you can assume that the actual evaporation is approximately the PET, and ignoring deep drainage as a starting point. It should be noted that the "runoff" coefficient will be appropriate at a large enough scale so that shallow subsurface flows are also captured.
Dear Madam,
I suggest you to read the paper 'Identification of the Spatial Variability of Runoff Coefficients of Three Wet Zone Watersheds of Sri Lanka by K. R. J. Perera and N. T. S. Wijesekera (Prof).
Best
Miyuru
Article A Regional Analysis of Event Runoff Coefficients With Respec...
Thanks Miyuru, I went through the paper. As per their research, runoff coefficient is around 50%. It may be correct but I expected a little higher value. Secondly, there should be a monthly variation with varied ET values. I would like to see some more research on this since this is important in water resources planing.
Dear Prema,
The following articles can be useful to you:
Article Multi-Model Approach to Assess the Dynamics of Hydrologic Co...
Article Hydrological Response to Agricultural Land Use Heterogeneity...
Cheers
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