The runoff coefficient for a watershed gives a fair idea about the input-response relationship for the system. The major factors that affect the rainfall-runoff relationship can be broadly categorized into Physiographical and Climatological factors. The physiographical factors involve land use land cover, soil type, underlying geology, stream density, elevation, stream slope, land slope, etc.While the climatological factors include rainfall amount, rainfall intensity, antecedent soil moisture, evapotranspiration, etc. The effect of physiographical factors can easily be ascertained but how to relate the climatic parameters such as effect of evapotranspiration rates on runoff coefficient. Are there any metrics or statistical measures to analyze them?
https://www.itc.nl/library/papers_2005/msc/ereg/harssema.pdf
http://hydrology.usu.edu/RRP/userdata/4/87/RainfallRunoffProcesses.pdf
You can try using Curve Number method to evaluate the response and to explore changes in runoff resulting specific input. This is a rough method as it involves many assumptions.
I recommend using simulation or multivariate methods:
Multivariate methods: https://www.researchgate.net/publication/281809655_Effect_of_climate_and_land_cover_changes_on_watershed_runoff_A_multivariate_assessment_for_stormwater_management
Simulations:
https://www.researchgate.net/publication/225525415_Effect_of_Climate_Change_on_Watershed_System_A_Regional_Analysis
Article Effect of climate and land cover changes on watershed runoff...
Article Effect of Climate Change on Watershed System: A Regional Analysis
Hi Priyank,
The runoff coefficient is the ratio of discharge (Q) and precipitation (P): Q/P. If you consider a long time period where the initial water storage is the same as the water storage (S) at the end of the period the water balance of a catchment is dS/dt = P-Q-ET where dS is the change in storage, t is time and ET is evapotranspiration. Since dS/dt = 0, Q = P-ET and the runoff coefficient becomes (P-ET)/P or 1 - ET/P showing directly the influence of ET on the runoff coefficient.
The effect of other climatological factors such as precipitation intensity, precipitation amount, dry spell length etc. can be investigated using a hydrological model which complexity will depend on data availability, aim of the modelling and spatial and temporal variability of relevant hydrological processes.
Regards,
Martijn
One way is to use a hydrologic model to compute runoff from rainfall - both for current and projected future conditions. From there, you can compute runoff coefficients and its change due to climate.
Dear Priyank, It is commonly assumed that the quantity (volume) of runoff is a proportion (percentage) of the rainfall depth. Runoff [mm] = C x Rainfall depth [mm]. In rural catchments where no or only small parts of the area are impervious, the coefficient C, which describes the percentage of runoff resulting from a rainstorm, is however not a constant factor. Instead its value is highly variable and depends on the above described catchment-specific factors and on the rainstorm characteristics. For example, in a specific catchment area with the same initial boundary condition (e.g. antecedent soil moisture), a rainstorm of 40 minutes duration with an average intensity of 30 mm/h would produce a smaller percentage of runoff than a rainstorm of only 20 minutes duration but with an average intensity of 60 mm/h although the total rainfall depth of both events were equal. Runoff coefficients for large watersheds should not be applied to small catchment areas.
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