Tool Name	Upslope Area
Tool ID	4
Library ID	ta_hydrology
Version	1.0
Author(s)	O.Conrad (c) 2001

Description

This tool allows you to specify target cells, for which the upslope contributing area shall be identified. The result will give for each cell the percentage of its flow that reaches the target cell(s).
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This version uses all valid cells (not 'no data' values) of a given target grid to determine the contributing area. In case no target grid is provided as input, the specified x/y coordinates are used as target point.

References

Freeman, G.T. (1991): Calculating catchment area with divergent flow based on a regular grid. Computers and Geosciences, 17:413-22.

O'Callaghan, J.F. & Mark, D.M. (1984): The extraction of drainage networks from digital elevation data. Computer Vision, Graphics and Image Processing, 28:323-344.

Qin, C. Z., Zhu, A. X., Pei, T., Li, B. L., Scholten, T., Behrens, T. & Zhou, C. H. (2011): An approach to computing topographic wetness index based on maximum downslope gradient. Precision Agriculture, 12(1), 32-43. ResearchGate

Quinn, P.F., Beven, K.J., Chevallier, P. & Planchon, O. (1991): The prediction of hillslope flow paths for distributed hydrological modelling using digital terrain models. Hydrological Processes, 5:59-79. ResearchGate

Seibert, J. & McGlynn, B. (2007): A new triangular multiple flow direction algorithm for computing upslope areas from gridded digital elevation models. Water Resources Research, Vol. 43, W04501,
C++ implementation in SAGA by Thomas Grabs (c) 2007, contact: thomas.grabs@natgeo.su.se, jan.seibert@natgeo.su.se. Wiley

Tarboton, D.G. (1997): A new method for the determination of flow directions and upslope areas in grid digital elevation models. Water Resources Research, Vol.33, No.2, p.309-319. Wiley

Parameters

Name	Type	Identifier	Description	Constraints
Input
Target Area	grid, input, optional	TARGET
Elevation	grid, input	ELEVATION
Sink Routes	grid, input, optional	SINKROUTE
Output
Upslope Area	grid, output	AREA
Options
Target X coordinate	floating point number	TARGET_PT_X	The x-coordinate of the target point in world coordinates [map units]	Default: 0.000000
Target Y coordinate	floating point number	TARGET_PT_Y	The y-coordinate of the target point in world coordinates [map units]	Default: 0.000000
Method	choice	METHOD		Available Choices: [0] Deterministic 8 [1] Deterministic Infinity [2] Multiple Flow Direction [3] Multiple Triangular Flow Direction [4] Multiple Maximum Downslope Gradient Based Flow Direction Default: 2
Convergence	floating point number	CONVERGE	Convergence factor for Multiple Flow Direction algorithm	Minimum: 0.001000 Default: 1.100000
Contour Length	boolean	MFD_CONTOUR	Include (pseudo) contour length as additional weighting factor in multiple flow direction routing, reduces flow to diagonal neighbour cells by a factor of 0.71 (s. Quinn et al. 1991 for details).	Default: 0