Dataset Title

Arizona Topographic Relative Moisture Index 30m version 1

Authors

• Ryan E Lima (Northern Arizona University, 0000-0002-5352-7215) Ryan.lima@nau.edu
• Temuulen T. Sankey (Northern Arizona University, 0000-0002-7859-8394 )
• Abraham E. Springer (Northern Arizona University, 0000-0003-4826-9124)

Description

This raster data layer was created to assist in mapping suitability for groundwater recharge potential throughout the State of Arizona.

The Topographic Relative Moisture Index (TRMI) is a terrain-based index that estimates how wet or dry a location is likely to be based on its topographic attributes. TRMI incorporates several topographic parameters that influence moisture dynamics, including slope gradient, aspect, relative elevation (or topographic position), and landscape convexity or concavity [@parker1982]. Unlike purely hydrologic models (which might require soil or rainfall data), TRMI infers relative soil moisture patterns from topography. It’s based on the idea that topography controls moisture accumulation:

Lower areas (valleys, toeslopes) → accumulate water → wetter.

Upper areas (ridges, shoulders) → shed water → drier.

Slope steepness → steeper slopes drain faster → drier.

Aspect → affects solar radiation → south-facing slopes (in northern hemisphere) tend to be drier.

Geographic Coverage

• Latitude: [30.5162255350522, 37.8474133318948]
• Longitude: [-115.428691746036, -107.349953619422]
• CRS: EPSG:4269, NAD83 Geographic Coordinate System (degrees)

• Easting (m): [74,884.55, 850,317.80]
• Northing (m): [3,381,660.51, 4,198,137.36]
• CRS: EPSG:26912, NAD83 UTM Zone 12N (meters)

Temporal Coverage

• N.A.

File Descriptions

| File Name | Description | Format | Size | |-----------|-------------|--------|------| |AZHUC8p_USA|Shapefile for Arizona including HUC8s within the US|ESRI shapefile|1,586 KB| |Slope_AZH8_US_scaled.tif |30m slope raster scaled 1-10 |TIFF 30m Raster |3,561,320 KB| |TPI_AZH8_US.tif| Unscaled TPI raster| TIFF 30m Raster|3,561,320 KB| |TPI_AZH8_US_scaled.tif |DESCRIPTION |TIFF 30m Raster |3,561,320 KB| |Geomorphon_AZH8_US_scaled.tif|DESCRIPTION |TIFF 30m Raster |890,822 KB| |Aspect_AZH8_US_scaled.tif|DESCRIPTION |TIFF 30m Raster |388,720 KB| |TRMI_AZH8_US.tif|DESCRIPTION |TIFF 30m Raster |3,560,667 KB| |TRMI_AZH8_US_scaled.tif|DESCRIPTION |TIFF 30m Raster |3,561,320 KB|

Data Variables

| Variable Name | Unit | Description | |---------------|------|-------------|

Methodology

TRMI was calculated as per @parker1982 by reclassifying and then summing each of the input layers; slope (degrees) (1-10), slope configuration or topographic position index (TPI)(1-10) [@dereu2013], geomorphon (ArcGIS Pro 3.4.0 Spatial Analyst Toolbox--Geomorphon Landform Tool) (1-20), and aspect (degrees azimuth) (1-20). The resulting TRMI values were between 4 and 60, subsequently reclassified into 10 classes with equal interval breaks to create a scaled TRMI layer (sTRMI).

DEM creation

1-arcsecond tiles were downloaded from the national map. The tiles were then merged into a mosaic and clipped to the extent of the AZH8_US polygon. The following tiles were combined: ["USGS_1_n38w114_20240614.tif","USGS_1_n38w115_20240614.tif","USGS_1_n32w109_20240416.tif","USGS_1_n32w110_20240416.tif","USGS_1_n32w111_20240401.tif", "USGS_1_n32w112_20240401.tif","USGS_1_n32w113_20210615.tif","USGS_1_n32w114_20240401.tif","USGS_1_n33w109_20240416.tif","USGS_1_n33w110_20240416.tif", "USGS_1_n33w111_20240401.tif","USGS_1_n33w112_20240401.tif","USGS_1_n33w113_20241016.tif","USGS_1_n33w114_20241016.tif","USGS_1_n33w115_20241016.tif", "USGS_1_n33w116_20240327.tif","USGS_1_n34w108_20240416.tif","USGS_1_n34w109_20240416.tif","USGS_1_n34w110_20240416.tif","USGS_1_n34w111_20240402.tif", "USGS_1_n34w112_20240402.tif","USGS_1_n34w113_20241016.tif","USGS_1_n34w114_20241016.tif","USGS_1_n34w115_20241016.tif","USGS_1_n34w116_20240327.tif", "USGS_1_n35w108_20240416.tif","USGS_1_n35w109_20240416.tif","USGS_1_n35w110_20240606.tif","USGS_1_n35w111_20240402.tif","USGS_1_n35w112_20240402.tif", "USGS_1_n35w113_20241016.tif","USGS_1_n35w114_20241016.tif","USGS_1_n35w115_20241016.tif","USGS_1_n35w116_20221019.tif","USGS_1_n36w108_20240416.tif", "USGS_1_n36w109_20240416.tif","USGS_1_n36w110_20240606.tif","USGS_1_n36w111_20220303.tif","USGS_1_n36w112_20240614.tif","USGS_1_n36w113_20240614.tif", "USGS_1_n36w114_20240402.tif","USGS_1_n36w115_20231102.tif","USGS_1_n36w116_20231102.tif","USGS_1_n37w108_20220801.tif","USGS_1_n37w109_20220720.tif", "USGS_1_n37w110_20241031.tif","USGS_1_n37w111_20241031.tif","USGS_1_n37w112_20240614.tif","USGS_1_n37w113_20240614.tif","USGS_1_n37w114_20240614.tif", "USGS_1_n37w115_20240614.tif","USGS_1_n37w116_20231102.tif","USGS_1_n38w108_20220720.tif","USGS_1_n38w109_20220720.tif","USGS_1_n38w110_20241031.tif", "USGS_1_n38w111_20241031.tif","USGS_1_n38w112_20240614.tif","USGS_1_n38w113_20240614.tif"]

The DEM_AZH8_US_30m was not included due to its size, however it can be made available upon request or created by combining the publicly available tiles listed above

Geomorphon calculation

The 'Geomorphon' tool in ArcGIS (and originally from r.geomorphon in GRASS GIS) is an automated landform classification tool. It analyzes a DEM (Digital Elevation Model) and assigns each pixel to a geomorphic form based on the local terrain shape around that pixel.

parameters = {"Distance Units":"cells","Flat Angle Treshold": 1, "Search Distance":10} (default)

Scaling Geomorphon for TRMI

| Geomorphon landform | Scaled value (1-20) | |---------------------|----------------------| | Pit | 20 | | Valley | 18 | | Hollow | 14 | | Footslope | 12 | | Flat | 10 | | Slope | 8 | | Spur | 6 | | Shoulder | 4 | | Ridge | 2 | | Peak | 1 |

: Geomorphon landforms and associated suitability values depicting wetness values associated with those landforms from lowest (1) to highest (20).

Slope and slope scaling

Slope was calculated from the DEM_AZH8_US_30m.tif by running the Surface Parameters tool in ArcGIS Pro

| Steepness (degrees) | Scaled Value (1-10) | |---------------------|----------------------| | \<3.0 | 10 | | 3.0 - 5.9 | 9 | | 6.0 - 8.9 | 8 | | 9.0 - 11.9 | 7 | | 12.0 - 14.9 | 6 | | 15.0 - 17.9 | 5 | | 18.0 - 20.9 | 4 | | 21.0 - 23.9 | 3 | | 24.0 - 26.9 | 2 | | >27.0 | 1 |

: Slope steepness and the wetness value (1-10) which is summed as part of the TRMI calculation.

Aspect and Aspect Scaling

Aspect was calculated from the DEM_AZH8_US_30m.tif by running the Surface Parameters tool in ArcGIS Pro

Scaling was conducted using the following logic in raster calculator

"Con("Aspect_1arc" == -1, 10, Int(10 + 10 * Cos(("Aspect_1arc") * 3.14159265 / 180)))"

| Aspect ° | Description | Wetness Value| |--------------|------------------------------------------------|--------------| | -1 | Neutral (flat areas) | 10 | | 0 ° (N) | Wettest (Shaded, least evaporation) | 20 | | 45 ° (NE) | Moist, receives moderate sun | 16 | | 90 ° (E) | Neutral (morning sun, less drying) | 10 | | 135 ° (SE) | Drying increases | 6 | | 180 ° (S) | Driest (maximum sun exposure) | 1 | | 225 ° (SW) | Quite dry | 4 | | 270 ° (West) | Neutral (afternoon sun, retains some moisture) | 10 | | 315 °(NW) | Moist, cooler | 16 | | 360 ° (N) | Wettest | 20 |

: Aspect or Azimuth ° from 0 °(North, 180 ° (South) to 360 ° (North) with -1 representing flat areas. Wetness values 1-20 were applied to these aspects as shown.

TPI calculation and scaling

Topographic Position Index compares the elevation of each cell in a DEM to the mean elevation of a specified neighborhood around that cell. Positive TPI values represent locations that are higher than the average of their surroundings, while negative values represent areas that are lower than their surroundings. TPI values near zero are either flat, or areas of constant slope (Weiss 2001).

TPI was calculated by creating a mean elevation raster with circular neighborhood with a radius of 10 cells. The mean elevation raster was then subtracted from the DEM to give positive and negative values which ranged from 318 to -282, TPI was then scaled between 10 and 1 based on wetness.

|TPI value |Slope Configuration| Scaled Value| |-----------|-------------------|-------------| |-282.322 |low areas, valleys (Concave)| 10| |0 |neutral, flats, slopes (straight)| 5.5| |318.078| high areas, ridges, peaks (Convex)| 1|

Scaling was done with the following function within the raster calculator tool:

Con("TPI_circ10cell" <= -5, 10, Con("TPI_circ10cell" >= 5, 1, Float(10 - (("TPI_circ10cell" - (-5)) / (5 - (-5))) * 9)))

TRMI calculation

Topographic Relative Moisture Index (TRMI) was calculated by summing the wetness values for aspect, slope steepness, geomophon, and TPI by summing, resulting in values between 3 and 60

$$TRMI = (Aspect + Slope + Geomorphon + TPI)$$

TRMI values were then rescaled to 1-10 with linear rescaling using the following equation

$$TRMI scaled = \frac{(TRMI - 3)}{((60-3)*9)}$$

Methodology References

• Parker, A. J. (1982). The topographic relative moisture index: An approach to soil-moisture assessment in mountain terrain. Physical Geography, 3(2), 160–168. https://doi.org/10.1080/02723646.1982.10642224

• De Reu, J., Bourgeois, J., Bats, M., Zwertvaegher, A., Gelorini, V., De Smedt, P., Chu, W., Antrop, M., De Maeyer, P., Finke, P., Van Meirvenne, M., Verniers, J., & Crombé, P. (2013). Application of the topographic position index to heterogeneous landscapes. Geomorphology, 186, 39–49. https://doi.org/10.1016/j.geomorph.2012.12.015

• Weiss, A. (2001). Topographic Position and Landforms Analysis [Poster]. ESRI User Conference.

Quality Control/Limitations

• visually inspected
• Limitations: Unlike purely hydrologic models (which might require soil or rainfall data) (TRMI) is a terrain-based index that estimates how wet or dry a location is likely to be based on its topographic attributes.

Licensing

CC BY-NC 4.0 https://creativecommons.org/licenses/by-nc/4.0/

Citation

Please cite this dataset as:

Lima, R.E., Sankey, T.T., Springer, A.E. (2025). Arizona Topographic Relative Moisture Index 30 meter raster v1 , 2025 [Dataset]. HydroShare. https://doi.org/10.xxxx/xxxxx

Related Publications

• Lima et al., (In Review). Mapping landscape suitability for thinning to reduce evapotranspiration and enhance groundwater recharge in semi-arid ponderosa pine forests. Journal of Hydrology: Regional Studies.

Funding

Arizona Board of Regents for funding this research through the Technology and Research Initiative Fund (TRIF) through the Arizona Tri-University Recharge and Water Reliability Project (ATUR)