Section 2.0: Elevation-Precipitation correlation

The charts function in BAGIS V3 includes a set of new scatterplots to show the correlation between elevation and PRISM precipitation for the AOI and for the SNOTEL/Snow Course locations. The customizable settings for this functionality may be found in the lower right-hand corner of the BAGIS Map Settings window. Generating the represented precipitation correlation charts is an optional task that increases the processing time for both generating zones and publishing tables. Check the box next to 'Generate Elev-Precip Table and Scatter Plot' to enable this functionality.

By default the elevation and precipitation values are aggregated by each PRISM cell, that is, there is a value (or point) on the chart indicating the elevation and precipitation values for each cell. You also have the option of specifying that the values be aggregated using a zone layer, like an HRU layer. To aggregate by zone, select that option and then select a zone aggregate layer. The Select button for a zonal aggregate layer will be enabled when you click the Zone Layer button. You can choose from any discrete (integer) rasters that are present in the layers.gdb folder of the current AOI. Use the BAGIS AOI Utilities form to add a new discrete raster layer to the AOI if you wish to use it as zone aggregate layer.

You also have the option specifying an attribute layer to use as a partition raster. The requirements for a partition raster are similar to the zone aggregate layer. The partition raster must be a discrete raster that exists in the layers.gdb of the current AOI. BAGIS will write the majority value from the partition raster into a column on the Elev-Precip spreadsheets. You can use Excel's filtering function to filter the spreadsheets and chart according to values in the partition raster. Click the clear button to remove an unwanted attribute layer from your analysis.

Note that the majority value for Aspect is always written into a column on the Elev-Precip spreadsheets and can also be used for filtering.

The source layers for elevation-precipitation correlation analysis are generated when the '4. Generate Zones' button is clicked. If you make changes to the correlation settings, you will need to regenerate the zones for your changes to be reflected. When the correlation layers are present and ready to be used in chart generation, their status will show as 'Ready'. The layer names are printed in blue on the BAGIS Maps Settings window directly above the '4. Generate Zones' button.

When the correlation layers are 'Ready', click the Tables button to generate the BAGIS tables and charts, including the elevation-precipitation correlation tabs. The output graphics and tables are stored in the Basin Analysis Excel spreadsheet in tabs that start with the prefix 'Elev-Precip'. The correlation chart includes regression lines, slope value, and intercept value. See the sample below: