USGS California Comparison of Streamflow Maps

Tracking California Water Availability with USGS Streamflow Comparison Maps

This tool enables side-by-side visual analysis of two different time periods to identify spatial and temporal change in water availability. Users can contrast current monthly data against the previous year to see exactly how California’s water landscape has evolved.

The USGS Comparison of Streamflow Maps tool allows users to view and contrast two different regional streamflow maps side-by-side to identify temporal or spatial trends.

Key Features and Functionality

This side-by-side comparison tool displays two different monthly streamflow maps to identify geographic and temporal shifts. Users can contrast different years or months to visualize how California's regional water status has evolved.

Side-by-Side Visualization: This utility displays two regional maps concurrently, facilitating direct visual contrast between different periods or metrics.
Geographic Filtering: Users can select a specific Geographic area (such as California) or a broader Water Resource Region for comparison.
Flexible Data Types:
- Map type: Users can choose the primary data category, such as "Monthly streamflow (month of year)".
- Sub type: Allows further refinement of the data view, such as "HUC streamflow".
Temporal Customization: Two date input boxes (Date (YYYYMM)) allow users to specify the exact months and years to compare (e.g., comparing December 2024 to December 2025).
Interactive Maps: Each map in the comparison view can be clicked to open a larger, more detailed version of that specific data.

Understanding the Comparison

The maps use a standardized color scale based on percentages to show how conditions shifted between two selected dates:

Red: Low
Dark Red (<10): Much below normal
Orange (10–24): Below normal
Green (25–75): Normal
Light Blue (76–90): Above normal
Dark Blue (>90): Much above normal
Black: High
Grey: No Data

By comparing the colors across the same geographic areas in both maps, users can quickly identify regions that have become wetter, drier, or remained stable over the selected timeframe.

Learn More About Tracking California Water Levels

Use the guides below to navigate the various tools and data visualizations provided by the USGS. These resources are designed to help you interpret real-time streamflow maps, historical runoff comparisons, and regional water conditions across California.