Home Preparing Industrial Stormwater Programs for the 2026–2027 Wet Season

Preparing Industrial Stormwater Programs for the 2026–2027 Wet Season

As California approaches the 2026–2027 wet season, industrial facilities have an opportunity to review their stormwater programs and confirm that controls, monitoring procedures, and personnel are prepared for wet-weather operations.

In its August 2026 outlook, the National Oceanic and Atmospheric Administration’s (NOAA’s) Climate Prediction Center reported that El Niño was strengthening, with a greater than 90 percent chance of becoming a very strong event during fall and winter 2026–2027. The outlook also indicated a 69 percent chance that the event could reach historic strength during the October through December 2026 period. However, the agency emphasized that impacts associated with El Niño are not guaranteed.

A strong El Niño does not necessarily result in exceptional rainfall throughout California. Precipitation can vary substantially by location, storm track, and time within the season. Accordingly, the outlook should not be interpreted as a site-specific rainfall forecast. It does, however, provide a timely reminder for industrial facilities to evaluate their stormwater programs before significant rainfall occurs.

Wet-Season Readiness Under the Industrial General Permit

Facilities subject to California’s National Pollutant Discharge Elimination System (NPDES) General Permit for Stormwater Discharges Associated with Industrial Activities, commonly referred to as the Industrial General Permit (IGP), must implement site-specific stormwater controls, conduct monitoring, and maintain supporting documentation.

The frequency, timing, and intensity of storms can affect how an industrial stormwater program performs. More frequent or intense rainfall may increase runoff volumes, mobilize accumulated pollutants, place additional demands on Best Management Practices (BMPs), and create more opportunities to evaluate stormwater discharge quality.

Additional storm activity does not, by itself, indicate noncompliance. Monitoring results can be influenced by several factors, including:

Monitoring results should be evaluated in the context of site-specific conditions and applicable permit requirements.

Recommended Preseason Review

Before the wet season, facility operators should consider reviewing the following program elements:

The review should consider both routine rainfall and higher-flow conditions. Controls that perform adequately during smaller storms may respond differently when runoff volumes increase.

Potential vulnerabilities may include insufficient containment, sediment accumulation, clogged inlets, bypass around controls, erosion, or untreated runoff from areas that were not previously identified as significant pollutant sources.

Facilities should prioritize source controls that reduce or eliminate pollutant exposure before runoff occurs. Treatment controls may provide an additional layer of protection, but they should not replace appropriate housekeeping, preventive maintenance, material management,

and operational controls.

Using Monitoring Data to Guide Improvements

Stormwater monitoring should support ongoing evaluation of program performance rather than function solely as a reporting exercise. Facilities should review monitoring results after each sampled storm, when practicable, and consider whether the data indicate recurring patterns, emerging concerns, or opportunities to improve controls.

A single monitoring result may not fully characterize long-term stormwater performance. Evaluations should consider rainfall conditions, sampling locations, industrial activities, maintenance history, prior results, and other relevant site-specific information.

When monitoring results identify a potential concern, facilities should document their evaluation and implement appropriate follow-up actions consistent with applicable permit requirements. This approach allows facilities to make informed adjustments during the reporting year rather than waiting until annual reporting is underway.

A Practical Opportunity to Prepare

The current El Niño outlook introduces uncertainty regarding the coming wet season, but it also provides an opportunity for industrial facilities to review their stormwater programs proactively.

Preseason preparation can help facilities:

Regardless of how much precipitation California receives, an effective industrial stormwater program should reflect current site conditions, properly maintained controls, trained personnel, and timely review of monitoring information.

Preparing before the first significant storm remains one of the most practical steps a facility can take to support consistent stormwater program implementation.