Configuring Simulation Settings

First published: October 2026
Last updated: October 23, 2026

[!NOTE] The simulation engine allows you to control the simulation length, time resolution, and stochastic realizations to match your exact hydrologic modeling objectives.

Once your CLIGEN parameters are calibrated, you can run synthetic climate simulations directly in your web browser. This guide explains each setting in detail.

1. Simulation Duration (Horizon)

The Duration controls how many years of continuous synthetic weather the engine will generate in a single run.

Supported options: - 1 Year: Excellent for rapid testing and visualizing daily hyetographs and freeze-thaw cycles. - 10 Years: Great for verifying decadal annual averages and monthly precipitation distributions. - 30 Years: Mirrors standard meteorological climate normal horizons; recommended for baseline infrastructure sizing. - 50 to 100 Years: Ideal for mine tailings facility water balance modeling, long-term reservoir storage risk analysis, and rare storm recurrence estimation. - Custom Horizon (Up to 500 Years): For advanced risk assessments, long-term containment, or dam safety evaluations.

Performance Note: Browser-based simulations generate approximately 100 years of daily weather in under 2 seconds.

2. Time Step Resolution

The simulator supports both daily and sub-daily time steps:

Daily (24-Hour) Time Step (Default)

• Generates 1 row per calendar day: Date, Total Daily Precipitation Depth, $T_{\max}$, and $T_{\min}$.
• Best for long-term continuous water balances, reservoir routing, snowpack accumulation/melt, and crop water modeling.

Sub-Daily Downscaling (Hourly / 15-Minute)

• When sub-daily resolution is enabled, each wet day is downscaled into an internal storm hyetograph using CLIGEN's peak storm intensity ($I_p$) and time-to-peak ($t_p$) formulation.
• Generates realistic storm pulse shapes (e.g. convective thunderstorms peaking in the afternoon).
• Crucial for urban storm water runoff, culvert sizing, and flash-flood modeling.

3. Number of Realizations (Ensemble Runs)

A single 30-year simulation represents one possible future weather trajectory (one realization).

• 1 Realization: Standard run for time series generation and visual inspection.
• Ensemble (5 to 100 Realizations):
• Generates multiple independent statistical realizations from the same underlying CLIGEN parameter set.
• Enables the calculation of confidence bands (10th percentile, 50th median percentile, 90th percentile).
• Helps engineers answer questions like: "Across 100 possible 30-year futures, what is the 90th percentile annual rainfall, and how dry is the 10th percentile drought?"

4. Random Seed Control

Stochastic generation relies on pseudorandom number generators. The Climate Simulator allows you to set: - Random Seed (Auto / Fixed): - Auto (Randomized): Every time you click Run Simulation, a new seed is used, yielding a unique, fresh weather realization. - Fixed Seed (e.g., 42 or 12345): Produces the exact same sequence of weather numbers every time. This is invaluable when you need reproducibility for client presentations, academic studies, or regulatory reporting.

Starting the Simulation

1. Configure your desired Duration, Time Step, and Realizations.
2. Click the green Run Simulation button.
3. A progress indicator will display while the synthetic series is computed.
4. When finished, the results will automatically display in the Simulation Analysis panel below.