What are the categories and ranges of the Surface Water Supply Index (SWSI)?

The Surface Water Supply Index (SWSI) uses specific categories and ranges to describe the water supply conditions, ranging from extreme drought to extremely wet conditions. While these categories can vary depending on the specific implementation, a common set of categories and their corresponding ranges are as follows:

Extremely Wet: SWSI > +3.0

Very Wet: +2.0 < SWSI ≤ +3.0

Moderately Wet: +1.5 < SWSI ≤ +2.0

Slightly Wet: +1.0 < SWSI ≤ +1.5

Near Normal: -1.0 ≤ SWSI ≤ +1.0

Slightly Dry: -1.5 < SWSI < -1.0

Moderately Dry: -2.0 < SWSI ≤ -1.5

Severely Dry: -3.0 < SWSI ≤ -2.0

Extremely Dry: SWSI ≤ -3.0

These categories help to interpret the SWSI values in a meaningful way, allowing for the assessment of water supply conditions and the communication of these conditions to stakeholders. Here's a brief description of each category:

Analyze Hydrological Drought using Surface Water Supply Index - SWSI

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Extremely Wet: Indicates an abundant water supply significantly above the normal level.

Very Wet: Indicates a water supply that is well above the normal level.

Moderately Wet: Indicates a water supply that is above normal levels.

Slightly Wet: Indicates a slightly above-normal water supply.

Near Normal: Indicates average or expected water supply conditions.

Slightly Dry: Indicates a slightly below-normal water supply.

Moderately Dry: Indicates a water supply that is below normal levels.

Severely Dry: Indicates a significantly below-normal water supply.

Extremely Dry: Indicates a very low water supply, often associated with extreme drought conditions.

These categories and ranges are essential for water resource management, helping to trigger specific management actions and responses to varying water supply conditions. They are often used by agencies and organizations to monitor and report on water availability and to inform drought preparedness and response plans.

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