Drought Index Calculator — SPI & Palmer Drought Severity

Calculate the Standardized Precipitation Index (SPI) and Palmer Drought Severity Index (PDSI) for drought monitoring.

 
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Physical Constants Reference
ConstantSymbolValue
Speed of lightc2.99792458×10⁸
Planck's constanth6.62607015×10⁻³‴
Boltzmann constantkʙ1.380649×10⁻²³
Avogadro's numberNₐ6.02214076×10²³
Gravitational constantG6.6743×10⁻¹¹
Gas constantR8.31446
Elementary chargee1.602176634×10⁻¹⁹
Electron massmₑ9.1093837015×10⁻³¹
Proton massmₚ1.67262192369×10⁻²⁷
Fine-structure constantα7.2973525693×10⁻³
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Formula Definitions

The Drought Index Calculator — SPI & Palmer Drought Severity works by applying a well-defined formula to the values you enter. Understanding the formula behind the calculation helps you interpret the result and check that your inputs are correct. Below we break down the key components that drive the Drought Index.

The core formula used by this calculator is:

Result = f(physical quantities, constants, conditions)

Each variable in the formula has a specific meaning:

  • physical quantities — Measured values with units entered into the Drought Index.
  • constants — Physical or chemical constants (e.g. CODATA values, gas constant, Avogadro's number).
  • conditions — Temperature, pressure, concentration, or environmental state of the system.
  • Result — Computed physical or chemical quantity with associated units.

Note: Compare results with standard reference values or published experimental data.

How to Use This Calculator

  1. Enter the physical or chemical quantities. Enter the physical or chemical quantities with correct units into the Drought Index Calculator — SPI & Palmer Drought Severity input fields.
  2. Verify conditions. Verify or adjust the conditions such as temperature, pressure, concentration, or environmental parameters.
  3. Apply the scientific formula. Press Calculate to apply the scientific formula or physical law.
  4. Compare with reference values. Review the result and compare it with standard reference values, CODATA constants, or published experimental data.

Glossary and Definitions

Physical quantity
A measurable property of a physical system, expressed as a numeric value with units.
Constant
A fixed, well-defined value (e.g. a CODATA constant) used across scientific calculations.
Significant figures
The digits in a measurement that carry meaning, reflecting the precision of the instrument.
Reference value
A published standard or experimental value used to validate a calculated result.
Drought index calculator
A key concept referenced by the Drought Index: Calculate the Standardized Precipitation Index (SPI) and Palmer Drought Severity Index (PDSI) for drought monitoring.
SPI calculator
A key concept referenced by the Drought Index: Calculate the Standardized Precipitation Index (SPI) and Palmer Drought Severity Index (PDSI) for drought monitoring.
Palmer drought
A key concept referenced by the Drought Index: Calculate the Standardized Precipitation Index (SPI) and Palmer Drought Severity Index (PDSI) for drought monitoring.
Drought severity
A key concept referenced by the Drought Index: Calculate the Standardized Precipitation Index (SPI) and Palmer Drought Severity Index (PDSI) for drought monitoring.

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Frequently Asked Questions