Table 4 Overview of selected climate variables and their derivation periods.

Average precipitation

Catchment-averaged precipitation (mm)

Annual precipitation averaged over each catchment.

²⁰⁸

12 months

Morton’s potential evapotranspiration

Catchment-averaged potential evapotranspiration

Morton’s equation, then averaged over each catchment.

²⁰⁸

12 months

Temperature

Catchment-averaged temperature (°C)

Annual temperature averaged over each catchment

²⁰⁸

12 months

Standardised Precipitation Index (SPI)

Identification of wetter and drier periods

Gamma distribution using a 1900–1999 reference period

^130,209

12, 24, 36, and 48 months

Standardised Precipitation Evaporation Index (SPEI)

Identification of longer periods of aridity

Gamma distribution using a 1900–1999 reference period. Morton’s PET estimate.

^{210,211,212,213,214,215}

12, 24, 36, and 48 months

SPI-flood index (Severe Floods)

Frequency of severe flooding

Number of consecutive months in a year with Standardised Precipitation Index ranging from 1.5 to 2.0

^130,216,217

12, 24, 36, and 48 months

SPI-flood index (Extreme Flood)

Frequency of extreme flooding

Number of consecutive months in a year with Standardised Precipitation Index ≥2.0

^130,216,217

12, 24, 36, and 48 months

SPI-drought index

SPI-drought index (Severe Drought)

Frequency of severe droughts

Number of consecutive months in a year with Standardised Precipitation Index ranging from −1.5 to −2.0

^130,216,217

12, 24, 36, and 48 months

(Extreme Drought)

Frequency of extreme droughts

Number of consecutive months in a year with Standardised Precipitation Index ≤−2

^130,216,217

12, 24, 36, and 48 months