Droughts#

Consecutive Dry Days (CDD)#

Meteorological drought can in its simplest form be described by a lack of precipitation. The Consecutive Dry Days (CDD) diagnostic calculates the longest period of dry days based on user defined thresholds.

More details and usage examples can be found in the CDD recipe documentation.

Potential or Reference Evapotranspiration (PET, ET0)#

The Potential Evapotranspiration (PET) is a measure of the evaporative demand of the atmosphere. It represents the amount of water that would evaporate from a reference surface, i.e. fully watered grass land. pet.R is able to calculate PET based on a method of users choice (pet_type). The methods require different input variables for example:

  • Penman: tas, tasmin, tasmax, sfcWind, rsds, clt, hurs, ps

  • Hargreaves: tasmin, tasmax, (rsds, pr)

  • Thornthwaite: tas

A complete list and more details can be found in SPEI recipe documentation.

Standardized Precipitation-Evapotranspiration Index (SPEI)#

Meteorological droughts are often described using the Standardized Precipitation Index (SPI; McKee et al, 1993), which in a standardized way describes local precipitation anomalies.

Because SPI does not account for evaporation from the ground, it lacks one component of the water fluxes at the surface and is therefore not compatible with the concept of hydrological or agricultural drought. The Standardized Precipitation-Evapotranspiration Index (SPEI; Vicente-Serrano et al., 2010) has been developed to also account for temperature effects on the surface water fluxes, by estimating the Potential Evapotranspiration (PET).

More details and usage examples can be found in the SPEI recipe documentation.

Available recipes and diagnostics#

Diagnostics are stored in diag_scripts/droughts/. An incomplete list of diagnostics that are used in different recipes is shown below. Some recipes might use additional diagnostics. See the corresponding recipe documentation for more details.:

  • cdd.py: calculate Consecutive Dry Days (CDD)

  • pet.R: calculate Potential Evaporanspiration (PET)

  • spei.R: calculate Standardized Precipitation-Evapotranspiration Index (SPEI)

User settings#

The configuration that can be used in the recipes is documented in the corresponding recipe or diagnostics API documentation linked in the list above. SPEI recipe documentation.

Variables#

  • pr (atmos, daily/monthly mean, time latitude longitude)

  • tas (atmos, monthly mean, time latitude longitude)

  • tasmin (atmos, monthly mean, time latitude longitude)

  • tasmax (atmos, monthly mean, time latitude longitude)

  • sfcWind (atmos, monthly mean, time latitude longitude)

  • rsds (atmos, monthly mean, time latitude longitude)

  • rsdt (atmos, monthly mean, time latitude longitude)

  • clt (atmos, monthly mean, time latitude longitude)

  • hurs (atmos, monthly mean, time latitude longitude)

  • ps (atmos, monthly mean, time latitude longitude)

References#

  • Martin, E.R. (2018). Future Projections of Global Pluvial and Drought Event Characteristics. Geophysical Research Letters, 45, 11913-11920.

  • McKee, T. B., Doesken, N. J., & Kleist, J. (1993). The relationship of drought frequency and duration to time scales. In Proceedings of the 8th Conference on Applied Climatology (Vol. 17, No. 22, pp. 179-183). Boston, MA: American Meteorological Society.

  • Vicente-Serrano, S. M., Beguería, S., & López-Moreno, J. I. (2010). A multiscalar drought index sensitive to global warming: the standardized precipitation evapotranspiration index. Journal of climate, 23(7), 1696-1718.