Aridity Index - (Prec ECMWF Land/PET MODIS)
Hyper-arid lands (AI <0.05)
Arid lands (0.05≤ AI <0.2)
Semi-arid lands (0.2≤ AI <0.5)
Dry sub-humid lands (0.5≤ AI <0.65)
The United Nations Environment Programme (UNEP) defines drylands according to an Aridity Index (AI), which is the ratio between average annual precipitation and potential evapotranspiration; drylands are lands with an AI of less than 0.65.
Drylands are further divided, on the basis of AI, into hyper-arid lands(AI <0.05), arid lands(0.05≤ AI <0.2), semi-arid lands (0.2≤ AI <0.5) and dry sub-humid lands(0.5≤ AI <0.65).
The Aridity Index (AI) is calculated for the years 2001 to 2020 using the total precipitation product derived from ERA5-Land data from the European Centre for Medium-Range Weather Forecasts (ECMWF) and the potential evapotranspiration product derived from MOD16A2 MODIS/Terra Net Evapotranspiration 8-Day L4 Global 500m version 6 image collection.
National Aeronautics and Space Administration (NASA) – MODIS
MOD16A2 v006 - MODIS/Terra Net Evapotranspiration 8-Day L4 Global 500 m SIN Grid
The Potential Evapotranspiration product comes from MOD16A2 MODIS/Terra Net Evapotranspiration 8-Day L4 Global 500m version 6 image collection to generate a time series for the period 2000 to 2017.
500 x 500 m
Global time series available from 2000 to present.
High temporal resolution: Daily revisit time, graph shows less-cloudy image during 16/8 days
European Centre for Medium-Range Weather Forecasts (ECMWF)
ERA5-Land is a reanalysis dataset providing a consistent view of the evolution of land variables over several decades at an enhanced resolution compared to ERA5.
ERA5-Land has been produced by replaying the land component of the ECMWF ERA5 climate reanalysis. Reanalysis combines model data with observations from across the world into a globally complete and consistent dataset using the laws of physics. Reanalysis produces data that goes several decades back in time, providing an accurate description of the climate of the past.
The pixel size is 0.1 deg (approx. 9 km at the equator)
Pixel size: 9 x 9 km (0.1 deg)
ERA5-Land data is available from 1981 to three months from real-time.
Monthly aggregates have been calculated based on the ERA5-Land hourly values of each parameter.