Observations for


Drought Return Periods

This map shows the return periods for a certain precipitation deficit (compared to a normal situation). Here it is possible to visualize the return periods for a precipitation deficit of 20%, 40% 60% or 80%.

For example, if the maps indicates a return period of 4 years for a precipitation deficit of 20% is means that here you can expect a precipitation deficit of 20% every four years.

The Drought Atlas is provided by the Water Centre for Arid Zones in Latin America and teh Caribbean (CAZALAC).



Nunez, J.H., K. Verbist, J. Wallis, M. Schaeffer, L. Morales, and W.M. Cornelis. 2011. Regional frequency analysis for mapping drought events in north-central Chile. J. Hydrol. 405 352-366.

Which method is used to estimate the return period?

The method used is a frequency analysis of historical events. Historical precipitation data are used to fit a probabilistic distribution. This distribution is used to identify the frequency with which we may expect rainfall events with a certain magnitude.

The method applied takes in consideration the low availability of data, data are grouped in regions with similar climatology. This allows the use of more robust statistics.

To be able to alleviate the effect of extreme events the method is based on L-moments instead of normal moments. In this way extreme events do not affect the selection of the probabilistic distribution. This method is chosen because it is more suitable for the region which is characterized by inter annual variability and short data series.

Here you can find more detailed information on the method.

Dataset Documentation

Drought Atlas of Latin America and the Caribbean Dataset
Data Source
CAZALAC Center, Drought Atlas
Regional Frequency Analysis using L-Moments


Contact mwar_lac@unesco.org with any technical questions or problems with this Map Room.