Climate Variability and Change—Hydrological Impacts (Proceedings of the Fifth FRIEND World Conference held at Havana, Cuba, November 2006), IAHS Publ. 308, 2006, 338–343.

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Drought in Costa Rica: temporal and spatial behaviour, trends and the relationship to atmospheric circulation patterns

CHRISTIAN BIRKEL¹ & SIEGFRIED DEMUTH²

1 Escuela de Geografía, Universidad de Costa Rica, Sede Rodrigo Facio San Pedro, San José, Costa Rica

cbirkel@fcs.ucr.ac.cr

2 IHP/HWRP Secretariat, Federal Institute of Hydrology, Am Mainzer Tor 1, D-56068 Koblenz, Germany

Abstract The temporal and spatial behaviour of droughts in Costa Rica has been studied applying the threshold level approach to 17 streamflow stations for the common period 1973–2003. Drought indices such as drought duration, deficit volume (severity) and the number of droughts (frequency) were determined utilizing a constant non-seasonal Q₉₀ and seasonal Q₇₀ exceedence percentile from a flow duration curve. Temporal drought characteristics were generally of long duration and low deficit volume in the dry season and droughts of short duration and high deficit volume tend to cluster in the wet season. This could be a feature of the threshold, or the standardization procedure or the seasonality of the flow regime. Spatial drought characteristics show distinctive regional patterns in terms of variability indices and drought risk. The non-parametric Mann-Kendall trend test shows just one significant (a = 0.05) positive result in terms of historic trends in increased severity and frequency (at the Northern Zone). Although the majority of test results are non-significant, a clear spatial pattern of positive and negative trends can be seen. The link between atmospheric circulation patterns and regional streamflow drought point towards regional patterns of a direct atmospheric-control (Pearson r > 0.5).

Key words drought; threshold level method; drought pattern; Mann-Kendall Test; atmospheric circulation; ENSO; El Niño

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