Climate Variability and Change—Hydrological Impacts (Proceedings of the Fifth FRIEND World
Conference held at Havana, Cuba, November 2006), IAHS Publ. 308, 2006, 111–116.
Regionalization of low flow in Costa Rica
ALEXIA PACHECO1, LARS
GOTTSCHALK2 & IRINA KRASOVSKAIA2
1 C.S. Estudios Básicos de Ingeniería, Instituto Costarricense de Electricidad, PO Box 10032-1000, San José, Costa Rica
2 Department of Geosciences, University of Oslo, PO Box 1047 Blindern, N-0316 Oslo, Norway
Abstract The starting point of this
study is the so-called derived distribution function approach for low flows.
This approach is extended to apply to PUT (Pit Under Threshold) data from humid
tropical conditions. A general theoretical distribution is derived that applies
to exponentially distribute dry spells with a nonlinear low flow recession
below a threshold level. Regionalization of PUTs is based on a fixed threshold
level—the median, which is mapped for
the whole country. The low flow data
are normalized with respect to the median.
The normalized sample distributions are grouped with respect to
characteristic features (form of sample distribution, average length of dry
spells and intensity of events) and a theoretical regional distribution is
estimated for each grouped sample. The methodology has been applied to a set of
low flow data from 63 gauging stations in Costa Rica. Important issues are the
definition of the common threshold, the relation between dry spells defined
from precipitation and runoff records, respectively, characteristic features
for grouping of sample distributions as well as principles for parameter
estimation of the regional curves of the grouped samples.
Key words regionalization; low flow; dry
spells; Costa Rica