"Tales from a Flood Hydrologist: Implications for western tropical Latin America"

Presented by Peter Waylen, UF Department of Geography

Monday, February 8, 2010

4:00 PM - 5:00 PM

Room 112 Newins-Ziegler Hall


Abstracts of 2 papers: 

Flooding and the El Niņo-Southern Oscillation phenomenon along the Pacifc coast of Costa Rica
Peter Waylen and M. Sadi Laporte
Hydrol. Process. 13, 2623-2638 (1999)

The rivers of western Costa Rica are prone to considerable interannual variability in flooding, which in the
most severe years can lead to loss of life, property and national infra-structure. Flood generating processes are
exclusively rainfall driven, but are complex in both their spatial and temporal distribution due to the variety of
oceanic and continental influences which impinge on the region, and to the various natures and timings of
their responses to the El Niņo-Southern Oscillation (ENSO) phenomenon. Annual floods and partial duration
series derived from daily discharge records from four basins within the Pacifc watershed are analysed using a
series of standard probability distributions and parameters estimated by means of L-moments. The observed
temporal and spatial patterns of flood events are consistent with the documented meteorological processes and
also exhibit marked changes in behaviour between the two extreme phases of the ENSO phenomenon.
Particularly noticeable in this regard are; the variable length of the short dry season, the veranillos, which is
related to the strength of the northeast trades, and interrupts the rainy season; the number of floods in the
period immediately following the veranillos, which is positively associated with the number of tropical storms in
the Caribbean basin; and the number of cold fronts emanating from North America during the boreal winter.

Annual and inter-annual variability of the present climate in northern South America and southern Mesoamerica
Germa´n Poveda, Peter R. Waylen, Roger S. Pulwarty 
Palaeogeography, Palaeoclimatology, Palaeoecology - 2006

Present climate of northwestern South America and the southern Isthmus is detailed in terms of major hydro-climatic controls,
supported by evidence from station records, reanalysis data and satellite information. In this tropical region, precipitation is the
principal hydro-climatological variable to display great variability. The primary objective is to view the controls that operate at
intra-seasonal to inter-decadal time scales. This is a topographical complex region whose climate influences range in provenance
from the South Atlantic to the Canadian Prairies, and from the North Atlantic to the Eastern Pacific. The situation is further
complicated by interactions and feedbacks, in time and space, between these influences, which are interconnected over various
scales. The greatest single control on the annual cycle is the meridional migration of the Inter-tropical Convergence Zone and its
pattern of associated trade winds. Consideration of these alone and their interaction with the Cordilleras of the Andes and Central
America produce a variety of unimodal and bimodal regimes. Regionally, two low level jet streams, the westerly Choco jet (58N)
and the easterly San Andre´s jet (12-148N), and their seasonal variability, have tremendous significance, as do mesoscale
convective storms and mid-latitude cold fronts from both the northern (bnortesQ) and southern (bfriagemsQ) hemispheres. There
are many examples of hydro-climatological feedbacks within the region. Of these the most notable is the interaction between
evaporation over the Amazon, precipitation onto the eastern Andes and streamflow from the headwaters of the Amazon. This is
further compounded by the high percentages of recycled precipitation over large areas of the tropics and the potential impacts of
anthropogenic modification of the land surface. The El Nin~o-Southern Oscillation phenomenon (ENSO) is the greatest single cause
of interannual variability within the region, yet its effects are not universal in their timing, sign or magnitude. A set of regional
physical connections to ENSO are established and their varying local manifestations are viewed in the context of the dominant
precipitation generating mechanisms and feedbacks at that location. In addition, some potential impacts of longer run variations
within the ocean-atmosphere system of the Atlantic are examined independently and in conjunction with ENSO. This review of the
climatic controls and feedbacks in the region provides a spatial and temporal framework within which the highly complex set of
factors and their interactions may be interpreted from the past.

From: Williams,Claire C
Sent: Friday, February 05, 2010 9:10 AM
To: [log in to unmask]
Subject: [WEC-GRAD-L] Note Correction- WEC Seminar 2-8-10 @ 4PM, 112 NZ Hall - Dr. Peter Waylen

Dear Friends and Colleagues, 
Dr. Peter Waylen from the UF Department of Geography has generously agreed to present some of his recent climatic and hydrologic research from tropical western South America and southern Central America.