Modeling and Prediction of Stream Discharge and Sedimentation Yield in the
Cesar basin, Columbia, under the Impact of Climate Change
Karen Chinchilla and Manfred Koch
Department of Geohydraulics and Engineering Hydrology, University of Kassel, Germany
During the last decades the concentration increase of greenhouse gases in the atmosphere has led to the
ubiquitous problem of global warming. According to the IPPC's (Intergovernmental Panel of Climate
Change), fourth assessment report of 2007, global warming is unequivocal, as evidenced by rising
temperatures, melting glaciers and increased averages levels of the oceans. Colombia, located in South
America, is considered rich in water resources - which is true to some extent- but these resources are not
only distributed unevenly, but these are neither easily accessible nor do they comply with accepted quality
requirements in many parts of the country. In addition, in many provinces of Columbia, the ecosystems
that support the sustainability of water resources there are heavily exploited (as in case of the Andean
moorlands/forest), or there are inadequate land management practices that put extra pressure on the water
resources. For this reason, changes in the amount of water from the watersheds could lead to imbalances
in the availability of this resource for the country and compromise the ability to efficiently address
extreme events, like floods, which have been witnessed more frequently in recent years. These adverse
impacts of global climate change could be exacerbated further by changes in regional weather patterns, as
some hydrologists have reported that the sensitivity of hydrological systems to climatic variability can be
high. Given this situation, there arises the need for more precise studies to estimate the impacts of climate
change and climate variability on the local hydrological cycle with its effect on agricultural activity. This
study focuses on the Cesar basin, which is comprised of four major ecoregions: Sierra Nevada of Santa
Marta, the Serrania of Perija, Cesar River valley and the Zapatosa swamp. This basin is very important for
the country, because of its rich agricultural and livestock production, owing to its fertile soils. On the other
hand, as agricultural activity is often carried out without appropriate conservation technology, removal of
natural vegetation cover, loss of topsoil, increase erosion, soil compaction, decline in soil wildlife layers
and subsequent decline of the agricultural productivity has occurred. Adding to this is an enormous
increase of precipitation in the area, which has resulted in frequent flooding of agricultural land in the
recent past. With these premises, the current research intends to assess the impact of climatic change on
the water resources and, in particular, on the stream discharge and sedimentation yield in the Cesar Basin.
This will require the projection of future climate for different scenarios as well as the estimation of the
subsequent response of the basin's hydrologic system. The research requires several steps to be taken,
such as climate model (GCM) projections and their downscaling, hydro-climatology data processing, and,
finally, hydrologic modeling of the basin's water resources and of sediment yield. At this stage of the
study, the SWAT- (Soil and Water Analysis Tool) hydrological watershed model is being used to simulate
the various hydrological processes, namely, streamflow, that have occurred in the basin in the recent past.
To that avail, 30 years of hydro-meteorological time series data for the basin has been acquired and
processed to make it usable as input in SWAT, as well as for the calibration of the downscaled GCMprojections. As this data suffers from quite a few inadequacies and gaps, various statistical procedures had
to be applied to clean and fill up the gaps and get consistent data series. Here we will report on some of
the issues associated with this task. In addition, GIS- data of the physical and chemical soil properties of
the region, soil- and land use maps, and Digital Elevation Model (DEM) data of the basin have been
processed for use in SWAT. Finally, we will present first results of the SWAT-calibrations on the
observed streamflow in the Cesar basin.