Using Satellite Information to Warn of Overflowing Rivers
May. 10 de 2012
By: Jeinst Campo Rivera, Unimedios
The crisis that Colombia has gone through over the past five years because of the rainy seasons has resulted in the destruction of millions of crops and numerous victims in much of the national territory. Experts agree that one of the gravest errors has been the lack of prevention and follow-up on the country's main river flows.
According to the Institute of Hydrology, Meteorology and Environmental Studies (Instituto de Hidrología, Meteorología y Estudios Ambientales – Ideam), the institution responsible for monitoring the behavior of water levels in the rivers, along with some of the Regional Autonomous Corporations (Corporaciones Autónomas Regionales – CAR), in Colombia there are around 800 hydrological stations distributed around the main hydrographic river flows such as the Magdalena, Cauca and Amazon, measuring and recording their levels directly or indirectly. However, even with this information they have not been able to accurately predict floods.
Thus, researchers at the Universidad Nacional de Colombia (National University of Colombia) in Palmira and from the IRD in France (Institut de Recherche pour le Développement) have been working for the last five years on the development and application of a hydrological monitoring network based on information obtained from space. The goal is to efficiently and precisely measure the levels of Colombia’s main rivers and observe their behavior over time.
One of these systems is already operating in the Orinoco basin. It was created by Professor Juan Gabriel León, who holds a doctorate in Earth and Environmental Sciences, along with Astrid Lili Puertas, an Environmental Engineering student. With data from the Envisat satellite, the researchers obtain information to determine the amount of water flowing through the rivers.
Without the need to install physical measurement stations on the rivers –which must be physically observed on a daily basis, as performed by the Ideam– the experts in 2008 were able to identify around 600 remote virtual stations or monitoring points in Colombia detected by satellite. Around 208 are located in the country's main river basins (see graphic 1).
Incomplete official information
“A virtual station is defined as any intersection that occurs between the sweep of a satellite and a body of water that it identifies, based upon which it is possible to obtain information on variations in water levels over a given period of time”, according to student Astrid Puertas.
The data on the Orinoco were organized by the researchers using the so-called Altico database (altimetry for Colombia), which they supplemented with hydrological data obtained from the Ideam. In this initiative, Professor León found that the Ideam furnished reports from only 20 of the 64 stations corresponding to this important basin, with incomplete reporting for some periods.
“If the authorities responsible for disaster prevention and the scientists consult this information, they will definitely be working based on incomplete records, which generates many uncertainties; that may be the reason why it is so difficult in this country to precisely predict the overflowing of the large rivers that cause flooding”, affirms the professor.
Using the Envisat satellite, the researchers at the National University identified 120 virtual stations in the Orinoco River basin (the world's third most abundant), obtaining precise information on variations in the water levels in 2002 and 2008.
By comparing the records of one of these virtual stations with those of a physical station installed in the field by the Ideam, whose geographical positions are exactly the same, a similarity is observed in their series, thus leading to the conclusion that the information obtained from space is accurate and reliable (see graphic 2).
Astrid Lili Puertas affirms that “this research is very important, not only because it provides supplementary data to those of the Ideam, but because it makes it possible to have a monitoring station anywhere in the country, regardless of the existing social or demographic conditions that would normally affect traveling to it. Meanwhile, it may be possible for scientists to gather key information on the Orinoco basin”.
Useful for generating early warnings
In addition to identifying virtual points from which to carry out satellite monitoring of the water levels in the basins, the researchers were able to estimate flows, in other words, to analyze the amount of water flowing through the rivers, which could make it possible to know beforehand at what specific level there could be an overflow.
“We make these assessments by applying a hydrological model, which could provide us, for example, with information on the limits of flooding”, says León.
However, the researchers clarify that it is the relevant entities that must be responsible for the prevention of natural disasters, and that this type of reports is reliable for feeding their early warning models.
Professor León concludes that “the control bodies must be called upon to work together with academia to develop high–impact projects, which are the basis for working to improve their modeling methodologies and prevention plans”.