Flooding early warning systems are articulated procedures that aim to alert the occurrence of river level increase or a possible flood, to the populations located downstream in risk areas in order to protect their lives. These procedures include monitoring of hydroclimatic conditions (rain and river levels), analysis of this hydroclimatic information, forecast of potential impacts, early dissemination of information to the population and the consequent actions based on a series of protocols that must be established by the appropriate entities.
In El Salvador, the actors responsible for flooding early warning systems are the Ministry of Environment (MARN) through the Department of Environmental Observatory (DOA), the Ministry of Interior through Civil Protection and the communities, in a coordinated work that has been developed and improved since 2002.
The research involved the development of tools that allow MARN the analysis of hydroclimatic information of telemetric stations that send information in real time, effectively and quickly, in order to identify variations that could generate some impact such as the arrive time to the risk zones, so hydrological parameters and hydrological modeling were developed in different basins of the country.
Some of the developed hydrological parameters helped identify different stages for each of which was established a procedure for action: monitoring, warning, and emergency alert. These hydrological parameters are as follows: a) thresholds of river levels; b) precipitation intensity thresholds; c) transit times of the current between hydrometric stations located in the same basin; d) relationship river levels at stations located in the same basin; e) relationship between rainfall amounts and increased river levels; f) isochronous curves that estimate the arrival time of level river increased to areas of potential impact; g) temporal distributions of rain. Hydrological modeling were performed based on models rain runoff, the results of which can set the stage hydrological level is expected in certain situations. These tools have proven to be very effective for early warning systems, because with developed hydrological parameters a quick analysis of recorded information is reached, which allows to take the necessary measures within the system, besides complementing results hydrological modeling, without subordinating the hydrological analysis to modeling results. The development of these tools has been carried out based on statistical and hydrological observation and analysis of historical flood information as well as information recorded by the telemetric stations, linking variables rain, river levels and affectation. These tools are updated as conditions change in land use in the basins, as well as changes in riverbeds situations of erosion or sediment deposition.