Orinoco River Extreme Floods
2018 Assessment

The Orinoco River is one of the longest rivers in South America at 2,740 km. Its drainage basin, also known as Orinoquia, covers 948,000 km² with 76% of it in Venezuela and the rest in Colombia. It is the fourth largest river in the world by discharge volume of water. The Orinoco river average discharge is 31,000 m³/s and the maximum water discharge is 89,300 m³/s measured in 2018. Although the variability of the Orinoco hydrological cycle could increase since the late 2010s, the causes has not been yet determined. The largest change over recent decades is a marked increase in very severe floods as register in 2012, 2017 and 2018. This paper aims to explain the hydrologic conditions that could have triggered the 2018 extreme flood in the Orinoco River by means of water levels data, remote sensing images and data from environmental agencies that monitoring climate condition around the world. Along the riverbanks, water levels stations allow quantifying changes in extreme events and analyzing their cause. Those stations, from upstream to downstream, are Jobal, Caicara, Ciudad Bolivar and Palua. Flood conditions affect cities as Ciudad Bolivar and Ciudad Guayana or the metropolitan area of Puerto Ordaz and San Felix at the Caroni-Orinoco River confluence. In 2018, emergency management agencies of Venezuela leaded the evacuation of a reported 14,000 nearby resident at Orinoco riverbanks.

Orinoco River floods could be link to macroclimatic events as Walker circulation or Madden-Julian oscillation for example. These macroclimate variables have a strong influence on hydrological condition on the river by a strong tropical Atlantic warming and tropical Pacific cooling. Ocean surface temperature warming is due to natural and manmade factor that chance atmospheric circulation. Geomorphometry conditions have not changed during last decades, however land cover could be a variable that increase those floods. The best understanding of Orinoco floods will contribute to promote an integrated management of flood and drought risk, design a forecasting system, an emergency action plan and hydraulic structures to protect cities and towns.