Extreme La Nina events occur when cold sea surface temperatures across the central Pacific Ocean create a strong temperature gradient to the Maritime continent in the west. This work projects an increase in frequency of La Nina events due to faster land warming relative to the ocean, and a greater chance of them occurring following extreme El Nino events. The El Nino/Southern Oscillation is Earth’s most prominent source of interannual climate variability, alternating irregularly between El Nino and La Nina, and resulting in global disruption of weather patterns, ecosystems, fisheries and agriculture1,2,3,4,5. The 1998–1999 extreme La Nina event that followed the 1997–1998 extreme El Nino event6 switched extreme El Nino-induced severe droughts to devastating floods in western Pacific countries, and vice versa in the southwestern United States4,7. During extreme La Nina events, cold sea surface conditions develop in the central Pacific8,9, creating an enhanced temperature gradient from the Maritime continent to the central Pacific. Recent studies have revealed robust changes in El Nino characteristics in response to simulated future greenhouse warming10,11,12, but how La Nina will change remains unclear. Here we present climate modelling evidence, from simulations conducted for the Coupled Model Intercomparison Project phase 5 (ref. 13), for a near doubling in the frequency of future extreme La Nina events, from one in every 23 years to one in every 13 years. This occurs because projected faster mean warming of the Maritime continent than the central Pacific, enhanced upper ocean vertical temperature gradients, and increased frequency of extreme El Nino events are conducive to development of the extreme La Nina events. Approximately 75% of the increase occurs in years following extreme El Nino events, thus projecting more frequent swings between opposite extremes from one year to the next.

/pdf/increased-frequency-of-extreme-la-nina-events-under-3hr8glfuln.pdf

Increased frequency of extreme La Niña events under greenhouse warming

https://www.iit.comillas.edu/docs/IIT-16-023A-Preview.pdf

An optimization framework for the integrated planning of generation and transmission expansion in interconnected power systems

Recent deforestation causes rapid increase in river sediment load in the Colombian Andes

. Providing reliable estimates of streamflow and hydrological fluxes is a major challenge for water resources management over national and transnational basins in South America. Global hydrological models and land surface models are a possible solution to simulate the terrestrial water cycle at the continental scale, but issues about parameterization and limitations in representing lowland river systems can place constraints on these models to meet local needs. In an attempt to overcome such limitations, we extended a regional, fully coupled hydrologic–hydrodynamic model (MGB; Modelo hidrologico de Grandes Bacias) to the continental domain of South America and assessed its performance using daily river discharge, water levels from independent sources (in situ, satellite altimetry), estimates of terrestrial water storage (TWS) and evapotranspiration (ET) from remote sensing and other available global datasets. In addition, river discharge was compared with outputs from global models acquired through the eartH2Observe project (HTESSEL/CaMa-Flood, LISFLOOD and WaterGAP3), providing the first cross-scale assessment (regional/continental  ×  global models) that makes use of spatially distributed, daily discharge data. A satisfactory representation of discharge and water levels was obtained (Nash–Sutcliffe efficiency, NSE > 0.6 in 55 % of the cases) and the continental model was able to capture patterns of seasonality and magnitude of TWS and ET, especially over the largest basins of South America. After the comparison with global models, we found that it is possible to obtain considerable improvement on daily river discharge, even by using current global forcing data, just by combining parameterization and better routing physics based on regional experience. Issues about the potential sources of errors related to both global- and continental-scale modeling are discussed, as well as future directions for improving large-scale model applications in this continent. We hope that our study provides important insights to reduce the gap between global and regional hydrological modeling communities.

https://hess.copernicus.org/articles/22/4815/2018/hess-22-4815-2018.pdf

A.M. Arango

Papers

Impact of the 2010–2011 La Niña phenomenon in Colombia, South America: The human toll of an extreme weather event