Abstract:The Weather Research and Forecasting (WRF) model has been successfully used in weather prediction, but its ability to simulate precipitation over areas with complex topography is not optimal. Consequently, WRF has problems forecasting rainfall events over Chilean mountainous terrain and foothills, where some of the main cities are located, and where intense rainfall occurs due to cutoff lows. This work analyzes an ensemble of microphysics schemes to enhance initial forecasts made by the Chilean Weather Agency in the front range of Santiago. We first tested different vertical levels resolution, land use and land surface models, as well as meteorological forcing (GFS/FNL). The final ensemble configuration considered three microphysics schemes and lead times over three rainfall events between 2015 and 2017. Cutoff low complex meteorological characteristics impede the temporal simulation of rainfall properties. With three days of lead time, WRF properly forecasts the rainiest N-hours and temperatures during the event, although more accuracy is obtained when the rainfall is caused by a meteorological frontal system. Finally, the WSM6 microphysics option had the best performance, although further analysis using other storms and locations in the area are needed to strengthen this result.

A dispute between Chile and Bolivia regarding the status and use of the waters of the Silala River, resulted in proceedings before the International Court of Justice, initiated in 2016. The magnitude of the effect of historical channelization in Bolivia on surface water flows emerged as a major point of disagreement. Based on modeling by the Danish Hydraulic Institute (DHI), using the MIKE‐SHE and MIKE‐11 modeling systems, Bolivia suggested initially that the channels had increased surface flow by 30%–40% and later by 11%–33%. In the opinion of Chile's international experts, these effects would be small. This paper reviews the use of DHI's models by Bolivia and, subsequently, by Chile. Concerns about Bolivia's modeling raised by Chile included the selection of boundary conditions, inconsistent use of the two models for different scenarios, the use of inconsistent topographies for different scenarios, unexplained additions of water and numerical instabilities affecting the results. To investigate these discrepancies, additional simulations were performed by Chile. DHI's MIKE‐SHE and MIKE‐11 models were used for all scenarios, with consistent topography, spring and surface water flow representation. Numerical instabilities were reduced by adjustment of time steps and channel topography. These simulations showed that removing the channels reduces surface flow by a maximum of 3.5 L/s, or 2.4%. The sum of the groundwater and surface water outflow decreases by 2.6 L/s or 1.0%. This small decrease lies within the modeling error but is consistent with the expected effect of minor changes in evaporation.This article is categorized under: Science of Water > Hydrological Processes Human Water > Rights to Water Science of Water > Methods