Extreme Precipitation in the Present and Future Climate over a Topographically Complex Region in a Tropical Environment

The assessment of potential changes in precipitation extremes in the future climate is essential for the development of robust climate adaptation and mitigation strategies. This is particularly key for regions such as the tropical South America, including Colombia, where there are different long-term signals throughout the region in both the average annual rainfall and the frequency of extremes, possibly tied to the complexity of topography in the region. Analysis of climate projections under future scenarios using global climate models (GCM), with a relatively coarse spatial and temporal resolution, does not allow an adequate assessment regarding extreme events. In this study we perform a dynamic downscaling of selected CMIP5 models using the WRF model over the northern South America Andean region. GCM outputs were used as initial and boundary conditions to simulate one reference period (1990-2000) and two periods throughout the 21st century (2040-2050 and 2090-2100) under the RCP4.5 scenario. The spatial resolution of the innermost domain is 3 km. We focus on studying potential changes in extreme precipitation events and the length of continuous dry periods. First, we evaluate the spatial distribution of the changes in the 90th and 95th percentiles in future 30-minute downscaled precipitation, comparing it to trends derived from in-situ data. Both simulations and observations show intensification of extreme events in regions of orographic precipitation enhancement, in the Magdalena and Cauca river valleys suggesting a link between topography (high slope regions) and changes in extreme precipitation. In order to understand this association, the analysis is extended to changes in atmospheric humidity and winds. Although an increase in extreme precipitation is projected over some regions, simulation showed a predominant decrease in daily, monthly and annual accumulated precipitation over the entire region.