Projections of Future Changes in Precipitation for Central America Using PRECIS Regional Climate Model

Central America has been identified as one of the regions in the world where potential climate change impacts on the environment can be pronounced. Climate of the region shows its variability mainly in precipitation. Interactions between regional atmospheric circulation patterns, trade winds and region's complex topography not only define different precipitation regimes for the Caribbean basin (windward) and the Pacific basin (leeward) but also modify the annual cycle of precipitation. These features can only be realistically simulated and studied by a regional climate model. We use the UK Hadley Centre PRECIS (Providing REgional Climates for Impact Studies) regional model to study climate change in Central America. The comparison between a control run and the SRES A2 (doubled CO2) run enables us to examine the projected changes in climate on a regional scale. The fidelity of model simulations is assessed by comparing the control run with observations and reanalysis data. PRECIS underestimates precipitation over Central America, which is also seen in nearly all global models as a result of underestimation of sea surface temperatures and an excessive smooth representation of regional topographical features. The summer rainy season in Central America is characterized by a bimodal distribution in precipitation, with maxima in June and September and a relative minimum during July-August known as the mid-summer drought (MSD). The mechanisms controlling this precipitation cycle in the region is discussed at length in the literature. However, how this cycle would change in future at a regional scale, is yet to be investigated in great detail. The PRECIS resolution of 25km allows us to study the annual cycle separately for the Pacific and Caribbean sides. The precipitation change in future differs considerably on the Atlantic and Pacific sides of Central America and is also a function of elevation. In the SRES A2 run, both sides experience a relative decrease in precipitation in the months of July and August. However, for other months, precipitation change in future on the Atlantic side differs considerably than that on the Pacific side. The Atlantic side not only experiences a reduction in precipitation throughout the year but also sees a change in the shape of the annual cycle where the MSD feature seem to disappear. The probability distributions of precipitation for different elevations predict that high elevation regions, in general, will become drier with a reduction in precipitation variability compared to lowlands. These aspects of the rainy season are very important for planning in key sectors such as agriculture and power generation, which are an integral part of the economy of the region.