Outlook on climate change adaptation in the Tropical Andes mountains

Projections

The clearest trend in the Tropical Andes is the increase in air temperature. The Tropical Andes are expected to experience some of the most drastic change in climate in South America (Urrutia and Vuille, 2009; Hijmans et al., 2005). However, projections of future climate change using different models in the Tropical Andes are highly uncertain, particularly for rainfall. For temperature there is a higher degree of agreement between the different models. This is partly because the topography of the region is too rugged to be captured by low-resolution global models. In addition, there is not a high density of meteorological stations, which would be needed for validating and calibrating climate models. Climate models, therefore, differ more from observations in the Andes than in other parts of South America. This is true for both models on temperature and precipitation projections. While especially in short-termprojections internal variability (“noise”) of the modelled processes is often larger than any trends, for longer time scales the signal-to-noise ratio improves and allows for deriving robust trends (in particular for temperature). El Niño and la Niña events have strong, though varying, effects on both precipitation and temperature in South America and the Tropical Andes. The overall frequency of El Niño events is expected to decrease slightly. Extreme El Niño events, however, are in recent studies predicted to increase in frequency due to global warming (Cai et al., 2014). El Niño events are also associated with extremely warm years, thereby adding to the predicted warming. Temperature Future warming is predicted to be highest in the mountains (Urrutia and Vuille, 2009; Bradley et al.,

2004). In all medium emission scenarios, by 2100 the coldest years in the Tropical Andes Mountains will be significantly warmer than the warmest years people have adapted to over the centuries (Vuille, 2013). This means that by 2100, temperatures will be unprecedented for current social and ecological systems. It is important to remember that climate variability, such as by ENSO events, will also affect how climate change manifests at particular times in the future. In a high-emission scenario (RCP8.5), temperatures in the Tropical Andes are expected to increase by 4.5-5°C by 2100 (Bradley et al., 2009; Hijmans et al., 2005). It should be noted that models vary greatly in their projections for the regions, and are particularly uncertain in mountain regions, but all models agree that temperature will increase (Valdivia et al., 2010). In some models, the Bolivian Altiplano is expected to experience 3-4°C warming (Anderson et al., 2011, Minvielle and Garreaud, 2011). A high-resolution model projects significantly greater warming at higher altitudes, from 3.5°C warming at 500 m to 4.8°C warming above 4,000 m on the western slopes (Urrutia and Vuille, 2009). In low emission scenarios, the expected warming has about half the amplitude. Available models also project a higher frequency of warming than today’s average in the years approaching 2100. Precipitation Most studies on precipitation focus on changes in total annual precipitation. However, for the Tropical Andes the main change may be in seasonal variability. In southern Peru and Bolivia, for instance, climate models predict more intense and concentrated rainy

Girl, Peru

seasons and longer dry seasons (Seth et al., 2010). However, it is important to recognize the high variance of precipitation patterns within these areas. The expected changes in total annual precipitation are generally low and uncertain in South America as a whole. However, models predict that in a high- emission scenario there will be significant changes for some sub-areas (Magrin et al., 2014). In general, wet areas will get wetter, and dry areas will mostly get drier. The north-western Andes of Colombia, Ecuador and Peru will experience increased rainfall, while a decrease is expected in the north-eastern Andes of Venezuela and Columbia, in southern Peru and in the Bolivian mountains (Vuille et al., 2008; Magrin et al., 2014; Hijmans et al., 2005).

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