Impacts of land cover changes and global warming on climate in Colombia during ENSO events

Colombia is highly vulnerable to climate change which may be intensified due to the climatic effects of regional deforestation. Here, we quantify the impact of historical (1900-2011) land cover changes (LCC) and of global warming during ENSO events (CC) on precipitation, temperature and surface energy balance components by running the Weather Research and Forecasting model WRF v3.9 at 10 km resolution. We find that historical anthropogenic CC causes a mean temperature increase of 0.77 +/- 0.02 degrees C in Colombia, which is more pronounced in high altitudes. Precipitation is enhanced by 0.98 +/- 0.30 mm/day (+ 9%), particularly over forested areas and reduced at the Pacific coast. LCC imply a reduction of precipitation particularly above the Andes (- 0.48 +/- 0.10 mm/day) and Caribbean Coast (- 0.67 +/- 0.12 mm/day), where LCC effects dampen CC effects by 24% and 72%, respectively. La Nina tends to intensify LCC and CC effects in the Andes but dampens them at the Coast, roughly by a factor of two compared to El Nino impacts in both regions. At the subregional level, LCC and CC can have impacts of similar magnitude on precipitation highlighting the need to precisely account for both drivers in hydroclimatic assessments. Contrary to almost all observations and similar simulations with climate models, WRF simulates a cooling bias after historical deforestation in Colombia, even with alternative WRF land surface models. We identify two main sources of biases in the default WRF parametrization to explain this inaccuracy: (1) surface shortwave radiation reflected after deforestation is overestimated; (2) associated evapotranspiration loss is underestimated. Improved model representation and validation of tropical vegetation properties are necessary to provide more robust and confident projections.