资源环境科技发展态势分析平台

Precipitation in the tropical Andes is strongly influenced by the ENSO phases and orographic effects. In particular, precipitation can be drastically reduced during El Nino. Decision-making about water resources relies on modelling precipitation as the main source for water availability. Here we evaluate ERA-Interim ' s capacity to represent precipitation in the mountainous central Colombian Andes, a strategic region for water supply and hydropower generation, for different phases of ENSO during 1998-2012. Our results show that ERA-Interim fails to reproduce important features of precipitation spatial and temporal variability during different ENSO phases. Most critical in these results is how ERA-Interim overestimates precipitation during the dry season in El Nino years, which corresponds to the most critical condition for water supply. We show that ERA-Interim limitations are likely related to its simplified representation of the complex topography in the region, which excludes the inter-Andean Cauca river valley. To improve this, we implement a dynamical downscaling experiment using the WRF regional climate model, including a sensitivity analysis that considers three convective parameterization schemes and a convection-permitting simulation. WRF downscaling outperforms ERA-Interim in the representation of precipitation during the dry season of El Nino years, especially through correcting positive precipitation biases. This improvement is related to a better representation of orographic effects in WRF simulations. Our results suggest that ERA-Interim and, more generally, climate simulations with comparable coarse resolutions, may produce misleading precipitation overestimations in the tropical Andes if they do not adequately represent inter-Andean valleys, with important implications for water resources management.