Aim To explain the relationship between topography, prevailing winds and precipitation in order to identify regions with contrasting precipitation regimes and then compare floristic similarity among regions in the context of climate change.Location Eastern slope of the tropical Andes, South America.Methods We used information sources in the public domain to identify the relationship between geology, topography, prevailing wind patterns and precipitation. Areas with contrasting precipitation regimes were identified and compared for their floristic similarity. ResultsWe identify spatially separate super-humid, humid and relatively dry regions on the eastern slope of the Andes and show how they are formed by the interaction of prevailing winds, diurnally varying atmospheric circulations and the local topography of the Andes. One key aspect related to the formation of these climatically distinct regions is the South American low-level jet (SALLJ), a relatively steady wind gyre that flows pole-ward along the eastern slopes of the Andes and is part of the gyre associated with the Atlantic trade winds that cross the Amazon Basin. The strongest winds of the SALLJ occur near the 'elbow of the Andes' at 18°S. Super-humid regions with mean annual precipitation greater than 3500 mm, are associated with a 'favourable' combination of topography, wind-flow orientation and local air circulation that favours ascent at certain hours of the day. Much drier regions, with mean annual precipitation less than 1500 mm, are associated with 'unfavourable' topographic orientation with respect to the mean winds and areas of reduced cloudiness produced by local breezes that moderate the cloudiness. We show the distribution of satelliteestimated frequency of cloudiness and offer hypotheses to explain the occurrence of these patterns and to explain regions of anomalously low precipitation in Bolivia and northern Peru. Floristic analysis shows that overall similarity among all circumscribed regions of this study is low; however, similarity among superhumid and humid regions is greater when compared with similarity among dry regions. Spatially separate areas with humid and super-humid precipitation regimes show similarity gradients that are correlated with latitude (proximity) and precipitation.

The ChocoJet Experiment (CHOCO-JEX) is an interinstitutional research program developed by the Universidad Nacional de Colombia, the General Maritime Directorate of the Ministry of National Defense of Colombia, the Colombian Air Force, and the Desert Research Institute. The main goal of CHOCO-JEX is to characterize the vertical structure of the low-level Chocó jet (ChocoJet) through observations and modeling. Thus, four 7-day intensive observation periods (IOPs) took place during different seasons in 2016, two over land and two over the far eastern Pacific off the coast of Colombia, including the deployment of upper-air soundings four times per day to monitor the predominant diurnal cycle and the synoptic and seasonal variability. Preliminary results show deeper westerly moisture flow and a stronger diurnal cycle over land than over ocean. IOP4 provides the first observational evidence of the southwesterly ChocoJet with mean winds of 5 m s–1. Diurnal cycles of zonal wind are coherent with mountain–valley and sea–land breezes at low levels and the easterly flow is predominant at midlevels. Potential temperature anomalies appear to be related to gravity waves that modulate the diurnal cycle of precipitation in the region.

We classified and characterized precipitation features (PFs) at annual and diurnal timescales during 1998–2011 over the tropical Americas and adjoining oceans using data from two instruments on board the Tropical Rainfall Measuring Mission (TRMM). Our scope included geographic distribution, frequency, area, rainfall rate, and polarization‐corrected temperatures (PCTs) of PFs in an effort to contrast different regions over Colombia, the Amazon River Basin, and the adjoining oceanic regions (Pacific Ocean and Caribbean Sea). Our results showed that mesoscale convective systems (MCSs) over the Caribbean Sea exhibited colder minimum PCTs than Pacific Ocean MCSs. Pacific Ocean MCSs had higher rainfall rates, however, than Caribbean Sea MCSs. Despite the fact that MCSs represented <1% of the total precipitation systems found, the MCSs contributed more rainfall over the study regions. Over the Pacific Ocean, for example, MCSs contributed approximately 57% of the total rainfall contributed by all precipitation systems identified over that region. Additionally, MCSs over the Pacific coast have their maximum frequency during the morning hours (0000–0600 Local Time) offshore and centred over the Pacific Ocean at 77.5°W. The annual cycle of PFs showed a marked bimodal annual cycle over Colombia, whereas over the Amazon Basin, Pacific Ocean, and Caribbean Sea, PFs were characterized by a unimodal annual cycle.

Colombia using regionalization and scaling concepts with the long-term flow field as the scaling variable. All data sets, methods, and results are included in HidroSIG, an available interactive hydrologic atlas of Colombia.