The synoptic mode of variability (SMV) refers to changes in atmospheric conditions over periods ranging from 2 to 10 days. In tropical regions, this variability is driven by tropical waves that have a clear signal on the wavenumber–frequency power spectra of precipitation. This study uses the ensemble empirical mode decomposition (EEMD) method to identify the SMV in daily precipitation and streamflows in 47 river basins over northern South America. We found the presence of the frequency bands with periods of 3–12 days and 6–18 days, which agrees with the SMV associated with tropical waves that modulate precipitation over the region. Furthermore, our results reveal that variance explained by the SMV in rainfall over each catchment is greater than the variance explained by those SMV in streamflows, which suggests that catchments efficiently filter out this variability. We found that SMV explains from 5% to 20% of streamflow variability for catchments ranging from 1000 km${}^2$ to 5000 km${}^2$. Additionally, the variance explained by SMV decreases as a power fit with the catchment area. Thus, this study characterizes the SMV for potential applications on regional hydrology, diagnosis, modeling, short-time forecasting, prediction, and management of water resources.

We use a Generalized Watershed Loading Function (GWLF) model to simulate streamflow in the Gualí River Basin. The model's performance is assessed using metrics such as percentage of bias (PBIAS), Nash–Sutcliffe efficiency (NSE), RMSE–observations standard deviation ratio (RSR), and Kling–Gupta efficiency (KGE) to indicate good performance. Furthermore, we analyze projections of precipitation and streamflow using several global climate models (GCMs) from the Coupled Model Intercomparison Project Phase 6 (CMIP6) and three shared socioeconomic pathways (SSP1-2.6, SSP2-4.5, SSP5-8.5). Despite the uncertainties and coarse resolution, our results show that increases in the mean streamflow and significantly decreasing trends in projected precipitation and streamflow are observed from 2015 to 2099 under the SSP5-8.5 scenario. Furthermore, our findings suggest an increase in long-term mid-flow and low-flow. Moreover, this work provides a methodological framework for hydrological modeling in small tropical river basins, by incorporating data from GCMs while raising concerns and caveats. This study offers valuable insights into the potential effects of climate change on streamflow in an Andean river basin characterized by volcanic activity and significant human impacts. The findings reported here provide useful information for future decisions related to water supply for the social, environmental, and productive sectors in the seven towns within the catchment.

This study investigates how convectively coupled tropical easterly waves (TEWs) affect the Choco low-level jet (ChocoJet) as they move across the western Caribbean. The ChocoJet is a low-level flow over the eastern Pacific (EPAC) that modulates precipitation patterns over the tropical eastern Pacific and northwestern South America. By combining data from the Organization of Tropical East Pacific Convection (OTREC; August–September 2019), ERA5 reanalysis products, and satellite data, we analyze precipitation and circulation patterns during convectively coupled and nonconvectively coupled TEWs, comparing them to non-TEW days. During convectively coupled TEWs days, the ChocoJet strengthens and becomes more southerly, while the ITCZ moves northward, leading to enhanced precipitation over the western Caribbean and drier conditions over the northern part of the Colombian Pacific. In contrast, nonconvectively coupled TEW days exhibit reduced precipitation and precipitable water over the Caribbean and far EPAC, with a layer of northeasterly flow centered at 850 hPa flowing over a shallower, weaker, and more westerly ChocoJet. Additionally, convectively coupled TEWs are associated with a weaker western Caribbean and far eastern Pacific pressure gradient compared to nonconvective TEWs. These observable and predictable synoptic-scale circulation–precipitation relationships contribute to a better understanding of hydrometeorological variability in the region. Significance Statement: Tropical easterly waves and related convective organization traversing the Caribbean Sea are important sources of synoptic-scale precipitation–circulation variability in the far eastern Pacific and Colombian Pacific. This eastern tropical Pacific study aims to identify precipitation–circulation relationships that enhance the understanding of synoptic-scale meteorological phenomena.

We studied the projections of streamflows under climate change scenarios in the Upper Orinoco River Basin by using precipitation from 15 global and regional climate models for the period 2020–2099. For this purpose, we calibrated and validated a hydrological model with a very good performance. Our results show that both precipitation and streamflow have a significant reduction for the RCP8.5 scenario that ranges from 5 and 7% in relation to the long-term means at the end of the century. The changes in both variables are not significant for the RCP2.6 scenario. Moreover, we compute several indicators of change in the streamflow to quantify alterations in high-, mid-, and low-range flows. Our results suggest that the main alterations for the future runoff would be evidenced in the mid-range and low flows, which could increase around ∼5 and ∼25%, respectively. These alterations could lead to changes in the hydrological, environmental, and ecological balance of the basin. This work provides information regarding the possible effects of climate change on the streamflow of one of the most important river basins of northern South America, which is pivotal for supporting future decision-making on water supply for social, environmental, and productive sectors.

The far Eastern Tropical Pacific (EPAC) and Western Colombia are one of the rainiest places on Earth, and the Choco low-level jet (ChocoJet) is one of the processes that influence the formation of copious precipitation and convection organization in this region. This study investigates the projected changes in precipitation in this region using historical and future simulations based on model output from two models contributing to the Coupled Model Intercomparison Project phase 6 (CMIP6). In close agreement with observations, models simulate that ChocoJet intensity is directly proportional to precipitation in the region. This relationship is also found far inland in Central America, the northwestern part of South America Pacific Coast, and the intermountain valleys of the Colombian Andes. Late 21st century simulations show a southward migration in mean and regional daily precipitation consistent with a decreased ChocoJet intensity. The weaker ChocoJet is related to a projected increase in EPAC tropical sea surface temperatures (SSTs) and an increased frequency and intensity of the warm phase of the Niño 1+2 SST interannual variability.

Convectively Coupled Kelvin Waves (CCKWs) play a key role in synoptic variability and can trigger extreme hydrometeorological events. This study characterizes the influence of CCKWs on seasonal precipitation patterns and extreme precipitation events (EPEs) over northern South America. Using a filtered OLR dataset, we found that precipitation anomalies associated with CCKWs are sensitive to the selected index region. A sensitivity analysis identified a region in the Colombian Pacific exhibiting the strongest precipitation anomalies linked to CCKWs. At seasonal scales, March–May (MAM) is the season with the highest CCKW activity, and its convective phase is associated with enhanced precipitation over the far eastern Pacific, western Amazonia, and northern Colombia, while suppressed convection dominates northwestern Brazil. In addition, three regions exhibit increases of up to 30% in EPE occurrence during convective-phase Kelvin waves: (i) the northwestern Amazon, (ii) northwestern Colombia, and (iii) the Peruvian coast. In contrast, EPE occurrence in the Colombian Pacific appears largely independent of CCKW passage, likely due to the strong background climatological rainfall in the region. We also analyze a flooding event in Turbo, Colombia, on 9 May 2007, that occurred during the passage of a convective-phase Kelvin wave and was preceded by days of enhanced low-level southwesterly flow convergence and persistent rainfall. Understanding the influence of these intraseasonal oscillations on precipitation and EPEs is essential for improving regional weather forecasts and supporting the development of early warning systems.