Dengue virus (DENV) is an endemic disease in the hot and humid low-lands of Colombia. We characterize diverse temporal and spatial patterns of monthly series of dengue incidence in diverse regions of Colombia during the period 2007-2017 at different spatial scales, and their association with indices of El Niño/Southern Oscillation (ENSO) and local climatic variables. For estimation purposes, we use linear analysis tools including lagged cross-correlations (Pearson test), cross wavelet analysis (wavelet cross spectrum, and wavelet coherence), as well as a novel nonlinear causality method, PCMCI, that allows identifying common causal drivers and links among high dimensional simultaneous and time-lagged variables. Our results evidence the strong association of DENV cases in Colombia with ENSO indices and with local temperature and rainfall data. El Niño (La Niña) phenomenon is related to the intensification (weakening) of dengue cases at the national level and in most regions and departments, with maximum correlations occurring at shorter time lags in the Pacific region, closer to the Pacific Ocean. This association is mainly explained by the ENSO-driven increase in temperature and decrease in rainfall, especially in the Andes and Pacific regions. The influence of ENSO is not stationary (there is a reduction of DENV cases since 2005) and local climate variables vary in space and time, and thus it is not easy to extrapolate results from one site to another. The association between DENV and ENSO varies at national and regional scales when data are disaggregated by seasons, being stronger in DJF and weaker in SON. Specific regions (Pacific and Andes) control the overall relationship between dengue dynamics and ENSO at national scale, and the departments of Antioquia and Valle del Cauca determine those of the Andes and Pacific regions, respectively. Cross wavelet analysis indicates that the ENSO-DENV relation in Colombia exhibits a strong coherence in the 12 to16-months frequency band, which denotes the frequency locking between the annual cycle and the interannual (ENSO) timescales. Results of nonlinear causality metrics reveal the complex concomitant effects of ENSO and local climate variables (Fig. 1), offering new insights to develop early warning systems for DENV in Colombia.

Evapotranspiration from land surface and vegetation plays an important role as a source of precipitation at continental scale in South America, and more so over the Andes cordillera. We evaluate the local recycling of moisture in a complex orography region located in the Central Andes of Colombia (CAC; 4.5N to 7.5N, 78.6W to 71.4W), comprising the East, Central and West Andean ranges and the two inter-Andean valleys of the Magdalena and Cauca Rivers. To this end, we apply the offline atmospheric moisture tracking model, WAM-2layers (Water Accounting Model-2layers). The model input data comes from the ERA-Interim Reanalysis spanning the period 1980-2016 and at 0.125 x 0.125 degrees resolution. We estimate the spatial distribution of the evaporation recycling ratio εc (source moisture zones) and the precipitation recycling ratio ρc (sink moisture zones) at annual and seasonal timescales. According with our results, up to 63% of the average annual evapotranspiration returns as local precipitation in the CAC. Some specific zones of the Western Cordillera and the eastern hillside of the Central Cordillera are “hot spots” for local moisture recycling given the high values of both εc and ρc. At seasonal timescales, there is more activity of the identified source moisture zones during March-April-May (MAM) and June-July-August (JJA). The higher moisture recycling activity in those seasons interconnects two source regions of moisture: the eastern piedmont of the Eastern Cordillera with the eastern piedmont of the Central Cordillera. Both piedmonts also show high intensity rainfall rates. Finally, our work confirms the fundamental role of local recycled moisture to enhance the midnight and early morning peak of the diurnal cycle of precipitation in the CAC during JJA.

We study the consistency of long-term trends in the surface water balance of 63 sub-catchments of the Amazon River basin. Monthly time series of precipitation, evaporation, runoff and soil water storage are obtained from remote sensors and flow stations (CHIRPS, ETR-Amazon, ANA-Brazil and JPL-GLDAS). Missing data during the period 1995-2015 are reconstructed applying an adaptation of the methodology proposed by Kondrashov & Ghil (2006). Empirical mode decomposition (Huang et al., 1998) is applied to filter out different modes of natural variability, with the aim to isolate the long-term trend of time series. The Mann-Kendall and Sen tests are applied to the residue and the sign and magnitude of the trends was obtained. No generalized unidirectional trends were found for the Amazon basin for any of the variables studied (Table 1), although some unidirectional trends were found in groups of sub-catchments that belong to the same stream. The consistency of the general water balance equation [dS/dt=P(t)-E(t)-R(t)], and its long-term approximation [\overline{R} = \overline{P} - \overline{E}] were evaluated. The general water balance does not close for 37 sub-catchments, while in the long-term the error in the balance tends asymptotically to a constant value, different from zero, which indicates that in the period of 20 years studied the long-term condition is fulfilled, but there is no closure for the long-term water balance either. The consistency of the surface water balance equation was also studied regarding the signs of the trends, finding that in 32 (51%) of sub-catchments studied the trend signs are not consistent with the water balance equation. Finally, for the remaining 31 sub-catchments (with trends consistent in signs), the consistency of the water balance equation was evaluated regarding the magnitude of trends, finding closure errors on water balance of trends up to 281% of the average of the magnitudes. We discuss several reasons for the lack of closure of the water balance, including the very existence of trends that violate the stationary hypothesis underlying the long-term approximation of the surface water balance. The used data and some of the results are available on the supplemental files. The Raw Data CSV file contains the spatial average timeseries at the basin that drain to the flow stations for the water balance equation variables. The Filled Data CSV file contains those timeseries after appliying the reconstruction. MKtrends and SenTrendMagnitude CSV files contains the results of the appliying the Mann-Kendall and Sen trend tests to the filled data.

According to TRMM and GPM satellite precipitation composites, a broad maritime area over the far eastern Tropical Pacific and western Colombia houses one of the rainiest spots on Earth. This study aims to present a suite of mechanistic drivers that help create such a world-record breaking rainy spot. Previous research has shown that this oceanic and nearly-continental precipitation maximum has a strong early morning precipitation peak and development of a high density of mesoscale convective systems. We examined new and unique observational evidence highlighting the role of both dynamical and thermodynamical drivers in the activation and duration of organized convection. Results show the existence of a rather large combination of mechanisms, including: (1) dynamics of the Choco (ChocoJet) and Caribbean Low-Level Jets along their confluence zone, including the Panama semi-permanent low; (2) land breeze favors ChocoJet deceleration offshore, enhancing the nighttime and early morning low-level convergence; (3) vertical wind shear and tilting of vertical wind shear into vorticity lines that interact with convective outflows; (4) action of mid-level gravity waves, which support the strong diurnal variability; (5) mesoscale convective vortices related to subsidence in the stratiform region in long lasting MCSs reinforcing (3); and (6) the likely role of land surface-atmosphere interactions and the rainforest over western Colombia. This study emphasizes the multi-scale environmental processes associated with the formation of one of the rainiest spots on Earth and showcases new observations gathered during the Organization of Tropical East Pacific Convection (OTREC; August-September, 2019) which support the outlined mechanisms.