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The Colombian Andes (CA) are located over the northwestern corner of tropical South America (NW‐TropSA), where land and atmosphere interchange moisture and energy in a complex way owing to the orographic influence on the recycling of moisture over land. We aim to understand where and when water vapor evaporated from land turns into rainfall through moisture recycling, using the Water Accounting Model‐2layers (WAM‐2), an offline model to track atmospheric moisture forced with data from ERA‐5 at its native 0.25° resolution during 1980–2020. We define the spatiotemporal distribution of sources (high evaporation recycle ratios, ϵC) and receptors (high precipitation recycle ratios, ρC) of continental moisture at diverse timescales, including monthly, seasonal, annual and interannual (ENSO). Referring to the regional runs of WAM‐2 over NW‐TropSA (4°S–12°N/80°W–66°W), at elevations above 1,000 m.a.s.l., the CA has a mean annual ρC of 11% (ranging 6%–16%) and a mean annual ϵC of 35% (ranging 27%–40%). Moisture recycling in the CA exhibits a strong annual cycle over the region. The seasonal dynamic of moisture recycling shows two clear‐cut sources of moisture: the eastern foothills of the Eastern and Central ranges of the CA. Both foothills are also regions of high rainfall, although moisture recycling mechanisms differ. Sources of continental moisture grow spatially during September‐October‐November and March‐April‐May. The seasonal availability of moisture recycled coincides with regions where orography interacts with low level jets sourcing humidity. At interannual timescales, sources and receptors of continental moisture in the CA are modulated by the extreme phases of ENSO. Key Points: The orography of the Colombian Andes emerged as a critical factor shaping the interaction between land and atmospheric moisture fluxesFoothills and valleys of the Colombian Andes play a pivotal role in continental moisture recycling, in terms of convergence and divergenceENSO modulates both sources and receptors of continental moisture at interannual timescales [ABSTRACT FROM AUTHOR]

The global impacts of El Niño on precipitation have been long‐recognized, but more understanding of the mechanisms behind this influence is needed. For instance, previous studies have largely overlooked the potential impacts of El Niño on terrestrial moisture recycling (TMR). We perform a 40‐year forward tracking simulation to derive a global climatology of recycled precipitation and use a composite analysis to investigate how El Niño affects TMR. We identify seven regions where the El Niño impact on TMR is most significant and find that, in these regions, changes in precipitation and TMR are directly related: they increase or decrease together. In addition, we find a marked latitudinal contrast between the Southern Hemisphere, where TMR increases during El Niño, and the Northern Hemisphere and the tropics, where it decreases. Our results indicate that the weakening and strengthening of TMR can be behind precipitation changes caused by El Niño globally. Plain Language Summary: El Niño is recognized as a climate variability phenomenon with significant impacts on precipitation worldwide. However, the mechanisms behind these impacts are not fully understood. Here we use model simulations to argue that one of those mechanisms is the effect of El Niño on terrestrial moisture recycling (TMR), that is, the fraction of precipitation fed by atmospheric moisture originating not in the ocean but on the continents. We show that El Niño significantly affects TMR globally, especially in seven regions of South America, Africa, North America, Europe, and Asia. In these regions, precipitation and TMR increase or decrease together. We find a contrast between the South and North of the planet: during El Niño, TMR increases in the Southern Hemisphere while decreasing in the Northern Hemisphere and the tropics. Overall, our results indicate that TMR weakening or strengthening are previously overlooked mechanisms behind precipitation changes caused by El Niño globally. Key Points: El Niño exerts significant effects on terrestrial moisture recycling worldwideEl Niño's impacts on terrestrial moisture recycling are most significant in seven regions worldwidePrecipitation and terrestrial moisture recycling increase or decrease together due to El Niño [ABSTRACT FROM AUTHOR]

The terrestrial water cycle links the soil and atmosphere moisture reservoirs through four fluxes: precipitation, evaporation, runoff, and atmospheric moisture convergence (net import of water vapor to balance runoff). Each of these processes is essential for sustaining human and ecosystem well‐being. Predicting how the water cycle responds to changes in vegetation cover remains a challenge. Recently, changes in plant transpiration across the Amazon basin were shown to be associated disproportionately with changes in rainfall, suggesting that even small declines in transpiration (e.g., from deforestation) would lead to much larger declines in rainfall. Here, constraining these findings by the law of mass conservation, we show that in a sufficiently wet atmosphere, forest transpiration can control atmospheric moisture convergence such that increased transpiration enhances atmospheric moisture import and results in water yield. Conversely, in a sufficiently dry atmosphere increased transpiration reduces atmospheric moisture convergence and water yield. This previously unrecognized dichotomy can explain the otherwise mixed observations of how water yield responds to re‐greening, as we illustrate with examples from China's Loess Plateau. Our analysis indicates that any additional precipitation recycling due to additional vegetation increases precipitation but decreases local water yield and steady‐state runoff. Therefore, in the drier regions/periods and early stages of ecological restoration, the role of vegetation can be confined to precipitation recycling, while once a wetter stage is achieved, additional vegetation enhances atmospheric moisture convergence and water yield. Recent analyses indicate that the latter regime dominates the global response of the terrestrial water cycle to re‐greening. Evaluating the transition between regimes, and recognizing the potential of vegetation for enhancing moisture convergence, are crucial for characterizing the consequences of deforestation as well as for motivating and guiding ecological restoration. [ABSTRACT FROM AUTHOR]

The far eastern tropical Pacific is one of the rainiest locations on Earth. This region is characterized by a robust diurnal cycle with precipitation initiating over the Andes mountains in Colombia in the late afternoon and moving offshore overnight while organizing into mesoscale convective systems (MCSs). As the MCSs move westward, they can seed tropical easterly waves that develop into tropical cyclones. Novel measurements of near‐surface wind speeds and latent heat flux (LHFLX) from the Cyclone Global Navigation Satellite System (CYGNSS) mission and ERA5 reanalysis are used to evaluate changes to regional flow patterns, moisture, and LHFLX that favor a strong westward propagating diurnal cycle of precipitation in this region. Days with strongly versus weakly westward propagating diurnal precipitation are compared during the extended boreal summer of the CYGNSS era (May–October 2018–2021). Strongly propagating days have a more moist lower troposphere with stronger vertically integrated moisture flux convergence than days with weakly propagating precipitation. The enhanced low‐level moisture is supported by increased wind‐driven LHFLX from stronger regional flows including the Choco and Caribbean Low‐Level Jets and Panama and Papagayo gap winds. Increased offshore convergence and vorticity also help sustain convection during the days with strongly propagating precipitation. Background variations in the physical environment, as opposed to diurnal variations, seem more important for supporting a robust diurnal cycle of precipitation in the region. Plain Language Summary: The eastern tropical Pacific Ocean off the coast of Colombia is one of the rainiest locations on Earth. Thunderstorms frequently form in the late afternoon over the foothills of the Andes mountains and then move offshore into the eastern Pacific overnight and into the early morning while growing into bigger thunderstorms. These large thunderstorms are important because they can eventually lead to tropical cyclone development as they move westward over the eastern Pacific parallel to central America. We evaluate environmental conditions that favor days when thunderstorms move far away from the Colombian coast along central America versus days when thunderstorms stay closer to the Colombian coast. We find that days when the thunderstorms move farther away from the Colombian coast have more moisture near the Earth's surface. This enhanced moisture is supported by increased winds near the surface in the east Pacific and Caribbean that help transport moisture from areas near the Pacific equator and Caribbean to offshore of Colombia and transfer moisture from the far eastern Pacific Ocean surface into the overlying atmosphere. Measurements from eight microwave‐size satellites in space were critical to determine the role of the transfer of moisture from the ocean surface to the atmosphere. Key Points: An index is developed to distinguish between days with strong versus weak westward‐propagating diurnal precipitation in the far east PacificStrongly propagating days have increased low‐level moisture, regional circulations, and gap winds relative to weakly propagating daysCyclone Global Navigation Satellite System measurements show that increased moisture on the strongly propagating days is supported by increased wind‐induced latent heat fluxes [ABSTRACT FROM AUTHOR]

Convective processes are critical in the northernmost section of the Andes, where highly complex orography combines with tropical dynamics to produce intense precipitating systems. Data from satellite and ground radar have shown that Colombia's central Magdalena valley has a marked precipitation diurnal cycle, with high rainfall rates produced by deep convective events that intensify on the foothills of the surrounding valley. This study aims to contribute to the understanding of the orographic controls imposed on the convective activity observed in this important tropical valley. The atmospheric environments associated with convective events are assessed using WRF high-resolution simulations for a two-week period that includes intense rainfall events and marked dry spells. In addition, a simulation with modified orography is evaluated to analyze further the effect of topography in controlling the observed convective systems. The results suggest that northward and southward wind regimes channeled by the valley's topography and cross-valley flow result in a robust nocturnal convergence zone, which is associated with the strong diurnal cycle and the valley configuration. Furthermore, northerly low-level flow is an important source of moisture for convection in the valley. Additionally, results show midlevel tropospheric heating enhancement during days with more rainfall produced by convective systems in the western slope of the valley. The modified topography simulation suggests that circulation and precipitation in the valley are strongly dependent on the actual terrain features. [ABSTRACT FROM AUTHOR]

The South American Altiplano has a marked dry season during the austral winter (June to August, JJA). However, during this season synoptic meteorological conditions triggering heavy precipitation can damage socioeconomic activities, often causing the loss of human lives. Using daily in-situ precipitation data from 39 rain-gauge stations over the northern Altiplano ( 18 ∘ S - 15 ∘ S ; > 3000 m.a.s.l.) for the JJA season, we computed the historical percentile 90 (p90) and we identified extreme rainy days with precipitation higher than p90 in the 1980–2010 period. We identified 100 winter extreme precipitation events (WEPEs) over this region that can last between one to 16 days. The K-means analysis was applied to anomalies of geopotential height at 500 hPa from ERA-Interim data during the initial day or Day(0) of WEPEs lasting 1 day (42 cases), 2 days (19) and more than 2 days (39). We found 59 WEPEs characterized by an upper-level trough over the Peruvian-Chilean coast. At 850 hPa, these 59 WEPEs are also associated with cold surges along the eastern Central Andes, indicating an association between the upper-level trough and the cold surge in developing deep convection over the northern Altiplano. A lead-lag composite analysis further showed a significant lower- and mid-tropospheric moistening over the western Amazon 2 days before the onset of these 59 WEPEs, due to low-level northerly wind anomalies originating over equatorial South America. The other 41 WEPEs are associated with a low-level southerly wind regime crossing the equator and a mid-and upper-level low-pressure system over the Peruvian-Chilean coast. While the low-level southerly regime enhances mid-tropospheric moisture transport from the equator towards the Altiplano due to the developed shallow meridional circulation when propagating equatorward, a low-pressure system promotes intensification of upward motion, boosting the upslope moisture transport from the lowlands to the east of the Central Andes towards the Altiplano. [ABSTRACT FROM AUTHOR]

Earth's hydrological cycle critically depends on the atmospheric moisture flows connecting evaporation to precipitation. Here we convert a decade of reanalysis-based moisture simulations into a high-resolution global directed network of spatial moisture provisions. We reveal global and local network structures that offer a new view of the global hydrological cycle. We identify four terrestrial moisture recycling hubs: the Amazon Basin, the Congo Rainforest, South Asia and the Indonesian Archipelago. Network motifs reveal contrasting functioning of these regions, where the Amazon strongly relies on directed connections (feed-forward loops) for moisture redistribution and the other hubs on reciprocal moisture connections (zero loops and neighboring loops). We conclude that Earth's moisture recycling hubs are characterized by specific topologies shaping heterogeneous effects of land-use changes and climatic warming on precipitation patterns. By using network motifs, a new view of the global hydrological cycle is offered. With them, it is revealed that the Amazon rainforest is a one-of-a-kind moisture recycling hub, which shows that the ecosystem may be subject to increased vulnerability [ABSTRACT FROM AUTHOR]

This study assessed the precipitation recycling and moisture sources in the Colombian Pacific region between 1980–2017, based on the monitoring of moisture in the atmosphere through the Eulerian Water Accounting Model-2 layer (WAM2 layer) and the delimitation of the area contributing to terrestrial and oceanic moisture in the region is performed using the "precipitationshed" approach. The results indicate a unimodal precipitation recycling ratio for the North and Central Pacific and Patía-Mira regions, with the highest percentages between March and April, reaching 30% and 34%, respectively, and the lowest between September and October (between 19% and 21%). Moreover, monthly changes in the circulation of the region promote a remarkable variability of the sources that contribute to the precipitation of the study area and the spatial dynamics of the precipitationshed. From December to April, the main contributions come from continental sources in eastern Colombia and Venezuela, the tropical North Atlantic, and the Caribbean Sea, a period of high activity of the Orinoco Low-Level jet. In September, the moisture source region is located over the Pacific Ocean, where a southwesterly cross-equatorial circulation predominates, converging in western Colombia, known as the Choco Jet (CJ), decreasing the continental contribution. An intensified Caribbean Low-Level Jet inhibits moisture sources from the north between June and August, strengthening a southerly cross-equatorial flow from the Amazon River basin and the southeastern tropical Pacific. The March–April (September–October) season of higher (lower) recycling of continental precipitation is related to the weakening (strengthening) of the CJ in the first (second) half of the year, which decreases (increases) the contribution of moisture from the Pacific Ocean to the region, increasing (decreasing) the influence of land-based sources in the study area. [ABSTRACT FROM AUTHOR]

Land‐atmosphere interactions are critical for precipitation (PPT) over South America where terrestrial evapotranspiration (ET) constitutes a significant fraction of moisture for rainfall over the ecologically and socio‐economically vital Amazon (AMZ) and La Plata (LPB) river basins. We quantify the contribution of ET from AMZ and LPB to PPT over the continent with a focus on the intraseasonal time scale. Using numerical water tracers embedded in the Weather Research and Forecasting model we track the moisture originating from the two basins. Our findings indicate that approximately 40% of annual rainfall over the eastern foothills of the Andes originates as AMZ ET, and nearly 30% of rainfall over northern Argentina originates as LPB ET. Analysis of moisture transport during both phases of the dominant intraseasonal oscillation pattern over South America reveals an intraseasonal "sloshing" of LPB moisture between the South Atlantic convergence zone (SACZ) and southeastern South America (SESA) regions. AMZ and LPB each supply approximately 6% of moisture for SACZ PPT during periods of intraseasonal enhancement (positive anomalies), highlighting the importance of moisture from the Atlantic Ocean. For the SESA region, LPB supplies 26% of the moisture for PPT during periods of intraseasonal enhancement while AMZ supplies 5%. Plain Language Summary: Terrestrial moisture ‐ moisture that previously evapotranspired from the land surface ‐ plays a crucial role in the regional hydroclimate over South America through "recycling", a process by which terrestrial moisture contributes to precipitation (PPT) within the same region. Previous work has shown that the Amazon (AMZ) and the La Plata (LPB) basins, the largest river basins of South America, receive a large amount of PPT through recycling. This study investigates the changes in transport and recycling of terrestrial moisture from these basins at the 30–75 days timescale. We want to understand how variability in the continental‐scale circulation can affect the transport of terrestrial moisture. By using a numerical weather prediction model with the added capability of tracking moisture that originates as evapotranspiration within a specified source region (in this case, AMZ and LPB), we are able to track the motion, phase change and PPT of AMZ and LPB moisture throughout the domain. First, we present a detailed climatological analysis of recycling ratios for South American PPT and then we focus on the 30–75 days time‐scale to understand how the intraseasonal circulation modifies the geographical location of continental recycling patterns. Key Points: Evapotranspiration from Amazon and La Plata basins plays a crucial role in the regional water balance through recycling and moisture exportThe dominant intraseasonal hydroclimate oscillation over South America drives the transport of terrestrial moistureThere is a clear "sloshing" of terrestrial moisture between central‐east and southeastern South America at intraseasonal time scale [ABSTRACT FROM AUTHOR]

The hydroclimatology of Northern South America responds to the coupling between the Pacific and Atlantic oceans, the Amazon–Andes interactions, and the orographic barrier of the regional Andes. The relative contributions of oceanic and terrestrial moisture sources have been mostly evaluated in modelling studies, with limited observational data for validation. We combine observations from stable isotopes in precipitation and output from the Lagrangian moisture trajectory tracking model FLEXPART to characterize and contrast the relative contribution of oceanic (from the Atlantic and the Pacific) and terrestrial (from different regions in the continent) moisture sources to mean monthly precipitation in the Andes and Caribbean regions of Colombia. Our results indicate that most moisture becoming rain in the region has an atmospheric residence time that deviates from commonly assumed 10 days. These residence times vary between source and sink regions from 1 day in the case of recycling to more than 10 days in Andean precipitation originating in the Atlantic Ocean. Common integration times for both regions from all sources are commonly in the order of three to 7 days. Most precipitation in the region comes from terrestrial sources including moisture recycling from the same region (>30% for all months), the Orinoco River basin (up to 28% in April), and the northern Amazon basin (up to 17% in June, July, and August); followed by individually considered oceanic sources including the Tropical South Pacific (up to 30% monthly in October, November and December) and Tropical North Atlantic (up to 30% monthly for January). The fact that a significant proportion of rainfall is recycled highlights that water availability in the Andean and Caribbean regions of Colombia could potentially be altered by current widespread and pervasive changes in vegetation cover. More generally, our results highlight the need to assess the hydrological consequences of land cover change in South America, particularly in a country like Colombia where water, food, and energy security all depend directly on precipitation. [ABSTRACT FROM AUTHOR]

Previous soil moisture conditions play an important role in the design of hydraulic structures because they are directly related to the runoff threshold associated with a return period. These represent one of the main determinants of the runoff response of a drainage basin. One of the main difficulties facing hydrologists in Colombia lies in the time spent gathering and analyzing information related to the selection of antecedent moisture conditions. In this study, complete records from 19 rainfall stations located in the Atlántico region, Colombia, were used to analyze the cumulative precipitation during the 5 days prior to the annual maximum daily precipitation associated with different return periods using the Gev, Gumbel, Pearson Type III and Log Pearson Type III probability distributions. Different interpolation methods (IDW, kriging and spline) were applied to evaluate the spatial distribution of the antecedent moisture conditions. The main contribution of this research is establishing, using a probabilistic approach, the behavior of antecedent moisture conditions in a particular region, which can be used by engineers and designers to plan water infrastructure. This probabilistic approach was applied to a case study of the Atlántico region, Colombia, where the spatial distribution of antecedent moisture conditions was calculated for several return periods. The results indicate that the better results were obtained with the IDW interpolation method, and the Pearson Type III and Gumbel distributions also showed the best fits based on the Akaike criterion. [ABSTRACT FROM AUTHOR]

In this study, we identified the origin of the moisture associated with the tropical cyclones' (TCs) precipitation in the North Atlantic Ocean basin during their three well-differentiated life stages between 1980 and 2018. The HURDAT2 database was used to detect the location of 598 TCs during their genesis, maximum intensification peak, and dissipation phases. The global outputs of the Lagrangian FLEXPART model were then used to determine the moisture sources. Using a k-means cluster analysis technique, seven different regions were identified as the most common locations for the genesis and maximum intensity of the TC phases, while six regions were found for the dissipation points. Our results showed that the origin of moisture precipitating was not entirely local over the areas of TC occurrence. The North Atlantic Ocean to the north of the intertropical convergence zone at 10°N (NATL)—especially from tropical latitudes, the Caribbean Sea, and the Gulf of Mexico—provides most of the moisture for TCs (∼87%). The Atlantic Ocean basin southward of the ITCZ (SATL) played a nonnegligible role (∼11%), with its contribution being most pronounced during the TC genesis phase, while the eastern tropical Pacific Ocean made the smallest contribution (∼2%). The moisture supported by TCs varied depending on their category, being higher for hurricanes than for major hurricanes or tropical storms. Additionally, the approach permitted the estimation of the mean residence time of the water vapor uptake that produces the precipitation during TC activity, which ranged between 2.6 and 2.9 days. Significance Statement: Atmospheric moisture transport plays an important role in the genesis and intensification of tropical cyclones (TCs). In this study, we investigated the moisture source for the genesis, intensification, and dissipation of TCs in the North Atlantic Ocean basin using a Lagrangian approach. This model allowed us to track air masses backward in time from the target area to identify regions where air masses experienced an uptake of moisture prior to reaching the area of interest. The sources were identified individually for each TC, and the results were then combined to provide a broad general picture with some surprising outstanding results, such as the role of the North and South Atlantic and the eastern tropical Pacific as important moisture sources during the different TCs phases and intensities. [ABSTRACT FROM AUTHOR]

A study of the simulation of the Orinoco Low‐Level Jet (OLLJ) and the cross‐equatorial moisture transport over tropical South America using the Weather Research and Forecasting (WRF) model is presented. The focus is on the diurnal cycle and monthly means during one December‐January‐February (DJF) season (2003–2004). The sensitivity of the OLLJ and cross‐equatorial moisture transport to the representation of surface fluxes and turbulence is explored by using two different Land Surface Models (LSM) and three Planetary Boundary Layer (PBL) schemes. Different LSMs produce large differences in the sensible heat flux over the Orinoco basin, but no substantial differences in the flow at the entrance of the OLLJ. However, these changes in surface fluxes were associated with a change in the low‐level pressure gradient between the Orinoco and Amazon basins, and with up to 10% change in the simulated cross‐equatorial moisture transport. The largest effects from different PBL schemes were found in the low‐level flow near the Andes cordillera, and on the low‐level southward cross‐equatorial flow during the daytime. One of the PBL schemes exhibited a reduced moisture transport on the eastern flank of the Andes but enhanced southward transport around the core of the cross‐equatorial moisture flux. Another PBL scheme produced a stronger net cross‐equatorial moisture transport, with enhanced precipitation over the Andes‐Amazon region by up to 30% during the afternoon and up to 13% in the daily mean. Improved observations over the region are needed to evaluate which combination best represents the flow. Key Points: Land surface and Planetary Boundary Layer parameterizations can affect the simulation of the Orinoco low‐level jet and moisture transportSubstantial local changes in surface fluxes over the Orinoco basin do not substantially modify the simulated Orinoco low‐level jetGradients in surface fluxes between the Orinoco and Amazon basins are associated with modified cross‐equatorial moisture transport [ABSTRACT FROM AUTHOR]