3.1. Oceanic and continental contributions to precipitation
Our results show that the spatial and temporal scales at which each source region influences precipitation in the study area vary and, importantly, vary from the mean 10-day residence time commonly used as integration time (Table 1). For instance, while the oceanic contribution from the Pacific reaches the Andean region in 2 to 7 days (TSP and TNP), moisture originated in the Atlantic Ocean takes longer than 10 days to become precipitation (TA, TSA, STNA). Atlantic sources have a time scale for the optimal transport day in the 10-day global mean lifetime of water vapor, except for CARS (that is between 4 and 6 days for the Andean region and between 3 and 4 for the Caribbean region). Transport time scales for Pacific sources have differentiated features. TNP spends 2 days reaching the optimum transport time while TSP varies from 2 to 7 days for the Andean region, and from 8 to 9 for the Caribbean region. ORIC is the second largest terrestrial source with a time scale of moisture transport of around 4 days. The time transport from NAMZ to the Andean region is between 6 to 7 days and to the Caribbean region is 8 days. As expected, the largest spatial extents correspond to more distant source regions while the closest source regions have the lowest spatial extents and integration times. (Appendix A includes detailed information about climatological monthly diagnostic precipitation for different integration times).
[Insert Table 1]
We estimated the effective amount of precipitation from each source based on the percentage of diagnostic precipitation accounted for FLEXPART. Observational data from 1506 gauge stations along the entire region provided by the IDEAM (Colombia’s National hydroclimatic agency) were included in order to regionally validate the model results (Fig. 4). In general, the annual mean moisture contribution from the Atlantic (Pacific) ocean is larger in the Caribbean (Andean) region than for the Andean (Caribbean) region (Figure 5 and 6). The main atmospheric Atlantic sources for both target regions are TNA, TA, and CARS (Fig 5a, 5d). In the Andean region, TSP contributions are larger than TNP (Fig. 5b), while both Pacific sources have similar contributions for the Caribbean region (Fig. 5e). Terrestrial recycling accounts for more than 50% of the total (59.40% to the Andean and 56.74% to the Caribbean; Fig. 5c, 5f respectively and Fig. 6). The local atmospheric moisture from NOSA reaches the maximum contribution in 1 day. Overall, NOSA is the largest contributor among the terrestrial and oceanic sources, with an annual contribution of 37.98% (32.10%) for the Caribbean (the Andean) region. For the Caribbean (Andean) region, the atmospheric moisture from ORIC is comparable to the total contribution from the Pacific (Atlantic) Ocean. For both target areas, the contribution from the TNA (TSP), is the largest Atlantic (Pacific) source. As expected, moisture coming from the Amazon basin is higher for northern Amazon (NAMZ), and the contribution is greater in the Andean compared to the Caribbean region (Fig. 5c, 5f), but its relative importance is, on average, smaller than the other two terrestrial sources.
[Insert Figure 4]
[Insert Figure 5]
Moisture contributions to both regions have a marked seasonal behavior, with the relative contribution of oceanic and terrestrial sources varying through the year. For all months, terrestrial sources dominate moisture contributions in both regions (Fig. 6). The predominant oceanic moisture source for the first season of the year (JFM) is the Atlantic Ocean, with total monthly contributions greater than 26% for the Andean region, and greater than 41% for the Caribbean region (Fig. 6). More specifically, the TNA region has the largest contributions, with more than 17% for the Andean region (Fig. 5a) and more than 27% per month for the Caribbean region (Fig. 5d). In the Andean region, the Pacific Ocean is the most predominant oceanic moisture source From May to December, with the contributions are over 36% for the months SOND (Fig. 6a). Particularly the TSP is the major moisture contributor to the Andean region exceeding 33% per month in November (Fig. 5b). Between May and October, the Caribbean region receives moisture predominantly from the Pacific Ocean (Fig. 6b), intensifying these contributions in October – November as the ITCZ stays in the northern hemisphere over the Atlantic and eastern Pacific.
[Insert Figure 6]