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]