Tropical cyclones (TCs) are essential elements of the hydrological cycle in tropical and subtropical regions. In the present study, the contribution of TCs to seasonal precipitation around the tropical and subtropical North America is examined. When TC activity over the tropical eastern Pacific (TEP) or the Intra Americas Seas (IAS) is below (abovenormal), regional precipitation may be below (above-normal). However, it is not only the number of TCs what may change seasonal precipitation, but the trajectory of the systems. TCs induce intense precipitation over continental regions if they are close enough to shorelines, for instance, if the TC center is located, on average, less than 500 km-distant from the coast. However, if TCs are more remote than this threshold distance, the chances of rain over continental regions decrease, particularly in arid and semi-arid regions. In addition, a distant TC may induce subsidence or produce moisture divergence that inhibits, at least for a few days, convective activity farther away than the threshold distance. An analysis of interannual variability in the TCs that produce precipitation over the tropical and subtropical North America shows that some regions in northern Mexico, which mostly depend on this effect to undergo wet years, may experience seasonal negative anomalies in precipitation if TCs trajectories are remote. Therefore, TCs (activity and trajectories) are important modulators of climate variability on various time scales, either by producing intense rainfall or by inhibiting convection at distant regions from their trajectory. The impact of such variations on water availability in northern Mexico may be relevant, since water availability in dams recovers under the effects of TC rainfall. Seasonal precipitation forecasts or climate change scenarios for these regions should take into account the effect of TCs, if regional adaptation strategies are implemented.

International audienceThe Galapagos Archipelago is nearly devoid of freshwater resources, but during six months of the year, a fog layer covers the windward slopes of the main islands. In order to investigate the hydrological importance of this phenomenon, a monitoring network was set up on Santa Cruz Island, at the center of the archipelago. Meteorological parameters were monitored together with throughfall and stemflow at two stations: a first in a secondary forest at the lowest fringe of the fog layer (400 m a.s.l.), and a second in shrub lands of the Galapagos National Park, at the center of the fog layer (650 m a.s.l.). Cloud water interception was quantified from the wet canopy water budget, based on a modified \emph{Rutter}-type canopy interception model. This methodology allowed the estimation of fog interception for short time intervals (15 min) and avoided the subjective separation into individual rainfall events. Fog was found to be a negligible water input at the lower site, but contributed up to 26 $\pm$ 16\% of incident rainfall at the higher site. Wind was shown to enhance fog interception, but this alone could not explain the difference in fog catch between the two sites. Higher liquid water content and more frequent fog occurrence contributed to the difference as well. This study highlights that the presence of fog may induce a marked increase of net precipitation, but this effect is restricted to the summit areas exposed to winds, located in the center of the cloud belt

Easterly waves (EWs) are important moisture carriers and their variability can impact the total May-November rainfall, defined as seasonal precipitation, over the Tropical Americas. The contribution of EWs to the seasonal precipitation is explored over the tropical Americas using rain gauge stations, reanalysis data and a regional model ensemble during the 1980-2013 period. In the present study, EWs are found to produce up to 50% of seasonal rainfall mainly over the north of South America and contribute substantially to interannual regional rainfall variability. An observational analysis shows that the El Niño Southern Oscillation (ENSO) affects EW frequency and therefore, their contribution to seasonal rainfall. In recent years, tropical cyclone (TC) activity over the Main Development Region (MDR) of the tropical North Atlantic has a negative impact on regional seasonal precipitation over northern South America. High TC activity over MDR corresponds to below-normal precipitation because it reduces the EW activity reaching northern South America through the recurving of TC tracks. Recurving TC tracks redirect moisture away from the tropical belt and into the mid-latitudes. However, this relationship only holds under neutral ENSO conditions and the positive phase of the Atlantic Multidecadal Oscillation. A 10-member regional model multi-physics ensemble simulation for the period 1990-2000 was analyzed to show the relationships are robust to different representations of physical processes. This new understanding of seasonal rainfall over the tropical Americas may support improved regional seasonal and climate outlooks.

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