Search

We analyse the effects of deforestation and the projected differential sea surface temperature (SST) anomalies between the tropical North Atlantic and the eastern North Pacific on the mid‐summer drought (MSD) over southern Mexico and Central America. To address these issues, we performed a set of three 6‐year (1996–2001) sensitivity experiments with RegCM4 driven by the ERA‐Interim reanalysis and employing different SST (projected end of century patterns under the RCP8.5 scenario) and vegetation (turning forest landuse into grass) configurations. The model domain follows the specifications of the COrdinated Regional Downscaling EXperiment (CORDEX) for Central America. Results indicate that projected SST patterns cause the MSD signal to almost disappear from the regional mean annual cycle, with its spatial extent decreasing from ~82 to ~48%. In the vegetation sensitivity experiment, the MSD intensity increases along the Pacific coast and Central America, while the MSD spatial extent remains almost unchanged. These regional changes in MSD can be explained in terms of the regional precipitation response to deforestation, primarily due to changes in vertical moisture advection. [ABSTRACT FROM AUTHOR]

The southern Mexico and Central America (SMCA) region shows a dominant well‐defined precipitation annual cycle. The rainy season usually begins in May and ends in October, with a relatively dry period in July and August known as the mid‐summer drought (MSD); notable exceptions are the Caribbean coast of Honduras and Costa Rica. This MSD phenomenon is expected to be affected as the SMCA experiences an enhanced differential warming between the Pacific and Atlantic Oceans (PO‐AO) towards the end of the 21st century. Previous studies have suggested that this differential warming will induce a strengthening of the westward Caribbean low‐level jet (CLLJ) and that this heightened CLLJ will shift precipitation westwards, falling on the PO instead that within the SMCA region causing a severe drought. In this work we examine this scenario with a new model, the Rossby Center Regional Climate Model (RCA4), for the COordinated Regional climate Downscaling EXperiment (CORDEX) Central America domain, forced with different general circulation models (GCMs) and for different representative concentration paths (RCPs). We consider 25‐year periods as "present conditions" (1981–2005) and "future scenario" (2071–2095), focusing on the "extended summer" season (May–October). Results suggest that in the future the spatial extension of the MSD will decrease and that in certain areas the MSD will be more intense but less frequent compared to present conditions. Also, the oceanic differential warming, the intensification of the CLLJ, and the reduction in regional precipitation in the future scenario, suggested by previous works, were verified in this study. [ABSTRACT FROM AUTHOR]

In this note, a procedure to construct predictors is suggested that could take advantage of the increasing predictive skill of ENSO models. These so-called secondary forecast models (SFM) attempt to produce a forecast for a particular object application based on independent forecasts of ENSO. Although their predictive skill may be modest, these models can provide an alternate and objective forecast to the entirely subjective schemes more widely used. An example of the application of SFM to the forecast of the seasonal precipitation of a typical station of the Mediterranean Californias shows promising results.

The Mediterranean California Border Region ( MCBR) rainfall's relationship with El Niño-Southern Oscillation ( ENSO) and the Pacific Decadal Oscillation ( PDO) is reexamined for the period 1951-2014. When stratifying data by ENSO events we found that strong events of either sign yield the highest ENSO-rainfall correlation; but when the stratification was done by rainfall the wet seasons yield the highest ENSO-rainfall correlation. Most strong ENSO events have the same sign as PDO; but the ENSO-rainfall correlation for all ENSO-PDO same-sign events is almost undistinguishable from the full-record's correlation. Timewise stratification shows that 30-year climatological values ( MCBR precipitation, PDO and ENSO) and ENSO-rainfall correlations have decreased in recent years. [ABSTRACT FROM AUTHOR]

An ensemble of future climate projections performed with the regional climate model RegCM4 is used to assess changes in inter-annual variability of precipitation over Southern Mexico and Central America (SMECAM). Two different Global Climate Models (GCMs) from the coupled model intercomparison project phase 5 are used to provide boundary conditions for two different RegCM4 configurations. This results in four regional climate projections extending from 1970 to 2100 for the greenhouse gas representative concentration pathway RCP8.5. The precipitation variability over the SMECAM region and its dependence on the gradient between Atlantic and Pacific sea surface temperature (SST) anomalies are verified by reproducing SST anomaly patterns during wettest and driest years similar to those seen in observational datasets. RegCM4 does a comparably better job than the driving GCMs. This strong relationship between precipitation and SST anomalies does not appear to change substantially under future climate conditions. For the rainy season, June to September, we find a future change in inter-annual variability of precipitation towards a much greater occurrence of very dry seasons over the SMECAM region, with this change being more pronounced in the regional than in the global model projections. A greater warming of the Tropical Northeastern Pacific (TNP) compared to the Tropical North Atlantic (TNA), which causes stronger wind fluxes from the TNA to the TNP through the Caribbean Low Level Jet, is identified as the main process responsible for these drier conditions. [ABSTRACT FROM AUTHOR]