Efectos remotos del cambio de uso de suelo en el clima del sudeste de Sudamérica

Grandes áreas de Sudamérica están sufriendo cambios en el uso del suelo, en general, de origen antropogénico. El aumento de la precipitación en regiones áridas combinado con los avances tecnológicos incrementó la disponibilidad de tierras productivas. Esto derivó en un proceso de expansión de la frontera agrícola sobre zonas con vegetación natural. Desde el punto de vista hidroclimático, el reemplazo de vegetación natural por cultivos altera la partición de agua y energía en superficie. Al cambiar la vegetación se modifican propiedades biofísicas relacionadas a la misma tales como albedo, resistencia estomática o rugosidad de superficie. Este cambio en las propiedades produce efectos sobre las variables hidroclimáticas tanto locales como remotos. Este trabajo tiene por objetivo evaluar los efectos remotos de los cambios de cobertura del suelo mediante simulaciones con el modelo climático WRF (Weather Research and Forecasting). Se realizaron simulaciones asumiendo dos escenarios de cobertura/uso de suelo. Una simulación de control donde se simula el comportamiento del clima sin alterar la cobertura vegetal y una simulación donde se reemplaza bosques, pasturas y sabana por cultivos, ambas durante la primavera de 2002. Para evaluar los efectos remotos, se analiza el comportamiento de diferentes variables hidroclimáticas en diferentes regiones de Argentina y de Sudamérica donde no se realizaron cambios de cobertura. Los resultados indican que la expansión de cultivos sobre vegetación nativa modifica las propiedades biofísicas alterando en tiempo y espacio el comportamiento de variables hidroclimáticas. En particular, se observan cambios en los balances hidrológicos de diferentes regiones y también, cambios importantes en la circulación de los vientos.Eje: Ciencias Hidrológicas y Criósfera.Facultad de Ciencias Astronómicas y Geofísica

Efectos remotos del cambio de uso de suelo en el clima del sudeste de Sudamérica

Grandes áreas de Sudamérica están sufriendo cambios en el uso del suelo, en general, de origen antropogénico. El aumento de la precipitación en regiones áridas combinado con los avances tecnológicos incrementó la disponibilidad de tierras productivas. Esto derivó en un proceso de expansión de la frontera agrícola sobre zonas con vegetación natural. Desde el punto de vista hidroclimático, el reemplazo de vegetación natural por cultivos altera la partición de agua y energía en superficie. Al cambiar la vegetación se modifican propiedades biofísicas relacionadas a la misma tales como albedo, resistencia estomática o rugosidad de superficie. Este cambio en las propiedades produce efectos sobre las variables hidroclimáticas tanto locales como remotos. Este trabajo tiene por objetivo evaluar los efectos remotos de los cambios de cobertura del suelo mediante simulaciones con el modelo climático WRF (Weather Research and Forecasting). Se realizaron simulaciones asumiendo dos escenarios de cobertura/uso de suelo. Una simulación de control donde se simula el comportamiento del clima sin alterar la cobertura vegetal y una simulación donde se reemplaza bosques, pasturas y sabana por cultivos, ambas durante la primavera de 2002. Para evaluar los efectos remotos, se analiza el comportamiento de diferentes variables hidroclimáticas en diferentes regiones de Argentina y de Sudamérica donde no se realizaron cambios de cobertura. Los resultados indican que la expansión de cultivos sobre vegetación nativa modifica las propiedades biofísicas alterando en tiempo y espacio el comportamiento de variables hidroclimáticas. En particular, se observan cambios en los balances hidrológicos de diferentes regiones y también, cambios importantes en la circulación de los vientos.Eje: Ciencias Hidrológicas y Criósfera.Facultad de Ciencias Astronómicas y Geofísica

Efectos remotos del cambio de uso de suelo en el clima del sudeste de Sudamérica

Grandes áreas de Sudamérica están sufriendo cambios en el uso del suelo, en general, de origen antropogénico. El aumento de la precipitación en regiones áridas combinado con los avances tecnológicos incrementó la disponibilidad de tierras productivas. Esto derivó en un proceso de expansión de la frontera agrícola sobre zonas con vegetación natural. Desde el punto de vista hidroclimático, el reemplazo de vegetación natural por cultivos altera la partición de agua y energía en superficie. Al cambiar la vegetación se modifican propiedades biofísicas relacionadas a la misma tales como albedo, resistencia estomática o rugosidad de superficie. Este cambio en las propiedades produce efectos sobre las variables hidroclimáticas tanto locales como remotos. Este trabajo tiene por objetivo evaluar los efectos remotos de los cambios de cobertura del suelo mediante simulaciones con el modelo climático WRF (Weather Research and Forecasting). Se realizaron simulaciones asumiendo dos escenarios de cobertura/uso de suelo. Una simulación de control donde se simula el comportamiento del clima sin alterar la cobertura vegetal y una simulación donde se reemplaza bosques, pasturas y sabana por cultivos, ambas durante la primavera de 2002. Para evaluar los efectos remotos, se analiza el comportamiento de diferentes variables hidroclimáticas en diferentes regiones de Argentina y de Sudamérica donde no se realizaron cambios de cobertura. Los resultados indican que la expansión de cultivos sobre vegetación nativa modifica las propiedades biofísicas alterando en tiempo y espacio el comportamiento de variables hidroclimáticas. En particular, se observan cambios en los balances hidrológicos de diferentes regiones y también, cambios importantes en la circulación de los vientos.Eje: Ciencias Hidrológicas y Criósfera.Facultad de Ciencias Astronómicas y Geofísica

The imprint of strong-storm tracks on winter weather in North America

Northern Hemisphere winter storm tracks and their relation to winter weather are investigated using CFSR data. Storm tracks are described by isentropic PV maxima within a Lagrangian framework; these correspond well with those described in previous studies. Our diagnostics focus on strong-storm tracks, which are comprised of storms that achieve a maximum PV exceeding the mean value by one standard deviation. Large increases in diabatic heating related to deep convection occur where the storm tracks are most intense. The cyclogenesis pattern shows that strong storms generally develop on the upstream sectors of the tracks. Intensification happens towards the eastern North Pacific and all across the North Atlantic Ocean, where enhanced storm track-related weather is found. In this study, the relation of storm tracks to near-surface winds and precipitation is evaluated. The largest increases in storm track-related winds are found where strong storms tend to develop and intensify, while storm precipitation is enhanced in areas where the storm tracks have the highest intensity. Strong storms represent about 16% of all storms but contribute 30-50% of the storm precipitation in the storm track regions. Both strong-storm related winds and precipitation are prone to cause storm-related losses in the eastern US and North American coasts. Over the oceans, maritime operations are expected to be most vulnerable to damage offshore of the US coasts. Despite making up a small fraction of all storms, the strong-storm tracks have a significant imprint on winter weather in North America potentially leading to structural and economic loss

GCIP water and energy budget synthesis (WEBS)

As part of the World Climate Research Program\u27s (WCRPs) Global Energy and Water-Cycle Experiment (GEWEX) Continental-scale International Project (GCIP), a preliminary water and energy budget synthesis (WEBS) was developed for the period 1996–1999 from the “best available” observations and models. Besides this summary paper, a companion CD-ROM with more extensive discussion, figures, tables, and raw data is available to the interested researcher from the GEWEX project office, the GAPP project office, or the first author. An updated online version of the CD-ROM is also available at http://ecpc.ucsd.edu/gcip/webs.htm/. Observations cannot adequately characterize or “close” budgets since too many fundamental processes are missing. Models that properly represent the many complicated atmospheric and near-surface interactions are also required. This preliminary synthesis therefore included a representative global general circulation model, regional climate model, and a macroscale hydrologic model as well as a global reanalysis and a regional analysis. By the qualitative agreement among the models and available observations, it did appear that we now qualitatively understand water and energy budgets of the Mississippi River Basin. However, there is still much quantitative uncertainty. In that regard, there did appear to be a clear advantage to using a regional analysis over a global analysis or a regional simulation over a global simulation to describe the Mississippi River Basin water and energy budgets. There also appeared to be some advantage to using a macroscale hydrologic model for at least the surface water budgets

Global Meteorological Drought: A Synthesis of Current Understanding with a Focus on SST Drivers of Precipitation Deficits

Drought affects virtually every region of the world, and potential shifts in its character in a changing climate are a major concern. This article presents a synthesis of current understanding of meteorological drought, with a focus on the large-scale controls on precipitation afforded by sea surface temperature (SST) anomalies, land surface feedbacks, and radiative forcings. The synthesis is primarily based on regionally focused articles submitted to the Global Drought Information System (GDIS) collection together with new results from a suite of atmospheric general circulation model experiments intended to integrate those studies into a coherent view of drought worldwide. On interannual time scales, the preeminence of ENSO as a driver of meteorological drought throughout much of the Americas, eastern Asia, Australia, and theMaritime Continent is now well established, whereas in other regions (e.g., Europe, Africa, and India), the response to ENSO is more ephemeral or nonexistent. Northern Eurasia, central Europe, and central and eastern Canada stand out as regions with few SST-forcedimpacts on precipitation oninterannual time scales.Decadal changesin SST appear to be a major factor in the occurrence of long-term drought, as highlighted by apparent impacts on precipitation of the late 1990s ‘‘climate shifts’’ in the Pacific and Atlantic SST. Key remaining research challenges include (i) better quantification of unforced and forced atmospheric variability as well as land–atmosphere feedbacks, (ii) better understanding of the physical basis for the leading modes of climate variability and their predictability, and (iii) quantification of the relative contributions of internal decadal SST variability and forced climate change to long-term drought

An analysis of the warm-season diurnal cycle over the continental united states and northern Mexico in general circulation models

The diurnal cycle of warm-season rainfall over the continental United States and northern Mexico is analyzed in three global atmospheric general circulation models (AGCMs) from NCEP, GFDL, and the NASA Global Modeling Assimilation Office (GMAO). The results for each model are based on an ensemble of five summer simulations forced with climatological sea surface temperatures. Although the overall patterns of time-mean (summer) rainfall and low-level winds are reasonably well simulated, all three models exhibit substantial regional deficiencies that appear to be related to problems with the diurnal cycle. Especially prominent are the discrepancies in the diurnal cycle of precipitation over the eastern slopes of the Rocky Mountains and adjacent Great Plains, including the failure to adequately capture the observed nocturnal peak. Moreover, the observed late afternoon-early evening eastward propagation of convection from the mountains into the Great Plains is not adequately simulated, contributing to the deficiencies in the diurnal cycle in the Great Plains. In the southeast United States, the models show a general tendency to rain in the early afternoon - several hours earlier than observed. Over the North American monsoon region in the southwest United States and northern Mexico, the phase of the broadscale diurnal convection appears to be reasonably well simulated, though the coarse resolution of the runs precludes the simulation of key regional phenomena. All three models employ deep convection schemes that assume fundamentally the same buoyancy closure based on simplified versions of the Arakawa-Schubert scheme. Nevertheless, substantial differences between the models in the diurnal cycle of convection highlight the important differences in their implementations and interactions with the boundary layer scheme. An analysis of local diurnal variations of convective available potential energy (CAPE) shows an overall tendency for an afternoon peak - a feature well simulated by the models. The simulated diurnal cycle of rainfall is in phase with the local CAPE variation over the southeast United States and the Rocky Mountains where the local surface boundary forcing is important in regulating the diurnal cycle of convection. On the other hand, the simulated diurnal cycle of rainfall tends to be too strongly tied to CAPE over the Great Plains, where the observed precipitation and CAPE are out of phase, implying that free atmospheric large-scale forcing plays a more important role than surface heat fluxes in initiating or inhibiting convection.open383

North American monsoon and convectively coupled equatorial waves simulated by IPCC AR4 coupled GCMs

This study evaluates the fidelity of North American monsoon and associated intraseasonal variability in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) coupled general circulation models (CGCMs). Twenty years of monthly precipitation data from each of the 22 models' twentieth-century climate simulations, together with the available daily precipitation data from 12 of them, are analyzed and compared with Global Precipitation Climatology Project (GPCP) monthly and daily precipitation. The authors focus on the seasonal cycle and horizontal pattern of monsoon precipitation in conjunction with the two dominant convectively coupled equatorial wave modes: the eastward-propagating Madden-Julian oscillation (MJO) and the westward-propagating easterly waves. The results show that the IPCC AR4 CGCMs have significant problems and display a wide range of skill in simulating the North American monsoon and associated intraseasonal variability. Most of the models reproduce the monsoon rainbelt, extending from southeast to northwest, and its gradual northward shift in early summer, but overestimate the precipitation over the core monsoon region throughout the seasonal cycle and fail to reproduce the monsoon retreat in the fall. Additionally, most models simulate good westward propagation of the easterly waves, but relatively poor eastward propagation of the MJO and overly weak variances for both the easterly waves and the MJO. There is a tendency for models without undiluted updrafts in their deep convection scheme to produce better MJO propagation.open221

Domain choice in an experimental nested modeling prediction system for South America

The purposes of this paper are to evaluate the new version of the regional model, RegCM3, over South America for two test seasons, and to select a domain for use in an experimental nested prediction system, which incorporates RegCM3 and the European Community-Hamburg (ECHAM) general circulation model (GCM). To evaluate RegCM3, control experiments were completed with RegCM3 driven by both the NCEP/NCAR Reanalysis (NNRP) and ECHAM, using a small control domain (D-CTRL) and integration periods of January–March 1983 (El Niño) and January–March 1985 (La Niña). The new version of the regional model captures the primary circulation and rainfall differences between the two years over tropical and subtropical South America. Both the NNRP-driven and ECHAM-driven RegCM3 improve the simulation of the Atlantic intertropical convergence zone (ITCZ) compared to the GCM. However, there are some simulation errors. Irrespective of the driving fields, weak northeasterlies associated with reduced precipitation are observed over the Amazon. The simulation of the South Atlantic convergence zone is poor due to errors in the boundary condition forcing which appear to be amplified by the regional model. To select a domain for use in an experimental prediction system, sensitivity tests were performed for three domains, each of which includes important regional features and processes of the climate system. The domain sensitivity experiments were designed to determine how domain size and the location of the GCM boundary forcing affect the regional circulation, moisture transport, and rainfall in two years with different large scale conditions. First, the control domain was extended southward to include the exit region of the Andes low level jet (D-LLJ), then eastward to include the South Atlantic subtropical high (D-ATL), and finally westward to include the subsidence region of the South Pacific subtropical high and to permit the regional model more freedom to respond to the increased resolution of the Andes Mountains (D-PAC). In order to quantify differences between the domain experiments, measures of bias, root mean square error, and the spatial correlation pattern were calculated between the model results and the observed data for the seasonal average fields. The results show the GCM driving fields have remarkable control over the RegCM3 simulations. Although no single domain clearly outperforms the others in both seasons, the control domain, D-CTRL, compares most favorably with observations. Over the ITCZ region, the simulations were improved by including a large portion of the South Atlantic subtropical high (D-ATL). The methodology presented here provides a quantitative basis for evaluating domain choice in future studies