A Note on Soil Moisture Memory and Interactions with Surface Climate for Different Vegetation Types in the La Plata Basin

This work examines the evolution of soil moisture initialization biases and their effects on seasonal forecasts depending on the season and vegetation type for a regional model over the La Plata basin in South America. WRF–Noah simulations covering multiple cases during a 2-yr period are designed to emphasize the conceptual nature of the simulations at the expense of the statistical significance of the results. Analysis of the surface climate shows that the seasonal predictive skill is higher when the model is initialized during the wet season and the initial soil moisture differences are small. Large soil moisture biases introduce large surface temperature biases, particularly for savanna, grassland, and cropland vegetation covers at any time of the year, thus introducing uncertainty in the surface climate. Regions with evergreen broadleaf forest have roots that extend to the deep layer whose moisture content affects the surface temperature through changes in the partitioning of the surface fluxes. The uncertainties of monthly maximum temperature can reach several degrees Celsius during the dry season in cases when 1) the soil is much wetter in the reanalysis than in the WRF–Noah equilibrium soil moisture and 2) the memory of the initial value is long because of scarce rainfall and low temperatures. This study suggests that responses of the atmosphere to soil moisture initialization depend on how the initial wet and dry conditions are defined, stressing the need to take into account the characteristics of a particular region and season when defining soil moisture initialization experiments.Fil: Sörensson, Anna. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmosfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmosfera; ArgentinaFil: Berbery, Ernesto Hugo. University of Maryland; Estados Unido

Estudio de los efectos de la orografía sobre la circulación atmosférica sinóptico-planetaria, en casos marcadamente barotrópicos y baroclínicos

En esta tesis se estudian las características más sobresalientes de la circulación general de la atmósfera en el hemisferio sur en la que hace a la dinámica de los efectos orográficos, particularizando en los fenómenos de naturaleza marcadamente barotrópica por un lado y marcadamente baroclínica por el otro. Para ello se desarrolla un modelo barotrópico con el esquema de Arakawa y Lamb, el cual tiene la capacidad de conservar la energía total y la enstrofía potencial del sistema y es estable aún en presencia de pendientes abruptas del terreno . El objeto de desarrallar este madelo es estudiar el efecto dinámico de la Cordillera de los Andes en dos fenómenos de estructura marcadamente barotrópica: las ondas estacianarias y los anticiclones de bloqueo. Se modifica también un madelo baroclínico en ecuaciones primitivas y coordenadas esféricas con la coordenada σ en la vertical: se ha extendido el recinto de integración a un hemisferio, incluyéndosele un filtro de Fourier para las altas latitudes, se le han modificado las condiciones de borde y se le ha incorporado la difusión horizontal y vertical. En este modelo, de 5 niveles en la vertical, se ha incorporado a la topografía como regiones de aire estanco y es empleado para la simulación de desarrollos ciclogenéticos. Las experiencias realizadas con estos modelos muestran que para lograr una correcta representación de los fenómenos es necesario emplear una orografía realzada (conocida como "envelope orography"). Las simulaciones de las ondas estacionarias indican que la orografía produce campos semejantes a los observados al sur de 45º S para invierno y al sur de 35º S para verano. Esta comparación es desde el punto de vista espectral. Regionalmente, los campos simulados coinciden cualitativamente con los observados entre 110/120º O y 10º E y al norte de 70º S para ambas estaciones, aunque la coincidencia es más pronunciada para el verano. De todos los continentes, América del Sur (con la cordillera de los Andes) es el más importante para definir la configuración de los campos simulados. La Antártida, entre 50 y 70º S también hace un aporte a las ondas. Las simulacianes de bloqueos muastran que el mecanismo de Kalnay-Rivas y Merkine (1981) mantiene su validez al ser extendido a un hemisferio con geometría esférica y con una topografía realiata. Este mecanismo, más que la iniciación del bloqueo, explicaría su intensificación y mantenimiento. La ciclogénesis a sotavento de los Andes resulta más profunda y más al norte que en el caso de ausencia de orografía. La orografía tendría el efecto de aumentar principalmente la acción ciclogenética del término de la advección de espesores en la ecuación del desarrollo, debido al bloqueo del flujo en las capas bajas.Fil: Berbery, Ernesto Hugo. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Regional model simulations of the 2008 drought in southern South America using a consistent set of land surface properties

This work discusses the land surface-atmosphere interactions during the severe drought that took place in 2008 in southern South America. The drought was among the most severe in the last fifty years both in terms of intensity and extent. Once precipitation returned to normal values, it took about two months for the soil moisture content and vegetation to recover. The land surface effects were examined by contrasting long term simulations using a consistent set of satellite-derived annually varying land surface biophysical properties against simulations using the conventional land cover types in the coupled system Weather Research and Forecasting Model/Noah Land Surface Model (WRF/Noah). The new land cover data set is based on ecosystem functional properties that capture changes in vegetation status due to climate anomalies and land use changes.The results show that the use of realistic information of vegetation states enhances the model performance reducing the precipitation biases over the drought region as well as over areas of excessive precipitation. The precipitation bias reductions are traced back to the corresponding changes in greenness fraction, leaf area index, stomatal resistance and surface roughness. The simulation of temperature shows a larger bias over the domain´s central part, which is attributable to a doubling of the stomatal resistance that reduces the evapotranspiration rate and leads to a temperature increase. However, the temperature pattern using the novel data set shows improvements towards the eastern part of the domain. The overall results suggest that an improved representation of the surface processes contributes to the predictability of the system.Fil: Müller, Omar Vicente. Universidad Nacional del Litoral; ArgentinaFil: Berbery, Ernesto Hugo. University of Maryland; Estados UnidosFil: Alcaraz Segura, Domingo. Universidad de Granada; EspañaFil: Ek, Michael B.. National Oceanic And Atmospheric Administration

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

The International Summer School on Land Cover Change and Hydroclimate of the La Plata Basin

The La Plata Basin (LPB) in southern South America has been subject to land cover and land use changes (LCLUCs) since colonial times and with an accelerated rate in the last decades and over extensive areas. The work of Ameghino even suggested that there were relations between those land use changes and the frequency of droughts and floods in the region. Despite this early knowledge, not much is known of the potential impacts of LCLUC on the hydroclimate of the La Plata basin. Besides, over the last century much of the La Plata Basin has had a reported increase in precipitation and heavy rains, and these changes along with an increase in population growth - have resulted in more adverse effects from flooding. To draw attention to these issues, during two weeks in November 2009 the International Summer School on Land Cover Change and Hydroclimate of the La Plata Basin was organized at the grounds of the Itaip Hydropower Plant in Brazil. The school was the result of the combination of interests between the La Plata Basin Regional Hydroclimate Project, the Inter-American Institute for Global Change Research (IAI), and the International Hydroinformatics Center (IHC) in Itaip . LPB is an umbrella project endorsed by the Global Energy and Water Cycle Experiment (GEWEX) and the Climate Prediction and Variability (CLIVAR), both of the World Climate Research Programme (WCRP). LPB has made a priority to train young scientists and promote interdisciplinary collaborations in areas related to Climate, Hydrology, Ecology and Agriculture. The IAI, with a similar agenda, was a natural partner to develop this Summer School, which in turn benefited from Itaipu s interest in relating with the scientific community of neighboring countries. The choice of location (Itaip Technological Park) was made so that participants could relate research usually done at academic institutions to applications and operations at one of the largest hydropower plants in the world. The school was attended by 45 advanced graduate students and young scientists with different backgrounds from seven countries, including less technically advanced ones in the region.

Assessing Hydrologic Cycle Dynamics Using High-Resolution Satellite Imagery

CISESS Summer Internship ProgramThis study presents an investigation of the hydrologic cycle over a two-decade span (2000 – 2020) using high-resolution satellite products, in-situ measurements, and modeled data. The scope of this work encompasses an examination of the accuracy of satellite-based estimates in calculating the water budget, both on a global scale and within the Mississippi River Basin. The global assessment considers land areas spanning latitudes 90°S to 90°N, while the Mississippi River Basin includes the Lower Mississippi, Arkansas-Red, Missouri, Ohio, and North Central sub-basins. We utilize the IMERG version-6 and PERSIANN precipitation datasets to quantify water inflow over these regions. Correspondingly, water outflow estimates incorporate the GLEAM product for evaporation, G-RUN and ERA5 datasets for runoff, and SMOPS and SMAP estimates for changes in soil moisture. The assessment of water budget changes assesses the difference between Inflow (Precipitation) and Outflow (Runoff, Evaporation, Δ Soil Moisture) components. Our findings reveal discernible discrepancies in the global water budget over an annual cycle, indicating the presence of water “leaks”. These leaks, warranting further investigation, may be attributed to factors such as snow, ice, and groundwater dynamics, which fall outside the scope of this study. On a smaller basin scale, the closure of the water budget is estimated to fall within the combined products’ uncertainty. This provides additional validation for the suspected factors contributing to the global scale “leak.” Analyzing the annual water cycle components, we find the inherent variability and uncertainty associated with satellite-derived products. The study advances comprehension of hydrologic processes and underscores the imperative for enhanced accuracy in satellite-based measurements. Notably, our findings accentuate the importance of a closed water budget as a defining criterion for the accuracy of these satellite-derived products.Cooperative Institute for Satellite Earth System Studies (CISESS

Land use and land cover changes and their impacts on hydroclimate, ecosystems and society

This chapter presents recent advances in the understanding of the effect of land cover/land use changes on the hydrologic cycle, and identifies current gaps in the knowledge needed for useful decision-making and water resource management. Research achievements within a framework of Earth System Models (ESM) are introduced, and research needs and future challenges are identified. Land surface provides the lower boundary condition to the atmosphere over continents by controlling the fluxes of momentum, heat, water, and materials such as carbon. In turn, land surface conditions are substantially influenced by atmospheric conditions on various temporal scales. As such, a land-atmosphere coupled system is established through biogeochemical feedbacks. Current land surface models exhibit a wide variety of responses to the same forcings, suggesting the need for increased research at the land-atmosphere interface. Indeed, all Earth System Models require the inclusion and validation of the processes that pertain to the biogeochemical feedbacks. Anthropogenic activities that result in land use and land cover changes affect the land surface characteristics and consequently the land-atmosphere feedbacks and coupling strength. Therefore, human activities play a role in the land-atmosphere coupling system, and thus, in the climate system. Water is essential to societal needs that require the construction of reservoirs, extraction of ground water, irrigation, changes in land use, urbanization among many other influences. The extent and sustainability of those interferences in the natural system remains to be assessed at global scale

The agricultural expansion in South America's Dry Chaco: regional hydroclimate effects

<jats:p>Abstract. The Gran Chaco ecoregion is South America's largest remaining continuous stretch of dry forest. It has experienced intensive deforestation, mainly in the western part known as the Dry Chaco, resulting in the highest rate of dry-forest loss globally between 2000 and 2012. The replacement of natural vegetation with other land uses modifies the surface's biophysical properties, affecting heat and water fluxes and modifying the regional climate. This study examines land use and land cover changes (LULCCs) in the Dry Chaco from 2001 to 2015 and their effects on local and non-local climate and explores the potential impacts of future agricultural expansion in the region. To this end, Weather Research and Forecasting (WRF) model simulations are performed for two scenarios: the first one evaluates the observed land cover changes between 2001 and 2015 that covered 8 % of the total area of the Dry Chaco; the second scenario assumes an intensive agricultural expansion within the Dry Chaco. In both scenarios, deforestation processes lead to decreases in leaf area index (LAI), reductions in stomatal resistance, and increases in albedo, thus reducing the net surface radiation and, correspondingly, decreasing the turbulent fluxes, suggesting a decline in available energy in the boundary layer. The result is an overall weakening of the water cycle in the Dry Chaco and, most prominently, implying a reduction in precipitation. A feedback loop develops since dry soil absorbs significantly less solar radiation than moist soil. Finally, the simulations suggest that the Dry Chaco will intensify its aridity, extending drier and hotter conditions into the Humid Chaco. </jats:p&gt

Characteristics of droughts in Argentina's core crop region

This study advances the understanding and impacts of dry episodes on wheat, corn, and soybean yields over Argentina's core crop region. The production of these major crops is intense and is the main contribution to the country's gross domestic product. Our analysis focuses on the droughts' properties, including their magnitude, frequency at different timescales, duration, and severity. We analyzed 40 years of precipitation and soil moisture anomalies and their corresponding nonparametric standardized indices at timescales of 1, 3, and 6 months. The climate variables were complemented with 40 years of the crops' yield data. The percentage of drought occurrence in northeastern Argentina ranges between 12 % and 18 %, with the larger values located towards the core crop region's eastern–northeastern sector. An analysis of drought duration suggests that most cases tend to occur for periods shorter than 3 months, while a few can extend up to 1 year, and even fewer can last longer. More importantly, regardless of the duration, droughts have larger impacts during the crops' critical growth period. Corn and soybean have their critical growth periods during summer and are more sensitive to precipitation and soil moisture deficits than wheat, which has its critical growth period during spring. Quantification of the relation between the droughts' indicators during the crops' critical periods and detrended annual crop yields was performed. Large drought severity values during the crop-sensitive months result in significant crop yield losses. Results suggest that shorter-scale indicators during sensitive periods are more appropriate for predicting crop yield losses than the longer-scale indicators. This new approach can be helpful for regional decision-making systems that support planning by water managers and agricultural stakeholders.Fil: Sgroi, Leandro Carlos. Universidad Nacional del Litoral. Facultad de Ingenieria y Ciencias Hidricas. Centro de Estudios de Variabilidad y Cambio Climatico.; ArgentinaFil: Lovino, Miguel Angel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentina. Universidad Nacional del Litoral. Facultad de Ingenieria y Ciencias Hidricas. Centro de Estudios de Variabilidad y Cambio Climatico.; ArgentinaFil: Berbery, Ernesto Hugo. University of Maryland; Estados UnidosFil: Muller, Gabriela Viviana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentina. Universidad Nacional del Litoral. Facultad de Ingenieria y Ciencias Hidricas. Centro de Estudios de Variabilidad y Cambio Climatico.; Argentin

An evaluation of the ETA model during SALLJEX

The South American Low Level Jet Experiment took place during austral summer 2002-2003 and provided unique data sets to evaluate the veracity of models to represent atmospheric motions in the vicinity of the central Andes. The experiment focused on the wind maximum east of the Andes (SALLJ, South American Low Level Jet) and its role to transport moisture that feeds meso-scale convective systems over the La Plata basin. Such systems, as well as the SALLJ, exhibited a pronounced diurnal oscillation during SALLJEX, with maximum values at night. Special radiosonde observations were collected during this experiment at 06 and 18Z, when the diurnal cycle displays maximum amplitude. Such observations were not incorporated in the operational analyses and thus provide a unique data set to test the ability of models to reproduce the amplitude of diurnal oscillations in this region. In particular, the ETA model is yet lacking a comprehensive evaluation of its biases in this region of highly variable and steep orography. At the University of Maryland, Collini and Berbery integrated and archived model ETA model runs at 80 and 22km resolution, eight times a day, over two regions of different extent, in real time. These runs, when compared against radiosonde measurements of winds, moisture and temperature profiles, allow to identify model biases related to resolution, boundary conditions, and model description of the diurnal cycle. The presentation explores the ability of the model to regionally downscale large scale features and its potential use for regional climate assessments based on its performance over this particular season of enhanced observations. Preliminary results indicate that benefits of the higher resolution to describe the three-dimensional structure of the SALLJ are only apparent close to the Andes, with runs at both resolutions underestimating the amplitude of the diurnal cycle at low levels. Furthermore, the ETA runs are compared to identify dependence of representation of the diurnal cycle on resolution.Pages: 51-5