Annual drought flow and groundwater storage trends in the eastern half of the United States during the past two-third century

Low flow drainage from a river system, in the absence of precipitation or snowmelt, derives directly from the water stored in the upstream aquifers in the basin; therefore, observations of the trends of the annual lowest flows can serve to deduce quantitative estimates of the evolution of the basin-scale groundwater storage over the period of the streamflow record. Application of this method has allowed for the first time to determine the magnitudes of the trends in groundwater storage over the past two-third century in some 41 large prototypical basins in the United States east of the Rocky Mountains. It was found that during the period 1940–2007 groundwater storage has generally been increasing in most areas; these positive trends were especially pronounced in the Ohio and Upper Mississippi Water Resources Regions, but they were weaker in most other regions. Notable exceptions are the northern New England and especially the South Atlantic-Gulf regions, which saw prolonged declines in groundwater levels over this nearly 70-year long period. These observed long-term trends are generally in agreement with previous studies regarding trends of other components of the water cycle, such as precipitation, total runoff, and terrestrial evaporation. Over the most recent 20 years, from 1988 through 2007, except for the Ohio and the Souris-Red-Rainy regions, most regions have experienced declining average groundwater levels to varying degrees, with maximal values of the order of ?0.2 mm a^?1.     

Aurorae during the so-called Spörer minimum

It is shown that such data that exist on auroral observations in the period between 1450 and 1550 do not provide the conclusive evidence that some authors have claimed for the so-called ‘Spörer minimum’ in solar activity in this time.     

Similarity of scalars under stable conditions

The question whether two different scalars have the same behaviour in the surface layer under stable conditions is investigated. Similarity of two scalars is defined in terms of the equality of their corresponding dimensionless Monin-Obukhov similarity functions. Previous theoretical and experimental results concerning the issue are briefly reviewed: they are found to be contradictory. An analytical derivation of the square of the correlation coefficient between two scalars is obtained based on the correlation structure of the turbulent dissipation functions for stable conditions, when it can be assumed that the divergence of the vertical transport of scalar variance/covariance is negligible. The resulting expression elucidates some earlier conflicting results, and helps to establish the equality of the similarity functions for all scalars in the stable surface layer. A statistical analysis in the time domain is also performed using temperature and humidity turbulence data measured in nocturnal stable conditions during FIFE-89. Our results, both from the analytical derivation and the statistical analysis of turbulence data, confirm that under validity of the Monin-Obukhov similarity theory assumptions, the corresponding similarity functions for temperature and humidity are equal to within the statistical uncertainty of the measurements. An important consequence is that the eddy diffusivities of temperature and humidity are also equal.Now at SIMEPAR — Sistema Meteorológico do Paraná and UFPR — Universidade Federal do Paraná, Caixa Postal 318 CEP 80001-970, Curitiba PR Brazil.     

The extent of the unstable Monin-Obukhov layer for temperature and humidity above complex hilly grassland

Potential temperature, specific humidity and wind profiles measured by radiosondes under unstable but windy conditions during FIFE in northeastern Kansas were analyzed within the framework of Monin-Obukhov similarity. Around 86% of these profiles were found to have a height range over which the similarity, formulated in terms of the Businger-Dyer functions, is valid and for which the resulting surface fluxes are in good agreement with independent measurements at ground stations. When scaled with the surface roughness z ₀ = 1.05 m and the displacement height d ₀ = 26.9 m, for the potential temperature this height range was 45 (±31) (z – d ₀ )/z ₀ 104 (±54) and the comparison of the profile-derived surface fluxes with the independent measurements gave a correlation coefficient of r = 0.96. For the specific humidity these values are 42 (±29) (z – d ₀ )/z ₀ 96 (±38) and r = 0.94. In terms of the height of the bottom of the inversion H _i , in the morning hours the upper limit of (z – d ₀ ) in the Monin-Obukhov layer is approximately 0.3H _i , whereas for a fully developed ABL it is closer to 0.1H _i . Probably, as a result of the short sampling times and perhaps also of the small gradients under the windy conditions, the exact height range of validity was difficult to establish from a mere inspection of these profiles.     

A landslide database for Nicaragua: a tool for landslide-hazard management

A digital landslide database has been created for Nicaragua to provide the scientific community and national authorities with a tool for landslide-hazard assessment, emergency management, land-use planning, development of early warning systems, and the implementation of public and private policies. The Instituto Nicaragüense de Estudios Territoriales (Nicaraguan Geosciences Institute, INETER) began to compile the database in a digital format in 2003 as part of a comprehensive geographical information system for all types of geohazards. Landslide data have been obtained from a variety of sources including newspapers, technical reports, and landslide inventory maps. Inventory maps are largely based on fieldwork and aerial-photo analyses conducted by foreign development agencies in collaboration with INETER and other Nicaraguan institutions. This paper presents the sources of landslide information, introduces the database, and presents the first analyses of the data at national and regional scales. The database currently contains spatial information for about 17,000 landslides that occurred in mountainous and volcanic terrains. Information is mainly recorded for the period 1826–2003, with a large number of events that occurred during the disastrous Hurricane Mitch in October 1998. The oldest historical event is dated at 1570, some events are recorded as prehistorical, and other events have unknown dates of occurrence. Debris flows have been the most common types of landslides, both in volcanic and nonvolcanic areas, but other types, including rockfalls and slides, have also been identified. Intense and prolonged rainfall, often associated with tropical cyclones, and seismic and volcanic activity represent the most important landslide triggers. At a regional scale, the influence of topographic (elevation, slope angle, slope aspect) and lithologic parameters on the occurrence of landslides was analyzed. The development of the database allowed us to define the state of knowledge on landslide processes in the Nicaragua and to provide a preliminary identification of areas affected by landslides.