Soil erosion by water is one of the most important land degradation processes in Mediterranean environments. This process is strongly linked to problems of flooding and channel management. This art...

Erosion, flooding and channel management in Mediterranean environments of southern Europe:

FLOW phenomena that link the stratosphere and the troposphere are a key component of mid-latitude weather systems1, and can influence substantially the distribution of atmospheric gases and aerosols2,3. Little is known, however, about the detailed structure of these features. Here we combine satellite measurements with data from a weather prediction model to show that fine-scale structure can be resolved in intrusions of stratospheric air into the troposphere. We observe intrusions that develop into elongated (about 2,000km) and slender (about 200km) streamers which break up into a train of vortex-like disturbances while the streamer's tip splits and/or rolls up. The appearance of these structures might influence the daily development of weather systems, and will induce local, irreversible isentropic mixing of stratospheric air with the troposphere, possibly accounting for a substantial portion of the net stratosphere-to-troposphere exchange.

Structure of stratospheric intrusions into the troposphere

Evidence is presented pointing to the existence of rich and coherent subsynoptic and mesoscale flow features at tropopause levels. These features are related to, and evolve from, the classical V-shaped intrusions of stratospheric air down to tropospheric elevations. It is shown that intrusions can develop into elongated (∼2000–3000 km) and slender (∼200 km) streamers, and that thereafter such a streamer can roll up to form a train of stalactite-shaped vortex subentities with an accompanying substantial thinning of the intervening filament. In addition there are indications that the vortices themselves can develop a spirallike interior structure of interleaved stratospheric and tropospheric air. These inferences are based upon two independent but complementary sources: analysis of the potential vorticity distribution on tropopause transcending isentropic surfaces derived from the analysis fields of the European Centre for Medium-Range Weather Forecasts either directly, or indirectly using a contour advection technique; and imagery from the water vapor channel of the European Space Agency Meteosat 4 satellite. Streamers were observed to occur with a frequency of approximately one per week over central and southern Europe during the winter of 1991–1992. The fragmentation is linked to the instability or self-development of a filament of enhanced potential vorticity and it can modify or instigate surface weather systems. Moreover, by inducing a substantial and rapid enlargement of the intrusion's surface area it greatly enhances the potential for local irreversible mixing of stratospheric and tropospheric air.

Fragmentation of stratospheric intrusions

https://digital.csic.es/bitstream/10261/78823/1/Garc%c3%adaRuiz_Erosion%20in%20Mediterranean%20landscapes_Geomorphology2013.pdf

Erosion in Mediterranean landscapes: Changes and future challenges

. Recent evidences of the impact of persistent modes of regional climate variability, coupled with the intensification of human activities, have led hydrologists to study flood regime without applying the hypothesis of stationarity. In this study, a framework for flood frequency analysis is developed on the basis of a tool that enables us to address the modelling of non-stationary time series, namely, the "generalized additive models for location, scale and shape" (GAMLSS). Two approaches to non-stationary modelling in GAMLSS were applied to the annual maximum flood records of 20 continental Spanish rivers. The results of the first approach, in which the parameters of the selected distributions were modelled as a function of time only, show the presence of clear non-stationarities in the flood regime. In a second approach, the parameters of the flood distributions are modelled as functions of climate indices (Arctic Oscillation, North Atlantic Oscillation, Mediterranean Oscillation and the Western Mediterranean Oscillation) and a reservoir index that is proposed in this paper. The results when incorporating external covariates in the study highlight the important role of interannual variability in low-frequency climate forcings when modelling the flood regime in continental Spanish rivers. Also, with this approach it is possible to properly introduce the impact on the flood regime of intensified reservoir regulation strategies. The inclusion of external covariates permits the use of these models as predictive tools. Finally, the application of non-stationary analysis shows that the differences between the non-stationary quantiles and their stationary equivalents may be important over long periods of time.

/pdf/non-stationary-flood-frequency-analysis-in-continental-36f6t10615.pdf

Non-stationary flood frequency analysis in continental Spanish rivers, using climate and reservoir indices as external covariates

The nature of the rainfall rate R(t) as a transient random process is presented in the context of microwave attenuation and fade dynamics. Using 49 years of data recorded in Barcelona, the spectral densities of energy and power and the autocorrelation function are presented, together with their analytical model. Examples for specific rain events are also presented. Several regimes covering a wide range of intensities have been investigated, and it is found that the spectral densities all exhibit a similar form which is independent of the average regime of R considered. This leads to a mean frequency and a spectral width which appear to be universal constants and independent of the regime. Similar features are found for the autocorrelation function. The mathematical models and numerical values found are compared to the Maseng-Bakken model (1981) proposed in earlier work of fade dynamics, and the agreement is good. The method is proposed for modeling the denormalized autocorrelation, and hence the spectrum, using only the measured average rainfall rate during a period of interest. Finally, the average number of crossings per unit of time is modeled and compared to the experimental results, and the agreement is satisfactory. >

Spectral analysis of 49 years of rainfall rate and relation to fade dynamics

An investigation into the effect of the integration time T on the rain rate distribution P(R) is presented using a rainfall rate data bank of 49 years recorded at Barcelona (CCIR - Zone L), using a rapid response Jardi rain rate gauge. T extends from 1 to 60 min and P(R) extends to less than 10-3 %. The relation between the various T-distributions P(RT) is presented as well as the values of RT and R1 which give the same probability. The ratio RT/R1 and the potential expression R1 = aRbT are studied. Comparison with recent results from Canada confirms both the numerical value presented and the climatic dependence of the equi-probable ratio RT/R1.

Influence of rain gauge integration time on the rain rate statistics used in microwave communications

Using a 49 year point rainfall rate data bank the authors summarise the analysis and statistical modelling of the interval of time between exceedances of rain thresholds R. The study distinguishes between successive exceedances occurring within the same rain event (intra exceedances I/sub a/), and those occurring at different rain events (inter exceedances I/sub e/). The global study of both return periods or intervals I/sub i/ is also presented. The study is applied to a 49 year point rain rate data bank. It is found that the annual inter and intra intervals are well modelled by log normal distributions, and each set clusters to a single distribution when the intervals are normalized to their annual averages I/sub a/, I/sub e/.

Long term statistics of precipitation rate return periods in the context of microwave communications

The main meteorological features of catastrophic rainfall events in Catalonia are described Data come from several sources listed in the text Surface and upper air synoptic and some subsynoptic conditions under which these events occur are described Two kinds of events are identified, depending on the amount of forced lift required to release potential instability: Type A events, which take place on the coastal area when the forcing due to littoral and prelittoral hills is enough, and type B events require a large forced lift and occur near the Pyrenees Local topographical and mesoscale meteorological conditions turn out to have a relevant role in connection with such events

Meteorological Factors Associated with Floods in the North-Eastern Part of the Iberian Peninsula

The common quail (Coturnix coturnix) is one of the few species in which mate-switching (when different pair bonds are established within a single breeding attempt), has been recorded. In this study, we report the characteristics of pair bonds (description, number of males per female and duration) by monitoring a wild population of common quail (28 females and 49 males) by radiotracking. 57% of the females studied (n = 14) showed mate-switching, whereas 22% of the males were serially polygynous, successively forming pairs with a series of females. The fitness of females with mate-switching, measured in terms of clutch size and hatching success, did not differ from that of females bonded with one male. The analysis of paternity in three families by multilocus DNA fingerprinting revealed genetic polygamy in two of the nests studied. A male sired offspring with two females, and we obtained genetic evidence for intraspecific brood parasitism. We discuss how these behavioural and ecological observations may relate to the particular mating system of the common quail.

M. Puigcerver

Papers

Spectral analysis of 49 years of rainfall rate and relation to fade dynamics

Influence of rain gauge integration time on the rain rate statistics used in microwave communications

Long term statistics of precipitation rate return periods in the context of microwave communications

Meteorological Factors Associated with Floods in the North-Eastern Part of the Iberian Peninsula

Pair Bonding and Multiple Paternity in the Polygamous Common Quail Coturnix coturnix