Ana A. Paulo

Drought concepts and characterization : Comparing drought indices applied at local and regional scales

Abstract A better knowledge of droughts is required to improve water management in water scarce areas. To appropriately cope with droughts, there is the need to adopt adequate concepts relative to droughts and water scarcity, to properly use drought indices that help characterize them, including ones relative to their severity, and to develop prediction tools that may be useful for early warning and that may reduce the respective lead time needed for appropriate response. In this paper, concepts relative to drought and other water scarcity regimes are discussed aiming both to distinguish droughts from other water scarcity regimes and to base a common understanding of the general characteristics of droughts as hazards and disasters. Three main drought indices are described aiming at appropriate characterization of droughts: the theory of runs, the Palmer Drought Severity Index (PDSI), and the Standardized Precipitation Index (SPI). Their application to local and regional droughts in the region of Alentejo, Portugal is presented focusing on the respective comparison and possible adequateness for drought monitoring. Results indicate some difficulties in using the theory of runs, particularly because it requires a subjective definition of thresholds in precipitation and does not provide a standardized classification of severity. Results show that draught characterization with the PDSI and the SPI produce coherent information, but the PDSI is limited relative to the SPI because it requires more data to perform a soil water balance while the SPI needs only precipitation data, which are more easily available in numerous locations. It is concluded that adopting the SPI is appropriate, but there is advantage in combining different indices to characterize droughts.

Analysis of Local and Regional Droughts in Southern Portugal using the Theory of Runs and the Standardised Precipitation Index

The identification, monitoring and characterisation of droughts are of great importance in water resources planning. Mediterranean regions are especially affected by droughts. A study on local and regional analyses of droughts is applied to a southern region of Portugal, Alentejo, aiming at contributing to a better understanding of droughts in that region. The theory of runs and the SPI are applied at a local level in order to identify local droughts. Two time scales were used, the 3-month and the 12-month period. Further, also using the same methods, drought characteristics are derived for the region by identifying the drought periods, computing the regional coverage of drought and the drought magnitude. Results show that both methods are appropriate to characterise local and regional droughts and that the SPI is very helpful in identifying initiation and ending of droughts.

Network Characteristics of Successful Performance in Association Football. A Study on the UEFA Champions League

The synergistic interaction between teammates in association football has properties that can be captured by Social Network Analysis (SNA). The analysis of networks formed by team players passing a ball in a match shows that team success is correlated with high network density and clustering coefficient, as well as with reduced network centralization. However, oversimplification needs to be avoided, as network metrics events associated with success should not be considered equally to those that are not. In the present study, we investigated whether network density, clustering coefficient and centralization can predict successful or unsuccessful team performance. We analyzed 12 games of the Group Stage of UEFA Champions League 2015/2016 Group C by using public records from TV broadcasts. Notational analyses were performed to categorize attacking sequences as successful or unsuccessful, and to collect data on the ball-passing networks. The network metrics were then computed. A hierarchical logistic-regression model was used to predict the successfulness of the offensive plays from network density, clustering coefficient and centralization, after controlling for the effect of total passes on successfulness of offensive plays. Results confirmed the independent effect of network metrics. Density, but not clustering coefficient or centralization, was a significant predictor of the successfulness of offensive plays. We found a negative relation between density and successfulness of offensive plays. However, reduced density was associated with a higher number of offensive plays, albeit mostly unsuccessful. Conversely, high density was associated with a lower number of successful offensive plays (SOPs), but also with overall fewer offensive plays and “ball possession losses” before the attacking team entered the finishing zone. Independent SNA of team performance is important to minimize the limitations of oversimplifying effective team synergies.

Co-adaptation of ball reception to the serve constrains outcomes in elite competitive volleyball:

How impactful is volleyball’s “serve-reception game”? Its efficacy has been found to discriminate between winning and losing a match. But how does reception become (in)effective? Based on the theoretical rationale of ecological dynamics, we hypothesized that skilled receivers in volleyball would not display ready-made responses, but rather would co-adapt action modes during serve-reception to deal with the specific, emergent constraints of serve to achieve task goals. In order to examine this issue, we investigated whether the co-adaptation of serve and reception action modes was a significant predictor of set outcome in elite volleyball performance (win or loss), analyzing the first and last sets of the 2014 World League Finals matches (897 game-sequences). The power-jump and jump-float were the serving modes observed and the overhand, underhand-lateral, and underhand-frontal passes were the reception modes categorized. We found that the co-adaptation of serve and reception action modes predicted set outcome in the final set of a match. Receiving the jump-float serve with an overhand pass or underhand-lateral pass increased the odds of winning the final set by 200%. Results suggested that, at an expert level, mastering the overhand pass and the underhand-lateral pass gives teams a competitive edge. Receivers showing flexibility in action mode selection improved a team’s odds of successfully winning the final set of a match.

Predicting volleyball serve-reception at group level

ABSTRACT In a group-serve-reception task, how does serve-reception become effective? We addressed “who” receives/passes the ball, what task-related variables predict action mode selection and whether the action mode selected was associated with reception efficacy. In 182 serve-receptions we tracked the ball and the receivers’ heads with two video-cameras to generate 3D world-coordinates reconstructions. We defined receivers’ reception-areas based on Voronoi diagrams (VD). Our analyses of the data showed that this approach was accurate in describing “who” receives the serve in 95.05% of the times. To predict action mode selection, we used variables related to: serve kinematics, receiver’s movement and on-court positioning, the relation between receiver and his closest partner, and interactions between receiver-ball and receiver-target. Serve’s higher initial velocities together with higher maximum height, as well as smaller longitudinal distances between receiver and target increased the chances for the use of the overhand pass. Conversely, decreasing alignment of the receiver with the ball and the target increased the chances of using the underhand-lateral pass. Finally, the use of the underhand-lateral pass was associated with lower quality receptions. Behavioural variability’s relevance for serve-reception training is discussed.

Is Drought Occurrence And Severity Increasing Due to Climate Change? Analysing Drought Class Transitions With Loglinear Models

SPI time series in a 12 month time scale from 6 sites in Alentejo and Algarve, in the south of Portugal, within the period from October 1896 to September 2005, were divided into three or four periods depending on the data set length and a Loglinear modeling approach has been used to investigate differences relative to drought class transitions among these periods. Four drought severity classes were considered. The drought class transitions were computed for the different periods to form a 3-dimensional contingency table. The application of Loglinear modeling to these data allowed the comparison of the periods in terms of probabilities of transition between drought classes in order to detect a possible trend in time evolution of droughts which could be related to climate change