Droughts may be represented by two main characteristics—duration and severity. In this paper, a general methodology to evaluate the frequency and risk of the occurrence of droughts is presented using a bivariate drought characterization. The theory of runs is applied to model drought recurrence as an alternating renewal process, describing droughts simultaneously in terms of their durations and severities. Short historical records usually do not allow reliable bivariate analyses. However, tree ring reconstructions of droughts provide information about past events, allowing the analysis. An approach to adapt and include dendrochronology reconstructions combined with historical records to characterize droughts is presented. The proposed approach uses the stochastic structure of the residuals of paleo reconstructions to generate equally likely representations of past drought events. The procedure was applied to paleo and historical records in Texas Climatic Division 5 and compared with univariate analyses. T...

A detailed knowledge of soil water repellency (SWR) and water infiltration capacity of soils under different land uses is of fundamental importance in Mediterranean areas, since these areas are prone to soil degradation risks (e.g., erosion, runoff of polluting compounds) as a response to different hydrological processes. The present study evaluates the effects of land uses on SWR and soil hydraulic conductivity (SHC) by direct measurements at the plot scale in three areas representing (1) intensive agricultural use, (2) abandoned farmland, and (3) a forest ecosystem in Southern Spain under Mediterranean climatic conditions. The physico-chemical properties and water content of the experimental soils were also measured. Significant SWR and SHC differences were found among the analyzed land uses. Forest soils showed high SWR and low SHC, while the reverse effects (that is, low SWR and high SHC) were detected in soils subjected to intensive agriculture. Organic matter and bulk density were important soil properties influencing SWR and SHC. The study, demonstrating how land uses can have important effects on the hydrological characteristics of soils, give land managers insights into the choice of the most suitable land use planning strategies in view of facing the high runoff and erosion rates typical of the Mediterranean areas.

State estimation (SE) techniques are being applied to different network systems in order to convert system measurements into real information about the network state. SE applications to water systems are relatively novel, but these techniques have been implemented in other fields for decades. In those applications, observability analysis (OA) is required prior to application of SE techniques with different purposes: (1) to identify redundant information, (2) to detect elements that make no contribution in the subsequent SE process, or (3) to identify observable islands. However, no discussion has been found in the pertinent literature regarding any interest in applying OA to water networks, with there being only a few basic applications. The aim of this paper is twofold: first, to present the implementation of a novel algebraic OA approach to water networks, which is based on the application of a Gauss elimination technique to the measurement Jacobian matrix, and to discuss and justify the interesting aspects of implementing an OA in water transport networks (WTN) prior to using SE while also presenting the issues that this technique may resolve. The results obtained highlight the algorithm potential for real supply systems, improving the knowledge of what information provided by supervisory control and data acquisition (SCADA) systems is really worth compiling.