TIME SERIES ANALYSIS IN PERSPECTIVE1

ABSTRACT: By employing a set of criteria for classifying the capabilities of time series models, recent developments in time series analysis are assessed and put into proper perspective. In particular, the inherent attributes of a wide variety of time series models and modeling procedures presented by the authors of the 18 papers contained in this volume are clearly pointed out. Additionally, it is explained how these models can address many of the time series problems encountered when modeling hydrologic, water quality and other kinds of time series. For instance, families of time series models are now available for modeling series which may contain nonlinearities or may follow nonGaussian distributions. Based upon a sound physical understanding of a problem and results from exploratory data analyses, the most appropriate model to fit to a data set can be found during confirmatory data analyses by following the identification, estimation and diagnostic check stages of model construction. Promising future research projects for developing flexible classes of time series models for use in water resources applications are suggested.     

CONTEMPORANEOUS AUTOREGRESSIVE-MOVING AVERAGE (CARMA) MODELING IN WATER RESOURCES1

ABSTRACT: The Contemporaneous Autoregressive-Moving Average (CARMA) model is a simple and efficient model that can be used to fit many multivariate hydrological time series. For certain types of multistation river flow systems, the CARMA model is naturally obtained when the physical restrictions of the system or the characteristics of the data are taken in consideration during the formulation of the model. It is shown how the CARMA model can optimally be used to handle multiple time series where the number of observations in each series may be different. Adequate model building techniques, as well as computational and statistical efficient algorithms to estimate the parameters of the model, are given. The methodologies and applications of the CARMA model are illustrated with three examples. It is also shown how the full multivariate ARMA model may lead to losses in efficient of the estimators when the CARMA model is adequate.     

A RATIONALE FOR THE REGIONALIZATION OF PUBLIC WATER SYSTEMS1

ABSTRACT. A rationale is set forth for requiring and/or encouraging the consolidation or regionalization of all systems beneath certain population size levels based on the small water systems’ capability to produce an adequate supply of safe drinking water at a reasonable cost to customers. Estimates for basic costs of water service including personnel, other operation and maintenance and capital are made and a range of water rates is suggested based on reasonableness and acceptability to customers. Guidelines are then drawn for a moderate rate of $10.00 per month and an upper limit rate of $15.00 per month to show the sizes at which public water systems might be expected to achieve fiscal viability. Finally, recommendations are made to State and Federal governmental agencies concerning possible legislation, plans and programs to achieve better public water service through the regionalization or consolidation of small public water systems.     

REUSE OF AGRICULTURAL DRAINAGE WATERS: AN ECONOMIC ANALYSIS1

ABSTRACT The profitability of reusing agricultural drainage water for crop production depends on the salt tolerance of the crop being grown the salt concentration of the drainage water, the cost of obtaining it and price of good water. In the this paper the economics of drainwater resue is examined for six crops in two areas of southern California. The results suggest that drainwater reuse is not profitable for the fruit and vegetable crops considered but is profitable for the field crops considered when the price of good water is relatively high and cost of obtaining the draingage water is low.     

Importance of indirect nitrous oxide emissions at the field, farm and catchment scale

Direct and indirect nitrous oxide (N₂O) emissions and leaching losses from an intensively managed grazed pasture in the Ythan catchment, Aberdeenshire, UK, were measured and compared over a 17-month period. Simultaneous measurements of farm-wide leaching losses of N₂O were also made and catchment-wide fluxes were estimated from existing N leaching data. The relative importance of direct and indirect N₂O fluxes at the field, farm and catchment scale was then assessed. At the field scale we found that direct N₂O emissions were low (1.2 kg N ha⁻¹ year⁻¹, 0.6% of N input) with indirect N₂O emissions via drainage waters comprising a significant proportion (25%) of total N₂O emissions. At the whole-farm scale, the N₂O-N emission factor (0.003) for leached NO₃-N (EF_5-g) was in line with the IPCC's recent downward revision. At the catchment scale, a direct N₂O flux of 1.9 kg N ha⁻¹ year⁻¹ and an indirect flux of 0.06 kg N₂O-N ha⁻¹ year⁻¹ were estimated. This study lends further support to the recent downward revision of the IPCC emission factor for N₂O arising from leached N in surface and ground waters (EF_5-g) and highlights the need for multiple point sampling to ensure that the importance of indirect N₂O losses via drainage waters is not misrepresented at the farm and catchment scales.     

Modeling population effects of the Deepwater Horizon oil spill on a long-lived species

The 2010 Deepwater Horizon (DWH) oil spill exposed common bottlenose dolphins (Tursiops truncatus) in Barataria Bay, Louisiana to heavy oiling that caused increased mortality and chronic disease and impaired reproduction in surviving dolphins. We conducted photographic surveys and veterinary assessments in the decade following the spill. We assigned a prognostic score (good, fair, guarded, poor, or grave) for each dolphin to provide a single integrated indicator of overall health, and we examined temporal trends in prognostic scores. We used expert elicitation to quantify the implications of trends for the proportion of the dolphins that would recover within their lifetime. We integrated expert elicitation, along with other new information, in a population dynamics model to predict the effects of observed health trends on demography. We compared the resulting population trajectory with that predicted under baseline (no spill) conditions. Disease conditions persisted and have recently worsened in dolphins that were presumably exposed to DWH oil: 78% of those assessed in 2018 had a guarded, poor, or grave prognosis. Dolphins born after the spill were in better health. We estimated that the population declined by 45% (95% CI 14–74) relative to baseline and will take 35 years (95% CI 18–67) to recover to 95% of baseline numbers. The sum of annual differences between baseline and injured population sizes (i.e., the lost cetacean years) was 30,993 (95% CI 6607–94,148). The population is currently at a minimum point in its recovery trajectory and is vulnerable to emerging threats, including planned ecosystem restoration efforts that are likely to be detrimental to the dolphins’ survival. Our modeling framework demonstrates an approach for integrating different sources and types of data, highlights the utility of expert elicitation for indeterminable input parameters, and emphasizes the importance of considering and monitoring long-term health of long-lived species subject to environmental disasters. Article impact statement: Oil spills can have long-term consequences for the health of long-lived species; thus, effective restoration and monitoring are needed.