Streamflow Deficits Research Articles

Revisiting reservoir storage–yield relationships using a global streamflow database

Annual and monthly streamflows for 729 rivers from a global data set are used to assess the adequacy of five techniques to estimate the relationship between reservoir capacity, target draft (or yield) and reliability of supply. The techniques examined are extended deficit analysis (EDA), behaviour analysis, sequent peak algorithm (SPA), Vogel and Stedinger empirical (lognormal) method and Phien empirical (Gamma) method. In addition, a technique to adjust SPA using annual flows to account for within-year variations is assessed. Of our nine conclusions the key ones are, firstly, EDA is a useful procedure to estimate streamflow deficits and, hence, reservoir capacity for a given reliability of supply. Secondly, the behaviour method is suitable to estimate storage but has limitations if an annual time step is adopted. Thirdly, in contrast to EDA and behaviour which are based on time series of flows, if only annual statistics are available, the Vogel and Stedinger empirical method compares favorably with more detailed simulation approaches.

Seasonal and successional streamflow response to forest cutting and regrowth in the northwest and eastern United States

This study examined daily streamflow response over up to four decades in northwest conifer forest and eastern deciduous forest sites in the United States. We used novel methods to analyze daily observations of climate and streamflow spanning more than 900 basin years of record at 14 treated/control basin pairs where forest removal and regrowth experiments were underway in the period 1930–2002. In the 1 to 5‐year period after forest removal, maximum daily increases ranged from 2 to 3 mm at deciduous forest sites, to 6 to 8 mm at conifer forest sites. Significant spring surpluses persisted for up to 35 years in conifer forest basins, but winter and spring streamflow deficits appeared after 10 to 15 years of forest regrowth in eastern deciduous forest basins. In all 5‐yr posttreatment periods, absolute changes in daily streamflow were significantly more likely during moist, warm seasons, or during snowmelt seasons, but relative changes were more likely during warm seasons irrespective of moisture status. Both relative and absolute streamflow changes in the 1 to 5 and 15 to 25‐year periods after forest removal were significantly positively related to the age of the forest at the time it was cut. Eastern deciduous forests had been disturbed by logging or hurricane 12 to 56 years prior to forest removal, while Pacific Northwest conifer forests had been not experienced logging or wildfire for 90 to 450 years. Paired basin experiments provide a continuous, and continuously changing, record of vegetation structure, composition, and climate, and their effects on streamflow.

Priority Matters: Lessons from Tort Law for Proving Causation of Wildlife Harm and Allocating ESA Responsibility Between Water Users

The backbone of western water law is the basic notion of first-in-time-is-first-in-right. Beginning water law students have long been taught that under the law of prior appropriation, if there is not enough water in a stream to satisfy the reasonable uses of all diverters, junior users are obligated to close their headgates and pray for rain. Although the assertion of priority is rare, it would be hard to imagine a more fixed principle in water law. It is increasingly evident, however, that this fixed principle of priority is being ignored when the Endangered Species Act (ESA) is used to curtail diversions to assure sufficient instream flow for threatened and endangered species. Rather than impose the regulatory burden on junior appropriators, the federal wildlife agencies charged with enforcing the ESA have exercised discretion to pursue whichever appropriator they prefer. In several agency enforcement efforts, senior water rights holders have borne the brunt of obligations to provide more water. This article raises questions about how the ESA should be applied where streamflow deficits cause harm to endangered wildlife. To that end, the article reflects upon two basic principles of tort law, namely causation and allocation of responsibility in cases of harm caused by multiple tortfeasors. Although the key Supreme Court decision on the enforcement of the ESA - Babbitt v. Sweet Home Chapter of Communities for a Greater Oregon - requires federal wildlife agencies to prove that a person's habitat modifying activity, such as diverting water, is the proximate cause of harm to an endangered species, the rich body of tort law on causation has largely been ignored by the agencies and the courts. Similarly, tort law has been disregarded when it comes to deciding how responsibility for harm should be allocated among multiple habitat modifiers. By overlaying the learning of tort law on the system of prior appropriation, the article hopes to illuminate alternative approaches to allocating responsibility for river harm that are not only more equitable but more efficient.

Characteristics and Spatial Variability of Droughts in Idaho

An application of run theory to annual streamflow sequences in Idaho permits the assignment of return periods to historical drought events, based on the statistical characteristics of the streamflow record. For 63 stations with historical record lengths exceeding 30 years, several major periods of streamflow deficit have occurred, with return periods significantly greater than might be expected from a random sample of the long‐term stochastic process. Since drought severity is shown to be a function of spatially‐dependent statistics, a regional pattern to this severity is defined in terms of a drought potential index (DPI) which indicates the 100‐year return period deficit for flow periods less than the mean annual flow. The mapped DPI values vary significantly throughout the state, with several regions showing a much greater potential for persistent, severe streamflow deficits.