PRECIPITATION CHANGES FROM 1956 TO 1996 ON THE WALNUT GULCH EXPERIMENTAL WATERSHED1

ABSTRACT: The climate of Southern Arizona is dominated by summer precipitation, which accounts for over 60 percent of the annual total. Summer and non‐summer precipitation data from the USDA‐ARS Walnut Gulch Experimental Watershed are analyzed to identify trends in precipitation characteristics from 1956 to 1996. During this period, annual precipitation increased. The annual precipitation increase can be attributed to an increase in precipitation during non‐summer months, and is paralleled by an increase in the proportion of annual precipitation contributed during non‐summer months. This finding is consistent with previously reported increases in non‐summer precipitation in the southwestern United States. Detailed event data were analyzed to provide insight into the characteristics of precipitation events during this time period. Precipitation event data were characterized based on the number of events, event precipitation amount, 30‐minute event intensity, and event duration. The trend in non‐summer precipitation appears to be a result of increased event frequency since the number of events increased during nonsummer months, although the average amount per event, average event intensity, and average event duration did not. During the summer “monsoon” season, the frequency of recorded precipitation events increased but the average precipitation amount per event decreased. Knowledge of precipitation trends and the characteristics of events that make up a precipitation time series is a critical first step in understanding and managing water resources in semiarid ecosystems.     

ERODIBILITY OF URBAN BEDROCK AND ALLUVIAL CHANNELS,NORTH TEXAS1

ABSTRACT: Major erosion of urban stream channels is found in smaller basins in the North Texas study area with contributing drainage areas of less than ten square miles. Within these basins, four basic channel types are identified based on bed and bank lithologies: alluvial banks and bottoms, alluvial banks and gravel bottoms, alluvial banks with rock bottoms, and rock banks with rock bottoms. Most channels (75 percent) have alluvial banks with gravel or rock bottoms. Channel slopes are steep (.38 to.76 percent). Rock consists predominantly of shale and limestone. Channel cross sections are divided into the following four zones based on weathering, scour and entrainment mechanisms: soil zone, slake zone, rock zone and bed material zone. Erodibility of the channels is determined using multiple techniques including reach hydraulics and stream power computations, submerged jet testing, slab entrainment thresholds, and slake durability rates. Procedures are based on both empirical and modeled time series estimates of channel erosion. Field and modeled results support rates of erosion of up to four inches per year. Rates are tied to flow regime, climate, and type of channel bed and banks.     

SUBWATERSHED SPATIAL ANALYSIS TOOL: DISCRETIZATION OF A DISTRIBUTED HYDROLOGIC MODEL BY STATISTICAL CRITERIA1

ABSTRACT: Complex hydrologic models, designed for simulating larger watersheds, require a huge amount of input data. Most of these models use spatially distributed data as inputs. Spatial data can be aggregated or disaggregated for use as input to a model, which can impact model outputs. Although, it is efficient to minimize data redundancy by aggregating the spatial data, upscaling reduces the detail/resolution of input information and increases model uncertainty. On the other hand, a large number of model inputs with high degrees of disaggregation take more computer time and space to process. Hence, a balance between striving for a maximum level of aggregation and a minimum level of information loss has to be achieved. This study presents a definition of an appropriate level of discretization, derived by establishing a relationship between a model's efficiency and the number of subwater‐sheds modeled. An entropy based statistical approach/tool called Subwatershed Spatial Analysis Tool (SUSAT) was developed to find an objective choice of an appropriate level of discretization. The new approach/tool was applied to three watersheds, each representing different hydrologic conditions, using a hydrologic model. Coefficients of efficiency and entropy estimated at different levels of discretization were used to validate the success of the new approach.     

Sustainability Criteria for Decision Support in the UK Water Industry

The incorporation of sustainability assessment into decision-making processes is a key task for water service providers in the UK and elsewhere. This paper describes the development and application of a set of sustainability criteria, which have been developed and tested with project partners in the UK and Romania. They will be used in a 'guidebook' that will set out a framework to facilitate the inclusion of sustainability in the decision-making process. This work is part of the Sustainable Water Industry Asset Resource Decisions project to develop a multi-criteria analysis decision support system to assist water service providers to assess the relative sustainability of water/wastewater system asset development decisions.     

Modeling the relationships between land use and land cover on private lands in the Upper Midwest, USA

This paper presents an approach to modeling land-cover change as a function of land-use change. We argue that, in order to model the link between socio-economic change and changes in forest cover in a region that is experiencing residential and recreational development and agricultural abandonment, land-use and land-cover change need to be represented as separate processes. Forest-cover change is represented here using two transition probabilities that were calculated from Landsat imagery and that, taken together, describe a Markov transition matrix between forest and non-forest over a 10-year period. Using a three-date land-use data set, compiled and interpreted from digitized parcel boundaries, and scanned aerial photography for 136 sites (c. 2500 ha) sampled from the Upper Midwest, USA, we test functional relationships between forest-cover transition probabilities, standardized to represent changes over a decade, and land-use conditions and changes within sample sites. Regression models indicated that about 60% of the variation in the average forest-cover transition probabilities (i.e. from forest to non-forest and vice versa) can be predicted using three variables: amount of agricultural land use in a site; amount of developed land use; and the amount of area increasing in development. In further analysis, time lags were evaluated, showing that agricultural abandonment had a relatively strong time-lag effect but development did not. We demonstrate an approach to using forest-cover transition probabilities to develop spatially-constrained simulations of forest-cover change. Because the simulations are based on transition probabilities that are indexed to a particular time and place, the simulations are improved over previous applications of Markov transition models. This modeling approach can be used to predict forest-cover changes as a result of socio-economic change, by linking to models that predict land-use change on the basis of exogenous human-induced drivers.     

Acid rain in Asia

Acid rain has been an issue of great concern in North America and Europe during the past several decades. However, due to the passage of a number of recent regulations, most notably the Clean Air Act in the United States in 1990, there is an emerging perception that the problem in these Western nations is nearing solution. The situation in the developing world, particularly in Asia, is much bleaker. Given the policies of many Asian nations to achieve levels of development comparable with the industrialized world—which necessitate a significant expansion of energy consumption (most derived from indigenous coal reserves)—the potential for the formation of, and damage from, acid deposition in these developing countries is very high. This article delineates and assesses the emissions patterns, meteorology, physical geology, and biological and cultural resources present in various Asian nations. Based on this analysis and the risk factors to acidification, it is concluded that a number of areas in Asia are currently vulnerable to acid rain. These regions include Japan, North and South Korea, southern China, and the mountainous portions of Southeast Asia and southwestern India. Furthermore, with accelerated development (and its attendant increase in energy use and production of emissions of acid deposition precursors) in many nations of Asia, it is likely that other regions will also be affected by acidification in the near future. Based on the results of this overview, it is clear that acid deposition has significant potential to impact the Asian region. However, empirical evidence is urgently needed to confirm this and to provide early warning of increases in the magnitude and spread of acid deposition and its effects throughout this part of the world.     

On the relationship between objective increases in pay and employees' subjective reactions

This study explored whether two principles describe the relationship between the size of a pay increase (a bonus expressed as a percentage of current salary) and the attractiveness of that increase. Based on a sample of sales personnel (N = 639) and consistent with the constant proportion principle of the psychophysical law, pay increase attractiveness was unrelated to current salary level after controlling for the size of the percentage increase. In addition, at any given salary level, the relationship between the size of the increase and its attractiveness was curvilinear. The attractiveness of larger and larger bonus percentages continues to increase, but at a decreasing rate supporting the principle of diminishing returns.     

STREAM TEMPERATURE ESTIMATION FROM AIR TEMPERATURE1

ABSTRACT: Air temperatures are sometimes used as substitutes for stream temperatures. To examine the errors associated with this procedure, linear relationships between stream temperatures, T, and air temperatures, T_a, recorded for 11 streams in the central U.S. (Mississippi River basin) were analyzed. Weather stations were an average 42 miles (range 0 to 144 miles) from the rivers. The general equations, T_w= 5.0 + 0.75 T_a and T_w= 2.9 + 0.86 T_a with temperatures in °C, were derived for daily and weekly water temperatures, respectively, for the 11 streams studied. The simulations had a standard deviation between measurements and predictions of 2.7°C (daily) and 2.1°C (weekly). Equations derived for each specific stream individually gave lower standard deviations, i.e., 2.1°C and 1.4°C, respectively. Small, shallow streams had smaller deviations than large, deep rivers. The measured water temperatures follow the air temperatures closely with some time lag. time lags ranged from hours to days, increasing with stream depth. Taking into account these time lags improved the daily temperature predictions slightly. Periods of ice cover were excluded from the analysis.     

A MATHEMATICAL MODEL OF SALMONID SPAWNING HABITAT1

ABSTRACT: A simulation model [Salmonid Spawning Analysis Model (SSAM)] was developed as a management tool to evaluate the relative impacts of stream sediment load and water temperature on salmonid egg survival. The model is useful for estimating acceptable sediment loads to spawning habitat that may result from upland development, such as logging and agriculture. Software in common use in the USA were adapted for use in gravel bedded rivers and linked to simulate water temperature (the USFWS Instream Water Temperature, SNTEMP model) and water and sediment routing (the USAE Scour and Deposition in Rivers and Reservoirs, HEC-6 model, version 3.2). These models drive the redd (spawning nest) model (the USDA-ABS Sediment Intrusion Dissolved Oxygen SIDO model) which simulates sediment intrusion and dissolved oxygen concentration in the redd environment. The SSAM model predictions of dissolved oxygen and water temperature compared favorably with field data from artificial redds containing hatchery chinook salmon eggs.