Historical changes in hydroclimatic characteristics in four Lower Colorado River sub-basins are examined using the Mann-Kendall test for trends and Kendall's tau-b test for statistical association to better understand the processes taking place in these arid watersheds. During the historical record of 1906-2007, in general, temperatures have increased and streamflows have decreased while there has been no change in precipitation. Streamflow was found to have statistical association with annual maximum temperatures, El Nino/Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO). Using this knowledge, two-year and five-year streamflow predictions are made using climate data to force a statistical model. We find no predictive skill at the two-year range but significant (alpha =.05) predictive skill in two of the basins at the five-year range. The dominant climate predictor for the Paria River Basin is ENSO and for the Little Colorado River Basin it is temperature.

A continuous simulation streamflow model (i.e., SSARR - an acronym for Streamflow Synthesis and Reservoir Regulation) was evaluated and used to study winter streamflow from the Salt River Basin. This 4,306 square mile basin, which ranges in elevation from 2,200 to 11,500 feet, is associated with a diversity of watershed, vegetation, climatic and hydrologic characteristics. Program modifications allowed computation of potential evapotranspiration within the model. This provided improved flexibility in delineating simulation units and reduced the necessary time-dependent data inputs to daily values of precipitation and temperature. Refinement of initial parameter estimates and relationships was accomplished by trial and error methods. Four years of hydrometeorological data were utilized for model calibration and an additional four years used to test the validity of parameter estimates. Simulated hydrographs generally underestimated peak flows and overestimated recession flows following major rainfall events. The standard error of the estimate for simulated winter flows (November through May) was only 30,000 acre-feet for the calibration period but increased to approximately 120,000 acre-feet for the validation period. Average winter flows during the calibration and validation periods were 840,000 and 690,000 acre-feet, respectively. Approximately 25 to 45 percent of the winter runoff occurring after February 1, March 1 and April 1 could be predicted from simulated snowpack water equivalent and soil moisture conditions on the prediction date. High elevation portions of the basin were more efficient at producing streamflow from a given precipitation input than were the lower elevations. Maximum daily watershed efficiencies (ratio of generated runoff to rain and snowmelt inputs) usually occurred on the date of snowpack disappearance for the relatively high elevation simulation units. Simulated runoff volumes increased exponentially with increased basin precipitation but decreased linearly with increased basin air temperatures. For a selected winter period, simulations indicated streamflow response to a one-inch change in winter precipitation would be approximately 100,000 acre-feet, or 3.4 times greater than expected from a one-degree change in winter temperature.

Traditional flood-frequency techniques are based on the assumption that the observed flood record represents a sample that has been drawn from a single climatically homogeneous population of floods. A hydroclimatic approach was used to evaluate this assumption by identifying the circulation patterns and atmospheric flood-generating mechanisms which control the temporal and spatial variability of flooding. Mean monthly discharges and instantaneous peak flows of the partial duration series were analyzed for thirty gaging stations in the climatically sensitive, semiarid, Gila River basin for the period 1950 to 1980. Correlation fields and composite maps were constructed to define the relationship between 700 mb height circulation anomalies and mean monthly streamflow. Individual flood events were linked to climate by analyzing daily synoptic weather maps and classifying each flood event into one of eight hydroclimatic categories on the basis of the atmospheric mechanisms which generated each flow. The analysis demonstrated that floods and anomalously high streamflow in the Gila River basin originate from a variety of atmospheric processes which vary spatially, seasonally, and from year-to-year. The mechanisms most important for generating floods included winter fronts, cutoff lows, tropical storms, snowmelt, and widespread and localized summer monsoon-related circulation patterns. When flood discharges were grouped into hydroclimatically homogeneous categories, histogram plots of their frequency distributions exhibited means and variances that differed from those of the overall frequency distribution of the entire flood series. The means of the discharges generated by frontal precipitation and tropical storms tended to plot above the mean of the overall series, while the means of floods generated by snowmelt tended to plot below the overall mean. Flood estimates computed from a series containing mixed distributions were not the same as flood estimates computed from climatically homogeneous subsets of the same series. These results have implications for traditional flood-frequency analysis and other stochastic methods of analyzing hydrologic time series. The hydroclimatically-defined subgroups in the flood series of the Gila River basin indicate that nonhomogeneity and nonstationarity can be imparted to a hydrologic time series by differing atmospheric mechanisms alone.

Southwestern mixed conifer forests cover approximately 2.5 million acres in Arizona and New Mexico, and provide a wide range of commercial and noncommercial products. The problem is to develop a management prescription which will benefit the greatest mix of resources. An alternatives analysis predicted that a prescription that included small patch clearcutting, in addition to other stand modifications, would meet this criteria. The two Thomas Creek watersheds, in eastern Arizona, were used to validate and test the responses of the forest resources to the preferred prescription, and to increase the understanding of the mixed conifer forest system. The actual harvest created 63 small patch clearcut and group selection openings, averaging 1-2 acres, over 13% of the South Fork watershed. Overall stand density was reduced 34% to 132 square feet per acre. The harvest resulted in significant hydrological changes. Average annual streamflow increased by about 45%, or 1.72 inches, mostly because of increased winter runoff. A greater proportion of the snowmelt generated streamflow occurred earlier in the spring, while annual peak flows were increased by an average of 66%, or about 2.60 cubic feet per second per square mile. The number of days without flow decreased. Average watershed maximum snow water equivalents remained unchanged. The primary causes of the increases were reduced evapotranspiration and increased snow accumulation in the openings; however, it appears that the partially cut stand also contributed to the increases. The treatment benefitted the timber resource. Diameter growth on the South Fork increased for most species compared to the unharvested stand on North Fork. Stand gross growth remained unchanged, but the same volume was being added to fewer trees. The stand, including most openings, is well stocked with adequate numbers of natural and advance regeneration. The Thomas Creek prescription, after 8 years of evaluation, has achieved its objectives of increasing water yields and stand growth while insuring adequate regeneration. It has also benefitted many wildlife species as well as livestock. A similar prescription should increase water yields, by about 15,000 acre-feet annually, from the Upper Black River Basin without adversely impacting other forest resources.

In data-poor regions around the world, particularly in less-privileged countries, hydrologists cannot always take advantage of available hydrological models to simulate a hydrological system due to the lack of reliable measurements of hydrological variables, in particular rainfall and streamflows, needed to implement and evaluate these models. Rainfall estimates obtained with remotely deployed sensors constitute an excellent source of precipitation for these basins, however they are prone to errors that can potentially affect hydrologic simulations. Concurrently, limited access to streamflow measurements does not allow a detailed representation of the system's structure through parameter estimation techniques. This dissertation presents multiple studies that evaluate the usefulness of remotely sensed products for different hydrological applications and the sensitivity of simulated streamflow to parameter uncertainty across basins with different hydroclimatic characteristics with the ultimate goal of increasing the applicability of land surface models in ungauged basins, particularly in South America. Paper 1 presents a sensitivity analysis of daily simulated streamflows to changes in model parameters along a hydroclimatic gradient. Parameters controlling the generation of surface and subsurface flow were targeted for the study. Results indicate that the sensitivity is strongly controlled by climate and that a more parsimonious version of the model could be implemented. Paper 2 explores how errors in satellite-estimated precipitation, due to infrequent satellite measurements, propagate through the simulation of a basin's hydrological cycle and impact the characteristics of peak streamflows within the basin. Findings indicate that nonlinearities in the hydrological cycle can introduce bias in simulated streamflows with error-corrupted precipitation. They also show that some characteristics of peak discharges are not conditioned by errors in satellite-estimated precipitation at a daily time step. Paper 3 evaluates the dominant sources of error in three satellite products when representing convective storms and how shifts in the location of the storm affect simulated peak streamflows in the basin. Results indicate that satellite products show some deficiencies retrieving convective processes and that a ground bias correction can mitigate these deficiencies but without sacrificing the potential for real-time hydrological applications. Finally, spatially shifted precipitation fields affect the magnitude of the peaks, however, its impact on the timing of the peaks is dampened out by the system's response at a daily time scale.

This dissertation is put together from a set of three journal papers. The first paper describes how satellite imagery and spacecraft autonomy are used to advance the field of near real-time detection, monitoring, and rapid response to flooding. The second paper describes the ground instrumentation of an artificial water recharge basin field site close to Tucson with a network of inter-connected sensors to study the transient process of repeated flooding in real-time, and the third paper describes an effort to link together multiple ground-based and space-based remote sensing assets to an integrated and coordinated monitoring system for floods. Collectively, the three papers describe new breakthroughs in the field of flood detection and monitoring through the use of satellite onboard automation and Sensorweb networks.

We develop and test a probabilistic real-time streamflow-forecasting platform, Multimodel and Multiproduct Streamflow Forecasting (MMSF), that uses information provided by a suite of hydrologic models and satellite precipitation products (SPPs). The SPPs are bias-corrected before being used as inputs to the hydrologic models, and model calibration is carried out independently for each of the model-product combinations (MPCs). Forecasts generated from the calibrated models are further bias-corrected to compensate for the deficiencies within the models, and then probabilistically merged using a variety of model averaging techniques. Use of bias-corrected SPPs in streamflow forecasting applications can overcome several issues associated with sparsely gauged basins and enable robust forecasting capabilities. Bias correction of streamflow significantly improves the forecasts in terms of accuracy and precision for all different cases considered. Results show that the merging of individual forecasts from different MPCs provides additional improvements. All the merging techniques applied in this study produce similar results, however, the Inverse Weighted Averaging (IVA) proves to be slightly superior in most cases. We demonstrate the implementation of the MMSF platform for real-time streamflow monitoring and forecasting in the Mara River basin of Africa (Kenya & Tanzania) in order to provide improved monitoring and forecasting tools to inform water management decisions.

Actuellement, la Loire, voit sa géodynamique de plus en plus détériorée. Le déficit du transport solide provoque un enfoncement du lit mineur sur plusieurs secteurs du bassin Amont. Ceci a pour conséquence une déstabilisation progressive des ouvrages (digues, ponts) et l'érosion ou le colmatage des berges ainsi qu'une baisse du niveau piézométrique des nappes alluviales. Le traitement de ces problèmes passe par une meilleure connaissance des processus d'érosion et d'incision fluviale, le premier laissant place au second une fois que la couche « alluviale » a été totalement emportée, laissant apparaître un affleurement rocheux dans le lit du cours d'eau. Ce phénomène complexe est actuellement constaté en divers endroits de la Loire, dans la plaine du Forez. Nous proposons trois approches pour l'analyser.La première approche est fondée sur la modélisation numérique utilisant les équations de Barré-Saint-Venant, pour l'écoulement, couplées aux équations d'Exner et de Meyer-Peter Müller pour le transport solide. Ce modèle monodimensionnel permet d'obtenir la côte du fond du lit de la rivière et le flux solide au droit de chaque point de calcul.La seconde approche, mécaniste, consiste à déterminer de façon semi-empirique le taux d'incision du substratum marneux à partir de deux variables majeures: la puissance hydraulique totale et le coefficient d'abrasion en un point donné. La puissance hydraulique est calculée à l'aide d'un modèle hydraulique tandis que le nombre d'abrasion est une propriété mécanique de la marne qui est déterminée à partir d'essais en laboratoire. La troisième approche relève de la géochimie. Elle consiste à déterminer les provenances des matériaux contribuant à la recharge latérale des sédiments, à partir de leurs signatures géochimiques. Ceci a fait l'objet d'analyses en laboratoire sur des échantillons prélevés sur l'ensemble du linéaire entre Grangent et Balbigny. Les résultats obtenus montrent que ces approches indépendantes sont complémentaires et permettent une description à la fois qualitative et quantitative de l'enfoncement du lit de la Loire dans le secteur d'étude. / Currently, the Loire river, sees its geodynamic increasingly deteriorated. The deficit of sediment transport causes erosion of the bed on several areas of the basin. This results in a gradual destabilization of structures (dams, bridges), erosion or clogging of banks or a decline in piezometric level alluvial.Treating these problems requires a better understanding of the processes of erosion and river incision, the second succeeding the first, once the alluvial material of the bottom was completely removed, revealing a bed outcrop.This complex phenomenon is currently found in various parts of the Loire river, in the plain of Forez.We propose three approaches for this analysis.The first approach is based on numerical modeling using the equations of Barre-de-Saint-Venant, for flow, coupled with the equations of Exner and Meyer-Peter Müller for sediment transport. This monodimensional model allows the simulation of riverbed changement and sediment discharge, right each calculation point of grid mesh.The second approach is mechanistic and consists of determining the rate of marly bedrock incision by a semi-empirical method by the use of two major variables: the total hydraulic power and an abrasion coefficient. The hydraulic power is calculated using a hydraulic model, while the abrasion coefficient is a mechanical property of the marl which is determined from laboratory tests.The third approach is the geochemistry. It consists in determining the provenance of the materials from tributaries and in the main chanel by analyzing their geochemical signatures. This has been the subject of laboratory tests on samples taken across the linear from Grangent to Balbigny.The results obtained show that these independent approaches are complementary and provide both a qualitative and quantitative description of the incision of the Loire river in the study area.

The Ob is the third largest Eurasian river supplying heat and freshwater to the Arctic Ocean. These inputs influence water salinity, ice coverage, ocean temperatures and ocean circulation, and ultimately the global climate system. Variability of Ob River flow on long time scales is poorly understood, however, because gaged flow records are short. Eleven tree-ring width chronologies of Pinus sibirica and Larix sibirica are developed from the floodplain of the Lower Ob River, analyzed for hydroclimatic signal and applied as predictors in a regression model to reconstruct 8-month average (December-July) discharge of the Ob River at Salekhard over the interval 1705-2012 (308 yrs). Correlation analysis suggests the signal for discharge comes through air temperature: high discharge and floodplain water levels favor cool growing-season air temperature, which limits tree growth for the sampled species at these high latitudes. The reconstruction model (R-2 = 0.31, 1937-2009 calibration period) is strongly supported by cross validation and analysis of residuals. Correlation of observed with reconstructed discharge improves with smoothing. The long-term reconstruction correlates significantly with a previous Ob River reconstruction from ring widths of trees outside the Ob River floodplain and extends that record by another century. Results suggest that large multi-decadal swings in discharge have occurred at irregular intervals, that variations in the 20th and 21st centuries have been within the envelope of natural variability of the past 3 centuries, and that discharge data for 1937-2009 underestimate both the variability and persistence of discharge in the last 3 centuries. The reconstruction gives ecologists, climatologists and water resource planners a long-term context for assessment of climate change impacts.

The understanding of how different parts of a landscape contribute to streamflow by storing and releasing water has long been a central issue in hydrology. Knowledge about what controls streamflow dynamics across landscapes can further our understanding of how catchments store and release water, facilitate predictions for ungauged catchments, and improve the management of water quality and resources. This thesis makes use of data from the Krycklan catchment in northern Sweden. Streamflow data from 14 catchments (0.12 - 68 km2) with variable landscape characteristics such as topography, vegetation, wetland cover, glacial till soils and deeper sediment soils were used to investigate spatial patterns and controls on runoff. The differences in specific discharge (discharge per unit catchment area) between nearby catchments were large at the annual scale, and have the same magnitude as predicted effects of a century of climate change or the observed effects of major forestry operations. This variability is important to consider when studying the effects of climate change and land use changes on streamflow, as well as for our understanding of geochemical mass balances. Streamflow from different catchments was strongly related to landscape characteristics. The distribution of wetland areas had a particularly strong influence, with an annual specific discharge 40-80% higher than catchments with high tree volume on till soils. During drier periods, catchments with deeper sediment soils at the lower elevations of Krycklan had a higher base flow compared to both forested till and wetland catchments. This pattern was reversed at high flows. The storages releasing water to streams in downstream sediment areas were able to maintain base flow for longer periods and were less influenced by evapotranspiration compared to the more superficial till and wetland systems. The results of this thesis have led to a better understanding of the landscape wide patterns of streamflow during different seasons and time scales. The strong associations to landscape characteristics and variable spatial patterns with season and antecedent conditions form the basis for a conceptual understanding of the processes and spatial patterns that shape the heterogeneity of streamflow responses in boreal catchments. / Hur olika delar av landskapet påverkar vattenbalansen och bidrar till avrinning har länge varit en central fråga inom hydrologin. Kunskap om vad som styr avrinningsdynamiken i ett landskap kan öka vår förståelse av hur olika delar av landskapet bidrar till avrinning, hur avrinningsområden lagrar vatten och bildar avrinning, underlätta prognoser för avrinningsområden utan vattenföringsmätningar och förbättra hanteringen av vattenkvaliteten och vattenresurser. Denna avhandling använder data från Krycklans avrinningsområde i norra Sverige. Vattenföringsdata från 14 delavrinningsområden (0.12 - 68 km2) med olika landskapskarakteristik såsom topografi, vegetation och jordarter, användes för att undersöka rumsliga mönster hos avrinningen över olika tidsperioder samt hur landskapet påverkar variabiliteten. Skillnaderna i specifik avrinning (avrinning per areaenhet) mellan närliggande avrinningsområden var stor för årliga värden, och är i samma storleksordning som effekterna av stora skogsavverkningar samt av förutspådda effekter av det kommande seklets förväntade klimatförändringar. Denna variation är viktig att ta hänsyn till när man studerar hur klimatförändringar och ändrad markanvändning påverkar avrinningen, liksom för vår förståelse av geokemiska massbalanser. Avrinning från olika områden var starkt relaterad till deras landskapsegenskaper. Förekomsten av våtmarker hade ett särskilt starkt inflytande. Områden med en stor andel våtmarker hade 40-80% högre årlig specifik avrinning än områden med hög trädvolym på moränjordar. Under torrare perioder hade områden med djupare sedimentjordar hög avrinning jämfört med både områden med skog på morän och med våtmarker. Under höga flöden var detta mönster omvänt. De vattenlager som bidrar till avrinning i sedimentområden kan upprätthålla basflöde under längre tidsperioder och påverkas mindre av evapotranspirationen än de ytligare flödessystemen i morän och våtmarker. Avhandlingen har givit en bättre förståelse av avrinningens rumsliga variation under olika årstider och i olika tidsskalor. Det starka sambandet mellan landskapskarakteristik och avrinningens varierande mönster under olika årstider och lagringsförhållanden utgör en grund för en begreppsmässig förståelse av de processer och rumsliga mönster som skapar heterogeniteten i flödesrespons i boreala områden.