Com o objetivo de comparar o balanço hídrico e características do deflúvio e, também, de realizar a calibragem das micro bacias hidrográficas experimentais B e D, do Laboratório de Hidrologia Florestal Eng.º Agr. Walter Emmerich, estudou-se o comportamento hidrológico das duas microbacias durante um período de seis anos. A área do experimento está localizada à leste do Estado de São Paulo, no Parque Estadual da Serra do Mar - Núcleo Cunha, no limite entre a Serra do Mar e o Planalto Atlântico. O clima da região é úmido, com fortes influências dos efeitos orográficos da Serra do Mar. A precipitação média anual é superior a 2000 mm, podendo o ano hídrico ser dividido em um período caracterizado como úmido, que se estende de outubro a março, e um período seco, que compreende os meses de abril a setembro. Com área de 36,68 ha e 56,04 ha respectivamente, as microbacias B e D estão recobertas com vegetação secundária de Mata Atlântica, em solos do tipo Latossolo Vermelho Amarelo predominantemente, estabelecidos sobre rochas graníticas. No período compreendido entre outubro de 1986 a setembro de 1992, monitorou-se as duas microbacias, efetuando-se medições contínuas das descargas e das precipitações pluviométricas. Os componentes do balanço hídrico anual determinados foram a precipitação e o deflúvio. Pela diferença entre ambos, estimou-se a evapotranspiração, desconsiderando-se as variações de armazenamento de água no solo. As características do deflúvio estudadas foram as curvas de duração de fluxo do deflúvio diário, o escoamento direto e as taxas de pico de vazão de hidrogramas. Utilizando o método das microbacias pareadas, correlacionou-se o deflúvio anual, o deflúvio mensal, a quantidade de escoamento direto e o pico de vazão das microbacias B e D, por meio de regressões lineares, resultando em equações de calibragem das microbacias. A microbacia D foi considerada como controle no experimento. A média anual da precipitação, do deflúvio e da evapotranspiração foram, respectivamente: microbacia B - 2012 mm, 1473 mm e 539 mm; microbacia D - 2158 mm, 1555 mm e 603 mm. Em termos percentuais, a evapotranspiração das microbacias é da ordem de 30% da precipitação anual. O deflúvio médio diário das microbacias durante os períodos seco e úmido foram, respectivamente: microbacia B - 3,4 mm e 4,7 mm; microbacia D - 3,8 mm e 4,8 mm. Os fatores de resposta médios das microbacias B e D, calculados pelo quociente entre o volume de escoamento direto e a precipitação, estimados a partir de 88 hidrogramas, foram 0,23 e 0,12, respectivamente. Frente às análises efetuadas no presente trabalho pode-se concluir: 1) as microbacias são conservativas quanto ao consumo de água. Em comparação com outras florestas de clima tropical, a evapotranspiração anual da vegetação de mata atlântica do local ocorre a taxas consideravelmente menores; 2) as microbacias apresentam um regime de vazão bastante regular durante todo o ano hídrico. Em média, a produção de água no período das chuvas supera em apenas 10% a produção hídrica no período mais seco. O escoamento base é o principal componente do fluxo diário de água dos rios, abrangendo aproximadamente 90% do tempo de descarga na curva de duração de fluxo das microbacias. A contribuição do escoamento direto para o deflúvio diário restringe-se a cerca de 10% de todo o tempo do escoamento; 3) há uma diferença marcante entre a resposta hidrológica das duas microbacias devido às precipitações, em função da época do ano. No período das chuvas a proporção de escoamento direto é superior à verificada no período mais seco. As áreas geradoras de escoamento direto nas duas microbacias aumentam com a passagem da estação seca para a estação úmida e também com o incremento das chuvas. Embora pouco comum, a área mínima de contribuição do escoamento direto pode corresponder a 60% da superfície das microbacias; 4) o volume de escoamento direto da microbacia B, em geral, supera o da microbacia D. Uma maior proporção da superfície da primeira microbacia contribui para o escoamento rápido comparativamente à microbacia D. Para a maior parte das chuvas do período seco, não mais que 10% da microbacia D produz escoamento direto, enquanto na microbacia B, de 20% a 30% da superfície gera escoamento rápido. No período das chuvas, é bastante frequente que 30% da microbacia D participe na formação do hidrograma, enquanto 30% a 50% da área da microbacia B usualmente produz este componente do deflúvio; 5) há evidências de que a resposta hidrológica às chuvas, mais intensa na microbacia B que na microbacia D, decorre principalmente, da presença de grandes extensões de solos rasos localizados em terrenos de grande inclinação, concentrados desde as partes mais elevadas até as porções inferiores das vertentes da microbacia B; 6) com relação à calibragem das microbacias, as equações determinadas para o deflúvio anual e para o deflúvio mensal, com reduzidos erros padrão de estimativa, podem ser utilizadas para avaliação de um eventual tratamento experimental, ao contrário dos modelos obtidos para estimativa do volume de escoamento direto e do pico de vazão. Recomenda-se a inclusão de mais observações na tentativa de melhorar as equações para as duas últimas características do deflúvio. / Our main target is the comparison of the water balance and the streamflow characteristics, besides achieaving the calibration of B and D experimental watersheds in Walter Emmerich Hydrologic Laboratory. We have studied the hydrologic behaviour of the two small watersheds for six years. The area of the experiment is in the east of São Paulo State, in Serra do Mar State Park in the border between Serra do Mar and Atlantic Plateau, at Brazil. It\' s a wet area with hard influences of the orographic effects from Serra do Mar. The annual average precipitation is above 2,000 mm, and the water year can be divided in a wet period - from October to March - and a dry period - from April to September. There are 36.68 ha and 56.04 ha in the B and D small watersheds, respectively. They are covered with Mata Atlântica forest, principally in Red Yellow Latosols, in granite. From October 1986 to September 1992, we monitored the two watersheds, measuring discharge and precipitation continuously. The measured components of the annual water year were the precipitation and streamflow. From the difference between them we estimated the evapotranspiration, negleting the changes in soil moisture storage. The studied streamflow characteristics were: flow duration curves of daily streamflow, stormflow and peak flow rates of hydrographs. Applying the paired catchment method by means of linear regressions, we correlated the annual streamflow, monthly streamflow, the amount of stormflow and the peak discharge for the two watersheds, resulting in calibration equations. The D watershed was used as the control in the experiment. The mean annual precipitation, streamflow and evapotranspiration were respectively: B watershed - 2,012 mm; 1,473 mm and 539 mm; D watershed - 2,158 mm; 1,555 mm and 603 mm. Within percentage limits, the evapotranspiration of the watersheds is about 30% the annual precipitation. The mean daily flow of the watersheds during the dry and wet periods were respectively: B watershed - 3.4 mm and 4.7 mm; D watershed - 3.8 mm and 4.8mm. The mean hydrologic response of B and D watersheds - estimated by the rate between stormflow volume and precipitation, calculated from 88 selected hydrographs, were 0.23 and 0.12 respectively. The results permit the following conclusions: 1) B and D small watersheds are conservative in terms of water consumption. Comparing to other tropical forests, the annual evapotranspiration of forest in the Mata Atântica presents a remarkable smaller proportion; 2) the watersheds presents a rather regular discharge regime during all the water year. In average, the water yield in the rainy period is only 10% greater than the water yield in the drier period. The baseflow is the main component of the daily streamflow, occurring during 90% of the time on the flow duration curves of the catchments. The daily direct runoff contribution occurs only about 10% of the time of the streamflow; 3) there is a remarkable difference between the two watersheds hydrologic response due to precipitations in different seasons of the year. In the rainy period, the proportion of the stormflow is greater than the drier period. The generating area of stormflow in the two watersheds increase from the dry season to the wet season and with rainfall. Even though rare, the minimum contributing area can reach up to 60% of the total catchment area; 4) the stormflow volume of the B watershed is generally greater than the D watershed. During the dry period, 10% the area has a stormflow in the D watershed whereas 20% to 30% the area in B watershed produces a quickflow. During the rainy period, 30% D watershed usually contributes to the development of hydrograph, while 30% to 50% the B watershed surface usually produces this component of the flow; 5) the larger hydrologic responses to stronger rains in the B watershed than D watershed are mainly due to vast area of shallow soil in sloping ground which are concentrated from the top to the bottom in B watershed hillslopes; 6) the determined calibration equations for annual and monthly streamflow, with low standard error of estimate, could already be used to predict streamflow after an eventual experimental treatment in the B catchment. However, the models using volume of direct runoff and runoff peak were not significant with the available number of data.

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / Sabe-se que a Ãgua à um recurso essencial à sobrevivÃncia da humanidade. Gestores ambientais do mundo inteiro vÃm chamando atenÃÃo para o problema da sua escassez e mà gestÃo. O presente trabalho destacou que no Nordeste Brasileiro, particularmente no semiÃrido, a escassez hÃdrica acentua-se por conta das caracterÃsticas peculiares que o diferem de outros locais, tais como: a irregularidade pluviomÃtrica e a mà distribuiÃÃo das chuvas no tempo e no espaÃo. Desenvolveram-se modelos matemÃticos de previsÃo de vazÃes sazonais/interanuais que incorporam as informaÃÃes climÃticas, bem como a metodologia de incorporaÃÃo dessas previsÃes na operaÃÃo e gestÃo de hidrossistemas e no estudo de controle de cheias. Esses modelos basearam-se na metodologia dos K-vizinhos desenvolvida por Souza Filho e Lall, e nos modelos estatÃsticos de regressÃo. Apresentou-se, ainda, o software AcquaNet como mecanismo de auxÃlio na operaÃÃo de sistemas de reservatÃrios. Aplicou-se a metodologia em reservatÃrios do Estado do Cearà e do Nordeste do Brasil. Concluiu-se que a inclusÃo da previsÃo de vazÃes na operaÃÃo de sistemas de reservatÃrios pode ser um instrumento eficaz na gestÃo dos recursos hÃdricos à medida que agrega a este processo mais confiabilidade e qualidade, e, desde que corretamente utilizada, pode aumentar a geraÃÃo de capital do Estado. / It is known that water is a resource essential to human survival. Environmental managers around the world have been calling attention to the problem of water scarcity and mismanagement. This study highlighted that in the Northeast of Brazil, particularly in semi-arid, water scarcity is accentuated because of the peculiar characteristics that differentiate it from other places, such as the irregularity and poor distribution of rain in time and space. Mathematical models of seasonal/interannual streamflow forecasting incorporating weather information were developed, as well as the methodology for incorporating these forecasts in the operation, management and study of water systems and flood control. These models were based on the methodology of the K-neighbors developed by Souza Filho and Lall, and on the statistical regression models. The software AcquaNet was also introduced as a mechanism to aid in the operation of reservoir systems. The methodology was applied in reservoirs of the State of Cearà and the Northeast of Brazil. We conclude that the inclusion of streamflow forecasting in the operation of reservoir systems can be an effective tool in water management as this process adds more reliability and quality, and, if properly used, can increase the income generation of the State.

A finite element numerical model is developed for the modeling of coupled surface-water flow and ground-water flow. The mathematical treatment of subsurface flows follows the confined aquifer theory or the classical Dupuit approximation for unconfined aquifers whereas surface-water flows are treated with the kinematic wave approximation for open channel flow. A detailed discussion of the standard approaches to represent the coupling term is provided. In this work, a mathematical expression similar to Ohm's law is used to simulate the interacting term between the two major hydrological components. Contrary to the standard approach, the coupling term is incorporated through a boundary flux integral that arises naturally in the weak form of the governing equations rather than through a source term. It is found that in some cases, a branch cut needs to be introduced along the internal boundary representing the stream in order to define a simply connected domain, which is an essential requirement in the derivation of the weak form of the ground-water flow equation. The fast time scale characteristic of surface-water flows and the slow time scale characteristic of ground-water flows are clearly established, leading to the definition of three dimensionless parameters, namely, a Peclet number that inherits the disparity between both time scales, a flow number that relates the pumping rate and the streamflow, and a Biot number that relates the conductance at the river-aquifer interface to the aquifer conductance. The model, implemented in the Bill Williams River Basin, reproduces the observed streamflow patterns and the ground-water flow patterns. Fairly good results are obtained using multiple time steps in the simulation process.

Numerical models often fail to accurately simulate and forecast a hydrological state in operation due to its inherent uncertainties. Data Assimilation (DA) is a promising technology that uses real-time observations to modify a model's parameters and internal variables to make it more representative of the actual state of the system it describes. In this thesis, hydrological DA is first reviewed from the perspective of its objective, scope, applications and the challenges it faces. Special attention is then given to nonlinear Kalman filters such as the Extended Kalman Filter (EKF). Based on a review of the existing studies, it is found that the potential of EKF has not been fully exploited. The Soil and Water Assessment Tool (SWAT) is a semi-distributed rainfall-runoff model that is widely used in agricultural water management and flood forecasting. However, studies of hydrological DA that are based on distributed models are relatively rare because hydrological DA is still in its infancy, with many issues to be resolved, and linear statistical models and lumped rainfall-runoff models are often used for the sake of simplicity. This study aims to fill this gap by assimilating streamflow and surface soil moisture observations into the SWAT model to improve its state simulation and forecasting capability. Unless specifically defined, all ‘forecasts’ in Italic font are based on the assumption of a perfect knowledge of the meteorological forecast. EKF is chosen as the DA method for its solid theoretical basis and parsimonious implementation procedures. Given the large number of parameters and storage variables in SWAT, only the watershed scale variables are included in the state vector, and the Hydrological Response Unit (HRU) scale variables are updated with the a posteriori/a priori ratio of their watershed scale counterparts. The Jacobian matrix is calculated numerically by perturbing the state variables. Two case studies are carried out with real observation data in order to verify the effectiveness of EKF assimilation. The upstream section of the Senegal River (above Bakel station) in western Africa is chosen for the streamflow assimilation, and the USDA ARS Little Washita experimental watershed is chosen to examine surface soil moisture assimilation. In the case of streamflow assimilation, a spinoff study is conducted to compare EKF state-parameter assimilation with a linear autoregressive (AR) output assimilation to improve SWAT’s flood forecasting capability. The influence of precipitation forecast uncertainty on the effectiveness of EKF assimilation is discussed in the context of surface soil moisture assimilation. In streamflow assimilation, EKF was found to be effective mostly in the wet season due to the weak connection between runoff, soil moisture and the curve number (CN2) in dry seasons. Both soil moisture and CN2 were significantly updated in the wet season despite having opposite update patterns. The flood forecast is moderately improved for up to seven days, especially in the flood period by applying the EKF subsequent open loop (EKFsOL) scheme. The forecast is further improved with a newly designed quasi-error update scheme. Comparison between EKF and AR output assimilation in flood forecasting reveals that while both methods can improve forecast accuracy, their performance is influenced by the hydrological regime of the particular year. EKF outperformed the AR model in dry years, while AR outperformed the EKF in wet years. Compared to AR, EKF is more robust and less sensitive to the length of the forecast lead time. A combined EKF-AR method provides satisfying results in both dry and wet years. The assimilation of surface soil moisture is proved effective in improving the full profile soil moisture and streamflow estimate. The setting of state and observation vector has a great impact on the assimilation results. The state vector with streamflow and all-layer soil moisture outperforms other, more complicated state vectors, including those augmented with intermediate variables and model parameters. The joint assimilation of surface soil moisture and streamflow observation provides a much better estimate of soil moisture compared to assimilating the streamflow only. The updated SWAT model is sufficiently robust to issue improved forecasts of soil moisture and streamflow after the assimilation is ‘unplugged’. The error quantification is found to be critical to the performance of EKF assimilation. Nevertheless, the application of an adaptive EKF shows no advantages over using the trial and error method in determining time-invariant model errors. The robustness of EKF assimilation is further verified by explicitly perturbing the precipitation ‘forecast’ in the EKF subsequent forecasts. The open loop model without previous EKF update is more vulnerable to erroneous precipitation estimates. Compared to streamflow forecasting, soil moisture forecasting is found to be more resilient to erroneous precipitation input.

Magister Scientiae (Integrated Water Resource Management) / The Klein Berg River catchment is intensely cultivated with orchards, vineyards and wheat, while also ensuring a water supply to the main urban center, Tulbagh, and the two conservation areas (Waterval and Groot Winterhoek). The primary objective of this thesis is to determine channel change over a long and short time period, and to relate these changes to landuse change within the catchment. Assessing stability of a selected reach within the catchment was done on a short term basis with the use of erosion pins and cross profiles, while aerial photographs of over 55 years (acquired during 1942, 1967, 1987 and 1997) which were analysed using Geographic Informations Systems. Rainfall and discharge data, which were available for a period of 49-years were statistically analysed and used to determine trends. Vegetation characteristics were assessed by means of transects within the study reach. The results over the short time period (18 months) indicate noticeable channel change in the form of erosion and deposition within the channel. Bank material composition and riparian invasive alien vegetation play an important role in bank stability. Sand was the dominant grain size of the bank material, and fluvial entrainment occurred during periods of high flow. Woody alien trees prevent the growth of protective ground vegetation, and thus the soil is prone to erosion. Undercutting was also observed with the invasive woody trees, resulting in treefall. Debris dams were also common in the channel and depending on their position in the channel, either cause or prevent bank erosion. Landuse change over the 55-year period illustrated its effects on channel stability. Shrublands within the catchment has been replaced with invasive alien vegetation along the riparian zone, while shrublands along the Obiekwa Mountains, were replaced with cultivated lands. The patterns (shape and size) of lateral and point bars within the study area changed significantly within the 55-year period, which indicates a change in the discharge and sediment dynamics within the catchment. The change in sediment dynamics may be due to agricultural activities and urbanization. The increased trend in rainfall, especially during the winter season within the catchment is also an important catchment control. The study has revealed the integrated nature of variables within the catchment. It is thus recommended that a holistic and integrated approach at a catchment scale is required in the assessment of channel change of a river. / South Africa

O modelo Soil and Water Assessment Tool (SWAT) tem sido utilizado para avaliar os impactos do uso e manejo da terra nos recursos hídricos, sedimentos e agroquímicos em diversas escalas e condições ambientais em todo o mundo. Entretanto, pelo fato de ter sido desenvolvido em centros de pesquisa norte-americanos, alguns parâmetros e rotinas de simulação não refletem adequadamente determinados processos de bacias localizadas em regiões tropicais. Nesse sentido, o presente trabalho visou aprimorar a modelagem hidrológica do SWAT através da revisão e modificação de processos relacionados à simulação da evapotranspiração. Os procedimentos propostos incluíram a alteração das rotinas de dormência vegetal no código fonte do modelo e a modificação dos cronogramas de operações de manejo e parâmetros do banco de dados de crescimento das plantas, visando reproduzir com maior precisão o ciclo das culturas em bacias tropicais. As modificações foram testadas em cinco bacias localizadas no Estado de São Paulo, com áreas entre 42 e 5.959 km², sendo comparados os resultados obtidos antes e depois da implementação das mesmas. Com as alterações, a análise do balanço hídrico anual evidenciou um aumento nos valores de evapotranspiração de cerca de 61% nas bacias, aproximando-se dos totais anuais de evapotranspiração calculados através de métodos empíricos, bem como houve redução significativa do escoamento superficial. Verificou-se uma melhoria da simulação de vazão em todas as bacias, sendo obtidos valores superiores para o Coeficiente de Eficiência de Nash-Sutcliffe (NSE) quando comparados à simulação sem as alterações. A calibração e validação foram realizadas com base na simulação modificada, sendo obtidos valores de NSE mensais entre 0,71 e 0,93 na calibração e 0,53 e 0,88 na validação, enquanto os valores diários de NSE situaram-se entre 0,51 e 0,82 na calibração e 0,38 e 0,83 na validação. A calibração a partir de uma simulação na qual as distorções dos processos hidrológicos da bacia estivessem previamente minimizadas resultou em bons resultados sem alteração excessiva dos parâmetros, indicando uma simulação hidrológica de melhor consistência. / The Soil and Water Assessment Tool (SWAT) has been used to predict the impact of land management practices on water, sediment, and agricultural chemical yields in a wide range of scales and environmental conditions across the globe. However, originally developed in the United States, some parameters and routines are unrealistic for simulating in tropical watersheds. In this sense, this work aims to improve the hydrologic modeling of SWAT model by reviewing and modifying parameters and routines related to evapotranspiration process. In order to adequately represent crop growth in tropical basins, the proposed procedures included changes in dormancy routines of SWAT source code and modifications of scheduled management operations and plant growth database parameters. These modifications were tested in five different basins at São Paulo State, Brazil, with areas ranging from 42 to 5959 km², by comparing the results before and after their implementation. Annual water balance analysis showed an increase in evapotranspiration about 61% for basins, approaching the total annual evapotranspiration estimated by empirical methods. Hence, it was observed that surface runoff and base flow components showed a decrease. The modifications resulted in improved flow simulation for all basins, showing better Nash-Sutcliffe Efficiency Coefficient (NSE) values compared to the unchanged simulation. Calibration and validation processes used the modified simulation database, being achieved monthly NSE between 0.71 – 0.73 at calibration and 0.53 – 0.88 at validation, while daily NSE were 0.51 – 0.82 at calibration and 0.38 – 0.83 at validation. Overall, minimizing distortions in hydrological processes at pre-calibration step resulted in good estimations without excessive modification of parameters at calibration, attesting a consistent hydrological modeling for the basins analyzed.

Around the world, many forested areas have been and continue to be cleared for expanding agriculture. Canada’s remaining forested lands account for around 9% of the world’s forest cover. Although only a fraction is lost to deforestation annually (0.02%, 2013), Statistics Canada reports that conversion to agriculture is the most significant driver of forest loss. As climate changes and agricultural demand expands, this trend is expected to continue, and ecosystems will continue to be impacted by resulting habitat loss and hydrological changes that can impact infrastructure and communities. Additionally, changes to sediment and nutrient loadings can harm ecosystems and affect the downstream usability of freshwater supplies. The impact of increased sediment and nutrient concentrations in freshwater systems has been extensively documented in the literature. In some extreme cases, it can lead to anoxic ‘dead zones’ in riverine, lacustrine, and marine habitats. Many river systems in Canada have shown elevated nutrient levels in recent years, often tied to the expansion of agricultural land use and destruction of natural forests to increasing nutrient levels in downstream rivers, lakes, and oceans. This study applies numerical modelling to quantify the influence of forest loss, agricultural expansion and the application of best management practices (BMPs) on water quality and quantity in the South Nation Watershed in eastern Ontario, Canada. The land use in the watershed is mainly agricultural (over 60%) with forest (27%) that is unevenly distributed in the basin. Aerial photography surveys from 2008 and 2014 show a steady decline in forest cover. Recent water quality monitoring has shown nutrient concentrations at or above Canadian water quality standards in many parts of the basin. The Soil and Water Assessment Tool (SWAT) was used to model the watershed because of its capacity to simulate comprehensive land management scenarios and assess their impact on a variety of water quantity and parameters quickly and effectively. The work was performed in four steps: 1. Recent land use configurations (2008-2014) in the watershed were acquired, and simplified land use projections based on the direct substitution of cropland for forest land were developed. 2. A numerical model was calibrated and validated for the initial land use scenario. 3. These land use scenarios, as well as more hypothetical scenarios representing more extensive deforestation and reforestation, were used as the basis for hydrological modelling using 31 years of real-world meteorological observations. 4. Idealized vegetated filter strips (VFSs) and grassed waterways (GWWs) were added to the cropped land packages to study the potential of these practices to contribute to the management of water quality. Analysis of the 33 output datasets derived from simulations of the suite of land use scenarios with and without VFSs and GWWs leads to several conclusions, while also raising some questions. Generally, forests significantly reduce sediment, nitrate and phosphorus outputs to streams as well as slightly reducing water yield compared to cropped areas due to an increase in surface runoff, groundwater and lateral flow combined with the absence of tile drainage. Across subbasins, this translates to significant reductions in sediment, nitrate and total phosphorus loadings entering the river reaches and a slight increase in water yield. At the basin outlet near Plantagenet, Ontario, streamflow and sediment loading show to have little sensitivity to changes in forest and crop cover, while increased forest cover leads to significantly reduced nutrient loadings, particularly in late spring and early winter. It is clear from this work that continued deforestation will continue to drive further nutrient enrichment in the South Nation River, while VFSs seems to have a significant potential for offsetting some of this enrichment. Streamflow and sediment loadings, however, are not significantly impacted by foreseeable deforestation. The influence of land use change and BMPs was much more significant in the runoff than in exports from the basin, suggesting there would be value in further examination of water quality and quantity at a higher spatial density to expand on assumptions of in-stream processes made here.

The impacts of climate variability and change on streamflow are of increasing concern, particularly as human demands on water supplies compete with the needs of natural ecosystems. The consequences on the hydrological cycle are predicted to be most severe for mid- to high-latitude regions. Of particular concern is reduced mountain snow accumulation and related reductions in the snow- and glacier-derived water supply. In northern British Columbia (BC), recent snowpack declines have caused a unique water management challenge. Diminishing water security in a region considered water-abundant has intensified over the last decade. Characterizing the climate controls on hydrologic variability is a priority for developing baseline information required for water supply forecasting. This research focuses on developing multi-century, annually-resolved records of snow water equivalent (SWE) and streamflow to provide a better understanding of long-term hydroclimate variability for the design and implementation of management strategies that balance riverine ecosystem services, such as recreation and fish habitat, with increasing economic and social demands. Climate sensitive tree-ring chronologies provide the opportunity to extend instrumental records of hydroclimate by capitalizing on the influence of climate on both annual radial growth and seasonal runoff. Traditional dendrohydrology relies on moisture-limited tree species from dry, continental settings. This dissertation presents a new method by focusing on mid- to high-elevation conifers sensitive to snowpack variability. Ring-width and maximum latewood density records from mountain hemlock (Tsuga mertensiana (Bong.) Carriere), white spruce (P. glauca (Moench) Voss), and subalpine fir (Abies lasiocarpa (Hook.) Nutt.) stands were collected at sites in northern BC. Dendrochronological techniques were used to develop a: 1) 223-year record of April 1 SWE for the Stikine River basin; 2) 417-, 716-, and 343-year record of summer streamflow for the Skeena, Nass and Stikine rivers, respectively; and, 3) a 193-year reconstruction of summer-run Skeena River steelhead abundance based on the influence of ocean-atmospheric forcings on both radial tree growth and steelhead escapement. The April 1 SWE record suggests that there has been considerable variability in snowpack levels in the Stikine basin and a distinct in-phase relationship with seasonalized Pacific Decadal Oscillation (PDO) indices, not seen in basins to the south. The summer streamflow records also support a north-south “see-saw” effect, suggesting an association between moisture transport and atmospheric-ocean circulation in the region. In addition to the snow-sensitive tree-ring data, the streamflow models incorporated paleo-hemispheric records to improve predictive skill. Finally, the steelhead model described alternating intervals of persistently above-average and below-average abundance that corresponded to oceanic PDO-like influences and describe links to “warm-warm” ENSO-PDO years associated with in-river low flow periods. The reconstructions suggest that: 1) recent snowpack and streamflow declines are a rare event over a multi-century context; and, 2) existing instrumental records do not adequately represent the historic range of basin-specific hydroclimate variability necessary for new planning horizons. Mid- to high-elevation, snow-sensitive conifers have strong potential as paleohydrological proxies and for expanding the application of dendrohydrology to non-arid settings. Current conditions in northern BC, compounded by land use changes and climate change, are predicted to become more severe in the future. It is important that planning regimes incorporate long-term hydroclimate data to better understand and quantify how water supply and ecosystems will respond to future changes. / Graduate

Hydrological extremes associated with climate change are becoming an increasing concern all over the world. Frequent flooding, one of the extremes, needs to be analyzed while considering climate change to mitigate flood risk. This study forecasted streamflow and evaluated the risk of flooding in the Neuse River, North Carolina considering future climatic scenarios, and comparing them with an existing Federal Emergency Management Agency (FEMA) flood insurance study (FIS) report. The cumulative distribution function transformation (CDF-t) method was adopted for bias correction to reduce the uncertainty present in the Coupled Model Intercomparison Project Phase 6 (CMIP6) streamflow data. To calculate 100-year and 500-year flood discharges, the Generalized Extreme Value (GEV) (L-Moment) was utilized on bias-corrected multimodel ensemble data with different climate projections. The delta change method was applied for the quantification of flows, utilizing the future 100-year peak flow and FEMA 100-year peak flows. Out of all projections, shared socio-economic pathways (SSP)5-8.5 exhibited the maximum design streamflow, which was routed through a hydraulic model, the Hydrological Engineering Center’s River Analysis System (HEC-RAS), to generate flood inundation and risk maps. The result indicates an increase in flood inundation extent compared to the existing study, depicting a higher flood hazard and risk in the future. This study highlights the importance of forecasting future flood risk and utilizing the projected climate data to obtain essential information to determine effective strategic plans for future floodplain management.

Global flood forecasting can benefit developing countries and ungauged regions that lack observational data, computational infrastructure, and human capacity for streamflow modeling. Many technical challenges exist to provide flood predictions on a global scale. First, existing land surface forecasts use coarse resolution grid cells, which provide limited information when used for flood forecasting at local scales. There is, so far, no modeling system that can provide rapid and accurate global flood predictions with low cost. Second, accurate flood predictions often require integrating interdisciplinary models, data sources, and analysis routines into a workflow. Limited accessibility, reusability, and interoperability of models restrict integrated modeling from producing more reliable results. Web services have been demonstrated as an effective way for data and model sharing because of the capability of enabling communication among heterogeneous applications over the internet. However, publishing models or analysis routines as web services is still challenging and, hence, is not commonly done. To address the above challenges, I present a computational system for global streamflow prediction, using existing, well-established open source software tools, that quickly downscales the runoff generated from such coarse grid-based land surface models (LSMs) onto high-resolution vector-based stream networks then routes the results using a vector-based river routing model. A set of experiments are conducted to demonstrate the feasibility and credibility of this approach. I also present a tool to publish complex environmental models as web services by adopting the OpenGMS Wrapper System (OGMS-WS) and Docker. The streamflow prediction system is deployed as a web service using this tool, and the service is used to analyze the historical streamflow tendency in Bangladesh. Next, I present a ready-to-use tool called Tethys WPS Server, which provides a simplified and formalized way to expose web app functionality as standardized Open Geospatial Consortium (OGC) Web Processing Services (WPS) alongside a web app's graphical user interface. Three Tethys web apps are developed to demonstrate how web app functionality(s) can be exposed as WPS using Tethys WPS Server, and to show how these WPS can be coupled to build a complex modeling web app. In sum, this dissertation explores new computational approaches and software tools to advance global streamflow prediction and integrated environmental modeling.