Tanzania, like other developing countries in the tropics is severely affected by the degradation of water resources owing to improper land management practices. Such practices affect water supply through soil erosion which does not only cause sedimentation of rivers and water bodies but also leads to a reduction in the rainwater infiltration capacity of soils. This thesis seeks to demonstrate how the implementation of proper land management measures can reduce soil erosion and increase water supply in the Morogoro River catchment (Uluguru Mountains). The proper practices referred to are the soil and water conservation (SWC) approaches which include contour farming, fanya juu terracing and bench terracing. The thesis combines social science and geoscience methods in a synergetic manner to address this research problem. To understand how and to what degree SWC methods affect water fluxes and sediment yields, the hydrological model SWAT (Soil and Water Assessment Tool) was applied. Before carrying out the modelling procedures, it was necessary to examine the level of SWC adoption among farmers and factors influencing the process so as to establish the baseline. To this end, biophysical and socio-economic factors assumed to affect farmers’ adoption tendency were examined using a household questionnaire. Modelling results indicate that if correctly implemented contour farming, fanya juu terracing and bench terracing would significantly reduce sediment yield at different rates. The reduction would range approximately between 1% - 85% with the highest percentage change achieved by practicing the three SWC methods simultaneously. However, such SWC measures would not increase water flow annually owing to evapotranspiration losses. Nevertheless, according to modelling results groundwater storage would be increased by about 14% and hence contributing to water supply during the dry season. The household questionnaire survey suggests that the adoption of SWC methods in the study area is very low and complex. While age of the head of household, access to extension (professional) services, household annual income and proximity to the farm significantly influenced farmers’ decision to adopt SWC, gender of the head of household, slope characteristics of the farm, number of adults in the household and farmer’s perception on soil erosion effects had no considerable influence on adoption. Therefore, to successfully realize the SWC benefits demonstrated by the modelling results, smallholder farmers upstream of the catchment should be incentivized to implement proper land management practices. Payment for ecosystem services scheme appears to be a suitable strategy. To make this operational, the Tanzanian government should establish a national water fund which will finance watershed management activities. The methodological approach employed in this thesis is transferrable to other sites with problems comparable to the studied catchment.

No description available.

The Midwest US has experienced significant changes in agricultural land use and management practices in recent decades. Cropland expansion, crop rotation change, and crop phenology changes could lead to divergent environmental impacts on linked ecosystems. The overall objective is to examine agricultural land use and management changes and their impacts on water quality in the Midwest US, which is addressed in three separate studies. The first study examined spatial and temporal dimensions of agricultural land use dynamics in east-central Iowa, 2001-2012. Results of this study indicated that increases in corn production in response to US biofuel policies had been achieved mainly by altering crop rotation. This study also examined spatial relationships between cultivated fields and crop rotation practices with respect to underlying soils and terrain. The most intensively cultivated land had shallower slopes and fewer pedologic limitations than others, and the corn was planted on the most suitable soils. The second study characterized key crop phenological parameters (SOS and EOS) for corn and soybean and analyzed their spatial patterns to evaluate their change trends in the Midwest US, 2001-2015. Results showed that MODIS-derived SOS and EOS values are sensitive to input time-series data and threshold values chosen for crop phenology detection. The non-winter MODIS NDVI time-series input data, and a lower threshold value (i.e., 40%) both generated better results for SOS and EOS estimates. Spatial analyses of SOS and EOS values displayed clear south-north gradient for corn and trend analyses of SOS revealed only a small percentage of counties showed statistically significant earlier trends within a user-defined temporal window (2001-2012). The third study integrated remote sensing-derived products from the first two studies with the SWAT model to assess impacts of agricultural management changes on sediment and nutrient yields for three selected watersheds in the Midwest US. With satisfied calibration and validation results for stream flows, sediment and nutrient yields, considered under differing management scenarios, were compared at different spatial scales. Results showed that intensive crop rotation, advancing the planting date with the same length of growing season, and longer growing seasons, dramatically increased, maintained, and slightly reduced sediment, total nitrogen, and total phosphorous yields, respectively. Overall, these studies together illuminate relationships between broad-scale agricultural policies, management decisions, and environmental impacts, and the value of multi-temporal, broad-scale, geospatial analysis of agricultural landscapes. / Ph. D.

In 2011, the Deep River Portage-Burns Waterway Watershed was identified as a priority in the Northwest Indiana watershed management framework by the Northwester Indiana Regional Planning Committee. 319 grant cost-share programs were initiated in effort of maintaining and restoring the health of Deep River Portage-Burns Waterway Watershed. A watershed management plans have been developed for this watershed which proposed the implementation of vegetated filter strips (VFS) as an option. In this thesis work, the effectiveness of VFS as a best management practice (BMP) for the Deep River system was evaluated using a hydrological model scheme. <div><br></div><div>In this research, a Nonpoint Source Pollution and Erosion Comparison Tool (NSPECT) model and a Soil Water Assessment Tool (SWAT) model were constructed with required watershed characteristic data and climate data. The initial hydrologic and nutrient parameters of the SWAT model were further calibrated using SWAT Calibration and Uncertainty Programs (SWAT_CUP) with historical flow and nutrient data in a two-stage calibration process. The calibrated parameters were validated to accurately simulate the field condition and preserved in SWAT model for effectiveness analysis of BMP implementations. </div><div><br></div><div>To evaluate the effectiveness of VFS as a BMP, four different scenarios of VFS implementations along the Turkey Creek was simulated with the calibrated SWAT model. With the implementation of VFS in the tributary subbasin of Turkey Creek, the annual total phosphorus (TP) of the VFS implemented subbasin was reduced by 1.60% to 78.95% and the annual TP of downstream subbasins were reduced by 0.09% to 55.42%. Daily percentage of TP reductions ranged from 0% to 90.3% on the VFS implemented subbasin. Annual TP reductions of the four scenarios ranged from 28.11 kg to 465.01 kg.<br></div>

A degradação ambiental do Noroeste do Estado do Rio de Janeiro tem se intensificado nas últimas décadas devido às práticas agrícolas não preservacionistas. Esta situação, que decorre do uso inadequado do solo, tem implicado em mudanças na oferta hídrica em grau variável nos municípios da região com prejuízos econômicos nas atividades dos pequenos e médios proprietários rurais e na qualidade de vida. A abordagem para enfrentar problemas deste tipo depende da participação efetiva das instâncias de governo e dos órgãos responsáveis pela gestão dos recursos hídricos. No âmbito da hidrologia os modelos hidrológicos com base no uso e ocupação do solo são ferramentas que podem auxiliar com ótimo custo e benefício a geração de informações em bacias hidrográficas, instrumentadas ou não. Os modelos são úteis ao planejamento e à tomada de decisão por possibilitarem a previsão de vazões e simulação de cenários sobre o uso do solo e qualidade da água. Neste sentido, o presente estudo pretende dar sua contribuição ao avaliar a adequabilidade do modelo SWAT simular o processo chuva-vazão na microbacia experimental de Santa Maria e Cambiocó, com 13,5 km2, localizada na região hidrográfica do rio Muriaé, afluente do rio Paraíba do Sul. O SWAT tem sido empregado em bacias agrícolas nos EUA, na Europa e, atualmente, na China, sudeste asiático e Irã, entre outros países, e na última década maior inserção no meio acadêmico brasileiro. A versão 2005 do modelo foi utilizada por meio da sua interface SIG para simular as vazões médias diárias com base na precipitação medida no intervalo de 15 minutos no período de 2005/2006. As vazões simuladas foram comparadas com as vazões observadas no exutório da microbacia. Foram testadas as ferramentas de análise de sensibilidade e autocalibração. O método de calibração manual foi usado para o ajuste por tentativa e erro. Os parâmetros ajustados corresponderam ao CN2 e ESCO. Os valores obtidos na calibração para os coeficientes estatísticos R2, NSE, PBIAS e RSR foram 0,80, 0,80, 7,02 e 0,45, respectivamente, indicando escore muito bom, o que foi confirmado pela inspeção dos hidrogramas. As saídas validadas para período diferente da calibração forneceram para os mesmos coeficientes os valores 0,84, 0,80, 25,92 e 0,44. Os dois primeiros, com escore muito bom. O valor de PBIAS, no limite do satisfatório, e RSR, muito bom. O desempenho permitiu concluir que a simulação com o SWAT foi adequada. Em relação às pesquisas que têm sido realizadas no Brasil os valores obtidos para os indicadores foram semelhantes, indicando a capacidade do modelo para novos estudos nesta microbacia que considerem os usos consuntivos e cenários de uso do solo. / The environmental degradation in the Northwest region of the State of Rio de Janeiro has intensified in the last decades due to no preservationist agricultural practices. This arises from inappropriate land use that has been associated to changes in water supply to a varying extent in the Regions municipalities. These, has leaded to economic losses in the activities of small and medium rural homeowners, and quality of life decaying. The approach to address such problems depends on the active participation of government bodies and agencies responsible for water resources management. Hydrological simulation models can assist with great value and benefit to the generation of information in basins, instrumented or not. Models are useful for planning and decision making as they allow the discharges forecasting and simulation scenarios on land use and water quality. In this context, the study aims to make a contribution to assess the suitability of the rainfall-runoff component of the SWAT model in the Santa Maria and Cambiocó catchment, with 13.5 km2, located in Muriaés river basin, a tributary of the Paraíba do Suls river basin. SWAT has been employed in agricultural basins in the U.S., Europe, and currently in China, Southeast Asia and Iran, among other countries, and had in the last decade greater insertion in the Brazilian academia. The 2005 version of the model was used through its GIS interface to simulate the daily mean discharges based on rainfall measured at 15 minute intervals from 2005/2006. Simulated and observed discharges at catchments outlet gage station have been compared. Tools for sensitivity analysis and calibration were tested. Manual calibration adjustment was conducted with CN2 and ESCO parameters. The values obtained by calibration for the statistical coefficients R2, NSE, PBIAS and RSR were 0.80, 0.80, 7.02 and 0.45, respectively, indicating "very good" score. This was confirmed by inspection of hydrographs. The validation period for the different outputs provided the coefficients 0.84, 0.80, 25.92 and 0.44. The R2 and NSE matched a very good score. The PBIAS was at the limit of satisfactory and RSR, very good. The results showed that SWAT simulations were appropriate comparing with others studies in Brazil. The model can be recommended for further studies in this catchment for modeling consumptive uses and land use scenarios.

A degradação ambiental do Noroeste do Estado do Rio de Janeiro tem se intensificado nas últimas décadas devido às práticas agrícolas não preservacionistas. Esta situação, que decorre do uso inadequado do solo, tem implicado em mudanças na oferta hídrica em grau variável nos municípios da região com prejuízos econômicos nas atividades dos pequenos e médios proprietários rurais e na qualidade de vida. A abordagem para enfrentar problemas deste tipo depende da participação efetiva das instâncias de governo e dos órgãos responsáveis pela gestão dos recursos hídricos. No âmbito da hidrologia os modelos hidrológicos com base no uso e ocupação do solo são ferramentas que podem auxiliar com ótimo custo e benefício a geração de informações em bacias hidrográficas, instrumentadas ou não. Os modelos são úteis ao planejamento e à tomada de decisão por possibilitarem a previsão de vazões e simulação de cenários sobre o uso do solo e qualidade da água. Neste sentido, o presente estudo pretende dar sua contribuição ao avaliar a adequabilidade do modelo SWAT simular o processo chuva-vazão na microbacia experimental de Santa Maria e Cambiocó, com 13,5 km2, localizada na região hidrográfica do rio Muriaé, afluente do rio Paraíba do Sul. O SWAT tem sido empregado em bacias agrícolas nos EUA, na Europa e, atualmente, na China, sudeste asiático e Irã, entre outros países, e na última década maior inserção no meio acadêmico brasileiro. A versão 2005 do modelo foi utilizada por meio da sua interface SIG para simular as vazões médias diárias com base na precipitação medida no intervalo de 15 minutos no período de 2005/2006. As vazões simuladas foram comparadas com as vazões observadas no exutório da microbacia. Foram testadas as ferramentas de análise de sensibilidade e autocalibração. O método de calibração manual foi usado para o ajuste por tentativa e erro. Os parâmetros ajustados corresponderam ao CN2 e ESCO. Os valores obtidos na calibração para os coeficientes estatísticos R2, NSE, PBIAS e RSR foram 0,80, 0,80, 7,02 e 0,45, respectivamente, indicando escore muito bom, o que foi confirmado pela inspeção dos hidrogramas. As saídas validadas para período diferente da calibração forneceram para os mesmos coeficientes os valores 0,84, 0,80, 25,92 e 0,44. Os dois primeiros, com escore muito bom. O valor de PBIAS, no limite do satisfatório, e RSR, muito bom. O desempenho permitiu concluir que a simulação com o SWAT foi adequada. Em relação às pesquisas que têm sido realizadas no Brasil os valores obtidos para os indicadores foram semelhantes, indicando a capacidade do modelo para novos estudos nesta microbacia que considerem os usos consuntivos e cenários de uso do solo. / The environmental degradation in the Northwest region of the State of Rio de Janeiro has intensified in the last decades due to no preservationist agricultural practices. This arises from inappropriate land use that has been associated to changes in water supply to a varying extent in the Regions municipalities. These, has leaded to economic losses in the activities of small and medium rural homeowners, and quality of life decaying. The approach to address such problems depends on the active participation of government bodies and agencies responsible for water resources management. Hydrological simulation models can assist with great value and benefit to the generation of information in basins, instrumented or not. Models are useful for planning and decision making as they allow the discharges forecasting and simulation scenarios on land use and water quality. In this context, the study aims to make a contribution to assess the suitability of the rainfall-runoff component of the SWAT model in the Santa Maria and Cambiocó catchment, with 13.5 km2, located in Muriaés river basin, a tributary of the Paraíba do Suls river basin. SWAT has been employed in agricultural basins in the U.S., Europe, and currently in China, Southeast Asia and Iran, among other countries, and had in the last decade greater insertion in the Brazilian academia. The 2005 version of the model was used through its GIS interface to simulate the daily mean discharges based on rainfall measured at 15 minute intervals from 2005/2006. Simulated and observed discharges at catchments outlet gage station have been compared. Tools for sensitivity analysis and calibration were tested. Manual calibration adjustment was conducted with CN2 and ESCO parameters. The values obtained by calibration for the statistical coefficients R2, NSE, PBIAS and RSR were 0.80, 0.80, 7.02 and 0.45, respectively, indicating "very good" score. This was confirmed by inspection of hydrographs. The validation period for the different outputs provided the coefficients 0.84, 0.80, 25.92 and 0.44. The R2 and NSE matched a very good score. The PBIAS was at the limit of satisfactory and RSR, very good. The results showed that SWAT simulations were appropriate comparing with others studies in Brazil. The model can be recommended for further studies in this catchment for modeling consumptive uses and land use scenarios.

Submitted by Fabio Sobreira Campos da Costa (fabio.sobreira@ufpe.br) on 2016-07-15T11:43:49Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Tese_Jose_Yure_dos_Santos.pdf: 6049746 bytes, checksum: d533bc6b66a0573fffd96f9b53e94460 (MD5) / Made available in DSpace on 2016-07-15T11:43:50Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Tese_Jose_Yure_dos_Santos.pdf: 6049746 bytes, checksum: d533bc6b66a0573fffd96f9b53e94460 (MD5) Previous issue date: 2015-12-09 / FACEPE / Este estudo teve por objetivo realizar uma analise espaço-temporal dos processos hidrossedimentológicos na Bacia do Rio Tapacurá, localizada no Estado de Pernambuco, Nordeste brasileiro, mediante utilização de um modelo hidrossedimentológico integrado ao SIG e diferentes cenários de clima e uso do solo. Para a modelagem dos processos hidrossedimentológicos da bacia, foi utilizado o modelo Soil and Water Assessment Tool (SWAT), além de dados de clima, elevação, mapas e dados de uso e tipos de solo. O modelo SWAT foi utilizado para analisar os processos hidrossedimentológico (escoamento superficial, vazão, propagação e produção de sedimentos) em diferentes condições de clima e uso do solo: (i) condições atuais (período de 1995−2012); (ii) condições da década de 1970 (período de 1967−1974); e (iii) cenários futuros. Para avaliar os cenários futuros, foram utilizados dados previstos pelo modelo Eta−HadGEM para os cenários RCP 4.5 e RCP 8.5, nos períodos de 2011−2040, 2041−2070 e 2071−2099, além de duas condições distintas de uso e ocupação do solo: (a) uso do solo de 2001; (b) alterações hipotéticas (intensificação da monocultura de cana-de-açúcar, expansão de áreas urbanas e supressão de áreas de vegetação nativa). O modelo foi calibrado e validado usando dados observados de vazão, e a produção de sedimentos foi verificada usando dados disponíveis na seção sedimentométrica do Rio Tapacurá. A modelagem da Bacia do Rio Tapacurá, pelo modelo SWAT, apresentou bons resultados, com valores de R², NSE e PBIAS satisfatórios, tanto na fase de calibração e validação da vazão, quanto na verificação da produção de sedimentos. Na análise das alterações ocorridas no uso e ocupação do solo da Bacia do Rio Tapacurá, constatou-se que ocorreu uma acentuada alteração no uso e ocupação do solo, quando comparados os cenários de uso e ocupação do solo da década de 1970 e o cenário do período de 1995−2012. A vegetação nativa foi suprimida consideravelmente da bacia, para dar lugar às atividades agrícolas e pecuárias, com destaque para a expansão da monocultura da cana-de-açúcar, o que ocasionou uma produção de sedimentos maior no cenário de 1995−2012. Com relação à simulação de cenários futuros de alterações no clima e uso do solo, a produção de sedimentos estimada foi maior para o cenário de alterações hipotéticas de uso do solo e o cenário RCP 8.5 de mudanças climáticas. Quando comparada ao período base (1995−2012), a produção de sedimentos é superior em ambos os cenários de uso e ocupação do solo e mudanças climáticas. Em relação ao reservatório da Barragem de Tapacurá, de acordo com as projeções futuras, haveria uma potencialização da vazão e carreamento de sedimentos. / This study aimed to carry out a spatio-temporal analysis of runoff-erosion processes in the Tapacurá River basin, Pernambuco state, northeastern Brazil, by means of a runoff-erosion model integrated to the GIS and using different scenarios of climate and land use. For the modeling of basin runoff-erosion process, the Soil and Water Assessment Tool (SWAT) model was used in addition to climate data, elevation, maps and data use and soil types. The SWAT model was used to analyze the runoff-erosion process (surface runoff, flow, propagation and sediment yield) under different conditions of climate and land use: (i) current conditions (1995−2012 period); (ii) conditions of 1970’s decade (1967−1974 period); and (iii) future scenarios. To assess the future scenarios, data provided by the Eta-HadGEM model for RCP 4.5 and RCP 8.5 scenarios were used for the periods 2011−2040, 2041−2070 and 2071−2099, as well as two distinct conditions of land use and occupation: (a) land use 2001; (b) hypothetical changes (intensification of monoculture of sugarcane, expansion of urban areas and suppression of native vegetation areas). The model was calibrated and validated using observed flow data, and the sediment yield was verified using data available in sediment station at Tapacurá River. The Tapacurá river basin modelling, using the SWAT model, showed good results with satisfactory values of R², NSE and PBIAS as for the calibration and validation of the flow, as well for the verification of the sediment yield. In the analysis of changes in the land use and occupation within Tapacurá River Basin, it was found that there was a marked change in land use and occupation, when compared to the land use and occupation scenarios of 1970 and the scenario of 1995−2012. The basin native vegetation was considerably suppressed for agricultural and livestock activities, especially for the expansion of sugarcane monoculture, which caused greater sediment yield in the 1995−2012 scenario. Regarding the simulation of future scenarios of climate and land use changes, the estimated sediment yield was higher for the scenario of hypothetical changes in land use and the climate change RCP 8.5 scenario. Compared to the baseline scenario (1995−2012), the sediment yield is greater for both land use and occupation scenarios and climate changes. Regarding the Tapacurá reservoir, according to the future projections, there would be an enhancement of runoff and sediment yield.

No description available.

This study focuses on modeling the effects of forest management practices on eco-hydrological processes in the Antalya River Watershed, Turkey. With increasing global pressures from urbanization, deforestation, and climate change affecting water resources and ecosystems, understanding the impact of forest management on vital water sources is essential for sustainable water resource management and ecosystem protection. The Soil and Water Assessment Tool (SWAT) model assessed the hydrological impacts of afforestation and urban forest scenarios in the Antalya River Watershed—the model's parameterization, sensitivity analysis, and calibration phases accurately simulated base watershed processes. The validation process confirmed the accuracy of results, particularly in yearly time steps, providing a comprehensive understanding of the watershed's water management strategies. The results indicate that the afforestation scenario reduced surface runoff and increased lateral flow, decreasing erosion risk and improving groundwater recharge. Although soil evaporation and plant transpiration decreased, the increase in “revap” values highlighted higher water vapor emission from the soil, contributing to atmospheric water cycle processes. Similarly, the urban forest scenario resulted in decreased surface discharge and increased groundwater flow, indicating improved water retention and recharge capabilities. The increased evapotranspiration demonstrated the positive influence of trees and vegetation on the water cycle and atmospheric processes, emphasizing the significance of urban forest applications as valuable nature-based solutions for sustainable water resource management and conservation. In conclusion, implementing afforestation and urban forest initiatives can contribute to ecologically sound utilization of water supplies, enhance ecosystem functioning, and foster resilience in the face of environmental obstacles. The study emphasizes the potential benefits of afforestation and expanding green spaces in promoting sustainable water resources and mitigating erosion and flooding risks. The results of this study provide a scientific basis for policymakers and stakeholders to consider afforestation practices as a vital component of water resource management and watershed conservation strategies.

Watershed models are powerful tools for simulating different scenarios to understand the impact of management practices and are used to support and guide decision-making. However, there are often challenges and limitations to using watershed models in some areas of watershed modeling; 1) model calibration in the areas with data limitations; 2) acquiring complete weather data that accurately reflect watershed model responses; 3) accurate representation of manure operation in watershed models. This dissertation addresses each of the aforementioned challenges using new approaches and tools in three studies with the main objective of achieving a better prediction of water quality and quantity and enhancing watershed models. Chapter 2 presents a method (multi-basin calibration (MBC)) to estimate watershed model parameters that lack long-term streamflow records. In the MBC method, first, the Soil and Water Assessment Tool (SWAT) models are initialized individually for several similar neighboring watersheds with a short period of measured streamflow. Then, we aggregate the simulated and observed flows from each initialization with short histories to generate a combined observed-simulated streamflow record that is longer than the initial length of each individual member in order to increase the information content. The Nash-Sutcliffe efficiency (NSE) from this merged time series was used as the basis for calibrating using a differential evolution algorithm. To evaluate the MBC, SWAT models for three newly instrumented USGS gages in Lake Champlain Basin of Vermont, USA, were compared to the commonly used similarity-based regionalization (SBR) approach. Results demonstrate that short periods of hydrological measurement from multiple locations in a basin can represent a system similar to long-term measurements. Chapter 3 develops a method to generate a complete weather data time series with the integration of multiple Global Historical Climatology Network (GHCN) stations and to assess the benefit of much higher density, lower reliability precipitation measurements from private citizens collected by the Community Collaborative Rain, Hail, and Snow (CoCoRaHS) network data that was integrated into the GHCN. To evaluate the performance of the methodology, generated weather data is used to force the Soil and Water Assessment Tool (SWAT) models of 21 United States Department of Agriculture (USDA)-Agricultural Research Service (ARS)-Natural Resource Conservation Service (NRCS)-Conservation Effects Assessment Project (CEAP) watersheds to simulate daily streamflow. The results demonstrated that integration of multiple GHCN stations including higher-density, but perhaps lower-quality weather data can enhance model performance. A comparison with published SWAT model results further corroborated improved model performance using newly combined GHCN data. Chapter 4 develops a hybrid SWAT model, SWAT-Dairy, to accurately represent the impact of manure operation on nutrient transport. The SWAT-Dairy model incorporates process-based livestock routines, developed in the R platform, which quantify daily manure production, stored manure, daily total nitrogen (N) and phosphorus (P), organic and mineral N and P, and dynamic manure nutrient fractions based on animal characteristics, feed characteristics, and environmental conditions. Outputs are then used in SWAT to simulate the impact of livestock manure production. The new model, with simulated manure application management, is applied to a farm in the Little Otter Creek Basin in Vermont, US. Subbasin- and farm-level N and P losses from manure management using the new model were compared for different feed management scenarios. / Doctor of Philosophy / In the past few decades, watershed management has become more challenging due to rapid population growth, climate change, and agricultural practices. In order to achieve better watershed management strategies, it is essential to understand the complex interaction between different biological, physical, and chemical processes occurring in the watershed. Watershed models are useful tools that help scientists and engineers to understand and predict how climate and land-use changes and agricultural management practices affect different components of a watershed system. While watershed models have many advantages, they are often limited by challenges and obstacles, such as model parameter estimations in the areas with limited measured streamflow data, acquiring complete and accurate weather data, and explicit representation of animal management impacts on water quality in manure applications. This dissertation addresses the challenges mentioned earlier by developing new approaches and methods that improve water quality and quantity using watershed models. A long record of measured streamflow data is necessary for watershed models to accurately represent watershed systems and estimate the parameters that cannot be directly measured. However, many watersheds worldwide are not monitored or are newly instrumented with a short period of recorded data. Chapter 2 introduces a new approach (multi basin calibration (MBC)) that integrates short periods of recorded data from several watersheds to provide a similar representation of the watershed system as long-term records. MBC was compared with a commonly used method that requires long recorded streamflow data from a neighboring watershed. The results showed that MBC improved model results and captured hydrological processes better for the watershed with a short period of recorded data than the traditionally used method. Obtaining accurate weather data for a watershed model can also be challenging since land-based weather stations often contain missing data. In recent years, hydrological modelers and researchers have access to the much higher density of weather measurements from private citizens that collect data with inexpensive equipment. However, no study has evaluated the benefits of using much higher-density data from private citizens for watershed modeling. Chapter 3 presents a new methodology to acquire complete weather data time series with the integration of all weather stations, including higher density private citizen-based measurements. Then the weather data were used to force watershed models of 21 watersheds across the United States. The results showed that the new methodology provides weather data that reflect the watershed model response with satisfactory performance ratings in 18 out of 21 watersheds. Lastly, chapter 4 develops a dairy model and integrates it into one of the most commonly used watershed models, the Soil and Water Assessment Tool (SWAT), to investigate how different farm management scenarios impact manure production and nutrient contents as well as their consequent effect on water quality during manure application on farm fields.