Entender como o balanço hídrico de uma bacia hidrográfica é afetado pela conversão de florestas em cultivos agrícolas e pastagens permite avaliar os possíveis impactos da mudança de uso e cobertura do solo na sustentabilidade regional. Com o modelo hidrológico de grande escala VIC (Variable Infiltration Capacity) calibrado para as condições locais simulou-se os possíveis efeitos em três cenários de substituição da cobertura vegetal na bacia do rio Ji-Paraná, Rondônia. Um cenário imagina a substituição total da floresta pela cultura da soja, e nessas condições a vazão do rio aumentou em 28% durante o período chuvoso, e em até 70% na época seca, quando comparados às vazões atuais. Quando a substituição foi por pastagens esse aumento foi um pouco menor, 11% no período chuvoso e 16% no período seco. Esses dois cenários mutuamente exclusivos foram selecionados por representar condições extremas de uso do solo. Um terceiro cenário simulou a possível condição original da bacia coberta totalmente pela floresta. Esse último cenário permite inferir sobre as possíveis conseqüências das mudanças já ocorridas visto que as medidas de vazão são recentes (menos de 30 anos). Nessa condição a vazão sofreu redução de 9% durante o período chuvoso e de 20% no período seco. O modelo indicou ainda redução de 30% na evapotranspiração dessas culturas, durante o período seco, quando comparado ao cenário de floresta. / The understanding of how the water balance of a hydrographic basin is affected by the conversion of forests into crops and pasture allow to evaluate the possible impacts of the land use and land cover changes in the regional sustainability. Using a macro-scale hydrologic VIC (Variable Infiltration Capacity) model calibrated for local conditions we simulated the possible effects on the hydrology under three scenarios of land cover substitution of the Ji-Paraná basin, state of Rondônia (western region of Brazil). One scenario simulated the total replacement of forest by soybeans crops, under this condition the outflow of the river increased in 28% during the rainy period, and up to 70% at the dry period, when comparative to the current outflows. When forest was replaced by pastures, this increase was a little lower, 11% in rainy season and 16% in the dry period. These two exclusive scenarios have been selected by representing extreme conditions of land use. One third scenario simulated the possible original condition of the basin covered by forest. This last scenario allows to infer on the possible consequences of the actual changes since recent measures of outflow (less than 30 years). In this condition the outflow suffered a reduction of 9% during the rainy period and 20% in the dry period. The model indicated a decrease of 30% in evapotranspiration for these crops in dry period compared to the forest scenario.

Entender como o balanço hídrico de uma bacia hidrográfica é afetado pela conversão de florestas em cultivos agrícolas e pastagens permite avaliar os possíveis impactos da mudança de uso e cobertura do solo na sustentabilidade regional. Com o modelo hidrológico de grande escala VIC (Variable Infiltration Capacity) calibrado para as condições locais simulou-se os possíveis efeitos em três cenários de substituição da cobertura vegetal na bacia do rio Ji-Paraná, Rondônia. Um cenário imagina a substituição total da floresta pela cultura da soja, e nessas condições a vazão do rio aumentou em 28% durante o período chuvoso, e em até 70% na época seca, quando comparados às vazões atuais. Quando a substituição foi por pastagens esse aumento foi um pouco menor, 11% no período chuvoso e 16% no período seco. Esses dois cenários mutuamente exclusivos foram selecionados por representar condições extremas de uso do solo. Um terceiro cenário simulou a possível condição original da bacia coberta totalmente pela floresta. Esse último cenário permite inferir sobre as possíveis conseqüências das mudanças já ocorridas visto que as medidas de vazão são recentes (menos de 30 anos). Nessa condição a vazão sofreu redução de 9% durante o período chuvoso e de 20% no período seco. O modelo indicou ainda redução de 30% na evapotranspiração dessas culturas, durante o período seco, quando comparado ao cenário de floresta. / The understanding of how the water balance of a hydrographic basin is affected by the conversion of forests into crops and pasture allow to evaluate the possible impacts of the land use and land cover changes in the regional sustainability. Using a macro-scale hydrologic VIC (Variable Infiltration Capacity) model calibrated for local conditions we simulated the possible effects on the hydrology under three scenarios of land cover substitution of the Ji-Paraná basin, state of Rondônia (western region of Brazil). One scenario simulated the total replacement of forest by soybeans crops, under this condition the outflow of the river increased in 28% during the rainy period, and up to 70% at the dry period, when comparative to the current outflows. When forest was replaced by pastures, this increase was a little lower, 11% in rainy season and 16% in the dry period. These two exclusive scenarios have been selected by representing extreme conditions of land use. One third scenario simulated the possible original condition of the basin covered by forest. This last scenario allows to infer on the possible consequences of the actual changes since recent measures of outflow (less than 30 years). In this condition the outflow suffered a reduction of 9% during the rainy period and 20% in the dry period. The model indicated a decrease of 30% in evapotranspiration for these crops in dry period compared to the forest scenario.

Numerous studies indicate that the hydrology of a river basin is influenced by Land Use Land Cover (LULC) and climate. LULC affects the quality and quantity of water resources through its influence on Evapotranspiration (ET) and initiation of surface runoff while climate affects the intensity and spatial distribution of rainfall and temperature which are major drivers of the hydrologic cycle. Literature reports several works on either the effect of changing LULC or climate on the hydrology. However, changes in LULC and climate occur simultaneously in reality. Thus, there is a need to perform an integrated impact assessment of such changes on the hydrological regime at a basin scale. In order to carry out the impact assessment, physically-based hydrologic models are often employed. The present study focuses on assessment of the effect of changing LULC and climate on the hydrology of the Upper Ganga basin (UGB), India, using the Variable Infiltration Capacity (VIC) hydrologic model. In order to obtain the changes that have occurred in the LULC of the basin over a time period, initially LULC analysis is carried out. For this purpose, high resolution multispectral satellite imageries from Landsat are procured for the years 1973, 1980, 2000 and 2011. The images are pre-processed to project them to a common projection system and are then co-registered. The processed images are used for classification into different land cover classes. This step requires training sites which are collected during the field visit as part of this work. The classified images, thus obtained are used to analyse temporal changes in LULC of the region. The results indicate an increase in crop land and urban area of the region by 47% and 122% respectively from 1973 to 2011. After initial decline in dense forest for the first three decades, an increase in the dense forest is observed between 2000- 2011 (from 11.44% to 14.8%). Scrub forest area and barren land are observed to decline in the study region by 62% and 96% respectively since 1973. The land cover information along with meteorological data and soil data are used to drive the VIC model to investigate the impact of LULC changes on streamflow and evapotranspiration (ET) components of hydrology in the UGB. For the simulation purpose, the entire basin is divided into three regions (1) upstream (with Bhimgodha as the outlet), (2) midstream (with Ankinghat as the outlet) and (3) downstream (with Allahabad as the outlet). The VIC model is calibrated and validated for all the three regions independently at monthly scale. Model performance is assessed based on the criterion of normalized root mean square error (NRMSE), coefficient of determination (R2) and Nash-Sutcliffe efficiency (NSE). It is observed that the model performed well with reasonable accuracy for upstream and midstream regions. In case of the downstream region, due to lack of observed discharge data, model performance could not be assessed. Hence, the simulations for the downstream region are performed using the calibrated model of the midstream region. The model outputs from the three regions are aggregated appropriately to generate the total hydrologic response of the UGB. Using the calibrated models for different region of the UGB, sensitivity analysis is performed by generating hydrologic scenarios corresponding to different land use (LU) and climate conditions. In order to investigate the impact of changing LU on hydrological variables, a scenario is generated in which climate is kept constant and LU is varied. Under this scenario, only the land cover related variables are altered in the model keeping the meteorological variables constant. Thus, the effect of LU change is segregated from the effect of climate. The results obtained from these simulations indicated that the change in LU significantly affects peak streamflow depth which is observed to be 77.58% more in August 2011 in comparison with the peak streamflow of August, 1973. Furthermore, ET is found to increase by 46.44% since 1973 across the entire basin. In order to assess the impact of changing climate on hydrological variables, a scenario is generated in which LU is kept constant and climate is varied from 1971-2005. Under this scenario, land cover related variables are kept constant in the model and meteorological variables are varied for different time periods. The results indicate decline in the simulated discharge for the years 1971, 1980, 1990, 2000 and 2005, which is supported by decline in observed annual rainfall for the respective years. Amongst 1971 and 2005, year 2005 received 26% less rainfall resulting in 35% less discharge. Furthermore, ET is observed to be negligibly affected. To understand the integrated impact of changing LU and climate on hydrological variables, a scenario is generated in which both climate and LU are altered. Based on the data available, three years (1973, 1980 and 2000) are considered for the simulations. Under this scenario, both land cover and meteorological variables are varied in the model. The results obtained showed that the discharge hydrograph for the year 1980 has significantly higher peak compared to the hydrographs of years 1973 and 2000. This could be due to the fact that the year 1980 received maximum rainfall amongst the three years considered for simulations. Although the basin received higher rainfall in the year 1980 compared to that in 2000, ET from the basin in the year 1980 is found to be 21% less than that of the year 2000. This could be attributed to the change in LU that occurred between the years 1980 and 2000. Amongst the years 1973 and 2000, there is not much difference in the observed rainfall but ET for the year 2000 is observed to be significantly higher than that of year 1973. It is concluded from the present study that in the UGB, changing LULC contributes significantly to the changes in peak discharge and ET while rainfall pattern considerably influences the runoff pattern of the region. Future work proposed includes assessment of hydrologic response of basin under future LULC and climate scenarios. Also the model efficiency can be assessed by performing hydrologic simulations at different grid sizes.

<p dir="ltr">Tropical Cyclones (TCs) are intense low-pressure weather systems that acts as a meteorological monster causing severe rainfall and widespread freshwater flooding, leading to extensive damage and disruption. Quantitative precipitation estimates (QPEs) are crucial for accurately understanding and evaluating the impacts of TCs. However, QPEs derived from various modalities, such as rain gauges, ground-based merged radars, and satellites, can differ significantly and require thorough comparison. Understanding the limitations/advantages of using each QPE is essential to simulate a hydrological model especially to estimate extreme events like TCs. The objective of the dissertation is to 1) characterize the tropical cyclone precipitation (TCP) using three gridded products, 2) characterize the impact of using different QPEs in estimation of hydrological variables using a hydrology model, and 3) understand the usability of satellite-derived QPEs for eight cases of TC and its impact on the estimate of hydrological variables. The QPEs include near real-time and post-processed satellite data from NASA’s Global Precipitation Mission-Integrated Multi-sensor Retrievals for GPM Rainfall Product (IMERG), merged ground radar observations (Stage IV) from the National Centers for Environmental Prediction (NCEP), and interpolated gauge observations from the National Weather Service Cooperative Observer Program (GCOOP). The study quantifies how differences in rainfall intensity and location, as derived from these gridded precipitation datasets, impact surface hydrology. The Variable Infiltration Capacity (VIC) model and the geographic information system (GIS) routing assess the propagation of bias in the daily rainfall rate to total runoff, evapotranspiration, and flooding. The analysis covers eight tropical cyclones, including Hurricane Charley (2004), Hurricane Frances (2004), Hurricane Jeanne (2004), Tropical Storm Fay (2008), Tropical Storm Beryl (2012), Tropical Storm Debby (2012), Hurricane Irma (2017) and Hurricane Michael (2018) focusing on different regions in South-Atlantic Gulf region and land uses. The findings indicate that IMERG underpredicts precipitation at higher quantiles but aligns closely with ground-based and radar-based products at lower quantiles. IMERG reliably estimates total runoff and evapotranspiration in 90% of TC scenarios along the track and in agricultural and forested regions. There is substantial overlap ~ 70% between IMERG and GCOOP/Stage IV for the 90th percentile rainfall spatially for the case of TC Beryl 2012. Despite previous perceptions of underestimation, the study suggests that satellite-derived rainfall products can be valuable in simulating streamflow, particularly in data-scarce regions where ground estimates are lacking. The relative error in estimation is 12% and 22% when using IMERG instead of Stage IV and GCOOP rainfall data. The findings contribute to a broader perspective on usability of IMERG in estimating near real-time hydrological characteristics, paving the way for further research in this area. This analysis demonstrates that IMERG can be a reliable data product for hydrological studies even in the extreme events like landfalling TCs. This will be helpful in improving the preparedness of vulnerable communities and infrastructure against TC-induced flooding in data scare regions.</p>