Revisiting parameter sensitivities in the Variable Infiltration Capacity model

Despite the Variable Infiltration Capacity (VIC) model being used for decades in the hydrology community, there are still model parameters whose sensitivities remain unknown. Additionally, understanding the factors that control spatial variations in parameter sensitivities is crucial given the increasing interest to obtain spatially coherent parameter fields over large domains. In this study, we investigate the sensitivities of 43 soil, vegetation and snow parameters in the VIC model for 101 catchments spanning the diverse hydroclimates of continental Chile. We implement a hybrid local-global sensitivity analysis approach, using eight model evaluation metrics to quantify sensitivities, with four of them formulated from runoff time series; two characterizing snow processes, and the remaining two based on evaporation processes. Our results confirm an over-parameterization for the processes analysed here, with only 12 (i.e., 28 %) parameters found as sensitive, distributed among soil (7), vegetation (2) and snow (3) model components. Correlation analyses show that climate variables – in particular, mean annual precipitation and aridity index – are the main controls on parameter sensitivities. Additionally, our results highlight the influence of the leaf area index on simulated hydrologic processes – regardless on the dominant climate types – and the relevance of hard-coded snow parameters. Based on correlation results and the interpretation of spatial sensitivity patterns, we provide guidance on the most relevant parameters for model calibration according to the target processes and the prevailing climate type. Overall, the results presented here contribute to improved understanding of model behaviour across watersheds with diverse physical characteristics that encompass a wide hydroclimatic gradient from hyper-arid to humid systems.

A near-global, high resolution land surface parameter dataset for the variable infiltration capacity model

Hydrologic models predict the spatial and temporal distribution of water and energy at the land surface. Currently, parameter availability limits global-scale hydrologic modelling to very coarse resolution, hindering researchers from resolving fine-scale variability. With the aim of addressing this problem, we present a set of globally consistent soil and vegetation parameters for the Variable Infiltration Capacity (VIC) model at 1/16° resolution (approximately 6 km at the equator), with spatial coverage from 60°S to 85°N. Soil parameters derived from interpolated soil profiles and vegetation parameters estimated from space-based MODIS measurements have been compiled into input files for both the Classic and Image drivers of the VIC model, version 5. Geographical subsetting codes are provided, as well. Our dataset provides all necessary land surface parameters to run the VIC model at regional to global scale. We evaluate VICGlobal’s ability to simulate the water balance in the Upper Colorado River basin and 12 smaller basins in the CONUS, and their ability to simulate the radiation budget at six SURFRAD stations in the CONUS.

Efeitos da resolução espacial do modelo VIC na previsão de vazão diária a usinas hidroelétricas do Rio Uruguai

A geração elétrica brasileira é amplamente dependente das usinas hidroelétricas. Este estudo tem objetivo de verificar o desempenho de diferentes resoluções espaciais do modelo hidrológico semi-distribuído Variable Infiltration Capacity (VIC) acoplado ao modelo meteorológico numérico Eta, este adotado com resolução espacial fixa em 15 km, para a previsão de vazão diária de cinco usinas do Rio Uruguai, no sul do Brasil. O modelo hidrológico foi aplicado para as resoluções 0,04°, 0,08° e 0,16°, em que cada célula de grade contém propriedades uniformes de solo, relevo e vegetação. As usinas hidroelétricas de jusante da área de estudo apresentaram melhor desempenho de previsão de vazão diária pelo modelo VIC para as resoluções mais finas. Conforme o Inventário de Restrições Operativas Hidráulicas dos Aproveitamentos Hidroelétricos (ROH) do Operador Nacional do Sistema (ONS), o efeito da resolução espacial do modelo VIC também foi estudado quanto ao desempenho da previsão diária de riscos de cheias, a partir de matrizes de contingências. Nos picos de cheias, a sensibilidade do modelo a valores acima de cada restrição de segurança (atenção, alerta e emergência) mantém-se invariável igual a 100%, enquanto a precisão variou de 51 a 100%, ambas sem tendência significativa em relação à resolução espacial. Todas as usinas mostraram acurácia mínima de 98,3% e de forma crescente em relação à resolução espacial do modelo. A heterogeneidade de dados físicos foi fator limitante para os ganhos do refinamento da resolução espacial do modelo hidrológico. Palavras-chave: Modelo VIC. Previsão de vazão. Rio Uruguai. Matrizes de contingência.

PROBABLE INTENSIFICACIÓN DE LAS CONDICIONES DE DÉFICIT HÍDRICO SOBRE LA REGIÓN DEL COMAHUE ANTE DIVERSOS ESCENARIOS DE CAMBIO CLIMÁTICO

Las principales actividades socioeconómicas de la región del Comahue en el norte de la Patagonia argentina dependen directamente de la disponibilidad hídrica de los ríos Limay, Neuquén y Negro. En este trabajo, se aplicó el modelo hidrológico VIC (Variable Infiltration Capacity) a las cuencas de dichos ríos con el objetivo de estudiar el posible impacto que el cambio climático tendrá en la hidrología de la región durante las próximas décadas. La etapa de calibración del modelo mostró que la base de datos observacional disponible es insuficiente para llevar a cabo una adecuada calibración del modelo a nivel diario. Frente a esto, se aplicaron diversas correcciones a las temperaturas máximas y mínimas y precipitación por separado a nivel mensual, obteniéndose al disminuir las temperaturas en los Andes una calibración (1999-2009) y una validación (2011-2016) a nivel anual satisfactorias. Los cambios proyectados en precipitación y en temperaturas máximas y mínimas para lo que resta del siglo XXI y bajo los escenarios con forzante radiativo moderado y alto sugieren una disminución en la precipitación en los Andes neuquinos y un aumento en las temperaturas, lo cual daría lugar a una reducción en el caudal medio anual para los ríos de la región que tendería a acentuarse conforme aumente la concentración de gases de efecto invernadero.

Integration of 2D Lateral Groundwater Flow into the Variable Infiltration Capacity (VIC) Model and Effects on Simulated Fluxes for Different Grid Resolutions and Aquifer Diffusivities

Better representations of groundwater processes need to be incorporated into large-scale hydrological models to improve simulations of regional- to global-scale hydrology and climate, as well as understanding of feedbacks between the human and natural systems. We incorporated a 2D groundwater flow model into the variable infiltration capacity (VIC) hydrological model code to address its lack of a lateral groundwater flow component. The water table was coupled with the variably saturated VIC soil column allowing bi-directional exchange of water between the aquifer and the soil. We then investigated how variations in aquifer properties and grid resolution affect modelled evapotranspiration (ET), runoff and groundwater recharge. We simulated nine idealised, homogenous aquifers with different combinations of transmissivity, storage coefficient, and three grid resolutions. The magnitude of cell ET, runoff, and recharge significantly depends on water table depth. In turn, the distribution of water table depths varied significantly as grid resolution increased from 1° to 0.05° for the medium and high transmissivity systems, resulting in changes of model-average fluxes of up to 12.3% of mean rainfall. For the low transmissivity aquifer, increasing the grid resolution has a minimal effect as lateral groundwater flow is low, and the VIC grid cells behave as vertical columns. The inclusion of the 2D groundwater model in VIC will enable the future representation of irrigation from groundwater pumping, and the feedbacks between groundwater use and the hydrological cycle.

A stepwise surrogate model for parameter calibration of the Variable Infiltration Capacity model: the case of the upper Brahmaputra, Tibet Plateau

To alleviate the computational burden of parameter calibration of the Variable Infiltration Capacity (VIC) model, a stepwise surrogate model (SM) is developed based on AdaBoost. An SM first picks out the parameter sets in the range that the values of objective functions are close to the optimization objectives and then approximates the values of objective functions with these parameter sets. The ɛ-NSGA II (Nondominated Sorting Genetic Algorithm II) algorithm is used to search the optimal solutions of SM. The SM is tested with a case study in the upper Brahmaputra River basin, Tibet Plateau, China. The results show that the stepwise SM performed well with the rate of misclassification less than 2.56% in the global simulation step and the root mean square error less than 0.0056 in the local simulation step. With no large difference in the optimal solutions between VIC and the SM, the SM-based algorithm saves up to 90% time.