Future hydro-climatic changes: Role of physical processes and model biases

A large body of evidence unequivocally suggests that anthropogenic climate change is real and future hydro-climatic changes could have lasting impact on natural and human systems. However, due to the intrinsic complexity of the climate system and biases in the climate models, number of uncertainties associated with future climate change projections is quite large. Utilizing a suite of Earth-system modeling tools and statistical techniques, this dissertation seeks to investigate some of the most fundamental uncertainties in future climate change projections and hydrological impact assessments, within the context of large- and fine-scale processes and climate model biases. Using a bias correction technique and a multi-member ensemble of global climate model (GCM) simulations, I investigate the influence of sea surface temperature (SST) errors on future climate change projections. Results show that biases in SSTs distribution affect atmospheric circulation patterns and global precipitation distribution by amplifying atmospheric model errors. Furthermore, simulations with and without SSTs correction simulate statistically different future precipitation and temperature responses over many terrestrial and oceanic regions, implying that biases in SSTs distribution can significantly affect future global climate change projections. I further employ a high-resolution nested modeling system to investigate the uncertainty in global models’ projections for topographically complex South Asian summer monsoon region. The simulated dynamical features of the summer monsoon compared well with reanalysis data and observations. Further, I find that enhanced greenhouse forcing result in overall suppression of summer precipitation, a delay in monsoon onset, and an increase in the occurrence of monsoon break periods. Results provide evidence that both large- and fine-scale processes dictate South Asian summer monsoon response through changes in the large-scale monsoon flow and the fine-scale convective environment. I finally investigate the role of fine-scale climate change and the influence of climate model biases in hydrological impact assessment. I use high-resolution nested climate model simulations, covering the contiguous United States, and a bias correction technique to drive a hydrological model. Results indicate that biases significantly affect the simulated hydrological response to anthropogenic increase in greenhouse forcing. I find that the future hydrological response is heterogeneous across the United States. The fine-scale variation in the sign of hydrological changes highlights the role of fine-scale hydrological processes in dictating the future hydrological change. Further, I find that future hydrological response is dictated by both the absolute changes in precipitation and temperature and the changes in their daily extremes