Understanding Drivers of Subseasonal to Seasonal Streamflow Variability over Contiguous United States

Understanding of subseasonal to seasonal (S2S) drivers of streamflow and their causality provide useful insight for more efficient application of S2S climate predictions as well as translation of the same to watershed scale responses for the practitioners. A continental scale analysis of S2S streamflow variability over the contiguous United States (CONUS) is carried out with the objective of answering two key questions - (1) What are the key synoptic scale and basin scale hydrological drivers of spatio-temporal variability of streamflow at S2S time scale and how do we quantify the effects of individual attributes and their interactions? and (2) How does different combinations of the synoptic climate drivers, such as El Nino Southern Oscillation (ENSO) states, along with Madden Julian Oscillation (MJO), Pacific/North American (PNA) and North Atlantic Oscillation (NAO) states - determine the S2S scale variability of streamflow over the CONUS. We analyze hydrological and climatological forcings at 671 streamflow sites over CONUS from CAMELS (Catchment Attributes and Meteorology for Large-sample Studies) dataset. We first identify dominant hydrological and climatological predictors of 2 - 4 weeks streamflow over CONUS according to regional runoff generation process and identify seasonally varying clusters of snowmelt-driven, initial soil moisture-driven and rainfall-driven basins. Following that, we employ a Bayesian hierarchical model (BHM) for each of these hydro-climatological clusters to explain the causality of S2S streamflow drivers using synoptic scale weather patterns. Identification of dominant basin scale hydrological attributes on streamflow, as well as spatio-temporal influence of high frequency climate modes using BHM provide the basis for developing low-dimensional model for S2S forecasting.