What controls vulnerability of watersheds to climate and land use change across the United States?

Understanding the response of watersheds to climate and land use change is crucial for management of water resources. However, obtaining reliable projections of water resources remains a challenge in the wake of large uncertainties in projections of climate and land use change. Thus, alternative assessment criteria independent of projections of climate and land use change would be useful in providing decision makers with an approximate evaluation of vulnerability of a watershed to change. Here, we present an analysis to ascertain the vulnerability of watersheds to climate and land use change independent of future projections. Using a recently developed bottom up approach, we first identify critical thresholds of climate and land use change across 78 watersheds of United States. Then, we explore the relationship between critical climate thresholds and watershed characteristics to identify characteristics that are correlated to these thresholds. We perform this analysis for various streamflow indicators that capture the magnitude, frequency, and duration of flows. We find significant negative correlation between soil properties like average percentage sand and critical threshold of precipitation change causing vulnerability of indicator representing water availability - mean annual streamflow. This indicates that higher amounts of sand content in soils may be related with reduced vulnerability to climatic changes. We also find significant positive correlation between urban land use and critical threshold of precipitation change across the watersheds for mean annual streamflow. This suggests that watersheds with higher urban land use may be more vulnerable to precipitation change.