Non-linear hydrological and hydroclimatic behaviour is emerging as an important research topic.  Thresholds, as one type of non-linearity, are ubiquitous phenomena that influence predominance of process and behaviour across a spectrum of scales.  Increased interest in the impact of stress on hydroclimatic and water resource systems from climate change has lead to more interest in the concepts of resilience, thresholds as the apply to hydrological and hydroclimatic system states.   There are challenges in understanding the interplay among initial conditions and atmospheric forcing to create non-linear responses and how these are used to define system states.  We invite papers that (i) discuss best practices for defining states; (ii) suggest methods for identifying thresholds and tipping points; (iii) examine the concept of resilience in hydrology and hydroclimatology; and (iv) identify means by which to predict system state shifts.