Abstract
This chapter explains the climatic context in which hydrological drought occurs. Firstly, the relationships between typical hydroclimatic features of the world's major climate zones and hydrological drought are characterised. Across all climate zones, hydrological drought is associated with some anomaly in the timing, occurrence or persistence of atmospheric circulation. These anomalies are often connected to large-scale ocean-atmosphere modes of variation such as the El Niño Southern Oscillation. The consequent meteorological water balance deficits often propagate into hydrological drought, but the connection is not always straightforward: land surface characteristics and feedbacks can be critical to hydrological drought onset and, later, termination. Consequently, the spatial and temporal signature of hydrological drought can be quite different to the initial atmospheric anomalies. Notwithstanding the complexity of the climate–hydrology relationships, ongoing and additional future changes in the global climate system will inevitably be manifested in hydrological drought characteristics.