Hydrological System Complexity Induces a Drought Frequency Paradox

Abstract

Droughts occur as a result of a lack of water compared with normal conditions. Whilst this appears trivial, the exact drought definition of drought is not. Especially as different drought types are present, resulting from the different variables in a hydrological system, each with unique characteristics. We use a common drought definition, the percentile score, and apply the same definition across all drought types, to study whether the actual occurrence of droughts matches the definition. We focus on the data-rich Dutch province of Gelderland, to study droughts from observations across five major components of the terrestrial hydrological cycle. When a percentile threshold of 20% is used as drought definition, corresponding to a mild drought, droughts anywhere in the system occur at least three times more frequently (73% of the time). On the other hand, the situation where drought occurs across all components of the terrestrial hydrological cycle is more than four times less likely than the drought threshold of 20% (namely 5% of the time). This can be attributed by both (1) the different responses across the hydrological system, and (2) the spatial variability present within each component of the hydrological system. With this study, we show the existence of the drought frequently paradox: although droughts are seen and defined as rare from a scientific perspective, when viewed from a societal or operational water management perspective in typical hydrological systems subject to spatial variability and other system complexity, droughts become common, rather than rare. This paradox is a consequence of an inconsistent use of the percentile score drought definition between research and operational water management, and better communication between the two domains is needed in search for a universally accepted drought definition.

Where should hydrology go? An early-career perspective on the next IAHS Scientific Decade: 2023-2032

“…Monitoring drought events is complicated as they present themselves in different parts of the water cycle (i.e. soil moisture, groundwater, surface water) in different phases of the event (Buitink et al, 2021;van Loon, 2015).…”

Characterizing the 2022 Extreme Drought Event over the Poyang Lake Basin Using Multiple Satellite Remote Sensing Observations and In Situ Data

“…Hydrological drought refers to a specific occurrence in a particular region and the period where the availability of water resources is inadequate due to an insufficient or uneven distribution of precipitation. It is one of many global natural disasters [1]. Against the backdrop of ongoing global warming and human activities, extreme events are becoming increasingly frequent worldwide, causing severe damage to agriculture, water resources, and ecosystems, and having profound impacts on society, the environment, and the economy [1][2][3].…”

“…It is one of many global natural disasters [1]. Against the backdrop of ongoing global warming and human activities, extreme events are becoming increasingly frequent worldwide, causing severe damage to agriculture, water resources, and ecosystems, and having profound impacts on society, the environment, and the economy [1][2][3]. While the impacts of extreme drought events have been extensively documented, their measurement and definition remain challenging, underscoring the importance of identifying the characteristic features of such events within the research domain.…”

“…This study was performed with multi-satellite remote sensing data and in situ data, and the main objectives of this study were (1) to characterize the extreme drought event in the PLB in 2022, and (2) to identify drought events in the PLB. The findings of this research provide a novel approach to drought monitoring based on multi-source data, which holds practical significance for the development of satellite-based drought characterization.…”

Root Carbon Resources Determine Survival and Growth of Young Trees Under Long Drought in Combination With Fertilization

“…Droughts, however, are very tougher to be defined, and thus a universally accepted drought definition considering both water-deficit intensity and duration is still lack (Buitink et al, 2021). Previous drought-related forest and agricultural studies, especially manipulation experiments, mainly focused on the effects of drought intensity (e.g., various levels of watering, such as very limited, limited, and optimum watering) on trees or plants (Allen et al, 2010;Yu et al, 2021), while less is known about the effects of drought duration on trees' physiology, growth, and mortality.…”