Climate and rivers

Abstract

Over the last few decades as hydrologists have slowly raised their line of sight above the watershed boundary, it has become increasingly recognised that what happens in the atmosphere, as a major source of moisture for the terrestrial branch of the hydrological cycle, can strongly influence river dynamics at a range of spatial and temporal scales. Notwithstanding this, there is still a tendency for some in the river research community to restrict their gaze to the river channel or floodplain. However, Geoff Petts, the person to which this special issue is dedicated, understood well and widely encouraged a holistic view of river catchment processes. This included an acknowledgment of the role of climate, in its broadest sense, in shaping what happens within and without the river channel. The purpose of this paper therefore is to offer a broad overview of the role of some aspects of climate science in advancing knowledge in river research. Topics to be addressed include the role of climate in influencing river flow regimes, a consideration of the large‐scale climate mechanisms that drive hydrological variability within river basins at interannual to decadal timescales and atmospheric rivers and their link to surface hydrology. In reviewing these topics, a number of key knowledge gaps have emerged including attributing the causes of river flow regime changes to any one particular cause, the nonstationary and asymmetric forcing of river regimes by modes of climate variability and establishing links between atmospheric rivers, and terrestrial river channel processes, fluvial habitats, and ecological change.

Causes, impacts and patterns of disastrous river floods

“…Extreme river floods are typically caused by heavy and/or prolonged rainfall, and above 40 °N, by snowmelt and ice-jam-related processes 28 . Rainfalldriven floods are conditioned on storm tracks delivering atmospheric moisture to the catchment, usually from the ocean 29 . Atmospheric moisture can also originate from evaporation from wet landscapes far from the flood.…”

JAMES BUTTLE REVIEW: A resilience framework for physical hydrology

“…Stationarity is a practically useful concept most often applied in engineering design as it allows for the assumption that the past is indicative of the future, so that the probability density function derived from observations can be applied to design infrastructure used in the future (Milly et al, 2008). McGregor (2019) argues that since climate and hydrological systems are coupled, these tests need to be placed into the context of the overarching climate, even if the latter is nonstationary or variable. Furthermore, the window through which a variable is observed will influence the characterization of the selected time series (Koutsoyiannis, 2006), and changing this window alone could be responsible for a statistically significant change in the probability density function.…”

Professor Geoffrey Petts (1953–2018): An outstanding interdisciplinary river scientist

“…McGregor () contributes to theme 2 (river flows and flow regimes) by considering the links between climate and rivers, emphasising linkages with flow regimes and hydrological variability and introducing the concept of atmospheric rivers. Dixon and Wilby () further develop atmosphere—river flow linkages by illustrating how seasonal inflows to rivers feeding strategically important hydropower plants in Kyrgyzstan and Tajikistan can be forecast using information on El Niño conditions.…”