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Sensitivity of Catchment Transit Times to Rainfall Variability Under Present and Future Climates
Author(s) -
Wilusz Daniel C.,
Harman Ciaran J.,
Ball William P.
Publication year - 2017
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1002/2017wr020894
Subject(s) - environmental science , hydrograph , drainage basin , hydrology (agriculture) , surface runoff , storm , climate change , streams , spatial variability , meteorology , geography , geology , ecology , cartography , geotechnical engineering , computer network , oceanography , statistics , mathematics , computer science , biology
Hydrologists have a relatively good understanding of how rainfall variability shapes the catchment hydrograph, a reflection of the celerity of hydraulic head propagation. Much less is known about the influence of rainfall variability on catchment transit times, a reflection of water velocities that control solute transport. This work uses catchment‐scale lumped parameter models to decompose the relationship between rainfall variability and an important metric of transit times, the time‐varying fraction of young water (<90 days old) in streams (FYW). A coupled rainfall‐runoff model and rank StorAge Selection (rSAS) transit time model were calibrated to extensive hydrometric and environmental tracer data from neighboring headwater catchments in Plynlimon, Wales from 1999 to 2008. At both sites, the mean annual FYW increased more than 13 percentage points from the driest to the wettest year. Yearly mean rainfall explained most between‐year variation, but certain signatures of rainfall pattern were also associated with higher FYW including: more clustered storms, more negatively skewed storms, and higher covariance between daily rainfall and discharge. We show that these signatures are symptomatic of an “inverse storage effect” that may be common among watersheds. Looking to the future, changes in rainfall due to projected climate change caused an up to 19 percentage point increase in simulated mean winter FYW and similarly large decreases in the mean summer FYW. Thus, climate change could seasonally alter the ages of water in streams at these sites, with concomitant impacts on water quality.