The Role of Fuh's Parameter in Predicting Global Water Budget Deficits
and Runoff Ratio Sensitivity
Abstract
As patterns of precipitation and evapotranspiration change, human water
security and aquatic ecosystem health depend on understanding how
catchment characteristics interact with climate to control river flow
and water budget imbalances. We compiled estimates of precipitation,
actual and potential evapotranspiration, temperature, and river
discharge for over 1,148 catchments during the 2001-2020 period and used
these estimates to calculate water budget imbalances as well as changes
in runoff ratio and numerous river flow properties including timing,
magnitude, and variability of flow. We found that that the parameter
from Fuh’s equation (m) was a powerful predictor of hydrologic
sensitivity to climate fluctuations, but not necessarily the magnitude
of these changes. Specifically, water budget imbalances were almost
entirely explained by two catchment properties: m and aridity. Runoff
ratio sensitivity to temporal fluctuations in wetness index were also
best explained by m, compared to a host of other catchment
characteristics tested. In contrast to its predictive power for
sensitivity, m was a poor predictor of total changes in runoff ratio. A
subsequent correlational analysis between changes in runoff ratio and 66
geographic, climatic, land use, and human impact metrics, found that
fluctuations in climate were a far more powerful predictor of changes in
runoff ratio (and a suite of other flow properties) than m, indicating
that at the global scale, the magnitude of changes in climate dominate
the idiosyncratic catchment-level responsiveness to changes in climate,
emphasizing the paramount importance of addressing climate change in
protecting freshwater resources.