Climate-vegetation-soil interactions and long-term hydrologic partitioning: signatures of catchment co-evolution

摘要

Budyko (1974) postulated that long-term catchment waterbalance is controlled to first order by the available water and energy. Thisleads to the interesting question of how do landscape characteristics(soils, geology, vegetation) and climate properties (precipitation,potential evaporation, number of wet and dry days) interact at the catchmentscale to produce such a simple and predictable outcome of hydrologicalpartitioning? Here we use a physically-based hydrologic model separatelyparameterized in 12 US catchments across a climate gradient to decouple theimpact of climate and landscape properties to gain insight into the role ofclimate-vegetation-soil interactions in long-term hydrologic partitioning.The 12 catchment models (with different paramterizations) are subjected tothe 12 different climate forcings, resulting in 144 10 yr modelsimulations. The results are analyzed per catchment (one catchment modelsubjected to 12 climates) and per climate (one climate filtered by 12different model parameterization), and compared to water balance predictionsbased on Budyko's hypothesis (E/P = ϕ (E_p/P); E: evaporation,P: precipitation, E_p: potential evaporation). We find significantanti-correlation between average deviations of the evaporation index (E/P)computed per catchment vs. per climate, compared to that predicted byBudyko. Catchments that on average produce more E/P have developed inclimates that on average produce less E/P, when compared to Budyko'sprediction. Water and energy seasonality could not explain theseobservations, confirming previous results reported by Potter et al. (2005).Next, we analyze which model (i.e., landscape filter) characteristicsexplain the catchment's tendency to produce more or less E/P. We find thatthe time scale that controls subsurface storage release explains theobserved trend. This time scale combines several geomorphologic andhydraulic soil properties. Catchments with relatively longer subsurfacestorage release time scales produce significantly more E/P. Vegetation inthese catchments have longer access to this additional groundwater sourceand thus are less prone to water stress. Further analysis reveals thatclimates that give rise to more (less) E/P are associated with catchmentsthat have vegetation with less (more) efficient water use parameters. Inparticular, the climates with tendency to produce more E/P have catchmentsthat have lower % root fraction and less light use efficiency. Ourresults suggest that their exists strong interactions between climate,vegetation and soil properties that lead to specific hydrologic partitioningat the catchment scale. This co-evolution of catchment vegetation and soilswith climate needs to be further explored to improve our capabilities topredict hydrologic partitioning in ungauged basins.