An improved practical approach for estimating catchment-scale response functions through wavelet analysis

Authors: DWIVEDI, R. - University Of Arizona; EASTOE, C. - University Of Arizona; Knowles, John; MEIXNER, T. - University Of Arizona; MCINTOSH, J. - University Of Arizona; FERRE, P.A. - University Of Arizona; CASTRO, C. - University Of Arizona; WRIGHT, W.E. - University Of Arizona; NIU, G-Y - University Of Arizona; MINOR, R. - University Of Arizona; BARRON-GAFFORD, G.A. - University Of Arizona; ABRAMSON, N. - University Of Arizona; MITRA, B. - University Of Arizona; STANLEY, M. - University Of Arizona; CHOROVER, J. - University Of Arizona

Submitted to: Hydrological Processes
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/5/2021
Publication Date: 3/11/2021
Citation: Dwivedi, R., Eastoe, C., Knowles, J.F., Meixner, T., Mcintosh, J., Ferre, P., Castro, C., Wright, W., Niu, G., Minor, R., Barron-Gafford, G., Abramson, N., Mitra, B., Stanley, M., Chorover, J. 2021. An improved practical approach for estimating catchment-scale response functions through wavelet analysis. Hydrological Processes. 35(3), Article e14082. https://doi.org/10.1002/hyp.14082.
DOI: https://doi.org/10.1002/hyp.14082

Interpretive Summary: Water that has been stored below the soil surface for variable amounts of time contributes to both streamflow and vegetation growth in all types of environments. The amount of time this water has been stored can be expressed as a residence time with an associated transit time distribution that corresponds to the residence time distribution of subsurface waters that comprise a portion of streamflow. Similarly, the evapotranspiration time distribution corresponds to the residence time distribution of subsurface waters that support vegetation growth. These distributions can be challenging to determine because existing methods require continuous hydrological observations that are especially difficult to obtain in remote mountain terrain or in areas where precipitation is infrequent. In this work, we present a set of improved practical methods and use them to characterize transit time and evapotranspiration time distributions from a seasonally dry mountain catchment in Arizona, USA. The proposed methodology can also be employed to estimate catchment-scale response functions at sites where environmental water samples may have been collected for several years at irregular intervals. The approach developed by this work is robust even when input data contain many gaps, computationally inexpensive, and thus broadly applicable to mountain and/or semiarid catchments worldwide.

Technical Abstract: Catchment-scale response functions, such as transit time distribution (TTD) and evapotranspiration time distribution (ETTD), are considered fundamental descriptors of a catchment’s hydrologic and ecohydrologic responses to spatially and temporally varying precipitation inputs. Yet, estimating these functions is challenging, especially in headwater catchments where data collection is complicated by rugged terrain, or in semi-arid or sub-humid areas where precipitation is infrequent. Hence, we developed practical approaches for estimating both TTD and ETTD from commonly available tracer flux data in hydrologic inflows and outflows without requiring continuous observations. Using the weighted wavelet spectral analysis method of Kirchner and Neal [2013] for d18O in precipitation and stream water, we specifically calculated TTDs that contribute to streamflow via spatially and temporally variable flow paths in a sub-humid mountain headwater catchment in Arizona, USA. Our results indicate that composite TTDs most accurately represented this system for periods up to approximately one month and that a Gamma TTD was most appropriate thereafter. The TTD results also suggested that some contribution of subsurface water was beyond the applicable tracer range. For ETTD and using d18O as a tracer in precipitation and xylem waters, a Gamma ETTD type best matched the observations, and stable water isotopes were capable tracers for the majority of vegetation source waters. This study contributes to a better understanding of a fundamental question in mountain catchment hydrology; namely, how tracer input fluxes are modulated by spatially and temporally varying subsurface flow paths that support evapotranspiration and streamflow at multiple time scales