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Critical Zone Water Balance Over 13 Years in a Semiarid Savanna
Author(s) -
Scott Russell L.,
Biederman Joel A.
Publication year - 2019
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 - 10.1029/2018wr023477
Subject(s) - environmental science , evapotranspiration , water balance , water content , hydrology (agriculture) , precipitation , surface runoff , soil water , growing season , dns root zone , soil science , agronomy , geography , ecology , geology , geotechnical engineering , meteorology , biology
Quantifying how much and when precipitation (P) becomes runoff (R), evapotranspiration (ET), and drainage from the root zone (D) is key to understanding how climate and land use impact hydrology of the critical zone. We quantify water balance dynamics of a semiarid savanna with a summer/winter rainfall pattern with 13 years of water fluxes and soil moisture. We find multiyear P is partitioned 96% to ET and 7% to R, while D (−3%) is negligible when considering measurement uncertainty. While weather regulates ET over diurnal time scales, soil water inputs control seasonal to annual ET amounts. Seasonal water availability, estimated by soil moisture inputs, is more closely tracked by ET rather than time‐averaged soil moisture or P. Surprisingly, we find significant, episodic carryover of soil moisture from the summer to spring growing season. Abundant late‐summer P can supply ET in the subsequent spring, even after multimonth dry periods. However, over an annual cycle beginning in early summer, nearly all soil moisture is used by ET. Likewise, D beyond the monitored root zone, assisted by downward hydraulic distribution in plant roots, occurs within a season, but this is counteracted by subsequent ET extraction of deep moisture over the year. Thus, negligible long‐term D occurs, though there is considerable uncertainty in estimation of this small flux as the residual of much larger ones. These comprehensive, long‐term measurements support expectations about the overriding importance of ET in the dryland critical zone water balance and reveal an unexpected degree of interseasonal water storage.