Revisiting Continental U.S. Hydrologic Change in the Latter Half of the 20th Century.

An intensified hydrologic cycle and a large amount of monitoring flow data in the latter half of the 20th century attracted a lot of research on the continental U.S. hydrologic change. However, most previous studies are based on HCDN (Hydro-Climate Data Network) dataset with a period of ~1950s −1988. This study analyzed hydrologic change in continental U.S. based on MOPEX (international Model Parameter Estimation Experiment) hydrology dataset with a period of ~1950s −2000 for 302 watersheds (gages) across diverse climate, vegetation and soil conditions. This dataset is more representative of the latter half of the 20th century than HCDN. In contrast with previous studies, this study shows that only 20-30 % of watersheds present increasing trends in flow (streamflow, Q; baseflow, Q; baseflow index, BFI), and most (> 65 %) watersheds presents non-significant trends. Similar to previous studies, the watersheds with increasing trends in Q and Q are concentrated in Midwest and high plain (North-Central area) of USA. Climate contributes more to Q change (61 ± 25 % vs. 39 ± 25 %) but slightly less to Q change than human activity (49 ± 26 % vs. 51 ± 26 %) and much less to BFI change than human activity (−5 ± 61 % vs. 105 ± 61 %). A step change at ~1971 in Q and Q was found for 35-45 % but not for a large proportion of watersheds (50 % or more was reported by previous studies). This study provides new insights on the latter half of the 20th century's hydrologic cycle for the continental U.S. with a more representative dataset of this period. [ABSTRACT FROM AUTHOR]