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South Dakota School of Mines and Technology (2020)

Hydrologic and ecological drought in a semi-arid region of the northern Great Plains, USA

Tinant Charles Jason

Titre : Hydrologic and ecological drought in a semi-arid region of the northern Great Plains, USA

Auteur : Tinant Charles Jason

Université de soutenance  : South Dakota School of Mines and Technology

Grade : Doctor of Philosophy (PhD) 2020

Résumé
Drought is a complex and poorly understood natural hazard affecting more people than any other hazard. Drought differs from other natural hazards in some important ways. Droughts are disturbances of deficiency rather than excess that are characterized by their severity, intensity, duration, spatial extent, frequency and timing. Meteorological drought, an extended precipitation deficit over an extended period develops quickly, ends abruptly, and leads to other types of drought. Hydrologic drought can rapidly follow an absence of precipitation, particularly if antecedent soil moisture is low. Hydrologic drought impacts stream invertebrate communities, presenting a challenge for robust stream health assessments as changes in stream invertebrate communities are assumed to reflect only changes in land use. To assess the effects of hydrologic drought on stream invertebrate communities in a semiarid region of the Northern Great Plains, spatial and temporal differences in meteorological and hydrologic drought in gaged watersheds was characterized on the basis of watershed storage using Geographical Information Systems (GIS) layers and standard indices : the Standardized Precipitation Index (SPI) and the Standardized Streamflow Index (SSI). Watershed characterization results were applied to estimate hydrologic drought duration and magnitude in nearby ungaged watersheds for which stream health assessments had been conducted and the effect of hydrologic drought on some commonly used stream health metrics was modeled. Our results showed that watershed storage for the region differs at the Level IV ecoregion scale and is defined by two hydrologic gradients : an elevational gradient resulting from the Black Hills uplift and a soil textural gradient. While the differences in watershed storage have a moderate effect on hydrologic drought duration and magnitude, precipitation deficits quickly propagate through the hydrologic system resulting in the rapid onset of hydrologic drought for the region. In addition, we found stream health metrics differentially respond to hydrologic droughts (and wet periods) : the proportion of non-insects metric was unaffected by hydrologic drought ; and the Family Biotic Index (FBI) metric, a measure of invertebrate community tolerance to dissolved oxygen deficits caused by organic pollution, responded to long-duration hydrologic drought. However, the proportion of Diptera and proportion of Ephemeroptera, Plecoptera, and Trichoptera (EPT) metrics increased and decreased, respectively, in response to short-duration hydrologic drought. We conclude that while precipitation deficits have complex effects on regional streamflow deficits, these effects are largely explained by the regional geology ; and hydrologic gradients, based on the regional geology, can be used to estimate hydrologic drought in ungaged watersheds. Furthermore, while more work is needed, regional stream health assessment can be improved by selecting metrics that are insensitive to drought or by incorporating precipitation deficits (or excesses) from the beginning of the calendar year into stream health metrics that are sensitive to drought.

Présentation

Page publiée le 20 mai 2021