Journal of The American Water Resources Association最新文献

The Standardized Streamflow Index (SSI) has frequently been used to quantify drought by comparing periods of streamflow against a river's historical values. This study expands upon previous SSI methodologies by creating a more flexible, regionalized version of the metric for Iowa, a Midwestern state located in the central United States. Five drought regions were developed for Iowa that largely correspond to the state's Major Land Resource Areas. Several United States Geological Survey gauges were identified within each drought region and streamflow data were used to calculate daily water yields from 1960 to the present. SSI values calculated for both individual river sites and the entire drought region provide insights into the relative dryness of Iowa watersheds over the past several decades. The SSI methodology can be used to evaluate river dryness with limited data records and water yields of specific streams can be compared to each other and across the overall region. This study demonstrates the potential for developing versions of the SSI that enable real-time calculations at a daily scale at locations with limited historical streamflow data. The new SSI metric may be a valuable tool for decision-makers as state and federal agencies continue to identify and manage drought.

The Mississippi Embayment (ME) is one of the fastest groundwater depletion zones in the world. This study investigated stream-aquifer water exchange in the ME over a 115-year period (1900 to 2014) under normal and extreme climates (i.e., precipitation increased and decreased by 20%) with and without agricultural pumping for crop irrigation. The average daily water flow from the aquifer to the streams was always greater than vice versa under all climate scenarios. Under normal climate, the average daily water flow from the aquifer to the streams was 2.52 times larger without pumping than with pumping. While the extreme climate had discernable impacts, the groundwater pumping, but not extreme climate, was the major factor for low flows and drying streams in the ME. These findings are essential to groundwater resource management in the region and provide a critical reference for other parts of the world with similar conditions.

Unexpected and large spring precipitation events in the Colorado River Basin (CRB) that significantly alleviated an otherwise severe water shortage have been observed for over a century, such as the “Miracle May” of 2015. Although these events are often termed as “drought-busting” or “miracle events” by water managers and the media, they have not been extensively researched or characterized. In this collaborative study with water managers across the CRB, we propose a definition for these hard-to-predict, ultra-high precipitation events occurring during the late-snow or snowmelt season. This characterization provides a framework for quantifying the frequency and intensity of extreme dry-to-wet springtime transitions. Despite limitations of climate model simulations due to uncertainties and the inhomogeneous qualities, our findings suggest that such transitions may become less frequent and less intense in a warming climate. In view of the potentially wetter but less-snowy climate in the basin, the need for future research to more quantitatively assess these “miracle events” is emphasized.

In many Puget Sound streams, summer low flows have declined in recent decades, and are projected to decline further. Concerns that humans may be responsible have focused on two main causes: anthropogenic climate warming and aspects of development, including urbanization and the abstraction of groundwater. Difficulty in distinguishing their relative impacts has hindered the conception and design of strategies intended to restore and enhance future low flows. We analyzed trends in low flows over recent decades, separating the effects of these factors in two steps. First, low flow variation was assessed in 23 basins that are minimally disturbed by development. Low flows varied over time, and with elevation, in complex ways, consistent with the loss of snowpack at elevations >~800 m. Second, low flow trends in developed lowland basins were compared with trends in a minimally developed lowland reference basin. Flows in developed basins deviated from a purely climate-driven pattern in unique ways, reflecting unique histories of development. In 21 lowland basins, there was no consistent decline in low flows with increasing impervious land cover, at least between 2001 and 2019. Effects on low flows of private wells alone could be assessed in only one basin, but no impact was evident. An assessment of projected relative impacts on low flows of urbanization, rural development, and anthropogenic warming suggested that the latter will be the greatest.

Vegetation is an important component of stormwater control measures, as vegetation can reduce erosion and runoff. While grass is typically used in stormwater control measures, wildflowers can be planted to reduce maintenance and improve pollinator habitat. Previous studies have established that tillage followed by establishment of a vigorous vegetation stand can increase infiltration relative to compacted soils. Compost can also improve soil physical properties and fertility. The goal of this study was to evaluate potential improvements in infiltration using tillage together with compost and either grass or wildflowers. Wildflowers or grass were planted on tilled soil with or without compost at three sites in North Carolina. Bulk density, infiltration rate, root mass density, and penetration resistance were measured every 6 months over a 30-month period. A subset of plots received wheel traffic from a mower. Compost application reduced bulk density compared to tillage alone. Compost improved infiltration at two sites (46%–50%). Wildflowers improved infiltration at all sites (30%–43%) compared to grass. Few differences were observed in root mass and penetration resistance. Mower traffic reduced soil improvements more in grassed plots than wildflower plots due to higher mowing frequency. Results suggest compost and/or wildflowers together with tillage (at establishment) provide viable options to improve soil conditions and infiltration rate in construction impacted soils.

Many states in the Eastern U.S. have limited water withdrawal regulations, posing significant risks to water supply management during periods of low flows. While these states require water withdrawal permits, exemptions for grandfathered withdrawals that allow unregulated access to surface water are common. Such permit exemptions present a challenge to water supply management, as full utilization of allowable withdrawals by permit-exempt users could pose risks to maintaining adequate water supplies for current and projected demand. This study used reported permit exemption data in Virginia to understand the extent, volume, and potential impact of permit-exempt withdrawals on 30- and 90-day low flows. The permit-exempt withdrawal values used in this study were obtained from Virginia Department of Environmental Quality. Maximum permit-exempt withdrawal volumes were significantly higher than projected future demands in permitted users. The impacts of these withdrawals on drought flows were compared with the impacts presented by climate change and demand growth. Widespread reduction in flows was observed with the “dry” future climate change scenario, while impacts were more localized in the exempt users and the demand growth scenarios. The impacts of exempt users exceeded the impact of climate change and demand growth scenarios in many regions during low-flow periods. Therefore, more comprehensive water planning, policy and research is needed to address the impact of permit exemptions.

The hydrological model Soil Water Assessment Tool (SWAT) is widely used in water resources management worldwide. It is also used to simulate catchment hydrology in high-mountainous regions where glaciers play an important role. However, SWAT considers glaciers in a simplistic way. Although some efforts were done to overcome this limitation, there is no official version available that considers glaciers adequately. This strongly impairs its applicability in glacierized catchments. In this technical note, we propose a novel version of the traditional SWAT, called SWAT-GL, which introduces (1) a mass balance module and (2) a glacier evolution routine to represent dynamic glacier changes. Mass balance calculations are based on a conceptual degree-day approach, similar to the snow routine implemented in SWAT. Glacier evolution is realized using the delta-h (∆h) parameterization, which requires a minimum of data and is thus suitable in data-scarce regions. The approach allows users to simulate spatially distributed glacier changes. Annual mass balance changes are translated to distributed ice thickness changes depending on the glacier elevation. We demonstrate how SWAT-GL is technically integrated into SWAT and how glaciers are merged with the existing spatial units. Model code and test data are freely accessible to promote further model development efforts and a wide application. Ultimately, SWAT-GL aims to make SWAT easily applicable in glacierized catchments without the need of additional tools.

Climate change and rapid socioeconomic development have exacerbated the damage caused by hydrological droughts. To ensure effective drought defense and infrastructure development, it is essential to investigate variations in hydrological droughts. The primary objective of this study is to reconstruct the natural streamflow by using Soil and Water Assessment Tool (SWAT) hydrological modeling. The hydrological drought at different time scales (1, 3, 6, and 12 months) were measured using the streamflow drought index (SDI). The statistical parameters, including Nash–Sutcliffe Efficiency and the Coefficient of Determination, which yielded values of 0.84 and 0.82 during the calibration period and 0.78 and 0.76 during the validation period, respectively, showed a satisfactory SWAT model performance. Additionally, the Pettit test was used to identify a change point in streamflow within the 1991–2015 timeframe, leading to the division of the study period into two distinct phases: an undisturbed period (1991–1998) and a disturbed period (1999–2015). The SDI index-based analysis revealed 9.39% moderate drought and 3.13% severe drought during the undisturbed period, while 11.76% moderate drought and 7.35% severe drought may happen due to the human influences that occurred in the disturbed period. These findings enhance the understanding of the hydrological drought variations in the Soan River basin for optimizing the water resources management system and effectively preventing and mitigating drought-related damages.

Water quality trends in streams and rivers are impacted by several factors including land use of the watershed; however, it is unclear what influence changes in the land use of a watershed subsequently have on changes in discharge and water quality in streams and rivers. This study seeks to fill this gap by evaluating the relationship between changes in land use and changes in discharge and water quality at United States Geological Survey (USGS) stream gages over the period of 2008–2016. Using land cover data and discharge and water quality data from 60 USGS gages, regression methods were applied to determine the strength of relationship between land use changes and changes in water quality and quantity. Trends in discharge and water quality were mixed, with a majority of watersheds demonstrating a decrease in dissolved oxygen and turbidity, no overall trend for discharge, and increases in specific conductance. A regression analysis revealed that discharge, turbidity, and specific conductance were correlated with changes in individual land use types with an R² between 0.12 and 0.25. Combining the influences of multiple land uses in multivariate regression improved the predictions for discharge (R² 0.58) and specific conductance (R² 0.47), highlighting the magnitude for which land cover changes influence trends in water quality. Overall, this study demonstrates the impact that large-scale land use changes have on surface water quality.

Many agricultural watersheds rely on the voluntary use of management practices (MPs) to reduce nonpoint source nutrient and sediment loads; however, the water-quality effects of MPs are uncertain. We interpreted water-quality responses from as early as 1985 through 2020 in three agricultural Chesapeake Bay watersheds that were prioritized for MP implementation, namely, the Smith Creek (Virginia), Upper Chester River (Maryland), and Conewago Creek (Pennsylvania) watersheds. We synthesized patterns in MPs, climate, land use, and nutrient inputs to better understand factors affecting nutrient and sediment loads. Relations between MPs and expected water-quality improvements were not consistently identifiable. The number of MPs increased in all watersheds since the early 2010s, but most monitored nutrient and sediment loads did not decrease. Nutrient and sediment loads increased or remained stable in Smith Creek and the Upper Chester River. Sediment loads and some nutrient loads decreased in Conewago Creek. In Smith Creek, a 36-year time-series model suggests that changes in manure affected flow-normalized total nitrogen loads. We hypothesize that increases in nutrient applications may overshadow some expected MP effects. MPs might have stemmed further water-quality degradation, but improvements in nutrient loads may rely on reducing manure and fertilizer applications. Our results highlight the importance of assessing MP performance with long-term monitoring-based studies.