Atlantic Ocean Variability and European Alps Winter Precipitation

Winter precipitation (snowpack) in the European Alps provides a critical source of freshwater to major river basins such as the Danube, Rhine, and Po. Previous research identified Atlantic Ocean variability and hydrologic responses in the European Alps. The research presented here evaluates Atlantic Sea Surface Temperatures (SSTs) and European Alps winter precipitation variability using Singular Value Decomposition. Regions in the north and mid-Atlantic from the SSTs were identified as being tele-connected with winter precipitation in the European Alps. Indices were generated for these Atlantic SST regions to use in prediction of precipitation. Regression and non-parametric models were developed using the indices as predictors and winter precipitation as the predictand for twenty-one alpine precipitation stations in Austria, Germany, and Italy. The proposed framework identified three regions in the European Alps in which model skill ranged from excellent (West Region–Po River Basin), to good (East Region) to poor (Central Region). A novel approach for forecasting future winter precipitation utilizing future projections of Atlantic SSTs predicts increased winter precipitation until ~2040, followed by decreased winter precipitation until ~2070, and then followed by increasing winter precipitation until ~2100.

Hydrologic responses to climate and land-use/land-cover changes in the Bilate catchment, Southern Ethiopia

The likely effects of climate and land-use/land-cover (LULC) changes on hydrologic processes in Bilate catchment, Ethiopia were evaluated. The study emphasizes the evaluation of individual and combined impacts on hydrologic responses of climate and LULC changes. Climatic scenarios included a downscaled regional climate model from CORDEX-Africa. The CA–Markov model was used to project LULC. The results revealed that distinct changes on hydrologic responses occurred which follow the direction of climate and LULC changes. A 30.87% decline in rainfall resulted in about 4.09, 1.43 and 3.57% decline in runoff, groundwater and water yield, respectively. A rise in mean temperature by 1.3 °C resulted in 7 and 0.8% increase in potential and actual evapotranspiration, respectively. Runoff, groundwater and water yield are projected to decrease by 11.24, 12.54 and 11.54%; however, potential and actual evapotranspiration are projected to increase by 19 and 14.7%, respectively, under combined climate and LULC changes. The joint effects of climate and LULC changes on hydrologic responses in the forthcoming were higher than the variation trend of climate or LULC change alone. Climate change compared with LULC change has a higher impact on hydrologic responses. The results obtained provide further insight into future water balance, assistance in water resources planning and management.

How does water yield respond to mountain pine beetle infestation in a semiarid forest?

Mountain pine beetle (MPB) outbreaks in the western United States result in widespread tree mortality, transforming forest structure within watersheds. While there is evidence that these changes can alter the timing and quantity of streamflow, there is substantial variation in both the magnitude and direction of hydrologic responses, and the climatic and environmental mechanisms driving this variation are not well understood. Herein, we coupled an eco-hydrologic model (RHESSys) with a beetle effects model and applied it to a semiarid watershed, Trail Creek, in the Bigwood River basin in central Idaho, USA, to examine how varying degrees of beetle-caused tree mortality influence water yield. Simulation results show that water yield during the first 15 years after beetle outbreak is controlled by interactions between interannual climate variability, the extent of vegetation mortality, and long-term aridity. During wet years, water yield after a beetle outbreak increased with greater tree mortality; this was driven by mortality-caused decreases in evapotranspiration. During dry years, water yield decreased at low-to-medium mortality but increased at high mortality. The mortality threshold for the direction of change was location specific. The change in water yield also varied spatially along aridity gradients during dry years. In wetter areas of the Trail Creek basin, post-outbreak water yield decreased at low mortality (driven by an increase in ground evaporation) and increased when vegetation mortality was greater than 40 % (driven by a decrease in canopy evaporation and transpiration). In contrast, in more water-limited areas, water yield typically decreased after beetle outbreaks, regardless of mortality level (although the driving mechanisms varied). Our findings highlight the complexity and variability of hydrologic responses and suggest that long-term (i.e., multi-decadal mean) aridity can be a useful indicator for the direction of water yield changes after a disturbance.

Water Age in Stormwater Management Ponds and Stormwater Management Pond Treated Catchments

Increasing coverage of impervious surfaces in urban waterways result in 'flashy' hydrologic responses, elevated flood risk, and degraded water quality. Stormwater management ponds (SWMPs) are engineered into urban stream networks to mitigate this response. However, little is known about how SWMPs affect hydrological transit time at the catchment scale. This study aims to examine water age in SWMPs and catchments of varying SWMP control. Grab samples of ∂¹⁸O and ∂²H were collected bi-weekly from two SWMPs and five stream sites with varying land cover and stormwater control in their catchments. The damping ratio (DR), young water fraction (Fyw) and mean transit time (MTT) by sine-wave fitting were calculated for each sampled site. SWMP inlet water was consistently older than water arriving at SWMP outlets. MTT decreased as catchments SWMP control increased. Surficial geology was found to have the greatest influence on catchment MTT.

Water Age in Stormwater Management Ponds and Stormwater Management Pond Treated Catchments

Increasing coverage of impervious surfaces in urban waterways result in 'flashy' hydrologic responses, elevated flood risk, and degraded water quality. Stormwater management ponds (SWMPs) are engineered into urban stream networks to mitigate this response. However, little is known about how SWMPs affect hydrological transit time at the catchment scale. This study aims to examine water age in SWMPs and catchments of varying SWMP control. Grab samples of ∂¹⁸O and ∂²H were collected bi-weekly from two SWMPs and five stream sites with varying land cover and stormwater control in their catchments. The damping ratio (DR), young water fraction (Fyw) and mean transit time (MTT) by sine-wave fitting were calculated for each sampled site. SWMP inlet water was consistently older than water arriving at SWMP outlets. MTT decreased as catchments SWMP control increased. Surficial geology was found to have the greatest influence on catchment MTT.

Stream Flow

Changes in stream discharge after earthquakes are among the most interesting hydrologic responses because they are visible at Earth’s surface and can be dramatic. Here we focus on changes that persist for extended periods but have no obvious source. Such increases have been documented for a long time but their origins are still under debate. We first review some general characteristics of streamflow responses to earthquakes; we then discuss several mechanisms that have been proposed to explain these responses and the source of the extra water. The different hypotheses imply different crustal processes and different water–rock interactions during the earthquake cycle. In most instances, these hypotheses are under-constrained. We suggest that multiple mechanisms may be activated by an earthquake.

Separate and Combined Impacts of Land Cover and Climate Changes on Hydrological Responses of Dhidhessa River Basin, Ethiopia

Land cover and climate changes greatly influence hydrologic responses of a basin. However, the response vary from basin to basin depending on the nature and severity of the changes and basin characteristics. Moreover, the combined impacts of the changes affect hydrologic responses of a basin in an offsetting or synergistic manner. This study quantified the separate and combined impacts, and the relative contributions of land cover and climate changes on multiple hydrological regimes (i.e., surface runoff, streamflow, groundwater recharge evapotranspiration) for the Dhidhessa Subbasin. Land cover and climate change data were obtained from a recent study completed for the basin. Calibrated Soil and Water Analysis Tool (SWAT) was used to quantify the impacts. The result showed that SWAT model performed well for the Dhidhessa Subbasin in predicting the water balance components. Substantial land cover change as well as an increasing temperature and rainfall trends were reported in the river basin during the past three decades. In response to these changes, surface runoff, streamflow and actual evapotranspiration (AET) increased while groundwater recharge declined. Surface runoff was more sensitive to land cover than to climate changes whereas streamflow and AET were more sensitive to climate change than to land cover change. The combined impacts played offsetting effect on groundwater recharge and AET while inconsistent effects within study periods for other hydrologic responses. Overall, the predicted hydrologic responses will have negative impacts on agricultural production and water resources availability. Therefore, the implementation of integrated watershed management strategies such as soil and water conservation and afforestation could reverse the negative impacts.