Parameter Adjustment to Prevent the Overestimation of Peak Discharge in a Small Watershed

We revisit empirical methods to prevent the overestimation of peak discharge in a small watershed, in particular investigating the time-area method, which has not been considered in the overestimation problem of peak discharge. To avoid misapplying the same inlet time between the unit hydrograph and rational formula, distinct parameter adjustments for each method are proposed. We adopt the secondary basin response time for the unit hydrograph, rainfall duration for the rational formula, and time of concentration for the time-area method, as suitable parameters to adjust the estimation of peak discharge. In conclusion, adding 10 minutes to secondary basin response time, 20 minutes to rainfall duration, and 30 minutes to time of concentration, respectively, yields estimates within a reasonable range of specific discharge in a small watershed.

Supplemental Material: Basin response to the Jurassic geodynamic turnover from flat subduction to normal subduction in South China

Table S1–S3 and Dataset S1–S2.

Supplemental Material: Basin response to the Jurassic geodynamic turnover from flat subduction to normal subduction in South China

Table S1–S3 and Dataset S1–S2.

The Role of Basin Geometry in Mountain Snowpack Responses to Climate Change

Snowmelt contributions to streamflow in mid-latitude mountain basins typically dominate other runoff sources on annual and seasonal timescales. Future increases in temperature and changes in precipitation will affect both snow accumulation and seasonal runoff timing and magnitude, but the underlying and fundamental roles of mountain basin geometry and hypsometry on snowmelt sensitivity have received little attention. To investigate the role of basin geometry in snowmelt sensitivity, a linear snow accumulation model and the Cold Regions Hydrological Modeling (CRHM) platform driven are used to estimate how hypsometry affects basin-wide snow volumes and snowmelt runoff. Area-elevation distributions for fifty basins in western Canada were extracted, normalized according to their elevation statistics, and classified into three clusters that represent top-heavy, middle, and bottom-heavy basins. Prescribed changes in air temperature alter both the snow accumulation gradient and the total snowmelt energy, leading to snowpack volume reductions (10–40%), earlier melt onsets (1–4 weeks) and end of melt season (3 weeks), increases in early spring melt rates and reductions in seasonal areal melt rates (up to 50%). Basin hypsometry controls the magnitude of the basin response. The most sensitive basins are bottom-heavy, and have a greater proportion of their area at low elevations. The least sensitive basins are top-heavy, and have a greater proportion of their area at high elevations. Basins with similar proportional areas at high and low elevations fall in between the others in terms of sensitivity and other metrics. This work provides context for anticipating the impacts of ongoing hydrological change due to climate change, and provides guidance for both monitoring networks and distributed modeling efforts.

Quantification of role of impedance contrast in site-city-interaction effects on the responses of buildings and basin

This paper presents the role of impedance contrast (IC) at the base of 2D deep elliptical basin (shape-ratio > 0.25) in the site-city-interaction (SCI) effects on both the SH- and SV-wave responses of buildings and basin. The obtained SCI effects in the form of reduction of fundamental frequencies of building (F02DSB) and basin (F02DB), corresponding amplification and splitting of the bandwidth of fundamental mode of vibrations of both the building and basin corroborates with the findings in the past SCI studies. The F02DB of basin and F02DSB of building are unaffected by an increase of IC during site-city-interaction, even though, there is an increase of F02DB of basin with an increase of IC in the absence of city. A drastic increase of SCI effects on the basin response but only minor increase of SCI effects on the building response with an increase of IC is observed for both the polarizations of the S-wave. However, the rate of increase of SCI effects with IC is more in the case of SV-wave responses of buildings and basin. The obtained larger % reduction of F02DB and corresponding amplification in the case of SH-wave responses as compared to those in the case of SV-wave responses may be due to the larger height of B16-buildings compared to B12-buildings used in the SV-wave simulations or due to the buildings behaving as a shear beam for the SH-wave or may be due to both.

Evaluating seasonal hydrological extremes in mesoscale (pre-)Alpine basins at coarse 0.5° and fine hyperresolution

Hydrological models are being applied for impact assessment across a wide range of resolutions. In this study, we quantify the effect of model resolution on the simulated hydrological response in five mesoscale basins in the Swiss Alps using the distributed hydrological model Spatial Processes in Hydrology (SPHY). We introduce a new metric to compare a range of values resulting from a distributed model with a single value: the density-weighted distance (DWD). Model simulations are performed at two different spatial resolutions, matching common practices in hydrology: 500 m × 500 m matching regional-scale models, and 40 km × 40 km matching global-scale modeling. We investigate both the intra-basin response in seasonal streamflow and evapotranspiration from the high-resolution model and the difference induced by the two different spatial resolutions, with a focus on four seasonal extremes, selected based on temperature and precipitation. Results from the high-resolution model show that the intra-basin response covers a surprisingly large range of anomalies and show that it is not uncommon to have both extreme positive and negative flux anomalies occurring simultaneously within a catchment. The intra-basin response was grouped by land cover, where different dominant runoff-generating processes are driving the differences between these groups. The low-resolution model failed to capture the diverse and contrasting response from the high-resolution model, since neither the complex topography nor land cover classes were properly represented. DWD values show that, locally, the hydrological response simulated with a high-resolution model can be a lot more extreme than a low-resolution model might indicate, which has important implications for global or continental scale assessments carried out at coarse grids of 0.5∘×0.5∘ or 0.25∘×0.25∘ resolution.