Influence of rainfall spatial resolution on flash flood modelling

Abstract. High resolution radar rainfall fields and a distributed hydrologic model are used to evaluate the sensitivity of flash flood simulations to spatial aggregation of rainfall at catchment scales ranging from 10.5 km2 to 623 km2. The case study focuses on the extreme flash flood occurred on 29 August 2003 on the eastern Italian Alps. Four rainfall spatial resolutions are considered, with grid size equal to 1-, 4-, 8- and 16-km. The influence of rainfall spatial aggregation is examined by using the flow distance as a spatial coordinate, hence emphasising the role of river network in the averaging of space-time rainfall. Effects of rainfall spatial aggregation are quantified by using a dimensionless parameter, represented by the ratio of rainfall resolution (Lr) to the characteristic basin length (Lw), taken as the square root of the watershed area. Increasing the Lr/Lw parameter induces large errors on the simulated peak discharge, with values of the peak discharge error up to 0.33 for Lr/Lw equal to 1.0. An important error source related to spatial rainfall aggregation is the rainfall volume error caused by incorrectly smoothing the rainfall volume either inside or outside of of the watershed. It is found that for Lr/Lw 1.0, around 50% of the peak discharge error is due to the rainfall volume error. Remaining errors are due to both the distortion of the rainfall spatial distribution, measured with respect to the river network, and to the reduced spatial variability of the rainfield. Further investigations are required to isolate and examine the effect of river network geometry on the averaging of space-time rainfall at various aggregation lengths and on simulated peak discharges

Rainfall estimation by combining radar and infrared satellite data for nowcasting purposes

The aim is to evaluate the use of infrared satellite precipitation estimates for nowcasting purposes in the context of a real-time flood-warning scheme. A radar-based calibration technique is described which is applied to the Negri–Adler–Wetzel scheme. This procedure employs radar data over a defined calibration area to estimate, for each satellite image, actual rain-rates to be used in the Negri–Adler–Wetzel scheme. Calibrated satellite estimates obtained from this procedure can be used to diagnose areas of precipitation beyond radar range, thus allowing an extension of precipitation nowcasting lead time. Calibrated estimates are compared with radar rainfall measurements and results are discussed for various sizes of integration area. Calibration reduces consistently both bias and variance of the error of the original Negri–Adler–Wetzel estimates, even for integration areas as small as 2000 km2. This indicates the capabilities of the new technique for nowcasting purposes over mediumsized river basins. Copyright © 1999 Royal Meteorological Societ

Towards the de\ufb01nition of a new river water line for North-Eastern Italy

In the last decades there has been active research on the relation between the stable isotopic composition of precipitation and climate variations at the regional scale. Particularly, the analysis of meteoric water lines is an important tool to understand climate processes at the local/regional scale. In this view, considering the strict relation between the isotopic composition of river water and the one of precipitation, surface running waters (i.e. rivers, streams, creeks) and their catchments can be considered as \u201cnatural pluviometers\u201d. In this study the analysis of the isotopic composition of surface waters was carried out in order to develop a new meteoric water line of North-East Italy. The dataset includes samples collected between 2012 and 2016 from i) small catchments, typically < 30 Km2 (Ressi Creek, Bridge Creek and Vauz Creek, Noce Bianco stream, Posina river), where it is easier to relate the stream water isotopic composition to distinct meteoric end-members (e.g., rainfall,snowmeltandglaciermelt);andii)largebasins(Adige:12,100Km2 andPo:71,000Km2)whichintegrate multiple components giving information at the regional scale. Preliminary results show that distinct river water lines are characterized by different slopes and intercepts. The slopes vary between 5.46 and 8.02, whereas the intercepts vary between -9.15 and 11.82. In particular river meteoricwaterlinesde\ufb01nedforRessiCreek(\u3b4Dh\uaf7.48 \u3b418O+10.27,n=831;R2 =0.88)andNoceBiancostream (\u3b4Dh\uaf7.66 \u3b418O+7.27, n=484; R2 = 0.95) con\ufb01rm the similarity with the meteoric line developed for northern Italy. On the contrary, the isotopic composition of streams in small (< 10 Km2) snow-dominated catchments (Bridge Creek and Vauz Creek) deviate from the North Italy meteoric line due to the important contribution of snowmelt that is typically characterized by a different isotopic signature compared to the precipitation input. River water lines for large basins (Po and Adige) are characterized by slopes and intercepts in the range of the Global Meteoric Water Line. Finally, it is important to emphasize that the current dataset, progressively updated, represents a snapshot of a short monitoring period and that future investigations are useful to highlight seasonal variations and on-going environmental changes

Complementarity between Combined Heat and Power Systems, Solar PV and Hydropower at a District Level: Sensitivity to Climate Characteristics along an Alpine Transect

Combined heat and power systems (CHP) produce heat and electricity simultaneously. Their resulting high efficiency makes them more attractive from the energy managers’ perspective than other conventional thermal systems. Although heat is a by-product of the electricity generation process, system operators usually operate CHP systems to satisfy heat demand. Electricity generation from CHP is thus driven by the heat demand, which follows the variability of seasonal temperature, and thus is not always correlated with the fluctuation of electricity demand. Consequently, from the perspective of the electricity grid operator, CHP systems can be seen as a non-controllable energy source similar to other renewable energy sources such as solar, wind or hydro. In this study, we investigate how ‘non-controllable’ electricity generation from CHP systems combines with ‘non-controllable’ electricity generation from solar photovoltaic panels (PV) and run-of-the river (RoR) hydropower at a district level. Only these three energy sources are considered within a 100% renewable mix scenario. Energy mixes with different shares of CHP, solar and RoR are evaluated regarding their contribution to total energy supply and their capacity to reduce generation variability. This analysis is carried out over an ensemble of seventeen catchments in North Eastern Italy located along a climate transect ranging from high elevation and snow dominated head-water catchments to rain-fed and wet basins at lower elevations. Results show that at a district scale, integration of CHP systems with solar photovoltaic and RoR hydropower leads to higher demand satisfaction and lower variability of the electricity balance. Results also show that including CHP in the energy mix modifies the optimal relative share between solar and RoR power generation. Results are consistent across the climate transect. For some districts, using the electricity from CHP might also be a better solution than building energy storage for solar PV

Towards Improved Understanding of Land Use Effect on Soil Moisture Variability: Analysis and Modeling at the Plot Scale

AbstractUnderstanding and characterizing the soil moisture spatial variability and its relevant physical controls is a main challenge in hydrological sciences. In this work we examine the spatial variability characteristics of soil moisture data at 0-30cm depth collected over three years (2006-2008) on a plot (about 200 m2) in Grugliasco (Po Plain, Northern Italy) by means of 21 Time Domain Reflectometry probes. The plot is divided into two subplots: one covered by grapevine plants, the other covered homogeneously by grass. The site is almost flat and the soil is sandy. The characteristics of the site allow to isolate he contribution of soil hydraulic properties and land use to soil moisture variability. Examination of the data shows higher soil moisture values in the vineyard han in the meadow, implying the influence of vegetation cover during the growing season; correspondingly, the spatial soil moisture variability is systematically lower in the vineyard than in the meadow. Evaluation of the main physical controls on the spatia mean and the variability of soil moisture is carried out by using a simple bucket model, forced by using local rainfal and evapotranspiration data. The model is calibrated by using mean soil moisture daily time series over one year for the two sites. The model accuracy is verified for the other two years, showing a relatively good prediction capability The model is also shown to be able to capture the main differences between the two sites in terms of spatia variability

Estimating the water budget components and their variability in a pre-alpine basin with JGrass-NewAGE

The estimation of water resources at basin scale requires modelling of all components of the hydrological system. Because of the great uncertainties associated with the estimation of each water cycle component and the large error in budget closure that results, water budget is rarely carried out explicitly. This paper fills the gap in providing a methodology for obtaining it routinely at daily and subdaily time scales. In this study, we use various strategies to improve water budget closure in a small basin of Italian Prealps. The specific objectives are: assessing the predictive performances of different Kriging methods to determine the most accurate precipitation estimates; using MODIS imagery data to assist in the separation of snowfall and rainfall; combining the Priestley-Taylor evapotranspiration model with the Budyko hypothesis to estimate at high resolution (in time and space) actual evapotranspiration (ET); using an appropriate calibration-validation strategy to forecast discharge spatially. For this, 18 years of spatial time series of precipitation, snow water equivalent, rainfall-runoff and ET at hourly time steps are simulated for the Posina River basin (Northeast Italy) using the JGrass-NewAGE system. Among the interpolation methods considered, local detrended kriging is seen to give the best performances in forecasting precipitation distribution. However, detrended Kriging gives better results in simulating discharges. The parameters optimized at the basin outlet over a five-year period show acceptable performances during the validation period at the outlet and at interior points of the basin. The use of the Budyko hypothesis to guide the ET estimation shows encouraging results, with less uncertainty than the values reported in literature. Aggregating at a long temporal scale, the mean annual water budget for the Posina River basin is about 1269 ± 372 mm (76.4%) runoff, 503.5 ± 35.5 mm (30%) evapotranspiration, and −50±129−50±129 mm (−−4.2%) basin storage from basin precipitation of 1730 ± 344 mm. The highest interannual variability is shown for precipitation, followed by discharge. Evapotranspiration shows less interannual variability and is less dependent on precipitation

Depth distribution of soil water sourced by plants at the global scale : a new direct inference approach

Funding Information Fondazione Cassa di Risparmio di Padova e Rovigo. Grant Number: Bando Starting Grants 2015Peer reviewedPostprin