From aquifers’ and rivers’ memory to a better low-flow forecasting model (original) (raw)

Variability of soil moisture memory for wet and dry basins

Soil moisture memory (SMM) is not only important for atmospheric weather/climate forecasting, but may also be useful in flood and drought prediction. Despite their importance, SMM studies are restricted in certain regions due to the scarcity of soil moisture data. To overcome this limitation, this study explains the variability of SMM in wet and dry basins, and shows an alternative way to predict the basin scale SMM using observed precipitation and potential evapotranspiration information only. This study presents the basin average SMM in the form of a timescale that indicates the duration of significant auto-correlations at 95% confidence intervals. The soil moisture autocorrelations were calculated using observed precipitation, potential evapotranspiration, streamflow and soil moisture data sets simulated using the XinAnJiang (XAJ) model, for 26 river basins across the USA. The XAJ model's capability to simulate seasonal cycles (temporal anomalies) of soil moisture was validated against cycles from the observed data set of the Spoon River basin of Illinois State, USA. Based on the validation experience, the XAJ model was thereafter used to simulate soil moisture data for the analysed basins. Basin scale SMM timescale ranges were computed from 11 to 133 days. The SMM timescale is highly influenced by precipitation variability and exhibits strong seasonality. Dry basins tend to show the highest memory during the winter months (December to February) and lowest in late spring (May). In contrast , wet basins have the lowest memory during winter and early spring (December to April) and highest in the late summer and early autumn (July to September). The SMM timescale displayed an exponential relationship with the basin aridity index, with an r 2 value of 0.9. This relationship could be a cheap source of basin scale SMM prediction from widely available observed data sets (actual precipitation and potential evapotranspiration), and thus, could afford some knowledge of SMM under no knowledge conditions.

Multi-annual variability and homogeneity of drought streamflow deficit

2011

Hydrological droughts and low flows are very important components of a river regime. They have a great impact on areas with restricted water resources and concomitant water balances. Water shortages are determined by many factors that are influential over time. Therefore, in the context of observed and predicted climatic changes, many lowland areas are partly affected or seriously put at risk from water deficits due to demands from public services, industry, agriculture, forestry, as well as water ecosystems degradation. Results of hydrological analyses of drought and low flows at a longterm, multiple year scale might provide efficient resource management during hydrological extremes, as well as assist with prevention and risk management strategies. Drought and low flows are well-known hydrological phenomena. However various methods define these processes in different ways. One approach is based on a threshold level, where runoff deficit periods are selected when runoff values are b...

Hydrological seasonal forecast over France: feasibility and prospects

Atmospheric Science Letters, 2010

This article presents a first evaluation of a hydrological forecasting suite at seasonal time scales over France. The hydrometeorological model SAFRAN-ISBA-MODCOU is forced by seasonal forecasts from the DEMETER project for the March-April-May period. Despite a simple downscaling method, the atmospheric forcings are reasonably well represented at the finest scale. The computed soil moisture shows some predictability with large regions of correlation above 0.3. Probabilistic scores for soil moisture and river flows for four different catchments are higher than that for atmospheric variables. These results suggest to go further for building an operational hydrological seasonal forecast system.

Benchmarking hydrological models for low-flow simulation and forecasting on French catchments

Hydrology and Earth System Sciences Discussions, 2013

Low-flow simulation and forecasting remains a difficult issue for hydrological modellers, and intercomparisons are needed to assess existing low-flow prediction models and to develop more efficient operational tools. This study presents the results of a collaborative experiment conducted to compare low-flow simulation and forecasting models on 21 unregulated catchments in France. Five hydrological models with different characteristics and conceptualizations were applied following a common evaluation framework and assessed using a common set of criteria. Two simple benchmarks were used to set minimum levels of acceptability for model performance in simulation and forecasting modes. Results showed that, in simulation as well as in forecasting modes, all hydrological models performed almost systematically better than the benchmarks. Although no single model outperformed all the others in all circumstances, a few models appeared more satisfactory than the others on average. In simulation mode, all attempts to relate model efficiency to catchment characteristics remained inconclusive. In forecasting mode, we defined maximum useful forecasting lead times beyond which the model does not contribute useful information compared to the benchmark. This maximum useful lead time logically varies between catchments, but also depends on the model used. Preliminary attempts to implement simple multi-model approaches showed that additional efficiency gains can be expected from such approaches.

Summer drought predictability over Europe: empirical versus dynamical forecasts

Environmental Research Letters

Seasonal climate forecasts could be an important planning tool for farmers, government and insurance companies that can lead to better and timely management of seasonal climate risks. However, climate seasonal forecasts are often under-used, because potential users are not well aware of the capabilities and limitations of these products. This study aims at assessing the merits and caveats of a statistical empirical method, the ensemble streamflow prediction system (ESP, an ensemble based on reordering historical data) and an operational dynamical forecast system, the European Centre for Medium-Range Weather Forecasts-System 4 (S4) in predicting summer drought in Europe. Droughts are defined using the Standardized Precipitation Evapotranspiration Index for the month of August integrated over 6 months. Both systems show useful and mostly comparable deterministic skill. We argue that this source of predictability is mostly attributable to the observed initial conditions. S4 shows only higher skill in terms of ability to probabilistically identify drought occurrence. Thus, currently, both approaches provide useful information and ESP represents a computationally fast alternative to dynamical prediction applications for drought prediction.

A Vision for Hydrological Prediction

Atmosphere, 2020

IMproving PRedictions and management of hydrological EXtremes (IMPREX) was a European Union Horizon 2020 project that ran from September 2015 to September 2019. IMPREX aimed to improve society’s ability to anticipate and respond to future extreme hydrological events in Europe across a variety of uses in the water-related sectors (flood forecasting, drought risk assessment, agriculture, navigation, hydropower and water supply utilities). Through the engagement with stakeholders and continuous feedback between model outputs and water applications, progress was achieved in better understanding the way hydrological predictions can be useful to (and operationally incorporated into) problem-solving in the water sector. The work and discussions carried out during the project nurtured further reflections toward a common vision for hydrological prediction. In this article, we summarized the main findings of the IMPREX project within a broader overview of hydrological prediction, providing a ...

The European 2015 drought from a hydrological perspective

Hydrology and Earth System Sciences Discussions, 2016

In 2015 large parts of Europe were affected by a drought. In two companion papers we summarize a collaborative initiative of members of UNESCO’s EURO FRIEND-Water program to perform a timely pan-European assessment of the event. In this second paper, we analyse the event of 2015 relative to the event of 2003 based on streamflow observations. Analyses are based on range of low flow and hydrological drought indices for about 800 records across Europe that were collected in a community effort based on a common protocol. We compare the hydrological footprints of both events with the meteorological footprints presented by Ionita et al. (2016), in order to learn from similarities and differences of both perspectives and to draw conclusions for drought management. Overall, the hydrological drought of 2015 is characterised by a different spatial extent than the drought of 2003. In terms of low flow magnitude, a region around the Czech Republic was most affected with annual low flows that ex...

Ensemble projections of future streamflow droughts in Europe

Hydrol. Earth Syst. Sci. Discuss., 2013

There is growing concern in Europe about the possible rise in the severity and frequency of extreme drought events as a manifestation of global change. In order to plan suitable adaptation strategies it is important for decision makers to know how drought conditions will develop at regional scales. This paper therefore addresses the issue 5 of future developments in streamflow drought characteristics across Europe. Through off-line coupling of a hydrological model with an ensemble of bias-corrected climate simulations (IPCC SRES A1B) and a water use scenario (Economy First), long term (1961-2100) ensemble streamflow simulations are generated that account for changes in climate, and the uncertainty therein, and in water consumption. Using extreme value 10 analysis we derive minimum flow and deficit indices and evaluate how the magnitude and severity of low flow conditions may evolve throughout the 21st century. This analysis shows that streamflow droughts will become more severe and persistent in many parts of Europe due to climate change, except for northern and northeastern parts of Europe. Especially southern regions will face strong reductions in low flows. Future wa-15 ter use will aggravate the situation by 10-30 % in Southern Europe, whereas in some sub-regions in Western, Central and Eastern Europe a positive climate signal may be reversed due to intensive water use. The multi-model ensemble projections of more frequent and severe streamflow droughts in the south and decreasing drought hazard in the north are highly significant, while the projected changes are more dissonant in 20 a transition zone in between.