Abstract
Abstract. An approach has been proposed to analyze the simulated hydrological extreme uncertainty related to the internal variability of the atmosphere ("climate noise"), which is inherent to the climate system and considered as the lowest level of uncertainty achievable in climate impact studies. To assess the climate noise effect, numerical experiments were made with climate model ECHAM5 and hydrological model ECOMAG. The case study was carried out to Northern Dvina River basin (catchment area is 360 000 km2), whose hydrological regime is characterised by extreme freshets during spring-summer snowmelt period. The climate noise was represented by ensemble ECHAM5 simulations (45 ensemble members) with identical historical boundary forcing and varying initial conditions. An ensemble of the ECHAM5-outputs for the period of 1979–2012 was used (after bias correction post-processing) as the hydrological model inputs, and the corresponding ensemble of 45 multi-year hydrographs was simulated. From this ensemble, we derived flood statistic uncertainty caused by the internal variability of the atmosphere.
Highlights
Analysis of meteorological data as well as climate model experiments show that the atmospheric circulation response to unprecedented global warming can lead to more persistent weather anomalies, that, in turn, may result in increase of flood hazard around the globe (e.g., Coumou and Rahmstorf, 2012)
To illustrate differences between individual ensemble members arising from the internal atmospheric dynamics, Fig. 3 shows simulated ensembles of time series of the above highflow severity indicators Qij (QT), Dij (QT) and QMAXij (i = 1,. . . , 45; j = 1979, . . . 2012). (For this example, Qij (QT) and Dij (QT) were calculated under the daily discharge threshold of QT = 6200 m3 s−1; this value was taken from flow duration curve under the exceedance level of 10 %)
Because of the stochastic atmospheric variability effect, an individual realization, which is produced by a hydrological model operating on outputs from atmospheric general circulation model (AGCM), does not contain any reasonable information on year-to-year changes in the specific hydrological variables under consideration
Summary
Analysis of meteorological data as well as climate model experiments show that the atmospheric circulation response to unprecedented (for the period of instrumental observations) global warming can lead to more persistent weather anomalies, that, in turn, may result in increase of flood hazard around the globe (e.g., Coumou and Rahmstorf, 2012). This is the case for the northern extratropics influenced by strong Arctic warming and corresponding changes of temperature gradients and atmospheric circulation (e.g., Semenov, 2003; Cohen et al, 2014). The regional climate is characterized by long snow accumulation period resulting to spring freshet season when most part of the annual runoff flows (60 %, on the average)
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