Simulation of the hydrodynamic behaviour of a Mediterranean reservoir under different climate change and management scenarios

Abstract

One of the most important current issues in the management of lakes and reservoirs is the prediction of global climate change effects to determine appropriate mitigation and adaptation actions. In this paper we analyse whether management actions can limit the effects of climate change on water temperatures in a reservoir. For this, we used the model EOLE to simulate the hydrodynamic and thermal behaviour of the reservoir of Bimont (Provence region, France) in the medium term and in the long term (2066-2095) using regionalised projections by the model CNRM-CERFACS-CNRM-CM5 under the emission scenarios RCP 4.5 and RCP 8.5. Water temperature projections were compared to simulations for the reference period 1993-2013, the longest period for which we had year-long data for both hydrology and meteorology. We calibrated the model using profile measurements for the period 2010-2011 and we carried an extensive validation and assessment of model performance. In fact, we validated the model using profile measurements for 2012-2014, obtaining a root mean square error of 1.08°C and mean bias of -0.11°C, and we assured the consistency of model simulations in the long term by comparing simulated surface temperature to satellite measurements for 1999-2013. We assessed the effect of the use of synthetic input data instead of measured input data by comparing simulations made using both kinds of data for the reference period. Using synthetic data resulted in slightly lower (-0.3°C) average and maximum epilimnion temperatures, a somewhat deeper thermocline, and slightly higher evaporation (+7%). To investigate the effect of different management strategies, we considered three management scenarios: i) bottom outlet and present water level; ii) bottom outlet and elevated water level; and iii) surface outlet and elevated water level. According to the simulations, the reservoir of Bimont will have a low rate of warming of the epilimnion of 0.009-0.024°C·yr -1 , but a rapid hypolimnion warming of 0.013-0.028°C·yr -1 . The increase in surface temperatures will augment evaporation. However, the length of the stratification period and the thermocline depth are not expected to change. Elevating the water level and using a surface outlet in the reservoir of Bimont, would result in reductions of surface temperature of a similar magnitude as the expected increase because of climate change.

An epilimnion and hypolimnion temperature model based on air temperature and lake characteristics

“…8 also shows that natural lakes tended to have lower values of E than reservoirs, because reservoirs tend to have less intense stratification than natural lakes. Subsurface outlets present in many reservoirs cause the lowering of the thermocline and a more gradual temperature gradient (Han et al, 2000;Prats et al, 2018b). As a consequence, we defined two different parameterizations of E as a function of lake depth, one for natural lakes and another for artificial lakes.…”

LakeSST: Lake Skin Surface Temperature in French inland water bodies for 1999–2016 from Landsat archives

“…The value of the calibration parameters depends on the available data (Andréassian et al, 2012;Prats and Danis, 2017) and it is interesting to test the long-term performance of a model, especially if it will be used to predict the effects of climate change or similar long-term effects. Satellite measurements have been used to assess the long-term performance of a hydrodynamic model of the reservoir of Bimont (Prats et al, 2018b). Satellite images are particularly useful for the application of two-dimensional and three-dimensional models.…”

“…Although air temperature data were corrected for altitude effects, local micrometeorological conditions at the reservoir of Bimont are probably different to those measured at the meteorological station of Aix-en-Provence (Prats et al, 2018b). For example, the wind field might be affected by local orography and relative humidity could be affected by the presence of the reservoir.…”

Future projections of temperature and mixing regime of European temperate lakes

“…Shatwell et al: Future projections of temperature and mixing regime observed to increase, decrease, or not change with increasing air temperature (Dokulil et al, 2006;Ficker et al, 2017;Kirillin et al, 2013Kirillin et al, , 2017Richardson et al, 2017;Winslow et al, 2017). Stratification strength and duration generally increase due to warming (Butcher et al, 2015;Kirillin, 2010), but patterns of change may have little regional coherence and cannot be reliably inferred from surface water trends (Read et al, 2014). We know even less about how warming influences the mixed-layer depth, which is important for instance for light availability for primary production.…”

“…Recently, a series of modelling studies reported the variable regional responses of lakes to projected climate change in the near future (e.g. Boike et al, 2015;Butcher et al, 2015;Dibike et al, 2011;Ladwig et al, 2018;Magee and Wu, 2017;Prats et al, 2018;Woolway et al, 2017). Such regional studies typically focus on the role of lake-specific factors, such as lake size, morphometry, and water quality in long-term lake trends due to local warming.…”