Estimating future stream connectivity using a water balance approach based on climate projections until 2100

Stream connectivity due to flow intermittency will be modified from its current pattern due to climate change. Restoring connectivity is then a matter of stream water availability within the basin, and it includes natural as well as man-induced factors. Among these pressures, the effects of global warming on the water budget are key to forecast the future behavior of each basin. Since stream flow is related to the hydrological balance, the response of river catchments to future climatic conditions can be implemented based on hydrological data. Hydrological as well as ecological concern is interested on how climate change will affect stream connectivity and on the identification of the most sensitive basins, so feasible adaptation plans related to connectivity management can be implemented. This study takes considers stream connectivity in the Segre and Cinca catchments, located in the Pyrenees watersheds of the Ebro River basin (NE Spain), by coupling climate change scenarios and hydrological estimations. From a methodological perspective, a water balance is estimated based on present data (1990-2017) to estimate the water budged components. Actual evapotranspiration is computed considering the basin land use distribution. A similar approach uses climate forecasts (Global Climate Model ECHAM5 (1961-2010); A1B) for this area in a 20-year periods until 2100. Climatic data result in an increase of temperature of 3.5Ž in the Pyrenees and 3.1Ž in the lower part of the central Ebro basin for 2100. Rainfall reduction is expected to be of 13.6 and 12.8%, respectively, for 2100. These projections are used to estimate the available water resources for the new hydrological conditions. In this sense, available resources will vary from a 39% of the precipitation as in the peri od 1990-2017 to 32% in 2100 in the Pyrenees, and from 16% to 8% in the low lands. This will modify the mean value of the stream discharge in each sub-basin. Expected stream flow reduction will then have an effect on the aquatic states that determine the ecological status [1]. However, since flow duration curves can be described by a log-normal distribution, future curves can de plotted using expected mean discharge and its standard deviation. As a result, low flow aquatic states, namely hyporheic and arheic, will increase their number of days; meanwhile the state associated to high flows, named hyperheic, will also slightly increase. In summary, this new conditions will also affect the stream-aquifer interaction and the relevance of groundwater flow as a paramount factor to overcome potential impacts [Funded by project Odysseus BiodivERsA3 2015-2016 Call PCIN-2016-168].