Stochastic properties and statistics of salt intrusion in estuaries in a warming climate

Salt intrusion is part of natural estuary dynamics, where saline water enters inland by tides and exchange flow, and is diluted by fresh river water. These processes and feedbacks are complicated and inherently stochastic; and it is not yet well understood how they determine the statistical behavior of the salt intrusion length. More importantly, there are large uncertainties regarding future changes of the forcing of the salt intrusion in a warming climate. In this presentation, we will introduce a new stochastic model that computes temporal changes of the salt balance equation with the decompositions of river discharge and salt intrusion length into deterministic and stochastic components. The developed framework is applied to field observations in the San Francisco Bay (USA) and shown to well reproduce general statistics of salt intrusion length. Next, the model is applied to estuaries in Europe under projected river discharge distributions up to 2100 using two large ensembles of the Community Earth System Model. The key assumption in the model is that the changes in the river discharge are the main driver that induces variability and changes in salt intrusion length in the coming decades. Our results show that there will be significant increase of salt intrusion during dry periods in many European estuaries, especially those at low latitudes. The analysis stresses that, for adequate water management, great attention is needed in monitoring and predicting salt intrusion lengths in the future.