Use of statistical methods to characterize the influence of groundwater on the thermal regime of rivers in Normandy, France: comparison between the highly permeable, chalk catchment of the Touques River and the low permeability, crystalline rock catchment of the Orne River

Abstract

Abstract The study of the temperature of two rivers in Normandy (France), the Orne and the Touques, between 2013 and 2018 allowed the main controlling factors regulating their thermal regime to be determined. The analysis was conducted by coupling different statistical treatments: linear regression between water and air temperatures, independent component analysis, principal component analysis and a multiple linear regression model. The temperature of the two rivers is mainly controlled by climatic factors but secondary regulation factors are demonstrated to play important roles: runoff for the two rivers and groundwater for the Touques. The influence of the chalk aquifer on river temperature appears to vary seasonally throughout the year, reaching its maximum in the early spring and increasing from upstream to downstream. The coupled use of the different statistical complex methods showed its validity in understanding both the temporal and spatial variations in water temperature and its correlation with the secondary factors, that could not be inferred from a simpler approach based on linear regression. These techniques could be valuable in other areas with rivers sufficiently monitored to determine the controlling water temperature factors and thus their sensitivity to climate change.