Changing river temperatures in northern Germany: trends and drivers of change

Abstract

Climate change is one of the main drivers of river warming worldwide. However, the response of river temperature to climate change differs with the hydrology and landscape properties, making it difficult to generalize the strength and the direction, of river temperature trends across large spatial scales and various river types. Additionally, there is a lack of long‐term and large‐scale trend studies in Europe as well as globally. In this study, we investigated the long‐term (25 years; 132 sites) and the short‐term (10 years; 475 sites) river temperature trends, patterns and underlying drivers within the period 1985–2010 in seven river basins of Germany. The majority of the sites underwent significant river warming during 1985–2010 (mean warming trend: 0.03 °C year−1, SE = 0.003), with a faster warming observed during individual decades (1985–1995 and 2000–2010) within this period. Seasonal analyses showed that, while rivers warmed in all seasons, the fastest warming had occurred during summer. Among all the considered hydro‐climatological variables, air temperature change, which is a response to climate forcing, was the main driver of river temperature change because it had the strongest correlation with river temperature, irrespective of the period. Hydrological variables, such as average flow and baseflow, had a considerable influence on river temperature variability rather than on the overall trend direction. However, decreasing flow probably assisted in a faster river temperature increase in summer and in rivers in NE basins (such as the Elbe basin). The North Atlantic Oscillation Index had a greater significant influence on the winter river temperature variability than on the overall variability. Landscape and basin variables, such as altitude, ecoregion and catchment area, induced spatially variable river temperature trends via affecting the thermal sensitivity of rivers, with the rivers in large catchments and in lowland areas being most sensitive. Copyright © 2016 John Wiley & Sons, Ltd.

Global Warming of Salmon and Trout Rivers in the Northwestern U.S.: Road to Ruin or Path Through Purgatory?

“…; Arora et al. ). Also common among regions, except where urbanization plays a complicating role (e.g., Kaushal et al.…”

“…), Germany (Arora et al. ), and the eastern USA (Rice and Jastram ). Sensitivity to climate forcing is probably higher in those regions due to rainfall‐dominated hydrologic regimes and less‐frequent winter periods when ATs are subzero.…”

“… and Arora et al. ) due to the inadequacies of historical monitoring networks and protocols (Orr et al. ).…”

“…Moreover, despite frequent predictions about accelerating or decelerating climate change (Easterling and Wehner 2009), Earth's warming rate has been remarkably constant since the 1970s (Rahmstorf et al 2017), so extrapolation of historical trends may provide some basis for forecasting, at least through midcentury, when most climate model projections are broadly similar (IPCC 2013). Despite the importance of trend estimates and emerging evidence that rivers and streams show global warming patterns (Morrison et al 2002;Webb and Nobilis 2007;Kaushal et al 2010;Isaak et al 2012;Chen et al 2016), robust descriptions of regional trends based on numerous long-term monitoring records are rare (but see Orr et al 2014 andArora et al 2016) due to the inadequacies of historical monitoring networks and protocols (Orr et al 2015).…”

Can spatial statistical river temperature models be transferred between catchments?

“…For example, the approximately 20 % variance explained by UCA in the Spey and Dee models is consistent with the 18-25 % of T w variability explained by discharge in Arora et al (2016). Smaller-scale variability tends to reflect drivers such as water residence time (and heat advection), water sources (Brown et al, 2006;, channel incision, gradient (Jackson et al, 2017b) and land use (Imholt et al, 2013) which are harder to accurately characterise from spatial datasets.…”