Separating the effects of changes in land cover and climate: a hydro-meteorological analysis of the past 60 yr in Saxony, Germany

Abstract

Understanding and quantifying the impact of changes in climate and in land use/land cover on water availability is a prerequisite to adapt water management; yet, it can be difficult to separate the effects of these different impacts. Here, we illustrate a separation and attribution method based on a Budyko framework. We assume that <i>E</i>_T is limited by the climatic forcing of precipitation <i>P</i> and evaporative demand <i>E</i>₀, but modified by land surface properties. Impacts of changes in climate (i.e. <i>E</i>₀/<i>P</i>) or land-surface changes on <i>E</i>_T alter the two dimensionless measures describing relative water <i>E</i>_T/<i>P</i> and energy partitioning <i>E</i>_T/<i>E</i>₀, which allows us to separate and quantify these impacts. We use the separation method to quantify the role of environmental factors on <i>E</i>_T using 68 small to medium range river basins covering the greatest part of Saxony within the period of 1950-2009. The region can be considered a typical Central European landscape with considerable anthropogenic impacts. In the long term, most basins are found to follow the Budyko curve which we interpret as a result of the strong interactions of climate, soils and vegetation. However, two groups of basins deviate. Agriculturally dominated basins at lower altitudes exceed the Budyko curve while a set of high altitude, forested basins fall well below. When visualizing the decadal dynamics on the relative partitioning of water and energy the impacts of climatic and land surface changes become apparent. After 1960 higher forested basins experienced large land surface changes which show that the air pollution driven tree damages have led to a decline of annual <i>E</i>_T in the order of 38%. In contrast, lower, agricultural dominated areas show no significant changes during that time. However, since the 1990s when effective mitigation measures on industrial pollution have been established, the apparent brightening and regrowth has resulted in a significant increase of <i>E</i>_T across most basins. In conclusion, data on both, the water and the energy balance is necessary to understand how long-term climate and land cover control evapotranspiration and thus water availability. Further, the detected land surface change impacts are consistent in space and time with independent forest damage data and thus confirm the validity of the separation approach

Deforestation reduces the vegetation-accessible water storage in the unsaturated soil and affects catchment travel time distributions and young water fractions

“…The overall pattern found here also broadly reflect the effects of land cover/use change in many different environments (Creed et al, 2014;Jaramillo and Destouni, 2014;Renner et al, 2014, van der Velde et al, 2014Moran-Tejada et al, 2015;Nijzink et al, 2016;Zhang et al, 2017;Jaramillo et al, 2018). The vast majority of these studies suggest that forest removal leads to an increase in the runoff ratio C R at the cost of reduced evaporation E A , although the magnitudes of these changes do substantially vary between individual catchments and studies, which is consistent with our physical understanding of the importance of forest for transpiration in hydrological systems.…”

Quantitative Evaluation of the Impact of Climate Change and Human Activity on Runoff Change in the Dongjiang River Basin, China

“…Rainfall and runoff patterns are attributed to numerous factors, with climate change and human activity being two of the major ones [7][8][9]. Given these observations, three main viewpoints can be concluded: (1) climate variability is more dominant in runoff change [10][11][12][13][14][15]; (2) human activity is more significant [16][17][18][19][20]; and (3) the effects of the two factors vary in different areas during different periods [21]. Kelly et al [22] suggested that a warming climate would lead to an increase in environmental melting and the disappearance of surface hail, which might cause hail damage and increase flood risk; Sterling et al [23] indicated that human activity could considerably affect evapotranspiration, which is one of the factors for runoff change on the basis of a water balance equation.…”

Basin-specific records of lake oligotrophication during the middle-to-late Holocene in boreal northeast Ontario, Canada

“…Elmslie et al (2020) hypothesize that the deposition of carbonate-rich clay materials from the surrounding landscape (Boreux et al, 2017) complicated the response of phototrophic communities during the warm and wet middle Holocene c. ~6000 cal yr BP. Such interactions between climate and catchment processes have been noted by previous studies but are difficult to separate using a single lake basin (Fritz and Anderson, 2013; Renner et al, 2014; Simpson and Anderson, 2009; Zhang et al, 2018).…”