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 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. In this paper we illustrate a separation and attribution method based on a Budyko framework. We assume that evapotranspiration (ET) is limited by the climatic forcing of precipitation (P) and evaporative demand (E0), but modified by land-surface properties. Impacts of changes in climate (i.e., E0/P ) or land-surface changes on ET alter the two dimensionless measures describing relative water (ET/P ) and energy partitioning (ET/E0), which allows us to separate and quantify these impacts. We use the separation method to quantify the role of environmental factors on ET using 68 small to medium range river basins covering the greatest part of the German Federal State of Saxony within the period of 1950–2009. The region can be considered as 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 ET on the order of 38 %. In contrast, lower, agricultural dominated areas show no significant changes during that time. However, since the 1990s effective mitigation measures on industrial pollution have been established and the apparent brightening and regrowth has resulted in a significant increase of ET 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 landsurface change impacts are consistent in space and time with independent forest damage data and thus confirm the validity of the separation approach

Dominant effect of increasing forest biomass on evapotranspiration: interpretations of movement in Budyko space

“…However, the Budyko framework (Budyko, 1974), which links water and energy availability to basin-scale hydrology, is required to further separate this combined effect (Zhang et al, 2001). The Budyko framework has already been applied to understand impacts on forest evapotranspiration in Germany by air quality (Renner et al, 2014) and in North America to differentiate the responses of forested basins to climate and human drivers (Creed et al, 2014;Jones et al, 2012;Wang and Hejazi, 2011;Williams et al, 2012). It has also been applied in China and at the global scale to study the hydrological effects of reforestation programmes and the forest controls on water partitioning (Fang et al, 2001;Huang et al, 2003;Li et al, 2016;Xu et al, 2014;X.…”

Effects of changes in land use and climate on water availability of a tropical catchment

“…the middle part of the Budyko curve). Using the aridity index as a correction for the basic concept (Renner et al, 2014), the results have improved but do not reduce the uncertainty inherent in the basic assumption.…”

“…However, Renner et al (2014) argue that the Tomer and Schilling (2009) concept cannot be applied to all hydro-climatic conditions and works only for a region where precipitation equals evaporative demand. They proposed an adaptation of the concept by considering the aridity index (ET 0 /P) to determine the climatic state of the study catchment.…”

“…This study extended the framework adapted by Renner et al (2014) by developing quantitative measures to estimate the land use and climate change impacts on streamflow alteration based on the changes of P ex and E ex . The period of analysis 1990-2013 for which hydro-meteorological time series were available was divided into two periods: a baseline and an altered period, when land use change and climate change might have contributed to streamflow change.…”

“…Wei and Zhang (2010) and Zhang et al (2012) used the modified double mass curve to exclude the effect of climate change on runoff generation in a deforested area. Tomer and Schilling (2009), Ye et al (2013) and Renner et al (2014) used a coupled water-energy budget approach to distinguish relative impacts of land use and climate change on watershed hydrology. A classical non-modelling approach is to employ trend analysis and change detection methods (Rientjes et al, 2011;Zhang et al, 2014).…”