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

摘要

Understanding and quantifying the impact of changes in climate and landuse/land cover on water availability is a prerequisite to adapt watermanagement; yet, it can be difficult to separate the effects of thesedifferent impacts. In this paper we illustrate a separation and attributionmethod based on a Budyko framework. We assume that evapotranspiration (E_T) is limitedby 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 E_T alter the twodimensionless measures describing relative water (E_T/P) and energypartitioning (E_T/E₀), which allows us to separate and quantifythese impacts. We use the separation method to quantify the role ofenvironmental factors on E_T using 68 small to medium range riverbasins covering the greatest part of the German Federal State of Saxonywithin the period of 1950–2009. The region can be considered as a typicalcentral European landscape with considerable anthropogenic impacts. In thelong term, most basins are found to follow the Budyko curve which weinterpret as a result of the strong interactions of climate, soils andvegetation. However, two groups of basins deviate. Agriculturally dominatedbasins at lower altitudes exceed the Budyko curve while a set of highaltitude, forested basins fall well below. When visualizing the decadaldynamics on the relative partitioning of water and energy the impacts ofclimatic and land-surface changes become apparent. After 1960 higher forestedbasins experienced large land-surface changes which show that the airpollution driven tree damages have led to a decline of annual E_Ton the order of 38%. In contrast, lower, agricultural dominated areas showno significant changes during that time. However, since the 1990s effectivemitigation measures on industrial pollution have been established and theapparent brightening and regrowth has resulted in a significant increase ofE_T across most basins. In conclusion, data on both, the water andthe energy balance is necessary to understand how long-term climate and landcover control evapotranspiration and thus water availability. Further, thedetected land-surface change impacts are consistent in space and time withindependent forest damage data and thus confirm the validity of theseparation approach.