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

Soil water depletion rates in a 115‐cm and a 170‐cm deep profile of Adelanto clay loam were compared with lysimetrically obtained consumptive use rates for periods of many days after measured water applications. When the soil was bare, the depletion rates were always higher than the rate of loss to the atmosphere, and the inferred flux at the 170‐cm depth was as high as 2 mm/day 8 days after irrigation. When the test plot was planted to sorghum (Sorghum vulgare Pers.) an initially strong downward flux at the 170‐cm depth reversed itself after about 10 days and became as high as 4 mm/day, representing upward flow of water from wet soil into the root zone above. The data imply that indiscriminate use of soil water depletion rates as representing consumptive use rates can be highly misleading at any time in an irrigation cycle. Further analysis shows that a rational and satisfactory correction of depletion data is not likely feasible, and, at any rate, unworkable for the condition of the experiment.

The distribution of irrigation water in an Adelanto clay loam profile was studied in a field plot by simultaneous, periodic observations of the water content and hydraulic head profiles. Successive measurement series were made with the plot bare and covered, bare, and planted to a sorghum crop (Sorghum vulgare Pers.). From the first two, the in situ and dynamic relations of water content to water pressure and to conductivity were obtained. From the cropped field data, the root‐extraction pattern was derived, using the established hydraulic properties of the profile. The data demonstrate the variability within depths and locations of water retention and conduction properties and the consequent problem of calculating fluxes. The mobile character of soil water is also evident, confirming the inadequacy of static concepts of soil water “constants” for a profile. Calculated root‐extraction rates agreed reasonably with independent lysimetric measurements of the water loss from the surface to the atmosphere.

Soil water characteristics obtained on soil cores in the laboratory at air pressures < 1 bar agreed substantially with pressure‐water content relations determined in the field. Thus, in field studies of soil hydraulics, measurement of either water content or pressure potential may suffice.When the laboratory data were supplemented with a doubletube measurement of the saturated conductivity, the relation between water content and conductivity was calculated using two methods. Of these, the one due to Millington and Quirk gave less accurate agreement with actual field measurements than did the method proposed by Laliberte, Corey and Brooks. The latter method, when based on double‐tube measurements in the field and pressure cells or similar measurements on cores in the laboratory, appears useful.Retention values measured with the pressure membrane method on disturbed soil samples were out of line with both field and core results, even when the disturbing treatments were minimized.

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 E_T 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 E_T alter the two dimensionless measures describing relative water E_T/P and energy partitioning E_T/E₀, which allows us to separate and quantify these impacts. We use the separation method to quantify the role of environmental factors on E_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 E_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 E_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