Reforestation and the reduction of water yield on the Southern Piedmont since circa 1940

Abstract

The southern Piedmont has undergone extensive cropland reversion during the twentieth century with row crops being replaced by forest and pasture. Ten continguous river basins with a total area of 54,020 km 2 had 10 to 28% of their respective areas reforested during the period 1919-1967. During the same period, water yield decreased 3 to 10 cm according to both regression and double-mass analysis. These reductions in water yield constituted a 4 to 21% decrease in annual stream discharge and were statistically significant for a majority of the basins. The reduction of water yields by forests tends to be greater for dry years than for wet years. There was little or no relation between the degree of reforestation and reductions of water yield at the scale of this study, but when our data are included with the universe of data, the variance of our data from the overall model is much less than in the universal set. The inclusion of our results extends the range and predictive power of the universal model, giving it greater utility for water yield planning.

Negative trade-off between changes in vegetation water use and infiltration recovery after reforesting degraded pasture land in the Nepalese Lesser Himalaya

“…These initial results were confirmed by several subsequent reviews, both for the (warm) (Bruijnzeel, 1990;Grip et al, 2005;Scott et al, 2005). Whilst the majority of experiments concerned small catchments (< 2 km 2 ), comparable results of increased water yield following forest removal and reduced flows following forestation were also obtained for much larger river basins (1100-175 000 km 2 ; Trimble et al, 1987;Madduma Bandara, 1997;Costa et al, 2003;Zhou et al, 2010). The fact that the bulk of the change in streamflow associated with such experiments was observed during conditions of baseflow (Bosch and Hewlett, 1982;Bruijnzeel, 1989;Farley et al, 2005) at first sight contradicted the reality of the forest sponge concept, and its very existence became questioned (Hamilton and King, 1983;Calder, 2005).…”

“…For example, substantial decreases in dry season flows following advanced surface degradation (Bartarya, 1989;Madduma Bandara, 1997) or large-scale reforestation (cf. Trimble et al, 1987;Zhou et al, 2010) would affect the availability of water for millions of people, both those depending directly on agriculture for their livelihoods and downstream city dwellers. Therefore, largescale reforestation campaigns and the subsequent use of the planted forests must be based on a sound assessment of what is to be expected hydrologically Van Dijk et al, 2012) and meteorologically (Ellison et al, 2011).…”

“…In other words, no positive effects of reforestation on soil water intake capacity could manifest and the observed reductions in water yield simply reflected the higher water use of the trees compared to the grasses and scrubs they replaced (cf. Trimble et al, 1987;Waterloo et al, 1999;Scott and Prinsloo, 2008).…”

Land cover and water yield: inference problems when comparing catchments with mixed land cover

“…Measurement error. Studies analysing data from small catchments have not been able to detect a significant change in stream flow when land cover is changed in less than 15-20 % of a catchment (Bosch and Hewlett, 1982; but see Trimble et al, 1987;Stednick, 1996). Arguably, this can be attributed to the influence of measurement noise on the analysis.…”

Strong increases in flood frequency and discharge of the River Meuse over the late Holocene: impacts of long-term anthropogenic land use change and climate variability

“…The results of paired catchment studies in temperate zones have established strong links between deforestation and increasing mean discharge, and vice versa (Andréassian, 2004;Bosch and Hewlett, 1982;Hornbeck et al, 1993;Sahin and Hall, 1996). In single basin studies, large increases in discharge due to deforestation, or decreases due to reforestation, have been noted in Europe (Gallart and Llorens, 2004;Keesstra, 2006), Africa (Mahe et al, 2005;Scott et al, 2005), North America (Trimble et al, 1987), and South America (Costa et al, 2003;Iroumé et al, 2005). Various modelling studies of European streamflow have simulated significant changes in response to land use change (Bultot et al, 1990;Klöcking and Hamberlandt, 2002;Wegehenkel, 2002).…”