On the forest cover–water yield debate: from demand‐ to supply‐side thinking

Abstract

Several major articles from the past decade and beyond conclude the impact of reforestation or afforestation on water yield is negative: additional forest cover will reduce and removing forests will raise downstream water availability. A second group of authors argue the opposite: planting additional forests should raise downstream water availability and intensify the hydrologic cycle. Obtaining supporting evidence for this second group of authors has been more difficult due to the larger scales at which the positive effects of forests on the water cycle may be seen. We argue that forest cover is inextricably linked to precipitation. Forest-driven evapotranspiration removed from a particular catchment contributes to the availability of atmospheric moisture vapor and its cross-continental transport, raising the likelihood of precipitation events and increasing water yield, in particular in continental interiors more distant from oceans. Seasonal relationships heighten the importance of this phenomenon. We review the arguments from different scales and perspectives. This clarifies the generally beneficial relationship between forest cover and the intensity of the hydrologic cycle. While evidence supports both sides of the argument – trees can reduce runoff at the small catchment scale – at larger scales, trees are more clearly linked to increased precipitation and water availability. Progressive deforestation, land conversion from forest to agriculture and urbanization have potentially negative consequences for global precipitation, prompting us to think of forest ecosystems as global public goods. Policy-making attempts to measure product water footprints, estimate the value of ecosystem services, promote afforestation, develop drought mitigation strategies and otherwise manage land use must consider the linkage of forests to the supply of precipitation.

The impact of forest regeneration on streamflow in 12 mesoscale humid tropical catchments

“…Table 4), possibly due to biases in the PRISM P map, uncertainties in the Q and/or catchment boundary data, water extractions, inter-basin groundwater transfers (potentially exacerbated by karst), and/or water recycling (e.g. Ellison et al, 2012), which combined may cancel out or amplify The decrease in Q was explained by the higher ET a of the regenerating vegetation. e Refers to changes in peak flows only.…”

Effect of National-Scale Afforestation on Forest Water Supply and Soil Loss in South Korea, 1971–2010

“…Previous studies that estimated the amount of water resources or the supply service of the Korean forestry [3,52,53] focused on assessing the current supply of water. On supply-side thinking, afforestation will raise water supply and strengthen the hydrological cycle [54]. Furthermore, vegetation destruction and land cover change resulting from deforestation could be the main cause of soil degradation and soil loss [41,55].…”

Effects of Forest Cover Change on Flood Characteristics in the Upper Citarum Watershed

“…Research have shown that forest harvesting has increased streamflow and rates of snowmelt and generally, such condition will occur in small headwater 2 catchments (< 1 km ). This shows that forest's role and its impact on water yield (including hydrologic cycle) varied and is still debated (Andre´assian 2004;Ellison et al 2012). Based on the weakness, this researches use a single catchment approach to evaluate the impacts of forest reduction on river discharge at large scale catchment (i.e.…”