DOI: 10.5285/5baa5d91-d552-4fc6-8a8c-29ae45192d77
title: Derived global responses of annual river flow to catchment forestation through time, between 1900 and 2018

description: This dataset reports the responses of annual river flow to forestation in 43 catchments and contains 770 data points. Data shows the change in river flow following forestation at annual time scales, along control river flow measurements and associated metadata from primary and secondary sources. Data collection, processing and interpretation were performed by Laura Bentley and David A. Coomes between January 2018 and October 2019. 

 Forestation was defined as a change in land cover from a stable, non-forested state to a forested one, independent of the long-term history of forest cover. Paired measurements of annual river flow following forestation (mm) and river flow under control land cover conditions (mm) are provided for each year that the catchment dataset satisfied our inclusion criteria.  River flow response is provided as both an absolute difference (mm) and as a percentage of control flow in the same year. Estimates of catchment annual precipitation, annual potential evapotranspiration, forest age, forest area, and the year of study are provided for each river flow response data point. Metadata are provided concerning catchment land cover history, land use history, catchment area, forest type, average climate and the method of forest establishment. The dataset contains catchments that were planted with trees and catchments in which forest cover regenerated without planting. Historical forest cover was reported in some catchments, and not reported in others. The 43 catchments a distributed unevenly across the globe, in 13 countries. The length of time series for each catchment varies from 2 years to 57 years, with and average duration of 19 years. 

description: The database was generated through a systematic search of published literature, conducted via Web of Science (1900-4th January 2018). Data was extracted from single and paired catchment studies identified in our search and from papers reviewed by Farley, Jobbágy, & Jackson (2005). 

Corrections were applied to control river flow values, based on linear regression, where extracted data had not been corrected for differences in climate and/or catchment between the two raw river flow data sets. Any single catchment studies that used a mechanistic catchment model to predict river flow had to report validation analyses for that model for the study to be incorporated. Studies were not included if treatments were a combination of deforestation and forestation, or if the study was a retrospective investigation of a known decrease in river flow.

Control river flow, treatment river flow, and river flow response to forestation (treatment minus control) are reported in millimetres. River flow response is also reported as a percentage of control river flow in the same year. Additional climate data was extracted from CRU TS4.3 (Harris, Jones, Osborn, & Lister, 2014) using the location and extent of the experimental catchment and are reported in millimetres. The age of the established forest (years) was calculated as an area weighted mean. Where the change in forest area was not reported between two years of known forest area, the rate of expansion was assumed constant. Change in forest area is reported as a cumulative percentage of catchment area for each time series. All other variables are defined in the associated metadata. Some data sources did not report all information required by categorical data fields, and this is indicated by ‘NR’ (not reported). Where river flow and climatic data were reported graphically, these were extracted using PlotDigitizer (Huwaldt, 2015). River flow and precipitation measurements reported at a greater than annual frequency were aggregated to annual time scales prior to entry into the dataset.
For further detail regarding the production of this data set, please refer to Bentley, L. & Coomes, D. (2020) Partial river flow recovery with forest age is rare in the decades following establishment Global Change Biology. DOI 10.1111/gcb.14954.