DOI: 10.5061/dryad.p8cz8w9kf
title: Temporal Human Pressure Index

description: It is widely accepted that the main driver of the observed decline in
 biological diversity is increasing human pressure on Earth’s ecosystems.
 However, the spatial patterns of change in human pressure and their
 relation to conservation efforts are less well known. We developed a
 spatially and temporally explicit map of global change in human pressure
 over two decades between 1990 and 2010 at a resolution of 10 km2.
  We evaluated 22 spatial data sets representing different
 components of human pressure  and used them to compile a Temporal
 Human Pressure Index (THPI) based on 3 data sets: human population
 density, land transformation, and electrical power infrastructure. We
 investigated how the THPI within protected areas correlate to
 International Union for Conservation of Nature (IUCN) management
 categories and the Human Development Index (HDI), as well as how the THPI
 was correlated to accumulative pressure using the original Human
 footprint. Since the early 90’s, human pressure increased 64% in
 terrestrial areas; the largest increases were in Southeast Asia. Protected
 areas also exhibited overall increases in human pressure, the degree of
 which varied with location and IUCN management category. Only wilderness
 areas and natural monuments (management categories Ib and III) exhibited
 decreases in pressure. Protected areas not assigned any category exhibited
 the greatest increases. High HDI values and greater mean elevation
 correlated with greater reductions in pressure across protected areas,
 while increasing age of the protected area correlated with increases in
 pressure. Our analysis is an initial step toward mapping changes in human
 pressure on the natural world over time. That only 3 data sets could be
 included in our spatio-temporal global pressure map, highlights the
 challenge to measuring pressure changes over time.
description: Data
 from 1) The inter-calibrated stable night lights  version 4, 2) The
 Gridded Population of the World (GPW) version 3, and 3) The History
 Database of the Global Environment (HYDE) 3.1 were spatially aggregated to
 a resolution of 5.0 arc minutes (approximately
 10km<sup>2</sup> at Equator), the original resolution of the
 HYDE 3.1 cropland data. This aggregation caused some loss of resolution
 for the other 2 data sets (approximately 2.8 km<sup>2</sup>
 for stable nightlights and 5 km<sup>2</sup> for human
 population density). For each terrestrial pixel, we calculated the
 difference between values in the first and last year. This was done
 separately for the 3 layers. We transformed human population density to
 the square root. Data transformation of variables is a standard procedure
 for spatial pressure mapping, and it allows comparison between different
 data types and distributions . We chose square-root transformation because
 it accounted for the expected declining impacts per person in densely
 populated areas but still had a range distribution similar to the original
 data (Supporting Information). The result was 3 maps displaying the change
 in absolute values of human population density, stable nightlights, and
 land use respectively. These maps had very different data
 ranges (human population, – 8,532 to 11,423 people per pixel; stable
 nightlights, -62 to 63 on an arbitrary scale; cropland, -86 -70% change).
 To account for these inherent differences, values for each layer were
 standardized on a scale of -1 to 1, which allowed us to summarize these 3
 different components of pressure. We used the same weighting as the
 original human footprint (Sanderson et al. 2002), giving equal weight to
 stable nightlights and human population while weighting land-use change at
 0.8 (for justification see Supporting Information). Finally, we combined
 the 3 layers by adding the values within each pixel and standardizing the
 resulting score on a scale of -100 to 100, where positive values mean
 increased human pressure and negative values mean decreased human
 pressure. This final product forms our temporal human pressure index
 (THPI), which measures changes in human pressure for the 3 data sets over
 15 years from 1990 to 2010.